Root Canal Configuration

INDEX

1. INTRODUCTION

2. BASIC STRUCTURE OF TOOTH: ENAMEL, DENTIN, PULP

3. ROOT CANAL COMPONENT

4. MORPHOLOGY OF ROOT CANAL SYSTEM

5. CLASSIFICATION OF ROOT CANAL MORPHOLOGY

6. ROOT CANAL ANATOMY OF MAXILLARY TEETH

7. ROOT CANAL ANATOMY OF MANDIBULAR TEETH

8. COMPLEX ROOT CANAL SYSTEM

9. VARIOUS TYPES OF ROOT CANAL SYSTEM

10. CONCLUSION

CHAPTER – 1 INTRODUCTION

INTRODUCTION

The fundamental basis of the endodontic specialty is the knowledge of root canal anatomy. Thus, a thorough understanding of the canal morphology and its variations in all groups of teeth is a basic requirement to improve the out- come of the endodontic therapy. In the past, a lot of research work was done on this subject, and the findings have had a noteworthy influence on clinical practice as well as on dental education. Therefore, it would be appropriate to take a brief look to the past to understand contemporary research approaches on the study of root canal anatomy. Authors that preceded this new image- processing technological era, to whom endodon- tics are greatly indebted, must be revisited ¹.

The success of endodontic treatment closely depends on complete knowledge of the complexity and variety of internal/external dental anatomy in order to identify, clean, shape and obturate the whole root canal.²

From the Latin anatomia, dissection, and from the Greek anatome, where ana means “up” and temnein means “to cut,”

The history of endodontic as a dental specialty is relatively recent and was born with the better understanding of the morphology and biology of teeth, as well as the development of endodontic techniques in the brief period of 30 years, from 1900 to 1930, after centuries of immobility ¹. Consequently, this historical overview was carried out considering the result of a long cultural and scientific evolution that simultaneously influenced medicine and its other biological branches, including dentistry.

From Classical Antiquity to Thirteenth Century

The ancient Greek anatomist Herophilus (c.335– c.280 B.C.), founder of the school of anatomy of Alexandria, and his disciple Erasistratus (c.310– c.250 B.C.) were the first physicians to perform systematic dissection of human bodies. Herophilus has been widely acknowledged as the “father of anatomy” and hailed as one of the greatest anatomists that ever lived. His revolutionary discoveries represented an important step in the ancient understanding of the human anatomy ³. Some centuries later, the works of Claudius Galenus (c.130–c.210 A.C.), usually known as Galen, have influenced several generations of physicians and the development of various scientific disciplines, including anatomy ⁴. In his writings, Galen did not just content to compile antique data but also to observe and experience ¹. From the time of Galen’s death until Renaissance, there was no substantial progress in the understanding of human anatomy. In the Middle Ages, the anatomical drawings of human beings were completely devoid of realism, and anatomical description of the teeth was limited to their quantity, position in the oral cavity, and number of roots ¹. Physicians suffered greatly from stasis and intellectual stagnation, once medical knowledge was limited to glossaries, commentaries, encyclopedias, and compendia of ancient works from Arabic writers such as Avicenna ⁴, Rhazes ⁵ and Albucasis ⁶. In the anatomical field, the influence of Galen’s writings continued to prevail.

From Fourteenth to the Seventeenth Century

The Renaissance, period that immediately followed the High Middle Ages (eleventh to thirteenth century) in Europe, was the turning point in which natural sciences and medicine were under the general principle of critical revisionism. At the end of the fourteenth century, medical science slowly found noteworthy progress because dissections became an accepted and officially recognized procedure in Bologna, Italy. This allowed Mondino de Liucci (1270–1326) to write his book Anathomia Corporis Humani ⁷, possibly the first work exclusively devoted to anatomy. In 1363, Guy de Chauliac performed the greatest synthesis of medical and surgical knowledge of his time by writing the famous book Chirurgia Magna . Again, however, description of teeth’s anatomy and physiology was presented superficially¹.

Antonie van Leeuwenhoek (1632– 1723), using a compound microscope created by himself, was the first author to describe the microscopic anatomy of the dentinal tubules. It led him to disagree with the predominant concept according to which teeth were like bone structures. He also published drawings of a sectioned mandibular molar showing its pulp chamber and the root canal . Marcello Malpighi (1628–1694) was also one of the greatest microscopist of this century. In his manuscript Observationes de dentibus, there are 27 sheets richly depicted by drawings of sectioned and non-sectioned human teeth in different angles ,some of which published in the posthumous edition of his Opera Medica, et anatomica varia , that remained unpublished until 1968. Undoubtedly, the works of Leeuwenhoek and Malpighi were too advanced for their time and lacked adequate practical application. Therefore, they remained neglected for at least another 150 years⁵.

From the Eighteenth to the Nineteenth Century

In 1728, the French dentist Pierre Fauchard (1678–1761), also known as the “father of modern dentistry,” published the first edition of his two-volume treatise entitled Le Chirurgien Dentiste ou Traité des dents ,universally acknowledged as the first scientific work of conservative, surgical, and prosthetic dentistry that reflected the state of the art of dental care at that time. However, despite the external morphology of teeth had been described in detail, no information was provided about the root canal anatomy. At the end of the eighteenth century, John Hunter (1728–1793) published two important books based on more than 15 years of observation and experimentation on human dentition . In 1870 in Germany,

Eduard Mühlreiter (1839–1917) published the first complete study on the root canal anatomy of human teeth in which the external and internal morphologies of teeth were compared through sagittal and horizontal sections . Even though it was a simple work in its essence, it proved to be extremely important because it served as inspiration to other researchers, such as Adolph Witzel (1847– 1906), to study the root canal anatomy. This author showed, for the first time, the anatomical variability of root canal system in maxillary premolars and the morphological changes of the pulp cavity of mandibular molars with aging . In the United States, Greene Vardiman Black (1836–1915) examined the external and internal morphology using images of sagittal and horizontal sections of each group of teeth . A few years later, Alfred Gysi (1865– 1957), using histological sections, published the first high-quality photomicrographs depicting the internal morphology of a carious molar and the pulp-dentin complex of another molar, in which it is possible to observe details of the soft connective tissue such as the vascular, lymphatic, and nervous elements . Nevertheless, it was only at the end of nineteenth century that some researchers finally realized the need for an in-depth research on the root canal morphology. It happened mostly because of the rise of misconceptions about root canal infection.

FROM TWENTIETH TO TWENTY- FIRST CENTURY

In 1903, Gustav Preiswerk (1866–1908) performed a profound and comprehensive research on the root canal anatomy. In his pioneering study , Wood’s metal, an alloy that melts at a low temperature, was molten and injected into the canal space. After complete decalcification of the teeth, three-dimensional metal models of the internal anatomy were obtained. It is important to point out that this method was developed by the Dutch anatomist Govard Bidloo (1649–1713) using melted bismuth , later improved by Brunn, who employed Wood’s metal, and used by Zuckerkandl in the study of pulp chamber ¹. This method, however, led to tooth overheating and the replicas were obviously incomplete, as the metal could not penetrate into the finer branches of the root canal system. Despite these methodological drawbacks, this innovative method allowed Preiswerk to observe that canal anastomosis was not rare. Since then, the classical descriptions of teeth with regular canal anatomy and a single apical foramen that appeared in almost all previous treatises started to be questioned. Guido Fischer (1877–1959) presented the challenging nature of the apical root anatomy for the first time in 1907. He obtained better results than Preiswerk by filling approximately 700 teeth with a collodion solution. This solution could penetrate all the branches of the root canal system and hardened in 2 or 3 weeks, providing a full three- dimensional replica of the canal. But the hardened collodion solution was fragile, and replicas of the subtler ramifications fractured easily. Fischer paid special attention to thin ramifications, little lateral branches, and apical terminations and classified the morphological variations of the root canal into simple ramifications or branches, lateral canals within the radicular dentin, intercommunicating canal system, and islands of hard tissue within the canal. The complexity and unpredictability of the root canal morphology led him to coin the nowadays widely used term “root canal system” (Kanalsystem). In the next 2 years, Fisher started to associate radiography with his macroscopic and microscopic observations , highlighting the morphological complexity of the root canal system. It may be said that the innovative three-dimensional anatomical studies of Preiswerk and Fisher resulted in huge advancement adding new and significant knowledge to dental literature, which stimulated other researchers to undertake further investigations on the anatomy of the root canal system. In 1911, the German anatomist Werner Spalteholz (1861–1940) developed a process by which organs could be made translucent and stained using assorted colors .This process was based on dehydration of the removed organs and the use of an optically transparent embedding material that has the same refractive index as the tissue of the organ itself. At this same year, in Japan, T. Okumura used numerous grinding sections to investigate the relation between the external and internal structure of the teeth . He measured several important root canal parameters including the position of the pulp chamber floor, the thickness of the dentinal wall, the distance from the cervical line to the furcation area, and the number, size, and shape of apical ramifications. However, this study was published in Japanese and, therefore, did not have the expected international recognition. In 1913, Spalteholz’s method was used for the first time by Fasoli and Arlotta, from the University of Milan, in Italy, to study the root canal anatomy . In the next years, this technique was modified and employed for the study of the internal anatomy by injecting fluid materials into the root canal system. Since then, it has been referred to as “clearing” or “diaphanization” technique., In the following years, the results obtained by the German school regarding root canal were finally confirmed by several authors from different countries .Wallace Clyde Davis (1866–1950) was the first author to detail the internal morphology of the root canal at the apical third and to address the problem regarding the inability to remove all pulp tissue from the root canal system. He prepared and photographed, at 25× magnification, 50 sectioning root apexes of different teeth from patients ranging from 25 to 45 years old .Davis also introduced the terms pulpotomy and pulpectomy in dentistry. With the publication of his book in 1920 ,he contributed to the endodontic knowledge of future dentists by favoring the development of nonempirical training techniques with scientific foundations. In 1926, T. Okumura showed, at the 16th International Dental Congress of Philadelphia, the results of his study using the Spalteholz’ method on the root canal anatomy of 2146 teeth. Okumura’s work is undoubtedly the most important anatomical study of the root canal system using diaphanization method because of the large sample and the conclusions reached. As an unfolding of his work, he categorized the canal anatomy into four types, according to the root shape, the divisions of the main root canal, and the presence of ramifications, being considered the first anatomicalbased classification of the root canal system. In 1928, the third and last work under Hess supervision was performed by Oskar Keller using 960 teeth , synthesizing all knowledge on root canal morphology since Preiswerk. In this study, a new method combined the Spalteholz technique with modifications and was virtually free of artifacts and suitable for highlighting even the smallest branches of the root canal system. Based on the three studies of Hess, in which the internal anatomy of almost 5000 teeth was studied, root canals ceased to be only “a complex structure” to become a well-defined structure in which scientific- based treatments could be developed and applied. In addition to the invasive techniques, X-ray imaging was soon found to constitute a valuable approach to understand variations in the internal structure of the human tooth. Using this method, Augustus Henry Mueller investigated extracted teeth filled with gutta-percha. It is important to point out that, at this same period in the Latin American, Pucci and Reig also performed an extensive study on root canal anatomy using radiography, diaphanization, and sectioning techniques. However, most of the in-depth research studies on canal anatomy conducted by them was not published in English, which avoided this knowledge to be spread throughout the world. In the years that followed, the advent of the Second World War affected most of the oral research centers around the world. As a consequence, several authors kept reproducing in their books the canal anatomy as previously reported by Mühlreiter ¹. After the war, Balint W. Hermann, known for introducing the calcium hydroxide in dentistry in 1920, published some images reproducing the complexity of the root canal morphology at the apical region .Some years later, David Green also studied the apical anatomy of all groups of teeth using stereomicroscopy .In a series of anatomical studies, Wilhelm Meyer reported a new protocol to reproduce three dimensionally the internal anatomy of 800 teeth based on drawings of sequential microscopic sections of the root canal systems . Quintiliano de Deus was the first author in Brazil who studied systematically the root canal anatomy of all teeth using diaphanization technique. He also evaluated the percentage frequency of lateral canals in each dental group . Later, Vertucci and colleagues made a significant step forward documenting a broad morphological variation in the root canals of different teeth using clearing technique, which became a standard method in further reports on root canal anatomy . These works closed the series of major studies on root canal morphology, accomplishing the results of Preiswerk , Fisher , Hess , and others. In the twentieth century, technological advancements allowed that a considerable range of other techniques was also successfully employed to visualize the anatomy of human teeth including three-dimensional wax models , digital radiography, resin injection , radiographic methods with radiopaque contrast media ⁸⁵, scanning electron microscopy , and others. Undoubtedly, these techniques have shown a great potential for endodontic research; however, while most of these methods required the partial or even full destruction of the studied samples, rendering irreversible changes in the specimens and many artifacts, others provided only a two-dimensional image of a three- dimensional structure . These inherent limitations have repeatedly been discussed in the literature, encouraging the search for new methods with improved possibilities . The early to mid-1990s, the first application of a computerized and digital approach based on micrographs of grinding sections was proposed. Using diamond and silicon carbide disks, Blašković-Šubat et al. and Lyroudia et al. cross- sectioned extracted teeth and photographed these sections using a camera attached to a stereomicroscope. Each photograph was then digitized, the shape was manually outlined, and the resulting stacks of labeled shapes were rendered in 3D using dedicated software. Although partly digital, this approach still required the destruction of the samples under study .The invention of X-ray computed tomography (CT) brought a significant step forward in diagnostic medicine . CT produces a two- dimensional map of X- ray absorption into a twodimensional slice of the subject. This is achieved by taking a series of X-ray projections through the slice at various angles around an axis perpendicular to the slice. From this set of projections, the X-ray absorption map is computed. By taking a number of slices, a three-dimensional map is produced.To maximize their effectiveness in differentiating tissues while minimizing patient exposure, medical CT systems need to use a limited dose of relatively low-energy X-rays (≤125 keV) and acquire data rapidly because the patient should not move during scanning. Besides, to obtain as much data as possible given these requirements, CT devices use relatively large (mm scale) and high-efficiency detectors. In 1990, Tachibana and Matsumoto were the first authors to suggest and evaluate the feasibility of CT imaging in endodontics. Because of high costs, inadequate software, and a low spatial resolution (0.6 mm), they concluded that CT had only a limited usefulness in endodontics as the acquired images were not accurate for detailed analysis. Further improvements in digital image systems have been used to evaluate the root canal anatomy in either ex vivo or in vivo conditions using nondestructive tools such as conventional medical CT , magnetic resonance microscopy , tuned-aperture computed tomography (TACT) , optical coherence tomography , and volumetric or cone beam CT (CBCT) . However, these digital image systems were hampered mainly by insufficient spatial resolution and slice thickness for the study of root canal anatomy . A decade after the CT scanner was created, Elliott and Dover developed the first high- resolution X-ray micro-computed tomographic device, and, using a resolution of 12 μm, the image of the shell of a Biomphalaria glabrata snail was produced. The term “micro” in this new device was used to indicate that the pixel sizes of the cross sections were in the micrometer range. This also means that the machine was smaller in design compared to the human version and was indicated to model smaller objects . More recently, micro-CT has gained increasing popularity in endodontics. This noninvasive, nondestructive, high-resolution technology allows three-dimensional study of the root canal system by reconstructing digital cross sections of the teeth, which can be stacked to create 3D volumes. These volumes can be used to generate computerized images of specimens that can be manipulated, sectioned, prepared, dissected, and measured to reveal both internal and external morphology . In endodontics, Nielsen et al. was the first authors to apply micro-CT technology to reconstruct the external and internal anatomy of four maxillary molars. Then, Dowker et al. and Bjørndal et al. used micro-CT to demonstrate root canal anatomy and the feasibility of using this methodological resource in different stages of the root canal treatment. Nowadays, despite the impossibility of employing microCT for in vivo human imaging, it has been considered the most important and accurate research tool for the study of root canal anatomy . As previously outlined, it is very important for the clinician to develop a complete understanding of the 3D morphologic features of root canal systems. The morphological studies of the last centuries gave us a better understanding of the internal anatomy of teeth and allowed the development of technological resources aiming to overcome the treatment limitations imposed by the anatomical complexities of the root canal. From the present century, it may be expected that this accumulated knowledge provides improvements in the endodontic science, making root canal treatment more predictable and successful. Therefore, the main purpose of this book is to focus on the complexity of root canal anatomy and discuss its relationship on the understanding of the principles and problems of shaping and cleaning procedures in order to provide thorough in-depth background knowledge of the internal anatomy of teeth.⁵

CHAPTER 2 - BASIC STRUCTURE OF TEETH :ENAMEL,DENTIN,PULP ENAMEL

Enamel is the most mineralized tissue of the body, forming a very hard, thin, translucent layer of calcified tissue that covers the entire anatomic crown of the tooth. It can vary in thickness and hardness on each tooth, from tooth to tooth and from person to person. It can also vary in color (typically from yellowish to grayish white) depending on variations in the thickness, quality of its mineral structure and surface stains. Enamel has no blood or nerve supply within it. It is enamel’s hardness that enables teeth to withstand blunt, heavy masticatory forces. Enamel is so hard because it is composed primarily of inorganic materials: roughly 95% to 98% of it is calcium and phosphate ions that make up strong hydroxyapatite crystals. Yet, these are not pure crystals, because they are carbonated and contain trace minerals such as strontium, magnesium, lead, and fluoride. These factors make “biological hydroxyapatite” more soluble than pure hydroxyapatite.¹ -³

Approximately 1% to 2% of enamel is made up of organic materials, particularly enamel- specific proteins called enamelins, which have a high affinity for binding hydroxyapatite crystals. Water makes up the remainder of enamel, accounting for about 4% of its composition.⁴

The inorganic, organic, and water components of enamel are highly organized: millions of carbonated hydroxyapatite crystals are arranged in long, thin structures called rods that are 4 µm to 8 µm in diameter. It is estimated that the number of rods in a tooth ranges from 5 million in the lower lateral incisor to 12 million in the upper first molar.¹,³ In general, rods extend at right angles from the dento–enamel junction (the junction between enamel and the layer below it called dentin) to the tooth surface. Surrounding each rod is a rod sheath made up of a protein matrix of enamelins. The area in between rods is called interrod enamel, or interrod cement. While it has the same crystal composition, crystal orientation is different, distinguishing rods from interrod enamel.¹ -³

Minute spaces exist where crystals do not form between rods. Typically called pores, they contribute to enamel’s permeability, which allows fluid movement and diffusion to occur, but they also cause variations in density and hardness in the tooth, which can create spots that are more prone to demineralization – the loss of calcium and phosphate ions – when oral pH becomes too acidic and drops . In demineralization, the crystalline structure shrinks in size, while pores enlarge.

Enamel is formed by epithelial cells called ameloblasts. Just before a tooth erupts from the gums, the ameloblasts are broken down, removing enamel’s ability to regenerate or repair itself. This means that when enamel is damaged by injury or decay, it cannot be restored beyond the normal course of remineralization. When a tooth erupts, it is also not fully mineralized. To completely mineralize the tooth, calcium, phosphorous, and fluoride ions are taken up from saliva to add a layer of 10 µm to 100 µm of enamel over time.

There are conditions that can affect the formation of enamel and thus increase the risk of caries. These include the genetic disorder amelogenesis imperfecta, in which enamel is never completely mineralized and flakes off easily, exposing softer dentin to cariogenic bacteria. Other conditions are linked with increased enamel demineralization, such as gastroesophageal reflux disease (GERD) and celiac disease.⁴,⁵

Abbildung in dieser Leseprobe nicht enthalten

FIGURE 2.1

DENTIN

Dentin is almost exclusively formed by the odontoblasts that are derived from embryonic connective ectomesenchymal cells from the cranial neural crest ⁷.The differentiating odontoblasts start the secretion of the predentinal proteins, followed by the initiation of enamel matrix secretion by the differentiating ameloblasts, at the site where the dentin- enamel junction (DEJ) is formed. During and right after the differentiation, the odontoblasts organize into a distinguished odontoblast cell layer, and the mineralization of organic matrix completes the formation of the first layer of dentin, mantle dentin ⁷. In the coronal part of the tooth, odontoblasts are tall cells, and their morphological and cell membrane polarization ⁸ is unique in the group of collagen-synthesizing cells. Odontoblasts form a single layer of cells between dentin and pulp, with the cell body located on a pulpal wall of dentin and odontoblast processes inserted into dentinal tubules (Figs. 2.1 and 2.2a). The cell bodies are 20–40 μm tall, depending on dentinogenic activity. The odontoblast process is a cytoplasmic process which penetrates into mineralized dentin tubules. The process has the 0.5–1 μm main trunk and thinner lateral branches ⁹.One of the longest controversies in dentin- pulp complex research has been the extent of odontoblast processes into dentinal tubules. This is caused by the conflicting results obtained with different research methods and by the possible differences between the species ⁹.In human teeth, most studies indicate that the odontoblast cell processes would not extend far from the dentin- pulp border (200–700 μm) (Fig. 2.2b).

Predentin and Mineralization Front The 10–30 μm layer of unmineralized predentin is located between odontoblasts and mineralized dentin (Figs. 2.1 and 2.2a). This is where the dentin organic matrix is organized before the controlled mineralization at the mineralization front to form intertubular dentin. The backbone of the organic matrix is type I collagen, whereas non- collagenous proteins— glycoproteins, proteoglycans, and enzymes—control the matrix maturation and mineralization. The mineralization front is often considered to be linear, but actually mineralized globular protrusions called calcospherites are common (Fig. 2.2a) ⁹. to form intertubular dentin.

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FIG. 2.2 Drawing of the dentin-pulp border. Odontoblast (OB) cell bodies with large nucleus at the pulpal terminus of the cell and cytoplasmic organelles form a tight cell layer separated from the mineralized dentin by predentin (PD) where the intertubular dentin organic matrix is organized before mineralization. Odontoblast The backbone of the organic matrix is type I collagen, whereas non- collagenous proteins— glycoproteins, proteoglycans, and enzymes—control the matrix maturation and mineralization. The mineralization front is often considered to be linear, but actually mineralized globular protrusions called calcospherites are common (Fig. 2.2a) ⁹.

DENTIN-ENAMEL JUNCTION

The dentin-enamel junction (DEJ) is not just an inactive interface between enamel and dentin but seems to be much more complex and interactive structure than previously believed ⁶ Phylogenetic, developmental, structural, and biological characteristics have led to the suggestions that instead of the DEJ, this structure should be termed the dentin-enamel junctional complex ¹⁰. The DEJ of human tooth is wavy, scalloped line between two mineralized structures. Laser- induced autofluorescence and emission spectroscopy demonstrate the DEJ as 7–15-μm-wide structure, which is distinct from both enamel and dentin ¹¹. The “primary” scallop size varies from 25 to 50 μm. They contain smaller (0.25– 2 μm) “secondary scallops” and intermingling sub-micrometer-sized ridges of dentin and enamel [¹²,¹³ ] .The scalloped form of the interface is thought to improve the mechanical attachment of enamel to dentin ⁶. However, human is among the very few species in which the scalloping DEJ has been demonstrated, questioning the role of this wavy structure to the enamel-dentin attachment. Instead of the scalloped form of the DEJ—or in addition to it— hydroxyapatite crystals extending through the DEJ into both structure [¹⁴ –¹⁶ ] and dentinal collagen fibrils reaching into enamel ¹⁷ may contribute to the durability and toughness of the DEJ under occlusal forces ⁶

MANTLE DENTIN

The mantle dentin is 5–30-μm-thick layer of the outermost dentin that in many aspects is different from the rest of the dentin. This is due to the different process of formation. The mantle dentin organic matrix is laid down during and immediately after the terminal differentiation of the odontoblasts and before their spatial organization into distinct cell layer. It also contains the remnant components of dental papilla, and the mechanisms of mineralization are different from what occurs at the mineralization front ⁴. It is devoid of large tubules; instead, multiple small ramifications of each tubule are present in the mantle dentin. The organic matrix in mantle dentin is less regular and contains so-called von Korff fibers consisting mainly of type III collagen ¹⁸. The mineral content of mantle dentin has also been thought to be lower than in circumpulpal dentin, but the differences may be very minor ¹⁴, and the change of the mineralization rate toward the pulp may be more gradual [¹⁵, ¹⁶ ]. Although mantle dentin has traditionally been considered to provide the elastic properties of dentin necessary to withstand high occlusal forces without enamel or dentin fractures, the actual “resilience zone” may be much wider ¹, even up to 500 μm ¹⁷. This may be contributed to the changes in tubular direction ¹⁷, changes in collagen fibril direction ¹⁸, and gradual increase in mineralization from the DEJ toward the pulp [¹⁵, ¹⁶ ].

CIRCUMPULPAL DENTIN

Primary and Secondary Dentin Primary dentin is formed fast during the formation and growth of the tooth and forms the main portion of dentin. After completion of primary dentinogenesis, dentin formation continues as secondary dentin at much slower rate (approximately 1/10) ⁶. The exact timing of the “end” of primary dentin formation has not been convincingly demonstrated, and animal experiments have indicated that primary dentin formation slows down gradually ²⁴. It is often difficult to distinguish secondary dentin from primary dentin even in histological or electron microscopy images, and in clinical conditions it is not possible at all.

COMPOSITION OF DENTIN EXTRACELLULAR MATRIX

Dentin organic matrix is in many ways similar to that in bone; in other ways, it is quite unique. The absence of type I collagen and high level of collagen cross-linking is typical features to mineralized tissue. About 90% of dentinal organic matrix is type I collagen, the rest being non-collagenous proteins such as proteoglycans and other proteins, growth factors and enzymes, and small amount of lipids ⁶. However, mature human odontoblasts produce type III collagen, and it is present in dentinal tubules ²⁶. Type III collagen is also found in dentinogenesis imperfecta ²⁷ and in reparative dentin under carious lesions ²², ²³.

DENTINAL TUBULES

Tubularity is an important characteristic of dentin, contributing, e.g., to the mechanical properties and behavior in dentin bonding. Although the tubules are generally believed to extend from the DEJ at right angles and run slightly S-shaped course through the dentin, the direction may be different immediately beneath enamel ²². There may also be differences in tubule orientation between the dental arches ²², which may reflect the response to loading of teeth under occlusal forces [⁶, ²² ]. Tubular density is highest, and the direction is straighter under the cuspal area ²⁹, where the odontoblast processes and dense nerve innervation have also been suggested to penetrate deeper into the tubules ⁶. These features may be related to the sensing of external irritation and regulation of dentin-pulp complex defensive reactions, since the cusp tips are the first to be worn in mastication ⁶.

PERITUBULAR DENTIN AND DENTIN SCLEROSIS

Peritubular dentin is highly mineralized circular cuff forming to the inner walls of dentinal tubules (Fig. 2.3). The name “peritubular” is, strictly speaking, incorrect, since “peri” (“around,” “surrounding,” “enclosing”) would indicate something that is formed around the tubules. A more correct phrase would be intratubular, but since “peritubular” has been and is still used extensively, this phrase will also be used here. Peritubular dentin formation causes an age- related reduction in tubular lumen even in intact dentin, best seen in the increased dentinal transparency advancing from the tip of the root toward the crown with age ³⁰.

In case of extensivewear or caries, the tubules may also be occluded by mineral crystals formed due to reprecipitation of minerals or from the mineral ions delivered from the pulpal side via dentinal fluid. This phenomenon is—confusingly—also called dentin sclerosis, although “reactive (dentin) sclerosis” might be the more appropriate term ⁶. Peritubular dentin is a separate phase from intertubular dentin, forming a distinct annulus within each tubule instead of intertubular dentin matrix-mediated crystallization (Fig. 2.3b). However, peritubular dentin is often heterogeneous, and several separate or connected mechanisms may occur at the same time [⁶, ¹⁵ ]. Peritubular dentin is perforated by tubular branches but also by several small fenestrations ³¹ (Fig. 2.3b), which allow tubular fluid and its components pass back and forth across the peritubular dentin. Peritubular dentin may thus not act only as a passive blockage of dentinal tubules but also contribute to the vitality and possibly even remodelling of mineralized dentin as a whole.

TERTIARY DENTIN

Tertiary dentin formation is a response to external irritation, such as wear, erosion, trauma, caries, or cavity preparation. The growth factors present in mineralized dentin and liberated during caries or wear are believed to initiate and control the tertiary dentin formation and structure ³². Tertiary dentin increases the mineralized barrier thickness between oral microbes and other irritants and pulp tissue, aiming to retain the pulp tissue vital and noninfected. The form and regularity of tertiary dentin depend on the intensity and duration of the stimulus. There are two kinds of tertiary dentin, namely, reactionary dentin, formed by original odontoblasts, and reparative dentin, formed by newly differentiated replacement odontoblasts (Fig. 2.4) [¹², ¹⁴ ]. Reactionary dentin is tubular and relatively similar to secondary dentin in structure, while reparative dentin is usually atubular (or poorly tubularized) and may present variable forms (Fig. 2.5). Reparative dentin is believed to be relatively impermeable, forming a barrier between tubular dentin and pulp tissue.

ROOT DENTIN

Root dentin bears strong resemblance but also certain distinct differences to coronal dentin. The outermost layer of root dentin, the granular layer of Tomes, is located right beneath the root cemenatum. It is thought to represent the mantle dentin with thin canaliculi and poorly fused globules which perhaps represent the mineralization pattern in the early stages of root dentin/cementum formation ⁶. The tubular density in root dentin is at least moderately [²⁹, ³³ ] or even drastically ³⁴ lower than in coronal dentin, especially in the most apical part [²⁴, ²⁸, ³⁰, ³¹ ]. The apical portion of human dentin has also other structural variations, such as relatively large number of accessory root canals, transient and repaired surface resorption, and cementum-like lining the apical root canal wall ¹¹. Interestingly, age- related root tubular sclerosis starts from the apical region and advances coronally [³⁵, ⁴² ], and it may be the main factor influencing permeability of root dentin [³⁸, ³⁹ ] (Fig. 2.6a). Root dentin has also other regional differences in permeability, as buccal/lingual root canal dentin has patent tubules, while the mesial/distal dentinpulp borders may be completely occluded with minerals [³⁸, ³⁹ ] (Fig. 2.6b). This kind of patterns of tubule patency may correspond to local stress distributions of the roots under occlusal loading ⁶.

AGE-RELATED CHANGES

The best known—and the most important in terms of clinical endodontology—age-induced changes in human dentin-pulp complex are the obliteration of the pulp chamber and root canals even in intact teeth, due to physiological slow- rate secondary dentin formation. In incisors, canines, and premolars, the physiological age- related obliteration usually advances from the coronal direction, while in molars the dentin in the pulp chamber floor may also grow toward the roof, contributing to the pulp chamber occlusion.⁴⁰

CARIES-AFFECTED DENTIN

The concept of minimally invasive dentistry limits the cavity preparation to the removal of caries- infected dentin, leaving the restoration to be adhesive-bonded to caries-affected dentin. The immediate bond strengths to caries-affected dentin are commonly 20–50% lower than to sound dentin and even lower with caries-infected dentin ⁴⁷. Caries-affected dentin has lower mineral content, increased porosity, and altered structure and distribution of dentin collagen and non- collagenous proteins ⁴⁸. These changes increase dentin wetness and significantly reduce dentin mechanical properties, such as hardness, stiffness, tensile strength, modulus of elasticity, and shrinkage during drying ⁴⁷ (Fig. 2.8), which make the dentin in and under the hybrid layer more prone to cohesive failures due to the polymerization shrinkage (Fig. 2.9) and under occlusal forces. In vitro experiments have shownthat even short exposure of dentin to lactic acid (the acid produced by S. mutans and mainly responsible for caries demineralization) at pH 5 significantly reduces dentin fatigue strength, increases the rate of crack extension, and reduces the fatigue crack growth resistance [⁴⁹, ⁵⁰ ] in a way that is not prevented by sealing the tubular lumens with adhesive resin ⁵⁰. Since fatigue crack and its growth are precursors to unstable fracture, lactic acid exposure, which has occurred in caries-affected dentin and may again occur, e.g., in secondary caries, substantially increases the likelihood of restored tooth failure by fracture at lower mastication forces ⁵⁰. And finally, deep restorations (typically present in endodontically treated teeth) are more prone to cracks and fractures, not only because of the weaker structure due to loss of tooth tissue but also because of the incremental crack extension with significantly lower cyclic stresses in deep vs. superficial dentin ⁵¹. Taken together, the age- and caries-related changes in dentin composition and structure that may have deleterious effects on dentin mechanical cannot be avoided. However, the dramatic consequences, such as catastrophic tooth fractures, can be avoided if the restorative procedures are performed not only to repair and limit the damage from caries but also to protect and preserve the tooth structure.

PULP

The pulp is the part in the center of a tooth made up of living connective tissue and cells called odontoblasts. The pulp is a part of the dentin–pulp complex (endodontium).[ The vitality of the dentin-pulp complex, both during health and after injury, depends on pulp cell activity and the signaling processes that regulate the cell's behavior.

STRUCTURAL FEATURES

The pulp is basically a loose connective tissue. Therefore, it contains a ground substance (intercellular substance) in which are embedded cells and fibres. Like other connective tissue, it contains supporting elements—the blood vessels and nerves.

The central region of both the coronal and the radicular pulp contains large nerve trunks and blood vessels. Peripherally, the pulp is circumscribed by the specialized odontogenic region composed of (1) the odontoblasts (the dentin-forming cells), (2) the cell-free zone (Weil’s zone), and (3) the cell-rich zones The cell-free zone is a space in which the odontoblast may move pulpward during tooth development and later to a limited extent in functioning teeth. This may be why the zone is inconspicuous during early stages of rapid dentinogenesis since odontoblast migration would be greatest at that time. The cell-rich layer composed principally of fibroblasts and undifferentiated mesenchymal cells is restricted to the coronal regions, as it is formed during the pre- eruptive phase of the tooth. During early dentinogenesis, there are also many young collagen fibers in this zone .

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FIGURE 2.3 Diagram of pulp organ, illustrating architecture of large central nerve trunks (dark) and vessels (light) and peripheral cell-rich, cell-free, and odontoblast rows. Observe small nerves on blood vessels

ZONES OF PULP

Table 2.1

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INTERCELLULAR SUBSTANCE

The intercellular substance is dense and gel like in nature, varies in appearance from finely granular to fibrillar, and appears more dense in some areas, with clear spaces left between various aggregates. It is composed of both acid mucopolysaccharides and protein. polysaccharide compounds (glycosaminoglycans and proteoglycans). During early development, the presence of chondroitin A, chondroitin B, and hyaluronic acid has been demonstrated in abundance.

Glycoproteins are also present in the ground substance. The aging pulp contains less of all of these substances. The ground substance lends support to the cells of the pulp while it also serves as a means for transport of nutrients from the blood vessels to the cells, as well as for transport of metabolites from cells to blood vessels.

Glycosaminoglycans being hydrophilic, forms a gel and contributes to high tissue fluid pressure of the pulp. Hyaluronan, in addition to mechanical function helps in cell migration. Versican forms the bulk of the proteoglycans. Syndecan, another important proteoglycan, attaches to the cell and acts as an adhesion molecule between fibroblast and collagen. It also binds signaling molecules like fibroblastic growth factor. Tenascin and fibronectin, which promote cell adhesion and cell migration are absent in areas of inflammation. Laminin, which is present in the basement membrane of blood vessels, also coats the odontoblast cell membrane. Integrins, the glycoproteins, which interact to form cell surface adhesion receptors were found in pulp to get attached to biologically active molecules like laminin and fibronectin.

FIBERS

The collagen fibers in the pulp exhibit typical cross-striations at 64 nm (640 Å) and range in length from 10 to 100 nm or more (Fig. 6.5). The main type of collagen fiber in the pulp is type I. Type III collagen is also present. Bundles of these fibers appear throughout the pulp. In very young pulp, fine fibers ranging in diameter from 10 to 12 nm (100 to 120 Å) have been observed. These fine fibers are called fibrillin. Downregulation and degradation of fibrillin helps in release of TGF-β, which in turn promotes the formation of a mineralized tissue barrier in exposed pulps.

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FIGURE 2.4 Typical collagen fibers of the pulp with 640 Å banding.

Pulp collagen fibers do not contribute to dentin matrix production, which is the function of the odontoblast. After root completion, the pulp matures and bundles of collagen fibers increase in number. They may appear scattered throughout the coronal or radicular pulp, or they may appear in bundles. These are termed diffuse or bundle collagen depending on their appearance, and their presence may relate to environmental trauma. Fiber bundles are most prevalent in the root canals, especially near the apical region.

CELLS OF THE PULP

The predominant cell of the pulp is the fibroblast. The cells unique to pulp are the odontoblasts. Apart from these cells, the pulp contains defense cells, undifferentiated mesenchymal cells, and pulpal stem cells.

FIBROBLASTS

The pulp organ is said to be consisting of specialized connective tissue because it lacks elastic fibers. Fibroblasts are the most numerous cell type in the pulp. As their name implies, they function in collagen fiber formation throughout the pulp during the life of the tooth. They have the typical stellate shape and extensive processes that contact and are joined by intercellular junctions to the processes of other fibroblasts (fig 2.4). Under the light microscope, the fibroblast nuclei stain deeply with basic dyes, and their cytoplasm is lighter stained and appears homogeneous. Electron micrographs reveal abundant rough- surfaced endoplasmic reticulum, mitochondria, and other organelles in the fibroblast cytoplasm (fig 2.5B). This indicates that these cells are active in pulpal collagen production. There is some difference in appearance of these cells depending on the age of the pulp organ. In the young pulp, the cells divide and are active in protein synthesis, but in the older pulp, they appear rounded or spindle shaped with short processes and exhibit fewer intracellular organelles. They are then termed fibrocytes. In the course of development, the relative number of cellular elements in the dental pulp decreases, whereas the fiber population increases (fig 2.5). In the embryonic and immature pulp, the cellular elements predominate, while in the mature pulp, the fibrous components predominate. The fibroblasts of the pulp, in addition to forming the pulp matrix, also have the capability of ingesting and degrading this same matrix. These cells thus have a dual function with pathways for both synthesis and degradation in the same cell.

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FIGURE 2.5 (A) Typical fibroblasts of pulp are stellate in shape with long processes. (B) Electron micrograph of pulp fibroblast.

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FIGURE 2.6 Age changes of dental pulp. Cellular elements decrease and fibrous intercellular substance increases with advancing age. (A)

Newborn infant. (B) Infant 9 months of age. (C) Adult.

Fibroblasts play an important role in inflammation and healing.

Fibroblasts secrete angiogenic factors like FGF-2 and VEGF, especially after injury, which help in healing. They are also shown to secrete colony-stimulating factors, which help in the migration of class II major histocompatibility expressing cells into the pulp tissue. They release inflammatory mediators cytokines and growth factors. In cell cultures, they form mineralized tissue like bone on stimulation.

Undifferentiated mesenchymal cells

Undifferentiated mesenchymal cells are the primary cells in the very young pulp, but a few are seen in the pulps after root completion.

They appear larger than fibroblasts and are polyhedral in shape with peripheral processes and large oval staining nuclei. The latter are distinctive because they lack a ribosome- studded endoplasmic reticulum and have mitochondria with readily discernible cisternae. They are found along pulp vessels, (Fig. 6.8) in the cell-rich zone and scattered throughout the central pulp. Viewed from the side, they appear spindle shaped. They are believed to be a totipotent cell and when need arises they may become odontoblasts, fibroblasts, or macrophages. They decrease in number in old age.

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FIGURE2.7 Defensecellsinpulp.

ODONTOBLASTS

Odontoblasts, the second most prominent cell in the pulp, reside adjacent to the predentin with cell bodies in the pulp and cell processes in the dentinal tubules. The number of odontoblasts corresponds to the number of dentinal tubules. They are approximately 5–7 µm in diameter and 25–40 µm in length. They have a constant location adjacent to the predentin, in what is termed the “odontogenic zone of the pulp” (Fig. 6.9). The cell bodies of the odontoblasts are columnar in appearance with large oval nuclei, which fill the basal part of the cell (Fig. 6.9). Immediately adjacent to the nucleus basally is rough-surfaced endoplasmic reticulum and the Golgi apparatus. The cells in the odontoblastic row lie very close to each other. Between odontoblasts gap, tight and desmosomal junctions exist (Fig. 6.10). Further toward the apex of the cell appears an abundance of rough-surfaced endoplasmic reticulum. Near the pulpal– predentin junction, the cell cytoplasm is devoid of organelles. Focal junctional complexes are present where the odontoblast cell body gives rise to the process. Actin filaments are inserted into this region. The clear terminal part of the cell body and the adjacent intercellular junction is described by some as the terminal bar apparatus of the odontoblast. At this zone, the cell constricts to a diameter of 3–4 µm, where the cell process enters the predentinal tubule (fig 2.7)

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FIGURE 2.8 Diagram of odontogenic zone illustrating odontoblast, cell-free, and cell-rich zones, with blood vessels and nonmyelinated nerves among odontoblasts.

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FIGURE 2.8 Close relation of adjacent odontoblasts. Note junctional complexes between cells (arrows).

The process of the cell contains no endoplasmic reticulum, but during the early period of active dentinogenesis, it does contain occasional mitochondria and vesicles. During the later stages of dentinogenesis, these are less frequently seen.

The odontoblast morphology and its organelles vary with the functional activity of the cell. An active cell is elongated whereas a resting cell is stubby. The active cell has a basally placed nucleus and a basophilic cytoplasm. The resting cell has little cytoplasm but amore hematoxyphilic nucleus.

There is also a striking difference in the cytoplasm of the young cell body, active in dentinogenesis, and the older cell. During this early active phase, the Golgi apparatus is more prominent, the rough- surfaced endoplasmic reticulum is more abundant, and numerous mitochondria appear throughout the odontoblast. A great number of vesicles are seen along the periphery of the process where there is evidence of protein synthesis along the tubule wall. The cell actually increases in size as its process lengthens during dentin formation.

When the cell process becomes 2 mm long, it is then many times greater in volume than the cell body. While the active cell is rich in organelles, the resting cell is devoid of organelles especially in the supranuclear region, where mainly lipid-filled vacuoles are present. Ultrastructurally, an intermediate stage between active and resting called transitional stage is recognized. In this stage, the cells are narrower with fewer organelles and with the presence of autophagic vacuoles. Recently, primary cilia have been identified in odontoblast. These cilia may play a role in response of odontoblasts to external stimuli.

The form and arrangement of the bodies of the odontoblasts are not uniform throughout the pulp. They are more cylindrical and longer (tall columnar) in the crown (Fig. 6.11A) and more cuboid in the middle of the root (Fig. 6.11B). Close to the apex of an adult tooth, the odontoblasts are ovoid and spindle shaped, appearing more like osteoblasts than odontoblasts, but they are recognized by their processes extending into the dentin. The pseudostratified arrangement seen in the coronal pulp is due to the crowding of cellsin this region (Fig. 6.11C). Ultrastructurally, ring-layered structures have been observed between aging odontoblasts that might be characteristic of aging teeth.

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FIGURE 2.9 Variation of odontoblasts in different regions of one tooth. (A) High columnar odontoblasts in pulp chamber. (B) Low columnar odontoblasts in root canal. (C) Flat odontoblasts in apical region.

Collagen is assembled in the odontoblast similar to that occurring in fibroblast. The noncollagenous proteins which are secreted by the odontoblast may be present in the same secretory granule along with the collagen.

Odontoblasts are end cells. They have lost the ability to divide.

When they die they have to be replaced by cells, which differentiate from the cell-rich zone. Odontoblast and subodontoblastic cells have been shown to undergo apoptotic cell death by apoptotic cell markers like bcl-2.

Odontoblasts release inflammatory chemokine interleukin-8 which is chemotactic for neutrophils. Nerve growth factor and its receptor found in the odontoblasts are chemoattractants for neutrophils. Nitric oxide synthetase are important enzymes for vasodilatation and blood pressure regulation. These have been identified in odontoblasts and endothelial cells of the pulp. This finding suggests that they may have a role in mediating cell proliferation and vasodilatation.

DEFENSE CELLS

In addition to fibroblasts, odontoblasts, and the cells that are a part of the neural and vascular systems of the pulp, there are cells important to the defense of the pulp. These are histiocytes or macrophages, dendritic cells, mast cells, and plasma cells. In addition, there are the blood vascular elements such as the neutrophils (PMNs), eosinophils, basophils, lymphocytes, and monocytes. These latter cells emigrate from the pulpal blood vessels and develop characteristics in response to inflammation.

The histiocyte or macrophage is an irregularly shaped cell with short blunt processes. In the light microscope, the nucleus is somewhat smaller, more rounded, and darker staining thanthat of fibroblasts, and it exhibits granular cytoplasm. When the macrophages are inactive and not in the process of ingesting foreign materials, one faces difficulty in distinguishing them from fibroblasts. In the case of a pulpal inflammation, these cells exhibit granules and vacuoles in their cytoplasm, and their nuclei increase in size and exhibit a prominent nucleolus. Their presence is disclosed by intravital dyes such as toluidine blue. These cells are usually associated with small blood vessels and capillaries. Ultrastructurally, the macrophage exhibits a rounded outline with short, blunt processes (Fig. 6.12). Invaginations of the plasma membrane are noted, as are mitochondria, rough-surfaced endoplasmic reticulum, free ribosomes, and also a moderately dense nucleus. The distinguishing feature of macrophages is aggregates of vesicles, or phagosomes, which contain phagocytized dense irregular bodies.

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FIGURE 2.10 (A) This histiocyte or macrophage is located adjacent to capillary in peripheral pulp. Characteristic aggregation of vesicles, vacuoles, and phagocytized dense bodies is seen to right of capillary wall. (B) Multivesiculated body characteristic of macrophage. Note typical invagination of cell plasma membrane (arrow). This cell is located adjacent to group of nonmyelinated nerve fibers seen on left.

DENDRITIC CELLS were found in close relation to and in contact with the cell membranes of the endothelial cell. These cells express macrophage-related antigens (CD14 and CD68) and were identified by their immunopositivity to HLA-DR monoclonal antibodies. These cells are similar to Langerhans cells. They present the antigen to the T cells. Some of these cells formed a reticular network in the connective tissue. In deciduous teeth, these dendritic cells were shown to be closely associated with odontoblasts. Their dendritic process sometimes extended into the dentinal tubules and made contact withthe odontoblastic process. Their numbers were found to increase in areas affected by caries, attrition, or restorative procedures. These suggest that they have an important role to play in immunosurveillance. In view of their close association with odontoblasts, it is suggested that these cells may have some regulatory function on the odontoblast. Immunocompetent cells present in deciduous teeth increased in number during shedding.

Both lymphocytes and eosinophils are found extravascularly in the normal pulp (Fig. 6.13), but during inflammation they increase noticeably in number. Most of the lymphocytes present in the pulp are T lymphocytes. Mast cells are also seen along vessels in the inflamed pulp. They have a round nucleus and contain many dark-staining granules in the cytoplasm, and their number increases during inflammation.

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FIGURE 2.11 (A) Small lymphocyte located in pulp. Cytoplasm forms narrow rim around large oval-to-round nucleus. (B) Eosinophil in extravascular location in pulp organ. Nucleus is polymorphic, and granules in cytoplasm are characteristically banded.

The plasma cells are seen during inflammation of the pulp (Fig. 6.14). With the light microscope, the plasma cell nucleus appears small and concentric in the cytoplasm. The chromatin of the nucleus is adherent to the nuclear membrane and gives the cell a cartwheel appearance.

The cytoplasm of this cell is basophilic with a light-stained Golgi zone adjacent to the nucleus. Under the electron microscope, these cells have a densely packed, rough-surfaced endoplasmic reticulum. Both immature and mature cells may be found. The mature type exhibits a typical small eccentric nucleus and more abundant cytoplasm 6The plasma cells function in the production of antibodies (T

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FIGURE 2.12 Cluster of plasma cells in pulp with early caries pulpitis.

Observe dense peripheral nuclear chromatin and cytoplasm with cisternae of rough endoplasmic reticulum. Source: (Courtesy C

Torneck, University of Toronto Dental School).

Table 2.1

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PULPAL STEM CELLS

Among the numerous stem cells that have been identified from dental tissues and characterized, those from the pulpal tissues include dental pulp stem cells (DPSCs) and stem cells from human exfoliated deciduous teeth (SHED). Stem cells are found in higher concentration in coronal pulp than in radicular pulp.

Pulpal stem cells express cytokeratin 18 and 19, indicating a potential for odontoblast differentiation and dentin repair at sites of injury. A comparative study of bone marrow and DPSCs indicates that they are influenced by different regulatory mechanisms to engage in bone and dentin formation, respectively. Dentin sialoprotein, a marker for dentin synthesis has been observed in DPSC transplants, while in bone marrow stem cell transplants expression of fibroblast growth factor (FGF) and matrix metalloproteinase (MMP-9) have been seen. Numerous growth factors including transforming growth factor (TGF), bone morphogenetic protein (BMP-2) and dentin matrix protein 1 (DMP-1) are capable of inducing proliferation and differentiation of DPSCs. DMP-1 has been shown to induce formation of dental pulp-like tissue in vivo.

Pulpal stem cells are pluripotential having the capacity for angiogenic, chondrogenic, osteogenic, adipogenic, and neurogenic differentiation, in some cases exceeding that of bone marrow stem cells. The pulpal tissues of exfoliated deciduous teeth and permanent third molars may serve as a suitable source of stem cells for future stem cell–based therapies as they are found to be viable after cryopreservation. The application of DPSCs in regenerative dentistry and medicine (regeneration of bone and neural tissues) holds great promise.

Blood vessels

The pulp organ is extensively vascularized. It is known that the blood vessels of both the pulp and the periodontium arise from the inferior or superior alveolar artery and also drain by the same veins in both the mandibular and maxillary regions. The communication of the vessels of the pulp with the periodontium, in addition to the apical connections, is further enhanced by connections through the accessory canals. These relationships are of considerable clinical significance in the event of a potential pathologic condition in either the periodontium or the pulp, because the infection has a potential to spread through the accessory and apical canals. Although branches of the alveolar arteries supply both the tooth and its supporting tissues, those periodontal vessels entering the pulp change their structure from the branches to the periodontium and become considerably thinner walled than those surrounding the tooth.

Small arteries and arterioles enter the apical canal and pursue a direct route to the coronal pulp (Fig. 6.15). Along their course they give off numerous branches in the radicular pulp that pass peripherally to form a plexus in the odontogenic region. Pulpal blood flow is more rapid than in most areas of the body. This is perhaps attributable to the fact that the pulpal pressure is among the highest of body tissues. The flow of blood in arterioles is 0.3–1 mm per second, in venules approximately 0.15 mm per second, and in capillariesabout mm per second. The largest arteries in the human pulp are 50–100 µm in diameter, thus equaling in size arterioles found in most areas of the body. These vessels possess three layers. The first, the tunica intima, consists of squamous or cuboid endothelial cells surrounded by a closely associated basal lamina. Where the endothelial cells contact, they appear overlapped to varying degrees. The second layer, the tunica media, is approximately 5-µm thick and consists of one to three layers of smooth muscle cells (Fig. 6.16). A basal lamina surrounds and passes between these muscle cells and separates the muscle cell layer from the intima. Occasionally, the endothelial cell wall is in contact with the muscle cells. This is termed a myoendothelial junction. The third and outer layer, the tunica adventitia, is made up of a few collagen fibers forming a loose network around the larger arteries. This layer becomes more conspicuous in vessels in older pulps. Arterioles with diameters of 20– 30 µm with one or occasionally two layers of smooth muscle cells are common throughout the coronal pulp (Fig. 6.17). The tunica adventitia blends with the fibers of the surrounding intercellular tissue. Terminal arterioles with diameters of 10–15 µm appear peripherally in the pulp. The endothelial cells of these vessels contain numerous micropinocytotic vesicles, which function in transendothelial fluid movement. A single layer of smooth muscle cells surrounds these small vessels. Occasionally, a fibroblast or pericyte lies on the surface of these vessels. Pericytes are capillary-associated fibroblasts. They are present partially encircling the capillaries. They have contractile properties and they are capable of reducing the size of the capillary lumen. Their nuclei can be distinguished as round or slightly oval bodies closely associated with the outer surface of the terminal arterioles or precapillaries.. Some authors call the smaller diameter arterioles “precapillaries.” They are slightly larger than the terminal capillaries and exhibit a complete or incomplete single layer of muscle cells surrounding the endothelial lining. These range in size from 8 to 12 µm.

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FIGURE 2.13 Branching artery and nerve trunk in the pulp.

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FIGURE 2.14 Small arteriole near central pulp exhibiting relatively thick layer of muscle cells. Dense basement membrane interspersed between endothelial and muscle cells (arrow). FIGURE 2.15 Peripheral pulp and small arteriole or precapillary exhibiting two thin layers of smooth muscle cells surrounding the endothelial cell lining of vessel. Nucleus at bottom left of figure belongs to a pericyte.

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FIGURE 2.15 Area near subodontoblastic plexus showing both myelinated and nonmyelinated axons adjacent to large capillary or precapillary. Endothelial cell lining is surrounded by basement membrane (arrow) and pericytes.

Veins and venules that are larger than the arteries also appear in thecentral region of the root pulp. They measure 100–150 µm indiameter, and their walls appear less regular than those of the arteries because of bends and irregularities along their course. The microscopic appearance of the veins is similar to that of the arteries except that they exhibit much thinner walls in relation to the size of the lumen.

The endothelial cells appear more flattened, and their cytoplasm does not project into the lumen. Fewer intracytoplasmic filaments appear in these cells than in the arterioles. The tunica media consists of a single layer or two of thin smooth muscle cells that wrap around the endothelial cells and appear discontinuous or absent in the smaller venules. The basement membranes of these vessels are thin and less distinct than those of arterioles. The adventitia is lacking or appears as fibroblasts and fibers are continuous with the surrounding pulp tissue. Occasionally, two venous loops will be seen connected by an anastomosing branch. Both venous-venous anastomosis and arteriole- venous anastomosis occur in the pulp. The arteriole-venous shunts may have an important role in regulation of pulpal blood flow.

Frequently arteriole or precapillary loops with capillaries are found underlying the odontogenic zone in the coronal pulp.

Blood capillaries, which appear as endothelium-lined tubes, are 8– 10 µm in diameter. The nuclei of these cells may be lobulated and have cytoplasmic projections into the luminal surface. The terminal network of capillaries in the coronal pulp appears nearly perpendicular to the main trunks. The vascular network passesamong the odontoblasts and underlies them as well. A few peripheral capillaries found among the odontoblasts have fenestrations in the endothelial cells. These pores are located in the thin part of the capillary wall and are spanned only by the thin diaphragm of contacting inner and outer plasma membranes of endothelial cells (Fig. 6.19). These fenestrated capillaries are assumed to be involved in rapid transport of metabolites at a time when the odontoblasts are active in the process of dentinal matrix formation and its subsequent calcification. Both fenestrated and continuous terminal capillaries are found in the odontogenic region. During active dentinogenesis capillaries appear among the odontoblasts adjacent to the predentin.

Later, after the teeth have reached occlusion and dentinogenesis slows down, these vessels usually retreat to a subodontoblastic position (Table 2.1).

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FIGURE 2.16 (A) Terminal capillary loops located among odontoblasts may be fenestrated. These capillaries have both thick and thin segments in their walls. (B) Endothelial cell wall bridges pores (arrows) and is supported only by basement membrane (**).

TABLE 2.3 Microcirculation of Pulp

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LYMPH VESSELS

Lymph capillaries are described as endothelium-lined tubes that join thin-walled lymph venules or veins in the central pulp. The lymphatic capillaries have thin walls. Cellular projections arise from the endothelial cells. The cells contain multivesicular structures, Weibel– Palade bodies, and paracrystalline inclusions. The lymphatic vessels were more numerous in the central part of the pulp than in the peripheral areas. The larger vessels have an irregular-shaped lumen composed of endothelial cells surrounded by an incomplete layer of pericytes or smooth muscle cells or both. Further, the lymph vessels differ from venules in that their walls and basement membrane show discontinuities, with the absence of RBCs but with the presence of lymphocytes in the lumen. In inflamed pulps, due to increased interstitial fluid pressure, gap junction develops between the endothelial cells of the dilated lymph capillaries. Lymph vessels draining the pulp and periodontal ligament have a common outlet. Those draining the anterior teeth pass to the submental lymph nodes; those of the posterior teeth pass to the submandibular and deep cervical lymph nodes.

NERVES

The abundant nerve supply in the pulp follows the distribution of the blood vessels. The majority of the nerves that enter the pulp are nonmyelinated. Many of these gain a myelin sheath later in life. The nonmyelinated nerves are found in close association with the blood vessels of the pulp and many are sympathetic in nature. They have terminals on the muscle cells of the larger vessels and function in vasoconstriction (Fig. 6.18). Thick nerve bundles enter the apical foramen and pass along the radicular pulp to the coronal pulp where their fibers separate and radiate peripherally to the parietal layer of nerves (Figs 6.20 and 6.21). The number of fibers in these bundles varies greatly, from as few as 150 to more than 1200. The larger fibers range between 5 and 13 µm, although the majority are smaller than 4 µm. The perineurium and the epineurium of the pulpal nerves are thin. The large myelinated fibers mediate the sensation of pain that may be caused by external stimuli.

The peripheral axons form a network of nerves located adjacent to the cell-rich zone. This is termed the parietal layer of nerves, also known as the plexus of Raschkow (Fig. 6.22). Both myelinated axons, ranging from 2 to 5 µm in diameter, and minute nonmyelinated fibers of approximately 200– 1600 µm (2000–16,000 Å) in size make up this layer of nerves. The parietal layer develops gradually, becoming prominent when root formation is complete.

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FIGURE 2.17 Major nerve trunks branch in pulp and pass to parietal layer, which lies adjacent to cell-rich zone. Cell-rich zone curves upward to right.

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FIGURE 2.18 Parietal layer of nerves is composed of myelinated nerve fibers. Cell-rich zone curves upward to right.

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FIGURE 2.19 Terminal nerve endings located among odontoblasts.

These arise from subjacent parietal layer.

NERVE ENDINGS

The mature deciduous teeth are well innervated, especially the coronal pulp, have many nerve endings terminating in or near odontoblast layer, with a few penetrating into the dentin. Nerve axons from the parietal zone pass through the cell-rich and cell-free zones and either terminate among or pass between the odontoblasts to terminate adjacent to the odontoblast processes at the pulp–predentin border or in the dentinal tubules. Nerve terminals consisting of round or oval enlargements of the terminal filaments contain microvesicles, small, dark, granular bodies, and mitochondria (Fig. 6.23). These terminals are very close to the odontoblast plasma membrane, separated only by a 20-µm (200 Å) cleft (Fig. 6.24). Many of these indent the odontoblast surface and exhibit a special relationship to these cells. Most of the nerve endings located among the odontoblasts are believed to be sensory receptors. Some sympathetic endings are found in this location as well. Whether they have some function relative to the capillaries or the odontoblast in dentinogenesis is not known. The nerve axons found among the odontoblasts and in the cell-free and cell-rich zones are nonmyelinated but are enclosed in a Schwann cell covering. It is presumed that these fibers lost theirmyelin sheath as they passed peripherally from the parietal zone. More nerve fibers and endings are found in the pulp horns than in other peripheral areas of the coronal pulp.

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FIGURE 2.19 Vesiculated nerve endings in predentin in zone adjacent to odontoblast process.

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FIGURE 2.20 Vesiculated nerve ending partially surrounded by an odontoblast process located adjacent to predentin. Note the uniform cleft-like space between the nerve ending and the odontoblast process.

Gap junction appears between odontoblasts.

Recently a great deal of information has been reported regarding the types of potential neurotransmitters that are present in the nerves of the dental pulp. Substances such as substance P, 5- hydroxytryptamine, vasoactive intestinal peptide, somatostatin, and prostaglandins, as well as acetylcholine and norepinephrine have been found throughout the pulp. The majority of these putative transmitters have been shown to affect vascular tone and subsequently modify the excitability of the nerve endings. Some of the neuropeptides, like calcitonin gene–related peptide (CGRP) and substance P are potent vasodilators, while others like norepinephrine and neuropeptide Y are vasoconstrictors. Some neuropeptides like substance P act as nociceptive transmitter, in that they help to transmit pain sensation, while others like somatostatin act against them.

Further, it has been suggested that these changes in vascular tone can also affect the incremental growth of dentin.

It is a feature unique to dentin receptors that environmental stimuli always elicit pain as a response. Sensory response in the pulp cannot differentiate between heat, touch, pressure, or chemicals. This is because the pulp organs lack those types of receptors that specifically distinguish these other stimuli (Table 6.5).

Table 2.4

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Functions

Inductive

The primary role of the pulp anlage is to interact with the oral epithelial cells, which leads to differentiation of the dental lamina and enamel organ formation. The pulp anlage also interacts with the developing enamel organ as it determines a particular type of tooth.

Formative

The pulp organ cells produce the dentin that surrounds and protects the pulp. The pulpal odontoblasts develop the organic matrix and function in its calcification. Through the development of the odontoblast processes, dentin is formed along the tubule wall as well as at the pulp–predentin front.

Nutritive

The pulp nourishes the dentin through the odontoblasts and their processes and by means of the blood vascular system of the pulp.

Protective

The sensory nerves in the tooth respond with pain to all stimuli such as heat, cold, pressure, operative cutting procedures, and chemical agents. The nerves also initiate reflexes that control circulation in the pulp. This sympathetic function is a reflex, providing stimulation to visceral motor fibers terminating on the muscles of the blood vessels. tubules. The changes in the odontoblast, subodontoblastic layer and type of tertiary dentin formation varies with the extent of caries exposing the dentin (open/closed lesion), its progression (active/slowly progressive lesion). The reparative dentin was found to be more atubular in closed/active lesions and more tubular in open/slowly progressive lesions.

After injury to the mature tooth, the fate of the odontoblast can vary according to the intensity of the injury. Milder injury can result in functional activity leading to focal secretion of a reactionary dentin matrix, called regeneration, while greater injury can lead to odontoblast cell death. Induction of differentiation of a new generation of odontoblast- like cells can then lead to reparative dentinogenesis.

Both the reparative dentin created in the pulp and the calcification of the tubules (sclerosis) are attempts to wall off the pulp from the source of irritation. Also, the pulp may become inflamed due to bacterial infection or by cutting action and placement of an irritating restorative material. The pulp has macrophages, lymphocytes, neutrophils, monocytes, and plasma and mast cells, all of which aid in the process of repair of the pulp. Although the rigid dentinal wall has to be considered as a protection of the pulp, it also endangers its existence under certain conditions. During inflammation of the pulp, hyperemia and edema may lead to the accumulation of excess fluid outside the capillaries. An imbalance of this type, limited by the unyielding enclosure, can lead to pressure on apical vessels and ischemia, resulting in necrosis of the pulp. In most cases, if the inflammation is not too severe, however, the pulp will heal since it has excellent regenerative properties

Table 2.5 Functions ofPulp

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REGRESSIVE CHANGES (AGING)

The age changes in the dental pulp are dealt in Chapter 17, Age Changes in Oral Tissues. Hence the age change in dental pulp is briefly summarized in this chapter. The age changes in the pulp are decrease in cellularity, increase of collagen fibres and their aggregation into bundles, decrease in vascularity and appearance of calcifications (Fig. 6.26A–D). The calcifications may be diffuse calcifications or nodular calcifications, termed as pulp stones or denticles. Pulp stones may lie free in the pulp, attached to dentinal wall, or embedded in it. If pulp stones has the structure of dentin, it is called true denticles, if not, false denticles

DEVELOPMENT

The tooth pulp is initially called the dental papilla. This tissue is designated as “pulp” only after dentin forms around it. The dental papilla controls early tooth formation. In the earliest stages of tooth development, it is the area of the proliferating future papilla that causes the oral epithelium to invaginate and form the enamel organs. The enamel organs then enlarge to enclose the dental papillae in their central portions (Fig. 6.25A). The dental papilla may play a role in determining whether the forming enamel organ is to be an incisor or a molar. Recent information indicates that the epithelium may have that information. At the location of the future incisor, the development of the dental pulp begins at about the 8th week of embryonic life in the human. Soon thereafter the more posterior tooth organs begin differentiating. The cell density of the dental papilla is great because of proliferation of the cells within it (Fig. 6.25A). The young dental papilla is highly vascularized, and a well-organized network of vessels appears by the time dentin formation begins (Fig. 6.25B).

Capillaries crowd among the odontoblasts during this period of active dentinogenesis. The cells of the dental papilla appear as undifferentiated mesenchymal cells. Gradually these cells differentiate into stellate-shaped fibroblasts. After the inner and enamel organ cells differentiate into ameloblasts, the odontoblasts then differentiate from the peripheral cells of the dental papilla and dentin production begins. As this occurs, the tissue is no longer called dental papilla but is now designated the pulp organ.

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FIGURE 2.20 (A) Young tooth bud exhibiting highly cellular dental papilla. Compare dense cell population to that of adjacent connective tissue. (B) Young tooth with blood vessels injected with India ink to demonstrate extent of vascularity of pulp. Large vessels located centrally and smaller ones peripherally among odontoblasts. Pulp surrounded by dentin and enamel. (C) Young tooth stained with silver to demonstrate neural elements. Myelinated nerves appear in pulp horn only after considerable amount of dentin has been laid down.

Axons of developing nerves reach the jaws and form terminals near sites of odontogenesis before tooth formation starts. Nerve fibers were first seen in the dental follicle in the 11th week of intrauterine life. In the 18th week, the nerve fibers were observed in the dental papilla. At that time, the first layers of enamel and dentin were being formed. At about 24th week, the nerve fibers reach the subodontoblastic region.

Subsequently, nerve fibers increase in number and those accompanying blood vessels form neurovascular bundles in the central portion of the developing pulp. During the fetal period, no subodontoblastic plexuses or nerve fibers in the predentin or in the dentin were observed. Few large myelinated nerves are found in the pulp until the dentin of the crown is well advanced (Fig. 6.25C). At that time nerves reach the odontogenic zone in the pulp horns. The sympathetic nerves, however, follow the blood vessels into the dental papilla as the pulp begins to organize. During development, dental pulp cells produce nerve growth factor and semaphorin 7A as well as brain-derived and glial cell line– derived neurotrophic factor, all of which help to innervate the pulp. Growth factors like neurotrophin and neurturin were shown not be involved in this process.

CLINICAL CONSIDERATIONS

Pathologic considerations

Pulpal inflammation or pulpitis is a response of the traumatized pulp, with trauma being a result of a bacterial infection as in dental caries or physical trauma to the tooth structure. Pulpal inflammation in milder forms could result in focal reversible pulpitis and may progress if left unchecked to acute and chronic forms of pulpitis. Well-vascularized pulpal tissues may at times in carious molar teeth of young adults and children with open apex exhibit a form of hyperplasia, seen clinically from an exposed pulp chamber as a protruding red mass of granulation tissue called pulp polyp or chronic hyperplastic pulpitis. This condition requires endodontic therapy or extraction of the tooth.

Inflammation within the pulp may also sometimes result in a condition called internal resorption or pink tooth. The outward resorption of dentinal walls by osteodentinoclasts (odontoclasts) results in the pulpal tissue appearing pink through the thin translucent enamel, hence the term pink tooth. This condition may require endodontic therapy. Pulpal infection can spread apically into the periodontal ligament causing granulomas, abscesses, and cysts.

Operative and endodontic considerations

Pulpal anatomy and the response of the pulp to the various filling materials used for restoration of teeth are of utmost importance to all practicing dentists.

Pulp chamber and its extensions

For all operative procedures, the shape of the pulp chamber and its extensions into the cusps, the pulpal horns, are important to remember. The wide pulp chamber in the tooth of a young person will make a deep cavity preparation hazardous, and it should be avoided, if possible. In some instances of developmental disturbances, the pulpal horns project high into the cusps, and the exposure of a pulp can occur when it is least anticipated. Sometimes, a radiograph will help to determine the size of a pulp chamber and the extent of the pulpal horns.

If opening a pulp chamber for treatment becomes necessary, its size and variation in shape must be taken into consideration. With advancing age, the pulp chamber becomes smaller (Fig. 6.26C), and because of excessive dentin formation at the roof and floor of the chamber, it is sometimes difficult to locate the root canals. In such cases, it is advisable when one opens the pulp chamber to advance toward the distal root in the lower molar and toward the lingual root in the upper molar. In this region, one is most likely to find the opening of the pulp canal without risk of perforating the floor of the pulp chamber. In the anterior teeth, the coronal part of the pulp chamber may be filled with secondary dentin, thus locating the root canal is made difficult. Pulp stones lying at the opening of the root canal may cause considerable difficulty when an attempt is made to locate the canals.

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FIGURE 2.21 These four diagrams depict pulp organ throughout life.

Observe first the decrease in size of pulp organ. (A–D) Dentin is formed circumpulpally but especially in bifurcation zone. Note decrease in cells and increase in fibrous tissue. Blood vessels (white) organize early into odontoblastic plexus and later are more prominent in subodontoblastic zone, indicating decrease in active dentinogenesis.

Observe sparse number of nerves in young pulp, organization of parietal layer of nerves. They are less prominent in aging pulp. Reparative dentin and pulp stones are apparent in oldest pulp, (D).

The shape of the apical foramen and its location may play an important part in the treatment of root canals. When the apical foramen is narrowed by cementum, it is more readily located because further progress of the broach will be stopped at the foramen. If the apical opening is at the side of the apex, as shown in Fig. 6.2B, not even radiographs will reveal the true length of the root canal, and this may lead to misjudgment of the length of the canal and the root canal filling.

Since accessory canals are rarely seen in radiographs, they are not treated in root canal therapy. In any event, it would be mechanically difficult or impossible to reach them. Fortunately, however, the majority of them do not affect the success of endodontic therapy.

When accessory canals are located near the coronal part of the root or in the bifurcation area (Fig. 6.3B), a deep periodontal pocket may cause inflammation of the dental pulp. Thus, periodontal disease can have a profound influence on pulp integrity. Conversely, a necrotic pulp can cause spread of disease to the periodontium through an accessory canal. It is recognized that pulpal and periodontal disease may spread by their common blood supply.

Pulpal response to restorative procedures and materials

Pulp capping is successful, especially in noninfected or minimally infected, accidentally exposed pulps in individuals of any age. In these instances, dentin is formed at the site of the exposure; thus, a dentin barrier or bridge is developed and the pulp retains vitality. Dentin bridge forms an effective continuous barrier only if operative debris and pulp capping material particles are removed.

All operative procedures cause an initial response in the pulp, which is dependent on the severity of the insult. The pulp is highly responsive to stimuli. Even a slight stimulus will cause inflammatory cell infiltration. A severe reaction is characterized by increased inflammatory cell infiltration adjacent to the cavity site, hyperemia, or localized abscesses. Hemorrhage may be present, and the odontoblast layer is either destroyed or greatly disrupted. It is of interest that most compounds containing calcium hydroxide readily induce reparative dentin underlying a cavity (Fig. 6.28). Most restorative materials also induce reparative dentin formations (Fig. 6.29). Usually, the closer a restoration is to the pulp, the greater will be the pulp response. Though the high pH of calcium hydroxide is bactericidal and promotes tertiary dentin formation, it has unstable physical properties in that particles of calcium hydroxide get into pulp causing pulpal inflammation. Newer composite resins used as pulp capping agents showed better sealing properties than the earlier composites and calcium hydroxide. Therefore, the bacterial leakage is less compared to calcium hydroxide leading to a better dentin bridge formation.

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FIGURE 2.22 Moderate cell response with formation of reparative dentin underlying cavity. Note viable odontoblasts have deposited tubular, reparative dentin.

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FIGURE 2.23 Diagram of reparative function of pulp organ to cavity preparation and subsequent restoration. Reparative dentin is limited to zone of stimulation.

More than calcium hydroxide, enamel matrix derivative was shown to be more capable of promoting reparative process in the wounded pulp. Mineral trioxide aggregate (MTA) has also been shown to be more effective than calcium hydroxide as pulp capping agents.

Inflammation, hyperemia, and necrosis were less but more odontoblasts and thicker dentin bridge formation was seen with MTA.

In future, incorporation of bioactive molecules like bone morphogenetic protein, TGF- β1, or purified dentin protein fractions in pulp capping materials, use of tissue-cultured dentin and stem cells to produce dentin, may radically alter the present treatment approaches.

The thickness of remaining dentin was shown to be important factor in maintaining the vitality of pulp. A minimum thickness of 5 mm or greater has a powerful influence on pulp vitality but little effect on reparative dentin formation and no effect on the intensity of inflammation. The number of vital odontoblast remaining after cavity preparation is a critical factor, apart from patient’s age which determines the ability of the pulp to form reparative dentin. Pain may be the only symptom in pulpitis and all other cardinal signs of inflammation like rubor (redness), calor (heat), or tumor (swelling) will not be appreciated clinically because pulp is situated deep within the tooth and surrounded by hard tissues of the tooth. Since the pulp contains only free nerve endings all forms of sensory stimuli like touch, pressure, or temperature to the pulp result in causing pain sensation only.

Pulpal pain

Pulpal pain worsens with the degree of inflammation. Stimuli causing pain act through large diameter A-δ or smaller diameter C-fibers. A-δ fibers are fast-conducting myelinated fibers and evoke a sharp pain, while nonmyelinated C-fibers are slow-conducting fibers and produce a dull pain on stimulation.

Changes occur in tissue fluid pressure in normal and inflamed pulps, and this largely determines whether pulp necrosis occurs. Tissue pressure is the hydrostatic pressure of the interstitial fluid surrounding the pulpal cells. It increases due to increase in blood flow and due to increased interstitial fluid, occurring as a result of inflammation. This will cause increase in lymph flow and increased absorption of fluid into the capillaries in the uninflamed area. This will help in transport of fluid from the pulp and thereby reduces the tissue fluid pressure to normal. Increased tissue pressure will promote outward flow of dentinal fluid through the exposed dentinaltubule.

This serves to protect the pulp against entry of harmful substances. If the compensatory mechanisms fail to reduce the tissue fluid pressure, a sustained increase in the pressure occurs, and this will compressthe blood vessels causing ischemia and necrosis.

In response to orthodontic forces, the pulp shows cell damage, inflammation, vasodilatation, and healing, all of which are associated with increased vascularity due to release of angiogenic growth factors.

Since dehydration causes pulpal damage, operative procedures producing this condition should be avoided. When filling materials contain harmful chemicals (e.g., acid in silicate cements and monomer in the composites), an appropriate cavity liner should be used prior to the insertion of restorations. Pulp has to be protected from damage due to heat transmission especially by metallic restorations by the use of bases.

Vitality of pulp

A vital pulp is essential to good dentition. Although modern endodontic procedures can prolong the usefulness of a tooth, a nonvital tooth becomes brittle and is subject to fractures. Therefore, every precaution should be taken to preserve the vitality of a pulp.

In clinical practice, instruments called vitalometers, which test the reaction of the pulp to electrical stimuli, or thermal stimuli (heat and cold) are often used to test the “vitality” of the pulp. These methods provide information about the status of the nerves supplying the pulpal tissue and therefore check the “sensitivity” of the pulp and not its “vitality.” The vitality of the pulp depends on its blood supply, and one can have teeth with damaged nerve but normal blood supply (as in cases of traumatized teeth). Such pulps do not respond to electrical or thermal stimuli but are completely viable in every respect.

Laser Doppler flowmetry, an electro-optical technique used in the recording of pulpal blood flow, has been found to be reliable in assessing the vitality of traumatized teeth. Also, transmitted-light photoplethysmography, which has been used to detect blood flow in young permanent teeth, may be of use in the assessment of pulp vitality.

The preservation of a healthy pulp during operative procedures and successful management in cases of disease are two of the most important challenges to the clinical dentist.

Summary

The pulp is a loose connective tissue occupying the pulp chamber in the crown and root canal in the root. Pulp communicates with the periodontal ligament through the apical foramen and through accessory foramina.

Zones of the pulp

Pulp can be divided into different zones; the odontogenic zone close to the pulp– dentin border, the cell-free zone of Weil beneath it, and the parietal zone in the remaining area.

Cells of the pulp Odontoblasts

The odontoblasts present in the odontogenic zone vary in size, shape, and arrangement. In the coronal pulp, they are columnar in shape and show a pseudostratified arrangement with an average diameter of 7.2 µm and 25–40 µm in length, becoming flatter and are arranged in a single layer in the root. Odontoblasts have a basal polarized nucleus and contact the adjacent cells focally with junctional complexes. The odontoblast morphology and its organelles vary with functional activity of the cell. In the active stage, as during the formation of primary dentin formation, the cell is elongated with all the organelles required for protein synthesis. In the resting stage, the cell is stubby with fewer organelles. They are terminally differentiated so they have to be replaced by undifferentiated mesenchymal cells when they die. The cytoplasmic process extending from the apical cytoplasm is usually devoid of organelles and extends to about two-third of the lengths of the dentinal tubules. The cell-free zone contains subodontoblastic plexus of nerves and vessels.

Fibroblasts and collagen fibers of the pulp

Pulp consists of fibroblasts, defense cells like histiocytes, plasmacells, and pluripotent undifferentiated mesenchymal cells, and stem cells.

The fibroblasts are the most numerous of the pulpal cells. They are star shaped and their process communicates with each other. They form and degrade collagen fibers and the ground substance. Pulp consists of loosely arranged type I fine collagen fibers. Their length varies from 10 to 100 nm.

Defense cells

The histiocyte is an irregularly shaped cell and appears similar to fibroblast. They are stained by vital dyes like toluidine blue.

Ultra-structurally, they show vesicles containing phagocytosed bodies.

Dendritic cells are antigen-presenting cells found in close relation to or contact with their processes to odontoblast or endothelial cells.

The plasma cells are seen only during pulpal inflammation. They are oval-shaped cells with eccentric nucleus. They produce antibodies.

Pulpal stem cells

These are pluripotent cells replacing injured odontoblast and produce dentin. They can be induced to proliferate and differentiate by numerous growth factors like TGF. Pulp of exfoliated deciduous teeth and third molars are a good source of pulpal stem cells and they are used in regeneration of dentin, bone, and neural tissues.

Pulpal blood vessels and circulation

The blood vessels are mainly arterioles of smaller size and thinner walls than elsewhere, the capillaries have fenestrations and there are arteriovenous communications. Blood flow in pulp is higher than in most areas of the body, in capillaries is high—it is about 0.08 mm per second. The circulation in pulp facilitates rapid transport of metabolites. Pericytes are cells with contractile properties and are seen on the surface of smaller arterioles. Blood vessels and nerves enter and leave through apical foramen. Blood vessels in the pulp communicate with the vessels in the periodontal ligament through main and accessory canals. Lymph vessels also said to follow the course of blood vessels. Lymph vessels draining anterior teeth drain into submental lymph nodes and those from posterior teeth drain into submandibular lymph nodes.

Nerves of the pulp

The nerves are of two types—the unmyelinated parasympathetic nerves which are unbranched and end in blood vessels to control the blood flow and the myelinated nerves and somatic nerves which lose their myelin sheath before they branch and form plexus in the cell-free zone. This plexus is often referred to as plexus of Raschkow. Some of these extend to end below the odontoblast and form synapse while others go up to predentin and loop backward while very few travel within the dentin tubules spiraling around the odontoblastic process. Since the pulp contains only free nerve endings, all forms of sensory stimuli result in pain sensation.

Functions of the pulp

The functions of the pulp are to produce dentin (formative function), nourish dentin (nutritive function), elicit pain to protect the tooth (protective function), and to repair injured dentin or arrest caries progression by forming reparative dentin (reparative function). In early odontogenesis, the pulp anlage interacts with oral epithelial cells to cause differentiation of enamel organ and dental lamina.

Development of pulp

The pulp is formed from dental papilla. After the peripheral cells of dental papilla differentiate into odontoblast and produce dentin, the rest of dental papilla becomes pulp. The earliest pulp of deciduous teeth develops by 8th week of embryonic life. The developing pulp is very cellular and very vascular. Nerves appear later (18th week) reach sub odontoblastic region by 24th week, the plexuses formation occurring still later.

Age changes in the pulp

The age changes in the pulp include decreased cellularity, increase in fibers with bundle formation, degeneration of nerves and calcifications. Pulp arterioles are end arteries and as pulp circulation is not collateral, inflammation of pulp results in necrosis.

CHAPTER 3 – INTRODUCTION

Knowledge of root canal anatomy is essential in order to explain the treatment plan to a patient, to properly examine radiological imaging of teeth and surrounding structures, and, most important, to perform invasive procedures. It is also required to avoid iatrogenic injuries during pulp chamber access, canal instrumentation, or post-space preparation procedures. In addition, it allows the detection of additional canals commonly correlated with persistent periapical disease. In summary, a deep understanding of the canal morphology is an imperative requirement for the success of the endodontic therapy. Root canal treatment is indicated when the pulp tissue of a tooth is damaged or infected because of decay, trauma, iatrogenic operative procedures, or deep fillings. Different bacteria from the oral cavity can adhere to dentinal surfaces, invade the dentinal tubules and produce pulpal inflammation that, lately, may spread throughout the complexities of the root canal system, compromising the periradicular tissues. This statement is supported by several clinical and laboratory studies which have demonstrated that the main etiology of endodontic failure is intraradicular infection ⁵² In this way, knowledge of the common anatomy and its variations would favor an effective reduction of bacterial population from the main root canal, by using a proper chemomechanical preparation and intracanal dressing protocols, able to reach both transversal and vertical extension of the root canal system , followed by obturation and coronal restoration, aiming to avoid future contamination or repopulation of the cleaned canal space by remaining bacteria ⁵³.

Anatomy of the Root Canal System The root canal system can be divided into two parts: the pulp chamber, located within the anatomic dental crown, and the root canal space, found inside the radicular portion of the tooth.

Pulp Chamber The pulp chamber is a cavity situated in the center of the crown and, under no pathological conditions, resembles the shape of the crown surface. In anterior teeth, pulp chamber and root canal are continuous, while, in posterior teeth, pulp chamber floor separates these two components. In premolars and molars, pulp chamber usually presents a square shape with six sides: the floor, the roof, and four axial walls identified as mesial, distal, buccal, or lingual (palatal). The pulp chamber roof usually presents projections or prominences associated to the cusps, mamelons or incisal edges, and denominated pulp horns . its morphology can be modified by the odontoblasts present in the pulp tissue. These cells produce secondary and tertiary dentin through patient’s life. Thus, in teeth with physiological wear or other irritation, continuous dentin formation (either physiological or reactionary) by primary odontoblasts may lead to a decrease in the pulpal space dimensions which, in some cases, can difficult root canal treatment. Strictly speaking, access to the root canal system in teeth with calcified pulp chamber is more challenging than in young permanent teeth. Based on the anatomical study of 500 teeth, Krasner and Rankow demonstrated that specific and consistent pulp chamber anatomy exists.⁵³ Then, they proposed some laws for aiding the determination of the pulp chamber position as well as the location and number of root canal entrances in each group of teeth (Figs. 3.1 and 3.2):

- Law of centrality: The floor of the pulp chamber is always located in the center of the tooth at the level of the cementoenamel junction (CEJ).
- Law of concentricity: The walls of the pulp chamber are always concentric to the external surface of the tooth at the level of the CEJ, i.e., the external root surface anatomy reflects the internal pulp chamber anatomy.
- Law of the CEJ: The distance from the external surface of the clinical crown to the wall of the pulp chamber is the same throughout the circumference of the tooth at the level of the CEJ—the CEJ is the most consistent, repeatable landmark for locating the position of the pulp chamber.
- Law of symmetry 1: Except for maxillary molars, the orifices of the canals are equidistant from a line drawn in a mesial-distal direction, through the pulp chamber floor.
- Law of symmetry 2: Except for the maxillary molars, the orifices of the canals lie on a line perpendicular to a line drawn in a mesial- distal direction across the center of the floor of the pulp chamber.
- Law of color change: The color of the pulp- chamber floor is always darker than the walls.
- Law of orifice location 1: The orifices of the root canals are always located at the junction of the walls and the floor.
- Law of orifice location 2: The orifices of the root canals are located at the angles in the floor-wall junction.

Law of orifice location 3: The orifices of the root canals are located at the terminus of the root developmental fusion lines.

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Fig. 3.1 Law of centrality, concentricity, and orifice locations observed through micro-CT sagittal and transverse cross-sectional planes from a maxillary first molar. (a) Detail of the pulp chamber; (b, c) projection of the root canal axis (white lines) converges to the center of the anatomical crown; (d) the projection of the pulp chamber floor into the coronal enamel dictates the ideal form of the access (green area)

In addition to knowing these laws, the use of illumination and magnification associated with special instruments, such as ultrasound tips, would provide the best approach to explore all anatomic variations of the pulp chamber in order to locate all canal orifices and avoid missed canals which has been considered one of the main causes of endodontic failure (Fig. 3.3). Amongst the most common missed canals associated to cases with persistent periapical disease are the second mesiobuccal canal of maxillary molars (MB2 canal), lingual canals of mandibular incisors and premolars, and the middle mesial and distolingual canals of mandibular molars.

MINIMALLY INVASIVE ENDODONTICS: CLINICAL CONSIDERATIONS

In recent years, considerable attention has been given to the anatomy of the pulp chamber. The use of the operative microscope, three- dimensional imaging technology, ultra- flexible files, and superior illumination has opened new possibilities, allowing minimally invasive procedures during endodontic treatment, mostly related to changes in access preparation (Fig. 3.4). This approach aimed to preserve tissue from healthy tooth structure in order to avoid structural failure in the future. This concept overlooks the traditional requirements of straight-line access and complete unroofing of the pulp chamber emphasizing the importance of preserving the pericervical dentin ⁵⁴. The pericervical dentin has been defined as the dentin near the alveolar crest extending 4 mm apical to the crestal bone . It has been quoted that the resistance to fracture is closely related to the amount of residual tooth structure at this level.

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Fig. 3.2 Micro-CT 3D reconstruction images of posterior teeth demonstrating the (a) laws of centrality and concentricity at CEJ level; (b) laws of color change and orifice locations 1, 2, and 3 (arrow: developmental fusion lines); and (c, d) laws of symmetry 1 and 2

Whereas there is no agreement if this procedure will lead to a better prognosis of the root canal treatment in clinics, laboratory studies have shown that contracted endodontic cavities are not deleterious for the cleaning and shaping process in incisors, premolars, and molars and conveyed a benefit of increased fracture resistance in mandibular molars and premolars ⁵⁵. Thus, efforts should be made to identify pulp chamber components without removing excessive dentin structure, when using magnification, and there is no risk to jeopardize the treatment outcome.

3.3 Root Canal

The root canal is the portion of the pulp canal space within the root of the tooth limited by the pulp chamber and the foramen that follows the external outline of the root. The root canal can be subdivided into two components, the main canal, which is mostly cleaned by mechanical means, and lateral components composed by isthmuses, accessory canals (furcation, lateral, and secondary canals) (Fig. 3.5), and some recesses of flattened- and oval- shaped canals (Fig. 3.6). In longitudinal section, canals are usually broader buccolingually than in the mesiodistal plane. The geometric cross-sectional shape of root canals has been classified by calculating the mean aspect ratio, defined as the ratio of the major to the minor canal diameters. The major diameter is the distance between the two most distant points of the canal in the buccolingual direction, while minor diameter is the longest chord through the root canal that could be drawn in the direction orthogonal to that of the major diameter. Accordingly, an oval-shaped canal has an aspect ratio between 1 and 2, a long oval canal higher than 2 but lower than 4, and a flattened canal higher than 4 (Fig. 3.7).

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Fig. 3.3 Root canal treatment of a maxillary first molar with necrotic pulp and asymptomatic apical periodontitis. The laws of color change and orifice locations can be observed in the image of the pulp chamber. Observe how different is the color of the pulp chamber compared to the canal walls and location of the canal orifices. The contracted access did not avoid the location and cleaning of the second canal of the mesiobuccal root, the so-called MB2 canal It is interesting to point out that, in a same tooth, canal cross sections may show different shapes at different levels of the root; but, at the apical third, it is more round or slightly oval in shape in comparison with the middle and cervical thirds ⁵⁶.

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Fig. 3.4 Coronal view of micro-CT reconstruction images of different teeth comparing the size of minimally invasive (left) and the conventional (right) access preparations

As mentioned, the anatomy of the root canal systems is often complex and can vary greatly in number and shape. Considering the large amount of variations, different classification systems have been proposed. These systems are based on the number of root canals that begin at the pulp- chamber floor, arise along the course of the canal, and open through an apical foramen. Recently, Versiani and Ordinola-Zapata ⁵⁷ reviewed the literature and described the 37 most common canal configurations including almost all anatomical configurations possible to be observed in a single root (Fig. 3.8).

ISTHMUS

An isthmus, also called transverse anastomosis, is a narrow, ribbon-shaped communication between two root canals that may contain vital tissue, necrotic pulp, biofilms, or residual filling material [⁵⁸,⁵⁹ ]. The presence of a partial isthmus, described as an incomplete communication with one or more patent openings between two main canals, has also been reported ⁵⁸. Isthmus may present different configurations (Fig. 3.9), and its prevalence is dependent on the type of teeth, the root level, and the patient’s age. Hsu and Kim ⁶⁰ classified the isthmuses configuration into five types:

- Type I: two canals with no notable communication.
- Type II: a hair-thin connection between the two main canals. - Type III: differs from type II because of the presence of three canals instead of two.
- Type IV: an isthmus with extended canals into the connection.
- Type V: there is a true connection or wide corridor of tissue between two main canals.

A summary of the isthmuses prevalence in mandibular and maxillary molars found in laboratory studies is shown in Table 3.1. It is noteworthy that experimental studies demonstrated the impossibility to obtain a complete mechanical debridement or chemical disinfection of the isthmus with the current technology, mostly because of the presence of hard tissue debris, packed into these areas during the mechanical preparation of the root canal system.. Clinical studies have also demonstrated that unfilled isthmuses can be commonly observed after root-end resection in cases referred for apicoectomy treatment.

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Fig. 3.5 Micro-CT 3D reconstructions of the internal anatomy of mandibular premolars showing the main com- ponents of the root canal system. (a) Main canal; (b) lat- eral canal (located at the coronal or middle thirds. When it begins at the furcation level is denominated furcation

These limitations, however, can be surpassed in nonsurgical treatment by using chemical agents with the ability to dissolve organic tissue at fins and isthmuses level associated with ultrasonic activation ⁶¹. Besides, with the advent of operatory microscope, it is possible to visualize, identify, and treat most of the isthmus areas with thin ultrasonic tips in both surgical and nonsurgical endodontic procedures, to ensure its debridement and seal ⁵⁷, ⁵⁹, ⁶¹.

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Fig. 3.6 3D reconstructions of the root canal system of 2 mesiobuccal roots of maxillary molars showing how the anatomical complexities of root canal components may affect the mechanical debridement. Areas in red represent the original anatomy, while areas in green are the dentin removed during preparation of both mesiobuccal canals. Root canals in (a) do not have significant lateral compo- nents; thus, root canal preparation was able to remove most of the dentinal surface of the original canal perime- ter. Only minor areas were not touched by the instru- ments; (b) in this case, there are significant lateral components, including an isthmus extending from the coronal to middle third (red areas) and an accessory canal in the apical third

ACCESSORY CANALS

Accessory canal is any branch of the root canal that communicates with the periodontal ligament, while a lateral canal is defined as an accessory canal located at the coronal or middle third of the root (Fig. 3.9d) ⁶². They are formed after a localized fragmentation of the epithelial root sheath develops, leaving a small gap, or when blood vessels running from the dental sac through the dental papilla persist ⁶³. Accessory canals represent potential pathways through which bacteria and/or their products from the necrotic root canal might reach the periodontal ligament and cause disease ⁶³. De Deus ⁶⁴ studied the frequency, location, and direction of the accessory canals in 1140 teeth and showed that 27.4% of the sample (n = 330) had accessory canals, especially in the apical area (17%), followed by the middle (8.8%) and coronal (1.6%) thirds. Similarly, Vertucci ⁶⁵ evaluated 2400 teeth and observed lower occurrence of canal ramifications in the middle (11.4%) and coronal (6.3%) thirds compared to the apical level (73.5%). Lateral canals are not usually visible in preoperative radiographs, but its presence can be suspected when there is a localized thickening of the periodontal ligament or a lesion on the lateral surface of the root (Fig. 3.10).

According to Weine ⁶⁶, lateral lesions can be radiographically classified into three types:

- Type I: lateral lesion with no apical lesion—as the infection progresses apically, it might reach a sufficiently large lateral canal to allow a substantial amount of bacteria and bacterial products to reach the lateral periodontium to cause inflammation.
- Type II: separate lateral and apical lesions—if the pathological process advances without professional intervention, an apical periodontitis lesion can also be visible.
- Type III: coalescence of lateral and apical lesions—in some cases, the type II condition can progress to the so-called “wraparound” lesion.

Fig. 3.7 Micro-CT transversal cross sections of the ana- tomical crown, pulp chamber, middle third, and 3 mm from the apex (from left to right) of (a) a mandibular inci- sor, (b) a mandibular premolar, and (c) a maxillary premolar. The canal is round-shape only at the coronal and apical thirds of the mandibular incisor, while both premolars have long oval- and flattened-shaped canals. The mandibular incisor presents an oval canal at the middle third level

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Fig. 3.8 Thirty-seven most common canal configurations including almost all anatomical configurations possible to be observed in a single root ⁶ (published with permission)

Actually, these types might represent different stages of the disease progression within the root canal space once the conditions of the tissue within lateral canals and apical ramifications reflect the conditions of the pulp in the main root canal ⁶³. Clinically, it is also relevant that lateral canals cannot be instrumented. In this way, its content can only be neutralized by means of effective irrigation with a suitable antimicrobial solution or with an additional use of intracanal medication. Canals connecting the pulp chamber to the periodontal ligament in the furcation region of a multi-rooted tooth are called furcation canals ⁶². These canals derived from entrapment of periodontal vessels during the fusion of the parts of the diaphragm, which will become the floor of the pulp chamber. In some cases, furcation canals have been associated to primary endodontic lesions in the interradicular region of multi- rooted teeth. Vertucci and Williams observed the presence of furcation canals in 13% of mandibular first molars ⁶⁷ and, in most of them (n = 7), the canal extended from the center of the pulpal floor, while in four and two specimens, respectively, the canals arose from the mesial and distal aspects of the floor. Later, Vertucci and Anthony observed the presence of foramina on both the pulp chamber floor and the furcation surface in 36% of maxillary first molars, 12% of maxillary second molars, 32% of mandibular first molars, and 24% of mandibular second molars. Recently, micro-computed tomographic studies have also demonstrated the presence of furcation canals in two-rooted mandibular canines and three- rooted mandibular premolars .

APICAL CANAL

The main root canal ends at the apical foramen (major foramen) which frequently opens laterally on the root surface, at a mean distance between 0.2 and 3.8 mm from the anatomic apex ⁶⁸, despite larger distances having been also reported . The anatomic apex is the tip or the end of the root as determined morphologically ⁶². Depending on the type of teeth, the apical foramen can coincide with the anatomic apex in a percentage frequency ranging from 6.7% to 46% of the cases ⁶⁵. Its diameter has been described between 0.21 and 0.39 mm ⁶⁹. The mesial roots of mandibular molars, the maxillary premolars, and the mesiobuccal roots of maxillary molars show the highest percentage of multiple apical foramina ⁶⁹. A previous study on root apexes of all groups of permanent teeth showed that the number of foramina on each root may vary from 1 to 16 ⁶⁷. The apical portion of the root canal having the narrowest diameter has been called “apical constriction” (minor foramen) ⁶². From the apicalconstriction, the canal widens as it approaches the apical foramen.

The topography of the apical constriction is not constant [⁴², ⁶⁷ ] main canal divides into multiple accessory canals (Figs. 3.5f and 3.9f) ⁶². In maxillary teeth, the percentage frequency of apical delta ranges from 1% (central incisors) to 15.1% (second premolars), while in mandibular teeth, its frequency varies from 5% (central incisors) to 14% (distal root of first molars) ⁶⁷. Clinically speaking, the infection of this tortuous and complex anatomical configuration with several portals of exit can be related as an etiologic factor of nonsurgical failures.

ROOT CANAL CURVATURE

Knowledge of the root canal curvature is also an important factor for choosing the appropriate chemomechanical protocol to prepare the root canal system. Before the introduction of nickel- titanium (NiTi) instruments, several iatrogenic procedures were associated with the preparation of curved canals including zips, separate instruments, ledges, and perforations. Nowadays, these iatrogenic complications are no longer a problem, except for the instrument separation. Therefore, this is one of the factors determining the difficulty of a treatment, and the likelihood of iatrogenic errors preoperative recognition of canal curvature is of utmost importance ⁷⁰. Nearly all root canals are curved in the apical third, particularly in a buccolingual direction, which is not evident on standard radiography ⁵⁹. In general, the curvature may vary from gradual curvature of the entire canal, sharp curvature of the canal near the apex, or a gradual curvature of the canal with a straight apical ending. Numerous methods have been proposed to determine root canal curvature [ ⁷¹ –⁷⁶ ], but the Schneider’s method has been the most widely used. Schneider ⁷⁷ classified single-rooted permanent teeth according to the degree of curvature of the root, which was determined by firstly drawing a line parallel to the long axis of the canal and then a second line connecting the apical foramen to the point in the first line where the canal began to leave the long axis of the tooth. The angle formed by these two lines was the angle of curvature, and its degree was classified as straight (≤5°), moderate (10–20°), or severe (25–70°). Another method was introduced by Weine ⁷⁸ and also relies on the definition of two straight lines, but it reflects the root canal curvature more accurately than Schneider’s method, especially in the apical part. A third proposal, geometrically equivalent to Weine’s method, was introduced by Pruett et al. ⁷⁹, but its major innovation was the concurrent measurement of the radius of curvature by the superimposition of a circular arc on the curved part of the root canal ⁷⁰. Therefore, Schneider angle, when used in combination with the radius and length of the curve, may provide a more precise method for describing the apical geometry of canal curvature. Clinically, different angled views are necessary to determine the presence, direction, and severity of the root canal curvature. Schäfer et al. ⁷¹ evaluated radiographically the curvature degree of 1163 root canals from all groups of teeth. The degree of curvature ranged from 0° to 75° and from 0° to 69° in clinical and proximal views, respectively. The highest degree of curvature was observed in the clinical view of the mesiobuccal canal of maxillary molars and in the mesial canals of mandibular molars. In several cases, the angles of proximal curvatures were higher than those of the clinical view (Fig. 3.13). Additionally, a secondary curvature (S-shaped canal) was observed in 12.3% and 23.3% of the maxillary and mandibular teeth, respectively.⁷¹

CHAPTER 4 - MORPHOLOGY OF ROOT CANAL SYSTEM MAXILLARY CENTRAL INCISOR EXTERNAL ROOT MORPHOLOGY

Maxillary central incisor is triangular to ovoid in shape and tapers toward the lingual. Root concavi-ties are normally not present in maxillary central incisors. The root trunk is generally straight and tapers to a blunt apex. The overall average length of the maxillary central inci-sor is 23.5 mm with an average crown length of 10.5 mm and an average root length of 13 mm.

ROOT NUMBER AND FORM

The majority of anatomic studies found that the maxillary central incisor is a straight, single-rooted tooth (Table 1-2), unless rare developmental anomalies are present.

CANAL SYSTEM

The maxillary central incisor is usually a single root canal sys- tem . Over 99% of the teeth had a single root canal and a single apical foramen. Mid-root and apical lateral canals and apical delta canals are common. These lateral canals with small arterioles and venules serve as collateral circulation. When the pulp becomes diseased, Schilder⁸⁵ referred them as “por- tals of exit” into the surrounding periodontal ligament space.

Relatively few studies have investigated the apical root anat- omy of teeth. Altman et al.⁸⁶ investigated 20 extracted maxil- lary central incisors. On histological examination, accessory or lateral canals were found in three quarters of the specimens, exhibiting one to four accessory canals. One specimen was found to have 20 separate foramina, but this anomalous canal anatomy occurred on a central incisor from a 9-year-old indi- vidual. They concluded that radiographic examination was not accurate in diagnosing accessory canals and that resorptions, appositions, pulp stones, and accessory canals were commonly found in the apical 2.5 mm of the maxillary central incisors.

The classic stereomicroscopic study of root apices by Green,⁸⁷ in 1956, found that the average diameter of the major foramen in the 50 teeth studied was 0.4 mm, while the accessory foramina were 0.2 mm or less in diameter. The average distance of the major apical foramen from the ana- tomical root apex was found to be 0.3 mm. Approximately 12% of the maxillary central incisors exhibited accessory foramina in their sample.

Mizutani et al.⁸⁷ investigated the anatomic location of the apical foramen in 30 maxillary central incisors. The root apex and apical foramen were displaced distolabially in the majority of the specimens. Coincidence of the apical foramen and root apex was found in only one out of six specimens (~17%).

Kasahara et al.⁸⁸ assessed the apical anatomy of 510 extracted maxillary central incisors. Apical ramifications were found in about 12% of cases. Lateral canals were pre- sent in 49%. Only 38.6% of the teeth had a simple main canal without lateral canals or apical ramifications. In this study, 90% of the foramina were located within 1.0 mm of the anatomical apex.

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FIGURE 4.1

A. Labial view of maxillary right central incisor.

B. Mesial view of maxillary right central incisor.

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FIGURE 4.2 Root cross-sections of the maxillary right central incisor.

VARIATIONS AND ANOMALIES

Seventy-five case reports of abnormalities of the maxillary central incisor were identified in a review of the literature (Table 1-4). The four most common variations or anomalies identified in decreasing order were talon cusps, two roots and two canals, one root and two canals and fusion. Ethnic vari- ations have been attributed for some coronal traits. Shovel- shaped incisor crowns with heavy lingual ridge formation and even labial buttressing to varying degrees are a common feature in Asian (including North Americans), Natives for- merly described as “Mongoloid” populations, but are rela- tively rare in Caucasian populations.⁸⁵

A study by Pecora and da Cruz Filho assessed the inci- dence of radicular grooves in the maxillary incisors of 642 patients. Loss of periodontal attachment associated with these grooves can result in a deep, narrow, vertical periodon- tal pocket. The incidence of radicular grooves was found to be 0.9% in the maxillary central incisors and 3.0% in maxil- lary lateral incisors. The prognosis, even with combined per- iodontal-endodontic treatment, in such cases can be poor. Reports of other types of root anomalies al-Nazhan reported a case of a central incisor with enamel hypoplasia and two canals in a single root. Examples of fusion with a supernumerary tooth, fusion with a maxillary lateral incisor gemina- tion,talon cusps, two canals, dens invaginatus, and maxillary central incisors with two roots are occasionally documented in case reports. A single case of gemination and fusion with a supernumerary tooth resulting in a tooth with three canals was reported by Hosomi et al.

An unusual combination of anomalies was reported by Lorena et al. Anomalies in the maxillary arch included shovel-shaped incisors, dens invaginatus, peg-shaped supernumerary teeth, and Carabelli cusps on the maxillary first molars in the absence of any developmental anomaly. McNamara et al. also reported a combination of anom- alies that included maxillary central and lateral incisors that had talon cusps, short roots and dens invaginatus, premolars with short roots, and Carabelli cusps on the maxillary first and second molars. A rare case of a labial talon cusp on a maxillary central incisor was reported by de Sousa et al.

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FIGURE 4.3 Dens invaginatus Type 3; three-canal maxillary right central incisor.

MAXILLARY LATERAL INCISOR EXTERNAL ROOT MORPHOLOGY

The cross-sectional root anatomy of the maxillary lateral incisor is described as being circular, oval, or ovoid in shape and tapers toward the lingual as illustrated in Figure 1-6. Root concavities are normally notpresent on the root of the maxillary lateral incisors. The root trunk is generally smaller than a central incisor and has a finer root tip, often terminating in a curve to the distal or lingual, or both (Figure 1-7). The overall average length of the maxillary lateral incisor is 22 mm with an average crown length of 9 mm and an average root length of 13 mm.

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FIGURE 4.4

A. Labial view of maxillary right lateral incisor.

B. Mesial view of maxillary right lateral incisor

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FIGURE 4.5 Root cross-sections of the maxillary right lateral incisor.

ROOT NUMBER AND FORM

Anatomical studies indicate that the maxillary lateral inci- sors are single-rooted virtually 100% of the time [5,7,11,14,31] as shown in Table 1-5. However, numerous case reports curvature demonstrates significant variability in anatomy. Most reported cases of two-rooted maxillary lateral incisors are a result of fusion or gemination and are usually associated with a macrodont crown. There are a few reported cases of two roots associated with normal crown dimensions. Anomalous two-rooted maxillary lateral incisors are usually associated with a developmental radicular lingual groove. Even in single-rooted maxillary incisor teeth, a deep gingivo-palatal groove may often result in localized periodontal disease.

CANAL SYSTEM

The maxillary lateral incisor usually presents with a single canal as demonstrated by the anatomical studies shown in Table 1-6. Mizutani et al. investigated the anatomic location of the apical foramen in 30 maxillary lateral inci- sors. The root apex and apical foramen were displaced dis- tolingually in a majority of the specimens. Displacements in all directions were also found in the study. Coincidence of the apical foramen and the anatomic root apex was found in only 2 (6.7%) of the specimens. Therefore, explo- ration of the apical foramen and constriction, with a fine pre-curved #10 size file tip, delicate tactile sense, and the electronic apex locator, is essential to locate the foramen. The use of CBCT, although not essential, may also help determine the degree and direction of curvatures of the canal system.

An early stereomicroscopic study of root apices by Green ⁸⁶ found that the average diameter of the major foramen in the 50 maxillary lateral incisors studied was 0.4 mm while the accessory foramina were 0.2 mm or less in diameter. The average distance of the major apical foramen from the anatomical root apex was found to be 0.3 mm. Approximately 10% of the maxillary lateral incisors exhib- ited accessory foramina.

VARIATIONS AND ANOMALIES

One hundred and thirty cases presented in 107 references illustrate the high degree and range of variability in the morphology of the maxillary lateral incisor. The most common variation reported was dens invaginatus (46 cases), followed by dens evaginatus (talon cusp), Maxillary lateral incisors often present with anomalous challenges. Complications resulting from radicular grooves have been well documented by Simon et al⁸⁹ The incidence of radicular grooves is 3.0% in maxillary lateral incisors in a study by Pecora and da Cruz Filho, and there are several case reports in the literature confirming the high probability of this finding.⁹⁰ Peikoff and Trott reportedthe histology of an endodontic-periodontic failure in a maxillary lateral incisor with an accessory root and a radicular groove (Figure 1-9). An SEM investigation of 14 extracted maxillary lateral incisors with radicular grooves concluded that direct communication between the groove and the pulp was evident in these specimens and that accessory canals were the primary mechanism of communication between the periodontium and the pulp. As with maxillary central incisors, the degree of shovel-shaped feature of the crown is varied and is often based on ethnic background. Again, this feature is common in Asian populations and rare in Caucasian populations.⁸⁸ Reports of this and other coronal anomalies associated with the maxillary lateral incisor are common.

Densinvaginatusor“densindente” can bepresentinvarious forms. Oehlers classified dens invaginatus into three types based on the severity of the defect. Type 1 dens invaginatus is an invagina- tion confined to the crown. Type 2 extends past the cemen- toenamel junction but does not involve periapical tissues. The most severe form and most complex to treat is a Type 3 defect. The invagination extends past the cementoenamel junction and may result in a second apical foramen. Combination of non-surgical and surgical therapy is often used to success- fully treat Type 2 and Type 3 cases Non-surgical management of the dens invaginatus, including the more severe Type 3 defects, have also been reported.[92,93,94] Occasionally, the vitality of the pulp in the main canal has been shown to be maintained while treating (surgically, non- surgically, or both) the accessory root and canal system, when there has been no communication between the root number and form Most studies have found that the maxillary canine has a single root 100% of the time as shown by the of anomalous root formation in maxillary lateral teeth document single (unilateral) teeth. Kannan et al. ⁹⁵ documented two unilateral and one bilateral incidence of dens invaginatus in their case of anomalous root formation in maxillary lateral teeth docu- ment single (unilateral) teeth. Kannan et al. ⁹⁵ documented two unilateral and one bilateral incidence of dens invaginatus in their case.

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FIGURE 4.6 Radicular developmental palatogingival groove.

A. Radiograph show lesion resulting from bacterial access along groove.

B. Extracted tooth shows extent of groove.

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FIGURE 4.7 Gemination of a maxillary right lateral incisor.

MAXILLARY CANINE

EXTERNAL ROOT MORPHOLOGY

The root of the maxillary canine is oval in shape and tapers toward the lingual as illustrated in Figure 1-10C. The root is wider labiolingually and is the longest root in the dentition. Prominent developmental depressions that appear as a double lamina dura on periapical radiographs can be present on both its mesial and distal surfaces, espe- cially in the middle third of the root.4,6 The root tip may be blunt or it may end in a fine, often curved tip. The overall average length of the maxillary canine is 27 mm with an average crown length of 10 mm and an average root length of 17 mm anatomic studies in it. However, there are case reports of two-rooted maxillary canines.⁹¹

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FIGURE 4.8

A. Labial view of maxillary left canine.

B. Mesial view of maxillary left canine.

ROOT CANAL SYSTEM

The maxillary canine usually has a single canal. A small per- centage of maxillary canines have two canals in a figure “8” form (4.7%). Of those having two canals, the majority (98.0%) join in the apical third and exit through a single foramen. Accessory (lateral) canals are not uncommon and become evident radiographically as midroot radiolucencies or sealer-puff after com-pletion of root canal treatment. The majority of lateral canals occur in the apical third of the tooth, but midroot lateral canals can also occur (Figure 1-11). Mizutani et al.87 investigated the anatomic location of the apical foramen in a sam- ple of 30 maxillary canines. The root apex and apical foramen were displaced disto-labially in the majority of thespecimens. Coincidence of the apical foramen and root apex was found in only 5 (16.7%) of the specimens. The use of the electronic apex locator is more reliable than the radiograph in determining the apical foramen or constriction in most canine teeth.

Green⁸⁶ found that the average diameter of the major foramen in 50 maxillary canines studied was 0.5 mm while the accessory foramina were 0.2 mm or less. The average dis- tance of the major apical foramen from the anatomical root apex was found to be 0.3 mm. Approximately 12% of the maxillary canines exhibited accessory foramina.

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FIGURE 4.9 Root cross-sections of the maxillary left canine.

VARIATIONS AND ANOMALIES

The maxillary canine usually presents very few anatomi- cal variations. An extensive literature review found 17 case reports. When variations do occur, the root is more frequently affected than the crown. However, there are occasional reports of both coronal and radicular anomalies. The root can be dilacerated or can have extreme variations in length. One individual with an extremely long root (41 mm) was reported by Booth. His patient was a 5´2˝ height, 31-year-old woman of Dutch ancestry ⁹¹.

Dens evaginatus, in a form of a lingual tubercle or talon cusp, was the most common variation or anomaly found associated with the maxillary canine. There are also reports of labial tubercles.⁹⁶ Dankner et al., in an extensive literature review and radiographic examination of 15,000 anterior teeth, found the overall incidence of dens evaginatus to be~1%. Their survey found no occurrences of dens evaginates in the maxillary canine. Between 1970 and 1995, there were only four case reports of dens evaginatus in the maxillary canine in their review.

Other variations reported in the literature include case reports with one root and two canals, two roots, dens invaginatus, and bilateral, supernumerary canines in a non-syndrome case. The two-rooted maxillary canine should be considered extremely rare, unlike the two-rooted mandibular canine, which in some genetic popu- lations can be a more frequent anomaly.⁹¹

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FIGURE 4.10

Maxillary left canine exhibiting radicular-form of dens- invaginatus type 3. Pulp tests were vital on initial examination.

MAXILLARY PREMOLAR EXTERNAL ROOT MORPHOLOGY

The root anatomy of the maxillary premolar can vary depending on whether one, two, or three roots are present. Also, a variation may exist inthe depth of the bifurcation or trifurcation of the root trunk. The more common two-rooted form is illustrated. As with all multirooted teeth, two radiographs exposed at different angulations or even CBCT images (if indicated), may be needed to better understand the actual root andcanal morphology.

The maxillary first premolar does exhibit ethnic variations with respect to root number. There are some common features to the various forms. The overall length of the maxillary first premolar is 22.5 mm with an average crown length of 8.5 mm and an average root length of 14 mm.

Prominent root concavities are present on both the mesial and distal surfaces of the root trunk. The mesial root concavity is more prominent and extends onto the cervical third of the crown. This results in a root that is broad labiolingually and narrow mesiodistally with a kidney shape when viewed in cross-section at the cementoenamel junction. These anatomical features have implications in restorative dentistry and in periodontal treatment, and are common areas for inadvertent endodon- tic root perforations.

Gher and Vernino⁹⁷ examined the external root shape as it is related to the development of periodontal defects.

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FIGURE 4.11

A. Buccal view of maxillary right first premolar.

B. Mesial view of maxillary right first premolar.

The Maxillary first premolar’s palatal aspect of the buccal root tip of two-rooted maxillary first premolars usually has a deep longitudinal depression along its length. About 78% of the 45 teeth in their study exhibited a buccal furcation groove. They concluded that a buccal root furcation groove was a normal anatomical feature in those two-rooted maxillary first premolars that havewell- formed buccal and lingual roots. The groove was not generally found in those two-rooted specimens with a furcation located in the apical third of the root. A study by Joseph et al. found an incidence of the buccal furcation groove in 62% of teeth with bifurcated roots.⁹¹

ROOT NUMBER AND FORM

The majority of anatomic studies found that the most common form of the maxillary first premolar is the two-rooted form. There was a wide variation in incidence of the number of roots in the anatomical studies cited. The incidence of three-rooted maxillary first premolars ranged from 0% to 6%. The ethnic background of the patients in many of the studies was not identified. The majority of studies reporting that the two-rooted form was most common had a probable Caucasian cohort, forming the majority of the population. Studies, which do identify ethnic background, have demonstrated distinct differences between Asian and Caucasian populations. Single-rooted maxillary first premolars are the dominant forms in Asian population and three-rooted forms are rarer by 1:4 ratio. Because of the significant influence of premolar with three very fine roots ethnic background in root number for this tooth, reports the means for all studies and separates the data between Asian and North American Native populations (both Sundadont and Sinodont Mongoloid) versus non- Asian populations. In addition to ethnic differences, studies vary in their definition, or do not identify what constitutes a bifurcated root. Walker utilized Turner’s classification and does not consider a root to be separate unless it is a distinct and sepa- rate root for at least half of the overall root length. However, Loh grouped teeth into one root, two roots (including two- root distinct and two-root fused), and three roots. The two-root fused category was defined as teeth with roots joined almost to the apex and with two canals at their ori- gin. The normal external three-root anatomy configuration is that of a mesiobuccal, distobuccal, and palatal root with morphology similar to that of a miniaturized maxillary three-rooted molar.

Sabala et al. studied all aberrant root and root canal morphology in 501 patient records. The occurrence of the same aberration on the contralateral tooth varied according to the type of anomaly. In four of 501 patients, who were found to have three-rooted maxillary first premolars, all were bilateral. Their study found that the more rare the anomaly, the greater the incidence of the anomaly occurring bilaterally. Anomalies occurring <1% were found to occur bilaterally up to 90% of the time.

CANAL SYSTEM

The majority of maxillary first premolars were found to have two canals, whether the tooth had a single- or double-root morphology. In 21 anatomical reports assessed, over 80% of the teeth had two canals. Ethnicity was a factor affecting the canal number. The incidence of a Vertucci Type I single canal was significantly higher in Asian populations compared to mixed non-Asian populations. The Vertucci and Weine classification sys- tems are useful in exploring any canal systems with double canals in single roots for endodontic therapy.

All the three-rooted first premolars in the anatomical studies were found to have a single canal in each root. The incidence of three canal maxillary premolar teeth ranged Regardless of the number of roots, the majority of maxillary first premolars (80.8%) had two separate canals and 73.6% had two separate foramina at the apex.

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FIGURE 4.12 Root cross-sections of the maxillary right first premolar.

VARIATIONS AND ANOMALIES

The most common variation reported for the maxillary first premolar was three roots and three canals (Table 1-13). Ethnic differences were found. The study by Loh reported a much lower incidence (50.6%) of the two- rooted maxillary first premolars in a Singaporean popula- tion compared to Sabala et al.’s study (98.4%) based in the United States. Tratman reported that the two-rooted first premolar was very uncommon in Asian stock as did Petersen in his study of the East Greenland Eskimo denti- tion. A more recent large anatomical study of 3202 maxillary first premolars in Japan by Aoki, found that 65.7% of the specimens were single rooted.

Three-rooted forms were reported to be rare variations in Asian populations. Mattuella et al. reported a variation of the maxillary first premolar with a longitudinal sulcus on the buccal surface of the buccal root. This variation resulted in a two-canal system in the buccal root as the root canal system narrowed with age and thus, three canals in teeth with two roots.

Gemination of the maxillary first premolar is rarely reported.

Taurodontism is another rare anomaly in premolars, as a group, and less common in the maxillary premolars compared to their mandibular counterparts. Taurodontism of roots and canal systems is explained in greater detail in the section on maxillary first molars. Llamas et al. found only three taurodont-like maxillary premolars in a sample of 379 extracted maxillary and mandibular premolars. Of the 16 cases of taurodontism in Shifman et al.’s review of radio- graphs, over a five-year period, none were maxillary first premolars. Madeira et al. studied 4459 premolars and found a total of 11 taurodont mandibular premolars (seven mandibular first premolars and four mandibular second premolars), but none in the maxillary premolars. Llamas et al. reported three taurodont maxillary first premolars of the 379 teeth.

The Weine Type IV root canal system (Vertucci’s Type V), with a wide buccolingual canal that branches into two api- cal canals and foramina in the apical third, may sometimes be confused as taurodont-like root canal anatomy, when it occurs in single rooted maxillary premolar teeth.⁹¹

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FIGURE 4. 13 Maxillary left first premolar with three roots and three canals

MAXILLARY SECOND PREMOLAR EXTERNAL ROOT MORPHOLOGY

The cross-sectional root anatomy of the maxillary second premolar in the mid-root area is described as oval or kidney shaped. Developmental depressions are often present on the mesial and distal aspects of the root, but generally less pronounced than on the maxillary first pre- molar. The typical single root trunk is broad buccolingually and is narrower mesiodistally (Figure 1-15). The root tip usually ends as a single blunt apex, but may be fine and divide into two or more, rarely three, apices. Curvature in the apical third is also not uncommon. The overall average length of the maxillary second premolar is 22.5 mm with an average crown length of 8.5 mm and an average root length of 14 mm.

ROOT NUMBER AND FORM

All of the anatomical studies cited found that the most com- mon form of the maxillary second premolar is a single root (Figure 1-15). The mean for data from eight anatomical studies of 9033 teeth is summarized in Table 1-14, resulting in a 91.5% incidence of single- rooted teeth. The incidence of two-rooted maxillary second premolars ranged from 1.6% to 20.4%, while the three-rooted form was a rare finding and ranged from 0% to 1%. Bilateral symmetry of the three-rooted form may be expected in many patients, as well as this anomaly occurs in both first andsecond premolar teeth.

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FIGURE 4.14

A. Buccal view of maxillary left second premolar.

B. Mesial view of maxillary left second premolar.

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FIGURE 4. 15 Root cross-sections of the maxillary left second premolar.

Canal System

The maxillary second premolar has a single canal in ~51.8% of the 4829 teeth examined in 16 anatomical studies (Table 1-15). Therefore,even though over 90% of these teeth have a single root, a high proportion will have two canals present. Canal explo- ration of maxillary second premolar teeth should be done with fine curved files, keeping in mind many types of the Vertucci’s or Weine’s classification of “two canals in one root” that may not always be apparent on the radiograph. The incidence of three canals was low in each of the anatomical studies. The majority of the teeth studied (63.6%) had a single canal and foramen at the apex.

Variations and anomalies

Relatively few case reports of variations and anomalies in the maxillary second premolar have been published (Table 1-16). The most common variation reported is the maxillary second premolar with three roots and three canals. These case reports also include examples of dens invaginatus, a deep distal root concavity, dens evaginatus, tauro- dontism, two roots, and threecanals.⁹¹

Three-rooted maxillary second premolar teeth do not seem to be as common as in first premolars.This anomaly is often bilateral and should be considered by exposing radio- graphs taken at different angles. Both first and second pre- molar triple-canal system anomalies do occur, but rarely.⁹⁸

MAXILLARY FIRST MOLAR EXTERNAL ROOT MORPHOLOGY

The maxillary first molar normally has three roots (Figure 1-16). The mesiobuccal root is broad buccolingually and has prominent depressions or flutings on its mesial and distal surfaces.⁹¹ The internal canal morphology is highly variable but the majority of the mesiobuccal roots contain two canals. The distobuccal root is generally rounded or ovoid in cross-section and usually contains a single canal. The palatal root is more broad mesiodistally than buccolingually and ovoidal in shape but normally con- tains only a single large canal. Although the palatal root generally appears straight on radiographs, there is usually a buccal curvature in the apical third. Depressions on the buccal and palatal surfaces of the palatal root can be pre- sent but are generally shallow. Gher and Vernino⁹⁷ found prominent depressions not only on the mesial aspect but also on the distal aspect of the mesiobuccal roots. Shallow depressions could also be found on the furcal side of the distobuccal and palatal roots.

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The overall average length of the maxillary first molar is 20.5 mm with an average crown length of 7.5 mm and an average root length of 13 mm.

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FIGURE 4.16 Maxillary First molar

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FIGURE 4.17 Maxillary First Molar

ROOT NUMBER AND FORM

The maxillary first molar root anatomy is predominantly a three-rooted form, as shown in all anatomic studies of this tooth (Table 1-17). The two-rooted form is rarely reported, and may be due to fusion of the distobuccal root with palatal root or the distobuccal root with the mesiobuccal root. The single root or conical form of root anatomy in the first maxil- lary molar is very rarely reported. Over 97.7% of maxillary first molars had three roots and 2.1% had two roots in 12 studies that included 2744 teeth. The four-rooted anatomy in its various forms is also very rare in the maxillary first molar and is more likely to occur in the second or third maxillary molars.

The incidence of fusion (Table 1-18) of any two or three roots was ~5.9%. The “C” shape canal mor- phology in the maxillary first molar is also a rare anomaly with an incidence varying from 0.09% to 0.3%.⁹⁹

CANAL SYSTEM

Internal root canal system morphology reflects the external root anatomy.The mesiobuccal root of the maxillary first molar contains a double root canal system more often than a single canal according to most of the anatomical studies. This review contains data on the canal morphology of the mesiobuc- cal root that included a total of 14,346 teeth from 71 studies (Table 1-19). The incidence of two canals in the mesiobuccal root was 59.4% and of one canal was 40.6%. The incidence of two canals in the mesiobuccal root was somewhat higher in laboratory studies (64.0%) compared to clinical studies (56.8%). Less variation wasfound in the distobuccal and palatal roots (Table 1-19). One canal was found in the distobuccal root in 98.8% of teeth, whereas the palatal root had only one canal in 99.3% of the teeth studied. Earlier in vitro studies of the mesiobuccal root canal system were slightly more likely to report two canals in the maxillary first molar than the in vivo clinical studies, but the incidence of location of a two-canal system in both clinical and laboratory studies appears to be increasing with the routine use of the SOM and other aids during the modified endodontic access opening procedure.12,459 The diagnostic tool that has had the greatest impact in both clinical and lab- oratory studies is CBCT. The Clearing Technique has been the “gold standard” in laboratory studies, and the CBCT is rapidly becoming the “gold standard” in clinical studies as well as in laboratory studies.However, it should be noted that nine of the in vitro laboratory studies reported an incidence of second mesiobuccal canal (MB-2) in 80% to 96% of the time. Four were clearing stud- ies, two utilized CT, and three used either an SOM or surgical telescopes. Two of the in vivo clinical studies reported an incidence of MB-2 of >80%.30,183 One study was a clinical RCT study and the other utilized CBCT. The two-canal system of the mesiobuccal root of the max- illary first molar has a single apical foramen ~59.7% of the time.

The single-canal system and single apical foramen in the distobuccal and palatal root of the maxillary first molar is the most predominant form, as reported in all studies, but the “gold standard” in laboratory studies, and the CBCT is rapidly becoming the “gold standard” in clinical studies as well as in laboratory studies.198–201,203–207,462–464 However, it should be noted that nine of the in vitro laboratory studies reported an incidence of second mesiobuccal canal (MB-2) in 80% to 96% of the time. Four were clearing studies, two utilized CT, and three used either an SOM or surgical telescopes.Two of the in vivo clinical studies reported an incidence of MB-2 of >80%. One study was a clinical RCT study and the other utilized CBCT.

The two-canal system of the mesiobuccal root of the max- illary first molar has a single apical foramen ~59.7% of the time (Table 1-19).

The single-canal system and single apical foramen in the distobuccal and palatal root of the maxillary first molar is the most predominant form, as reported in all studies, but multiple canals and more than one apical foramen variation does exist in ~1% of these roots in the studies reported (Table 1-19).

Variations and anomalies

The root and canal morphology of molar teeth varies greatly. Many studies provided no information on ethnic back- ground, age or gender, or possible explanations for variation observed. Walker reported on the ethnic differences in the root anatomy of maxillary first premolars, mandibu- lar first premolars, and the high incidence of three-rooted mandibular first molars in Asian patients. However, he did not report on the incidence of a MB-2 in the maxillary first molar. A study by Weine et al. determined that the inci- dence of MB-2 in a Japanese population was similar to the incidence reported for other ethnic backgrounds.

Age was found to have an effect on the reported incidence of MB-2. Fewer canals were found in the MB root due to increasing age and calcification.

Sert and Bayirli conducted a clearing study that identi- fied gender in a sample of 2800 teeth from Turkish patients. Although only 100 of each type of tooth for each gender was included in their study, a single Vertucci’s Type I canal was present in the mesiobuccal root in only 3% of men compared to 10% of women. There are conflicting results with respect to gender and the number of canals in other studies. Some studies compared in vivo versus in vitro tech- niques. Seidberg et al. in an in vivo study, reported 33.3% of the 201 teeth studied had an MB- 2 canal. This increased to 62% in their in vitro study of 100 teeth. Similar results were reported in a study by Pomeranz and Fishelberg. Only 31% of 100 teeth studied had an MB- 2 canal in their in vivo study compared to 69% of 100 teeth in their in vitro study. The in vitro portion of this study described the samples as extracted maxillary molars and may represent pooled data instead of maxillary first molar data alone. The definition of a canal as a treatable canal used in clinical studies12,28 versus the more complex canal configurations visible through clearing studies can also lead to different results.

The more common use of SOM or loupes in recent clinical studies has resulted in an increased prevalence of the clinical detection of the MB-2 canal on the floor of the pulp cham- ber.[12,25,132,197] The effect of magnification on the incidence of clinical location of MB-2 was assessed in a clinical study by Buhrley et al.197 The MB-2 canal was found in 71.1% of teeth when using SOM. The group using loupes found MB-2 in 62.5%. The lowest incidence of MB- 2 was in the group per- forming RCT without any magnification. MB-2 was found in only 17.2%. A study by Sempira and Hartwell25 found that use of an SOM did increase the incidence of finding MB-2. They attributed relatively low incidence in their study due to their characterization of a canal as one that must be negoti- ated and obturated to within 4 mm of the apex.

CBCT is being utilized more frequently now in both clinical and laboratory studies as well as in clinical prac- tice to assist in identifying both root and root canal morphology. As a result, the incidence of MB-2 as well as other canals detected is increasing. Eder et al. reported an incidence of 94.1% of MB-2 in an in vitro study, while Reis et al. reported an incidence of 88.5% in a recent clinical study using CBCT.

The incidence of many of the anomalies cannot be deter- mined due to the lack of data collection and population size. However, although rare, these anomalies can and do occur. Ninety-six case reports were reviewed and the most common anomalies associated with the maxillary first molar were two palatal canals in three-rooted teeth, taurodontism (Figure 1-17), and various forms of root fusion (Table 1-20).

Of all the canals in the maxillary first molar, the MB-2 can be the most difficult to find and negotiate in a clinical situa- tion. Knowledge from laboratory studies is essential to provide insight into the complex root canal anatomy. A study by Davis et al. compared the post debridement anatomy of the canals of 217 teeth. Injection of silicone impression material into the instrumented canalsrevealed that standard instrumentation left a significant portion of the canal walls untouched. Fins, web- bing, and portions of the canal were sometimes found not fully instrumented. Clinical instrumentation of this tooth, especially with respect to the mesiobuccal root, can be complicated. Failure to detect and treat the second MB-2 canal system will result in a decreased long-term prognosis. Stropko observed that by scheduling adequate clinical time, by using the recent magnifi- cation and detection instrumentation aids, and by having thor- ough knowledge of how and where to search for MB-2, the rate of location can approach 93% in maxillary first molars.⁹¹

Maxillary second molar external root Morphology

The maxillary second molar normally has three roots (Figure 1-18 and Table 1-21). The relative shape of each of the roots is similar to the maxillary first molar but the roots tend to be closer and there is a higher tendency toward fusion of two or three roots. There is usually more of a dis- tal inclination to the root or roots of this tooth compared to the maxillary first molar. There is also a general reduction in crown and root size in the posterior arch consistent with the reduction in facial profile of modern Homo sapiens.

The mesiobuccal root is broad buccolingually and has prominent depressions or flutings on its mesial and distal surfaces. The internal canal morphology is variable and anatomical studies indicate that the mesiobuccal root has almost an equal incidence of one or two canals. The dis- tobuccal root is generally rounded or ovoid in cross-section and usually contains a single canal. The palatal root is more broad mesiodistally than buccolingually and ovoidal in shape but normally contains only a single canal. Depressions on its buccal and palatal surfaces can be present but are usually shallow. Gher and Vernino⁹⁷ found prominent depressions on the distal aspect of the mesiobuccal roots. Lesser depres- sions could also be found on the furcal side of the distobuccal and palatal roots. The overall average length of the maxillary second molar is 19 mm with an average crown length of 7 mm and an average root length of 12 mm.

ROOT NUMBER AND FORM

The majority of maxillary second molars (85.8%) were three- rooted (Table 1-21). However, this is a lower incidence than that found in the maxillary first molar. The closer proximity of the roots results in a higher incidence of root fusion (26.4%) (Table 1-22) and C-shaped canals (4.9%) when compared to the maxillary first molar.

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FIGURE 4.18

Canal System

Mesiobuccal Canal System

In the most common three-rooted maxillary molar form, the shape of the root provides an indication of the shape of the internal canal morphology. The broad buccolingual and narrow mesiodistal dimension of the mesiobuccal root of the maxillary second molar may have one or two canals (Table 1-23). A wide range of canal incidence in the mesiobuc- cal root exists. Kulild and Peters reported that the norm would be a double-canal system and a low incidence of a single canal of 5.3%, while Hartwell and Bellizzi found a single canal in 81.8% of their specimens. It should be noted that the former paper was a laboratory study while the latter was a clinical finding.

The single canal is usually described as being kidney or ribbon-shaped. Eskoz and Weine suggested that age and continued deposition of secondary dentin in the isthmus can cause narrowing and possible occlusion in the mid portion resulting in two canals. There was a single apical foramen found in the mesiobuccal root over 64.7% of the time.⁹¹

The Palatal and Distobuccal Canal Systems

The distobuccal and palatal roots exhibit a single canal over 99% of the time (Table 1-23). Both these roots are rounder in cross-section and a single-canal system is the expected normal finding. In a retrospective clinical treatment paper by Peikoff et al.¹⁶⁵ on the different forms of canal anatomy found in maxillary second molar teeth, six variants were described. In a random selection of 520 clinical treatments in a specialist office, Variants 1 to 6 reported and depicted second molar anatomy types from; single canal in a fused root to four canals in four roots (Figures 1-19 and 1-20).

Variations and anomalies

Fifty case reports of anomalies associated with the maxillary second molar were reviewed (Table 1-24). The most com- mon anomaly cited for this tooth is the four-rooted variation with two palatal roots. Other variations such as two canals within one large palatal root have been reported, but with a much lower frequency.

A review article on the double palatal root by Christie et al. ¹⁰⁰ studied a retrospective collection of 16 clinical cases from their practice and eight teeth from six published case reports during a 25-year period. The highest occurrence of two palatal canals in double pala- tal roots (21/24 teeth) was found in the maxillary second molar tooth. The anomaly seemed to be grouped as three- root anatomy types; first, Type I, the two palatal roots being long and divergent; second, Type II, the two palatal roots being shorter, nearly parallel and comparable in shape and size to the two buccal roots (Figure 1-20); and third, Type III and IV were variations of root fusion that included a two-canal system, one entering the root from the palatal aspect. Subsequent case reports have tended to support this observation.⁹¹

In a study of 2636 posterior teeth in 875 Jordanian patients, a 4.4% incidence of taurodontism was found in the maxillary or mandibular molar teeth.¹⁰¹ The maxillary sec- ond molar had the highest incidence of taurodontism. Of the 116 teeth identified in the study, 31% were permanent maxil- lary second molars. Treatment of hypertaurodont teeth was described in two case reports. The ethnicity, if any, has not been established in this relatively rare root anomaly but it is no longer considered an exclusive primitive dental trait of Homo Neanderthal teeth.¹⁰² (For more details, see Chapter 26, “Endodontic retreatment and management of mishaps.”)

Mandibular central incisor External root Morphology

The mandibular central incisor is single rooted (Figure 1-21). The external form of the root is broad labiolingually and narrow mesiodistally. Longitudinal depressions are pre- sent on both the mesial and distal surfaces of the root. A cross-section of the root is ovoid to hourglass in shape due to the developmental depressions on each side.⁹¹. The overall average length of the mandibular central incisor is 21.5 mm with an average crown length of 9 mm and an average root length of 12.5 mm.4 In general, the mandibular central incisor is just slightly smaller than the mandibular lateral incisor in all dimensions.

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FIGURE4.19

Root Number and Form

The anatomical studies reviewed here reported that 100% of the mandibular central incisors were single-rooted teeth (Table 1-25). Variations from this form have either not been reported or not found in a review of the literature. An early study of the anatomy of the mandibular anterior teeth by Rankine-Wilson and Henry585 established that even with a single root, these teeth may contain a “bifurcated” or double- canal system.

Canal System

The shape of the canal system is either rounded or ribbon shaped. The majority of mandibular central inci- sors have a single canal. Table 1-26 shows that out of 7455 a single canal is found in 81.1%. Two separate canals were found in 18.8%, which is less frequent than that found in the mandibular lateral incisor. The inci- dence of three or more canals was quite rare (0.2%).

A single apical foramen was found in 96.5% of the teeth. Therefore, even when two separate canals have been found, the majority of these canals will join and exit near or at a single foramen. Even the single canal system in all lower anterior teeth is wide in a labiolingual direction and narrow mesiodistally, match- ing the external root outline. Fluting of the mesial and distal surfaces produces a figure eight shape single canal in cross section. As secondary dentin forms with age, the canal system takes on the shape of a double canal with a connecting isthmus, and should be treated as if it was a double canal when the root canal treatment is performed. Clements and Gilboe¹⁰³ and others have even recommended an incisal edgeaccess opening for a straight-line approach to the apical fora- men, when incisal edge wear is present or when a restora- tive crown is planned.

Green found that the average diameter of the major foramen in 200 pooled mandibular incisors was 0.3 mm while the accessory foramina were 0.2 mm or less in diameter. Approximately 12% of the pooled mandibular incisors exhibited accessory foramina. The average dis- tance of the apical foramen from the anatomical root apex was 0.2 mm.

Variations and anomalies

Few anomalies are reported for this tooth (Table 1-27). Of the 15 case reports reviewed, the most frequently reported anomaly was dens evaginatus (talon cusp).

Mandibular lateral incisor

External root Morphology

The mandibular lateral incisor is single rooted (Figure 1-24) and comparable in form and shape to the mandibular central incisor. The external form of the root is broad labiolingually and narrow mesiodistally. Longitudinal depressions are present on both the mesial and distal midroot surfaces.

A cross-section of the root is ovoid or hourglass in shape due to the developmental depressions on each side. The overall length of the average mandibular lateral incisor is 23.5 mm with an average crown length of 9.5 mm and an average root length of 14 mm.

In addition to being slightly larger in all dimensions, the major difference in tooth anatomy, compared with the and searching for the more frequently encountered, broader labiolingual canal system.⁹¹

Root Number and Form

All eight studies reviewing a pooled average of 3266 teeth, reported that 100% of the mandibular lateral incisors were single-rooted teeth (Table 1-28). Variations in root number from this form have either not been reported or not found in a review of the literature, except that reported by Slowey.¹⁰⁴

Canal System

The shape of the canal system is comparable to the mandibular central incisor and is either rounded or ribbon sha ped. The majority of mandibular lateral incisors haveasinglecanal,which is less than the percentagefound in the average mandibular central incisor (81.1%) (Table 1-29). Two canals were found in 24.6% of the specimens (Figure 1-25). The incidence of more than two canals was quite rare (0.04%). A single apical foramen was found in 95.8% of teeth. Therefore, similar to the mandibular central incisors, even when two sepa- rate canals have been found, the majority of the canals will join and exit through a single foramen.

Variations and anomalies

Very few anomalies have been reported for this tooth (Table 1-30). Dens evaginatus (talon cusp), dens invaginatus, and fusion were the main anomalies. Slowey¹⁰⁴ described a radiograph ofa rare mandibular lateral incisor with two distinct roottips.

Mandibular canine External root Morphology

The root of the mandibular canine is wider labiolingually and narrower mesiodistally in cross-section, which is larger and longer than, but similar to the shape, the other man- dibular anterior teeth (Figure 1-26). The projecting cusp tip of the mandibular canine is usually lingual to the long axis of the tooth length, while the cusp tip of a maxillary canine is labial to its long axis. Both canine roots are usu- ally straight but may occasionally have fine and curved tips. Developmental depressions are normally present on both the mesial and distal surfaces of the mid-root. The depres- sions can be relatively deep. Normally a single-rooted tooth,The overall average length of the mandibular canine is 27 mm with an average crown length of 11 mm and an aver- age root length of 16 mm that is comparable to the overall length of the maxillary canine.

Root Number and Form

The most common form of the mandibular canine is one with a single root (95.4%) The studies cited found an incidence of two roots ranging from 1.3% to 6.2%. A recent paper by Lee and Scott617 suggested that this trait is largely a European ethnicity trait (5.7%–9.2%), found most frequently in Basque, Spain, and is rarely found in Asian or sub-Sahara African populations. An earlier article by Scott and Alexandersen estimated the incidence of two- rooted mandibular caninesEuropean samples to be ~5% to 10% and very rare in Asian and African populations.

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FIGURE 4.20

Canal System

The mandibular canine usually presents with a single root canal system⁹¹ (Table 1-32). The incidence of a single canal is 90.5%. However, even in a single canal system, the root trunk is broad in a labiolingual direction and therefore very ovoid or figure-eight shaped incross-section. In the single-canal system, 97.9% have a single apical fora- men.Therefore, when two canals are pre- sent (9.5%) in a single-rooted mandibular canine, the most common configuration is the joining of the two canals beforeone variation of root morphology is a bifurcated root that may resemble a premolar root.At other times, when this bifurcation occurs, the furcation dividing the labial and lingual roots can be at any level on the root trunk and usually results in a smaller lingual rootlet at the apical third region. In rare occasions, even two separated roots can be exiting at the apex [Vertucci Type II (2-1) or Vertucci Type III (1-2-1)].

Green213 found that the average diameter of the major fora- men was 0.3 mm, while the accessory foramina were 0.2 mm or less. The average distance of the major apical foramen from the anatomical root apex was found to be 0.35 mm. Approximately 10% of the mandibular canines exhibited accessory foramina.

Variation and anomalies

The most frequent variation found in the mandibular canine is the presence of two roots and two canals (Table 1-33). A report by Alexandersen401 showed a high incidence (5.6%) of two-rooted mandibular canine teeth in an Iron-Age Danish population.

Although, the data from anatomical studies varies greatly with respect to the incidence of two roots, the mandibular canine has the highest incidence of all of the anterior teeth at 4.5%. The human primary canine teeth are more likely to exhibit two separate (bifurcated) roots. Other variations reported in the literature include two canals and two roots, two canals with a single apical foramen, three canals, dens invaginatus, and gemination.

Mandibular first premolar external root Morphology

The mandibular first premolar is typically a single-rooted tooth that is wider buccolingually and narrower mesiodistally, although two-rooted varieties do occur fairly frequently (Figure 1-28). Developmental depressions or grooves are frequently found on both the mesial and distal surfaces of the root resulting in an ovoid or slight hourglass- shaped root that tapers to the lingual. The depression on the distal root surface has been described as being deeper than the mesial root depression.

The overall average length of the mandibular first premo- lar is 22.5 mm with an average crown length of 8.5 mm and an average root length of 14 mm.⁹¹

Root Number and Form

The mandibular first premolar is normally a single-rooted tooth (Table 1-34); however, studies revealed an incidence of ~2.7% of bifurcated teeth.Three-rooted mandibular first premolars are extremely rare with an inci- dence of 0.2%.

Trope et al. found significant ethnic variations in root anatomy when comparing African American and Caucasian patients. Their study found an incidence of two root canals in 5.5% in Caucasian and 16.2% in the African American group of patients. Three- rooted mandibular first premolars are rare but are occasionally found in case reports (Figure1-29).

Scott and Turner described the accessory root as “Tome’s root.” Their anthropological review of ethnic differ- ences indicates that aboriginal Australians and sub-Sahara African populations have the highest incidence (>25%) of accessory roots. The lowest incidence (0%–10%) of Tome’sroot occurred in American Arctic, New Guinea, Jomon, and Western Eurasian populations.

The complexity of the root and root canal system is related to the presence and severity of radicular grooves.Tome’s root ranges from a shallow concavity to a deep groove, to complete furcation(s) of the root(s). The deeper the concavity, the more likely the presence of a C-shaped canal system within. Chen et al. studied the rela- tionship of radicular grooves and root canal morphology in the mandibular first premolars using Micro-CT and found that 40.9% of the teeth in their study sample had radicu- lar grooves. These grooves were primarily located on the mesial root surface (69.5%) and were more frequently asso- ciated with those teeth that had more complex root canal morphology.

Caucasian patients. Although the number of patients in each ethnic group was not identified, the study reported that 16% of the Caucasian patients had bifurcated canals com- pared to 21.6% of the African American patients. Sert and Bayirli found an incidence of two or more canals in 35% of men and 44% of women of Turkish descent, further reinforc- ing the importance of ethnic differences as well as possible gender differences.

Variations and anomalies

Twenty-five case reports of anomalies or variations of the mandibular first premolar were identified in a review of the literature (Table 1-36). The most common variation associ- ated with the mandibular first premolar was the three-rooted variation with three canals (Figure 1- 29). However, only five case reports in total were identified. Other reported developmental anomalies included “C”-shaped root canals in premolars, three canals in a single root,and three canals and two roots.. Discussion of dens evagina- tus, particularly in premolar teeth of patients of Asian eth- nicity is also found under mandibular second premolar tooth anomalies.

A study of 45,X chromosome women (and 45,X/46,XX chromosome) found more than one canal in one or more of the mandibular premolars in almost half of the 87 patients studied who had the genetic syndrome. Separate canals were found in 23% of the mandibular first premolars and 25% of the mandibular second premolars. The study concluded that X- chromosomes might have a gene or genes with aregulatory function for root development.⁹¹ Mandibular Second Premolar

External root Morphology

The mandibular second premolar is normally a single-rooted tooth (Figure 1-30) like the mandibular first premolar. The root is described as flat or convex on its mesial surface while the distal surface often (73%) has a longitudinal developmental depression.¹⁰⁷ A cross-section of the root is usually ovoid in shape, generally tapering to thelingual.

The overall average length of the mandibular second pre- molar is 22.5 mm with an average crown length of 8 mm and an average root length of 14.5 mm.

Root Number and Form

The mandibular second premolar is normally a single-rooted tooth. Trope et al.638 compared root and canal morphology in Caucasian and African American patients and found 1.5% incidence of two roots in mandibular second premolar teeth in Caucasian patients and 4.8% in African American patients. These differences were lower and not statistically significant in contrast to the differences (as high as one in six) found between these two groups in the mandibular first premolars.

Studies found multi-rooted mandibular second premolars to be quite rare (Table 1- 37). Two-rooted varieties comprised 0.5% of the teeth. Three-rooted forms were rarely foundand comprised 0.1% of teeth.

Canal System

Studies found a single canal in 91.3% of mandibular sec- ond premolars (Table 1-38). When a second canal system is located, it is usually fine and branches toward the lingual surface in the middle or apical third of the main canal. The incidence of two or more canals was 8.7%. The characteristic appearance of such a tooth on a periapical radiograph is of a clearly visible coronal canal that seems to abruptly fade-out in the apical region beyond the branching canal system.There was a single apical foramen 90.6% of the time. Serman and Hasselgren found that second mandibular premolars had a 7% incidence of having a divided canal or root. Trope et al. found ethnic differences between African American and Caucasian patients. African American group had a higher incidence (7.8%) of mandibular second pre- molars with two or more canals, while the incidence in the Caucasian group was lower (2.8%). These differences were not numerically significant in contrast to the results found with the mandibular first premolar canal systems.

Sert and Bayirli study of Turkish patients found an inci- dence of two or more canals in 43% of men and 15% of the women. The gender differences in this population were sig- nificant and this ethnic group, as a whole, demonstrated a higher incidence of multiple canals than the averages of the remaining anatomical studies reported although this could be considered a variant from the one canal in one root.

Another anomaly includes mandibular second premolars with dens evaginatus (odontome) (Figure 1-32). Densevagi- natus is a fairly common occurrence in Asian populations and is usually found in the mandibular premolars, although not exclusively. Merrill reported a high inci- dence (4.5%) of this anomaly in Alaskan Eskimos (Inuit) and American Indians, an observation serving to illustrate Alaskan natives’ties to their more recent Asian heritageVery often, when these teeth, with an occlusal enamel pro- jection, erupt into occlusion, the pulp is exposed by attrition of the tubercle and it becomes nonvital. Root development at this age usually presents with a large or blunderbuss apex. Various prophylactic treatments have been suggested over the dec- ades. However, endodontic therapy and/or apexogenesis is the most frequent outcome of this coronal anomaly.

C-shaped canal is a rare occurrence. The hypotau- rodont-like canal system may also appear in the mandibular second premolar tooth.¹⁰⁸

Mandibular first molar

External root Morphology

The mandibular first molar is typically a two-rooted, three- canal tooth (Figure 1-33). Themesial and distal roots arenormally widely separated, with a furcation level at ~3 mm buccally and lingually and 4 mm apical to the cementoenamel junction, respectively.

Both roots are broader buccolingually than mesiodistally, with the mesial root wider buccolingually than the distal root. The mesial root has concavities on both its mesialand distal surfaces and is angled slightly mesially before curving to the distal approximately mid-root. The mesial root is slightly rotated and tapers distally from buccal to lingual. The distal root is generally more ovoid in its cross-sectional shape, although a mesial concavity in the mid-root may make it appear “kidney-bean” shaped in cross-section.

The overall average length of the mandibular first molar is 21.5 mm with an average crown length of 7.5 mm and an average root length of 14 mm. Root length may vary consid-erably in some individuals, with overall tooth length in excess of 25 mm in both first- and second-mandibular molarteeth.

Root Number and Form

The mandibular first molar is typically a two-rooted form with a mesial and a distal root (Table 1-40). This anatomic form has an overall incidence of 85.6%. However, there are significant root anatomy differences when comparing Asia to non-Asianpopulations. Non- Asian popula- tions have a higher incidence of two roots (96.1%) while the Asian populations have a lesser incidence (77.7%). Therefore, three roots may occur in ~20% to 25% of Asian populations. Anatomical studies found that the three-rooted variety, with a bifurcated mesial or distal root or an additional supplementary root, had an overall incidence of 14.1%. Single-rooted forms, fused and four-rooted forms, were extremely rare and occurred in <1% of teeth.

There is a higher incidence of three roots (DLi supple- mentary) occurring in Asian populations, that includes North American Aboriginal peoples (Mongoloid groups). Thirteen of the 36 anatomical studies that specifically included Asian- ethnicity populations, showed a variation in incidence even within these population groups. The incidence of three- rooted mandibular first molars ranged from 10.1% in the Burmese92 to 29.3% in the Chinese.176 Non-Asian groups ranged from 0% to 13.3%. Radix entomolaris (as well as the single-rooted maxillary first premolar) may be used as one of the markers in following Asian origins in both ancient and modern individuals or groups. The incidence of single, fused, or C-shaped roots increases in themandibu- lar molar teeth from first to third molars.

Canal System

The mandibular first molar typically has two mesial and one distal canals (Table 1-41). The two-rooted forms have two canals in the mesial root 95.6% of the time. The mesial root canals may have a common exit foramen 1:3 (35.6%) or can exit separately as two or more apical foramina 2:3 (64.4%).

Slowey indicated that the mesiobuccal canal usually has a distinct buccal curvature at the floor of the chamber while the mesiolingual canal is straighter in the long axis to the root. The distal root usually has a single, broad, oval or kidney bean-shaped canal, but a two-canal system can occur in nearly one third of the distal roots, resulting in a four-canal system.

The three-rooted forms had two canals in the mesial root 97.8% of the time in an average of the three anatomical studies reported (Table 1-42). However, there was a single apical foramen 29.9% of the time. The distobuccal root had one canal 98.6% of the time and the distolingual or third root had a single canal 100% of the time.⁹¹

Variations and anomalies

Eighty-six case reports are included in Table 1-43. The most frequent reportedanomalies relate toadditionalcanalsin one or more of the roots. However, the most frequently reported vari- ation in root form is radix entomolaris (an anthropologic term for third root distolingually positioned). The additional reports of extra canals, supernumerary roots and canals, and taurodon- tism were not included in Table 6-43 (see Mandibular secondmolar and Chapter 26 for additional reports of taurodontism).

The mid-mesial canal is a concept that was described by Weine.It is a term that is gaining acceptance with numerous case reports from the more frequent use of CBCT examination and increased use of microscope and guide- path probing techniques in endodontic treatments. Table 1-41 shows that it was recorded in 1.1% of the mesial roots of the 5824 teeth in all studies studies reported (Table 1-42). However, there was a single apical foramen 29.9% of the time. The distobuccal root had one canal 98.6% of the time and the distolingual or third root had a single canal 100% of the time.⁹¹

Variations and anomalies

Eighty-six case reports are included in Table 1-43. The most frequent reportedanomalies relate toadditionalcanalsin one or more of the roots. However, the most frequently reported vari- ation in root form is radix entomolaris (an anthropologic term for third root distolingually positioned). The additional reports of extra canals, supernumerary roots and canals, and taurodon- tism were not included in Table 6-43 (see Mandibular secondmolar and Chapter 26 for additional reports of taurodontism).

The mid-mesial canal is a concept that was described by Weine.It is a term that is gaining acceptance with numerous case reports from the more frequent use of CBCT examination and increased use of microscope and guide- path probing techniques in endodontic treatments. Table 1-41 shows that it was recorded in 1.1% of the mesial roots of the 5824 teeth in all studies.

Mandibular second molar external root Morphology

The mandibular second molar normally has two roots (Figure 1-34). The mesial and distal roots are usu- ally closer or have a longer root trunk and slightly shorter radicular root ends, and are more frequently fused, compared to the mandibular first molar. The roots are broader bucco- lingually than mesiodistally. Root concavities are usually pre- sent on the mesial surfaces of both the mesial and distal roots and the distal surface of the mesial root.

The overall average length of the mandibular second molar is 20 mm with an average crown length of 7 mm and an aver- age root length of 13 mm. Therefore, the overall dimensions of the second molar are smaller than the first molar.

Root Number and Form

The mandibular second molar is two rooted ~67% of the time (Table 1-44). Root fusion, that becomes a single-root, conical or “C-shape” form, has an incidence of ~31.3%.

The incidence of a third root, usually the distolingual root, in mandibular second molars (1.3%) is not as high as in first mandibular molars (14.1%) (Table 1-44). However, patient of Asian ethnicity seemed to have a higher incidence of sin- gle or conical root.

Canal System

The mandibular second molar typically has two mesial and one distal canal (Tables 1-45 and 1-46). The mesial root of the mandibular second molar has a higher incidence of one canal (18.1%) than does the mesial root of the mandibular first molar (3.2%). Therefore, the two- rooted form may have only a two-canal system. On the other hand, since a distal root may have a double-canal system about 15% of the time, a four-canal system is not uncommon.

Mesial root canals may have a common foramen or may exit separately as two or more foramina, but the join- ing of the two canals is the most common form (Vertucci Type II).

Variations and anomalies

Due to the higher incidence of root fusion in the mandibu- lar second molar, C-shaped canals are not infrequent (Table 1-47). An extensive literature review by Fernandes et al.45 found that the incidence of C-shaped canals ranged from 0.6% to 41.3% in the Chinese population and from 31.3% to 45.5% in the Korean population. The incidence of root fusion is generally higher in studies of Asian patients with Hou and Tsai, reporting an incidence of fusion of 51.6% in the mandibular second molars in a Chinese population. In the same study, the maxillary second molar was found to have the highest incidence of fused roots (60.3%).

As would be expected, the incidence of C-shaped canals is often higher in Asian patients as well. Seo and Park reported an incidence of C-shaped canals in 32.7% of Korean patients and Gulabivala et al.92 reported an incidence of 22.4% in the Burmese. Manning49 reported a lower incidence of C-shaped canals at 12.7 but Caucasian ethnicity formed the majority of the patients. Studies in the United States by Weine et al. and Sabala et al.22 reported incidences of single root or C-shape of <10%. Ethnicity was not identified in either of these studies but it is likely that non-Asian patients formed the majority of the patients in both the studies. The data from the studies that differentiated single conical and C-shaped roots indicate that the incidence of these two canal systems is approximately equal (8.3% and 8.5%, respectively).

A variation in canal and root morphology was first termed as “C-shaped canal” by Cooke and Cox.38 This canal shape results from fusion of the mesial and distal roots on either buccal or lingual root surface. A deep radicular groove is formed by Hertwig’s root sheath that extends to the apical root end. The pulp canal system is of a “C” shape, which may vary in size with age of the patient.

Melton et al. described three categories of C-shaped canals and Haddad et al. added to the initial description. Category I is described as a continuous C-shaped canal from the pulp chamber to the apex. Category II is described as a “semi-colon” where one canal was separated by dentin from the C-shaped canal. The Category III, C-shaped anatomy, is described as having a C-shaped orifice with two or more dis- tinct and separate canals. Although there have been reported cases of C-shaped canals in other teeth such as the maxillary lateral incisor, maxillary first molar, maxillary second molar, maxillary third molar,82 mandibular first premo- lar, mandibular first molar, and the mandibu- lar third molar, with the most case reports are of the C-shaped mandibular second molar (Table 1-46). The inci- dence of C-shaped canals is the highest in mandibular second molars ranging from 2% to 44.5%.

Other reported anomalies of mandibular second molars include fused or single roots, additional canals in one or more of the roots and two canals.

Munir et al.found 12% incidence of taurodontism in 500 patients of a Punjab Dental Hospital. Two-thirds of the cases were meso-taurodontism (Figure 1-35) and <2% were considered hypertaurodont.

Just as in the other maxillary or mandibular molar teeth, hyper-taurodontism may occur in single instance in mandibu- lar second molar teeth, which require endodontic treatment.¹⁰⁹

SUMMARY

Maxillary Teeth

The preceding data aims to bring together the available knowledge of the anatomy of teeth in the human dentition in the dental literature. Because it comes from studies done with somewhat different methodologies and sources, it may not be amenable to meta-analysis, as such. However, some general observations and conclusions may be drawn about root and root canal anatomy of each tooth. Just as it is imperative to know what the normal anatomy of a tooth is, the range of variation and anomalous forms that a human tooth may take is equally important. The tooth bud and eventually the developing tooth come from genes of each parent. Therefore, each patient may present with a dentition that is unique and individual.

The maxillary incisor and the maxillary canine teeth are all represented as a single-rooted tooth when data from all studies are combined for analysis. Despite this superficial similarity in anatomy, there are some distinctive differences in the morphology and variations in these anterior teeth.

After compensating for access alignment on the lingual side of midline, a root canal system of a maxillary central inci- sor is usually the largest and straightest of all human teeth. Even the palatal root of a first maxillary molar generally has a curvature to the buccal in the apical region. Lateral canals and apical delta canal branches are common. Nonetheless, gemination and fusion in the incisors occurred at the highest rate of all the teeth in one study. Developmental anomalies may include talon cusps or dens evaginatus, dens invaginatus, and fusions, which produced “double teeth.” These and other anomalies outside the normal appearance of the maxillary central incisor are found in individual case reports.

The maxillary lateral incisor has a root canal system that is finer and oval in size and may curve in its apical portion to the distal, lingual, or both. Uncommon two rooted forms are reported up to 4% of the teeth, often a result of fusion of root forms with a root groove resulting. A lingual groove anomaly may be associated with both pulpal and periodontal pathol- ogy as first reported by Simon et al. The developmental lingual groove anomaly may occur in maxillary central inci- sor and maxillary canine teeth, but are much rarer.

The lateral incisor may show anomalies such as dens invaginatus, followed by dens evaginatus (talon cusp), palato- gingival grooves, and two roots and two canals fusion with peg-laterals and rarely three or four canals.

The maxillary canine was formerly known simply as the “cuspid.” It has been shrinking in size in the human denti- tion since the times of the late Miocene hominids, with closure of the canine diastema, as well. The canine is oval with a taper to the lingual as seen in cross-section, and a single-rooted tooth unless afflicted with developmental anomalies such as dens invaginatus or gemination. Dens evaginatus or “talon cusps,” usually located on the lingual, may also occur. There may be two canals within one root in <5% of teeth, but the canal usually exits as a single fora- men. Double-rooted maxillary canines occur rarely, com- pared to the mandibular canine teeth.

The maxillary first premolar tooth in its classic form is a “bicuspid” with two cusps and two roots of approximately equal size when viewed in standard dental anatomy and endodontic texts. Thus, the root trunk is wider in a bucco- lingual dimension. Both a double- rooted form and a sin- gle-rooted morphology occur, but the triple-rooted variant occurs with a frequency of 0.6% in Asian ethnicity and 2.3% in Caucasian populations.

Regardless of root number and ethnicity, the majority of maxillary first premolar teeth (80%) had a two-canal system.⁹¹ Anomalies such as taurodontism and dens evaginatus are relatively rare in maxillary premolar teeth.

The maxillary second premolar at times may resemble the first premolar in a slightly diminished size, and with simi- lar ethnicity differences in root and canal numbers. It has a single root form over 90% of the time. The two-rooted form comprises a range of 1.6% to 20% of the time. Although three-rooted forms exist, it is found in lesser numbers but often concurrent with a three-rooted first premolar. All stud- ies showed the majority of maxillary second premolars that had one root with either one- or two-canal system, termi- nated in one foramen ~64% of the time. Taurodontism or multi-foramen Vertucci Type IV–VIII and so forth canals were also noted in case reports.

Nearly 98% of maxillary first molar teeth have three roots. Only 2% are found as two-rooted varieties and single or conical root anatomy is rare. The palatal root is larger in diameter as is the internal root canal, often curving in the buccal direction that is rarely noted in periapical radiographs. Fusion may occur with any of the two roots, but is more likely encountered in the second maxillary molar, and more so with the third molar tooth.

The mesiobuccal root has two canals in >60% of the teeth. The incidence of conical C-shaped roots in a maxillary first molar is relatively low at 0.1% to 0.3%. Other anomalies may include two canals in the palatal root, taurodont molar (both genetic syndromes and otherwise), and multiple canal sys- tems beyond four canals at five-, six-, and even seven-canal molars.

The maxillary second molar will still most likely be a three-rooted tooth, but only 86% of the time. Incidence of fusion of roots into a two-rooted form may occur in 10% of the teeth, and interestingly the single-rooted form is at 4% and a four-rooted tooth may occur just <1% of the time. The incidence of double palatal roots is rare. Other anoma- lies include teeth with five or more than six canals, fusions and C-shape canals, and taurodontism in its hypo-, meso-, and hyper-taurodont forms. Taurodont teeth are no longer considered a trait specific to Homo neanderthalensis in Ice Age Europe, but genetic syndromes, recessive familial inheritance and no specific ethnicity have been implicated.

Mandibular Teeth

Just as the maxillary teeth of the human dentition have their own range of variation of crown, root, and root canal systems, the mandibular arch has its own unique characteristics. The opposing tooth and its antimere may be within the normal range or may be an anomaly in root number or canal num- ber. The genetic characteristics of size and root shape of the mandibular teeth also have evolved to fit the occlusion of the upper arch. The reduction in the size of teeth and profile of both alveolar processes seem to be happening more quickly in human evolution than the base of the lower mandible, thus leaving the protruding chin and jaw that is not found in other.

CHAPTER 5 – CLASSIFICATION OF ROOT CANAL SYSTEM

Successful root canal treatment requires a thor- ough knowledge of root canal morphology to properly access the root canal system and remove microorganisms and pulp tissue . Human tooth types have variations in terms of the number and shape of roots and root canals . For dades, this topic has been the subject of numerous experimental and clinical reports; Data from the classical work of Hess and Zürcher and those of recent investigations have demonstrated that classification systems that define root canal configurations are required. Weine et al , using sectioning and radio- graphic methods, were the first to categorize root canal configurations within a single root into three types dependent on the division of the main root canal along its course from the pulp chamber to the root apex . Vertucci et al. developed a classification system based on the evaluation of 200 cleared maxillary second pre- molars, wherein the pulp cavities were stained with dye; they found eight canal systems that were more complex than those described by Weine et al. Later, Weine added an additional category (Type IV) to his original system.⁵

Abbildung in dieser Leseprobe nicht enthalten

FIGURE 5.1

Diagrammatic representations of Weine’s clas- sification for root canal morphology (Weine et al. ¹⁰⁹ ).

Type I, a single canal from pulp chamber to the apex (1-1 configuration);

Type II, two separate canals leaving the chamber but merging short of the apex to form a single canal (2-1 configuration);

Type III, two distinct canals from pulp chamber to the apex (2 configuration);

Type IV, a single canal leaving the chamber and dividing into two separate canals at the apex (1-2 configuration). (b) Diagrammatic representa- tions of Vertucci’s classification for root canal morphology (Vertucci et al. ¹² ). Type I, a single canal from pulp chamber to the apex (1-1 configuration); Type II, two separate canals leaving the chamber but merging short of the apex to form a single canal (2-1 configuration); Type III, a single canal that divides into two and subsequently merges to exit as one (1-2-1 configuration); Type IV, two distinct canals from pulp chamber to the apex (2 configuration);

Type V, a single canal leaving the chamber and dividing into two separate canals at the apex (1-2 configuration);

Type VI, two separate canals leaving the pulp chamber, merging in the body of the root, and dividing again into two distinct canals short from the apex (2-1-2 configuration);

Type VII, a single canal that divides, merges, and exits into two distinct canals short from the apex (1-2-1-2 configuration);

Type VIII, three distinct canals from pulp chamber to the apex (3-3 configuration) (modified from Ahmed et al. and published with permission)

Other classifications have been introduced for specific tooth types, such as maxillary molars with four roots ¹¹⁰, maxillary premolars with three canals ¹¹¹, middle mesial canals ¹¹², and distolingual roots in mandibular molars . Recently, Kottoor et al. and Albuquerque et al. proposed a nomenclature to classify root canal anatomy in maxillary and mandibular molars, respectively. Despite these efforts to describe systemati- cally the diversity of canal configurations, addi- tional types of root canal morphology within different populations have been reported. Based on a review of previous reports and anatomical studies on root canal morphology using micro-CT technology, Versiani and Ordinola-Zapata described 37 root canal configurations that included the most common anatomical configurations observable in a single root . Notwithstanding these efforts, a simple classification system that can be applied for all root types and root canal configurations in all groups of teeth has not been established Objectives of the New Classifications Categorizing root canal configuration by type using simple Roman numerals has been done for more than 50 years. However, considerable data on the morphological variations of root canals have been generated , and current systems for categorizing canal configurations into certain types based on single numbers have become insufficient, inaccurate, and misleading. The time has now come to develop a coding system for describing root and root canal configurations that will aid clinicians, researchers, educators, and students/trainees.

The new classification system proposed in this chapter aims to be simple, accurate, and useful. It provides information on root and root canal anat- omy identified using any diagnostic method regardless of their accuracy and reliability. However, this system does not address the degree of root and root canal curvature, degree of root/ canal separation, and exact levels of bifurcation of canals/roots, accessory canals (lateral and fur- cation canals), and apical ramifications. These parameters were considered during the develop- ment of the proposed classification, but they added considerable complexity. Such additional information could be useful and even improve classification accuracy; however, the benefits of any new system must be the simplicity in order to achieve its universal adoption.

Many comprehensive classifications categorize developmental anomalies related to the root or root canal, such as dens invaginatus C-shaped canal , taurodontism , and super-numerary roots . For simplicity, the present classification will not reclassify abnormal- ities already addressed in theliterature.⁵

ROOT CANAL SYSTEM

The space within the tooth that contains pulp tis- sue. The root canal system can be divided into two portions: the pulp chamber, which is usually located in the anatomic crown of the tooth (or may extend to the coronal third of the root in double/multi-rooted teeth), and the root canal, encased in the root.

ROOT CANAL ORIFICE

The opening of the canal system at the base of the chamber where the root canal begins. Generally, it is located at or just apical to the cer- vical line

ROOT CANAL CONFIGURATION

The course of the root canal system that begins at the orifice and ends at the canal terminus.

MAJOR APICAL FORAMEN

The exit of the root canal onto the external root surface, which is normally located within 3 mm of the root apex.

MINOR APICAL FORAMEN/APICAL CONSTRICTION

The apical part of the root canal with the narrow- est diameter which is generally 0.5–1.5 mm from the major apical foramen ⁹¹. It is the reference point often used as the apical termination of canal instrumentation and filling procedures.

The Coding System of the New Proposed Classification The new classification can be adapted for root and root canal configurations. This system includes codes for three separate components:

1. Tooth number
2. Number of roots and their configurations
3. Root canal configuration

Tooth Number (TN) TN can be written using any numbering system (i.e., Universal Numbering System, Palmer Notation Numbering System, or FDI World Dental Federation System). Moreover, when a tooth cannot be identi- fied using one of the numbering systems (i.e., extracted teeth), a suitable abbreviation can be used, for example, “MCI” for “maxillary central incisor.” Number of Roots and Their Configurations The root number (R) is added as a superscript before the TN (RTN). For instance, 1TN means that tooth TN possesses one root. Any division of a root, whether in the coronal, middle, or apical third, will be coded as two or more roots. Accordingly, a bifurcation is represented as 2TN, and a trifurcation is represented as 3TN. Root details in double- and multi-rooted teeth are added on the right of the TN (RTN Rn), such as 2TN B P (B: buccal, P: palatal) and 3TN MB DB P (MB: mesiobuccal, DB: distobuccal, P: palatal). Root Canal Configuration The type of canal configuration in each root will be identified using a superscript number(s) after the TN starting from the orifice(s) (O) and through the canal (C) to the foramen (or foram- ina) (F) . Inevitably, the assessments of apical canal con- figurations may vary depending on the identifica- tion method, namely, experimental or clinical, which is subjective among different observers. For example, according to certain experimental Table 5.1 Summary of the codes allocated for single-, double- and multi-rooted teeth Tooth type Code Single- rooted 1TNO-C-F Double-rooted 2TN R1O-C-F R2O-C-F Multi-rooted nTN R1O-C-F R2O-C-F RnO-C-F TN tooth number, R root, O orifice, C canal; F foramen. One number is given if O = C = F 52 H. M. A. Ahmed et al. measurements of canal dimensions or clinical negotiability, apical bifurcations could be classified either as an apical delta/ramification (i.e. a complex ramification of the root canal branches located near, and open on, the root apex) or a division from the main canal (Type 1–2, for example). Evidently, a standard consistent view of such anatomy cannot be achieved. Therefore, the apical canal configura- tion type should be classified according to the method used and identification criteria.

SINGLE-ROOTED TEETH

For any canal, if the numbers of O, C, and F are the same, then a single code (1TNn) is used. Thus, 1111 describes a single-rooted maxillary right central incisor having one orifice, one canal, and one foramen (Fig. 5.3a), while 1142 describes a single-rooted maxillary right first premolar hav- ing two orifices, two independent canals, and two foramina (Fig. 4.3b). If the root has a varying number of O, C, and/ or F, then the configuration of the canal will be written to provide this detail (1TNO-C-F) (Fig. 4.3c, d). For instance, 1441-2 refers to a single-rooted mandibular right first premolar having one orifice and one canal initially but then bifurcating into two independent canals and having two apical foramina (Fig. 4.4c). 1411-2-1 refers to a single- rooted mandibular right central incisor having one orifice and one canal initially, but then bifur- cating into two independent canals and terminat- ing in one canal (Fig. 4.4d), and 1441-2-3 refers to a single-rooted mandibular right first premolar having one orifice and one canal initially that bifurcates into two independent canals and termi- nating in three apical foramina (Fig. 4.3e).

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FIGURE 5.2 Micro-CT 3D models of single-rooted teeth with root and root canal morphologies classified according to the new system

DOUBLE-ROOTED TEETH

If a tooth is double-rooted, then the code 2TN R1O-C-F R2O-C-F should be used where R1 and R2 describe the anatomy of the first and second roots. As mentioned previously, only one code will be applied if the number of orifice(s), canal(s), and foramen (foramina) is the same, in the same root. For example, 214 B1 P1 refers to a double-rooted maxillary right first premolar in which each root (B, buccal; P, palatal) encases a single root canal from the orifice to the main foramen (Fig. 4.4a). 237 M2-1 D1 refers to a double-rooted mandibular left second molar in which the mesial root encases two canals leaving the chamber that join into one canal until the apex, while the distal root encases a single root canal from the orifice to the main foramen (Fig. 4.4b). If the root bifurcates in the middle or apical third, and the root canal configuration is different Fig. 4.3 Micro-CT 3D models of single-rooted teeth with root and root canal morphologies classified according to the new system 4 New Proposal for Classifying Root and Root Canal Morphology 53 Fig. 4.4 Micro- CT 3D models of double-rooted teeth with root and root canal morphologies classified according to the new system. B buccal, P palatal, M mesial, D distal, L lingual Fig. 4.5 Micro-CT 3D models of multi-rooted teeth with root and root canal morphologies classified according to the new system. MB mesiobuccal, DB distobuccal, P palatal, MP mesiopalatal, DP distopalatal, DL distolingual below and above the level of bifurcation, then the code will be 2TN O-CR1C-F R2C-F, where ‘O-C’ is the root canal configuration coronal to the level of bifurcation and R1C-F and R2C-F are the continua- tion of the canal and number of foramina apical to the level of the bifurcation in either first (R1) or second (R2) roots, respectively .

Figure 4.4c shows a double-rooted maxillary left first premolar coded as 224 1B1- 2-1 P1 in which the level of root bifurcation locates at the middle third, and both roots have a common canal con- figuration coronal to the level of root bifuca- tion. Figure 4.4d shows a double-rooted maxillary left central incisor coded as 221 1M1 D1 in which the root bifurcates in the apical third and the root canal configuration below and above the level of bifurcation is different. Figure 4.4e shows similar anatomical variation in a mandibular canine.

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FIGURE 5.3 Micro-CT 3D models of single-rooted teeth with root and root canal morphologies classified according to the new system

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FIGURER 5.4 Micro-CT 3D models of single-rooted teeth with root and root canal morphologies classified according to the new system

MULTI-ROOTED TEETH I f the tooth is multi-rooted, then the code nTN R1O- C-F R2O-C-F RnO-C-F should be used. Figures 4.5 and 4.6 show the application of the new configuration system applied to several types of root canal systems. As an example, 317 MB1 DB1 P1 means that the maxillary right second 54 H. M. A. Ahmed et al. Fig. 4.6 Micro-CT 3D models of distinct groups of teeth with root and root canal morphologies classified according to the new system molar has three roots (MB, mesiobuccal; DB, distobuccal; P, palatal) with a single orifice, canal, and foramen in each root . 326 MB2-1 DP1 P1 means that the maxillary left first molar has three roots in which the MB root encases a type 2-1 canal, while the DP and P roots encase a root canal with a single orifice, canal, and foramen . Similarly, 427 MB2-1 DB1 MP1 DP1 means that the maxillary left second molar has four roots (MB, mesiobuc- cal; DB, distobuccal; MP, mesiopalatal; DP, dis- topalatal) in which the MB root encases a type 2-1 canal, and the DB, MP, and DP roots each encase a single orifice, canal and foramen 4 New Proposal for Classifying Root and Root Canal Morphology 55 . 347 M2 DB1 DL1 means that the man- dibular right second molar has three roots (M, mesial; DB, distobuccal; DL, distolingual) in which the mesial root has two independent canals, while DB and DL roots encase a single orifice, canal, and foramen (Fig. 4.5d). Similar considerations will be applied if one of the roots bifurcates in the middle or apical third, and the root canal configuration is different below and above the level of bifurcation.⁵

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FIGURE 5.5 Micro-CT 3D models of single-rooted teeth with root and root canal morphologies classified according to the new system

CHAPTER 6 - ROOT CANAL ANATOMY OF MAXILLARY TEETH

Guido Fischer demonstrated the challenging nature of the apical root anatomy for the first time in 1907 by filling approximately 700 teeth with a collodion solution. The complexity and unpre- dictability of the root canal morphology led him to coin the widely used terminology kanalsystem, which was translated to English as “root canal system.” So, the concept of a “single” root canal with a “single” apical foramen is mistaken. The root canal space is often complex, with canals that divide and rejoin, isthmuses, fins, anastomo- sis, accessory canals, and apical deltas. For this reason, it has been referred as a system, and its complexity has been demonstrated by several authors. Considering that the goal of endodontic therapy is the removal of all vital or necrotic tis- sue, microorganisms, and microbial by-products from the root canal space, a thorough under- standing of the canal morphology and its variations in all groups of teeth is a basic requirement for the success of the endodontic therapy.

The first step in understanding dental anatomy and to apply it for recording data in clinical practice is to learn some system of tooth notation. In this chapter, Universal Numbering, Palmer Notation, and International Numbering systems were used to identify each tooth group. Additionally, for a better comprehension and detailed study of root and root canal anatomy, several landmarks of importance were selected, and proper information acquired from the literature cited accordingly, including general description of the teeth , overall and root lengths , chronology of root formation , tooth axes angulation , number of roots , apical root curvature , root grooves , number and canal configuration , canal cross- sectional shape , canal taper , percentage frequency of transversal anastomosis and furcation canal , position of the apical foramen , accessory canals and apical ramifications , degree of canal curvature , and canal diameter 1 mm from the apical foramen . Occurrence of anatomical anomalies and important clinical remarks associated with the external and internal anatomy of each group tooth were also pointed out ⁵

Table 6.1 Morphological aspects of the root and root canal anatomy of maxillary central incisors

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Table 6.2 Morphological aspects of the root and root canal anatomy of maxillary lateral incisors

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Finally, information regarding the number of roots and root canals, as well as the most fre- quently observed root canal configurations, were depicted from recent epidemiological studies using CBCT technology and compiled in Tables 6.14 and 6.15. Considering that the anatomy of the maxillary and mandibular third molars varies greatly and is unpredictable, this group of teeth was not included in this chapter.

In accordance with information provided herein, a great deal of variation has been reported in the literature regarding the root and root canal morphologies of all groups of teeth, and these dissimilarities have been explained by method- ological differences, sample size, as well as eth- nicity, race, and gender of the studied population. Therefore, based on the mentioned criteria, this chapter aimed to summarize the most relevant morphological aspects of the root and root canal anatomy of all groups of teeth, depicting in tables data extracted from current and classical studies, illustrated by images acquired from non- destructive micro-CT technology.

Table 6.3 Morphological aspects of the root and root canal anatomy of maxillary canines

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Table 6.4 Morphological aspects of the root and root canal anatomy of maxillary first premolars

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Table 6.5 Morphological aspects of the root and root canal anatomy of maxillary second premolars

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Table 6.6 Morphological aspects of the root and root canal anatomy of maxillary first molars

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Table 6.7 Morphological aspects of the root and root canal anatomy of maxillary second molars

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Table 6.14 Combined data from CBCT studies on root and root canal morphology of maxillary permanent teeth

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MAXILLARY TEETH

The term maxillary refers to the upper jaw, or maxilla.

MAXILLARY CENTRAL INCISORS

The maxillary central incisors are centered in the maxilla, one on either side of the median line, with the mesial surface of each in contact with the mesial surface of the other. The pulp cavity follows the general outline of the crown and root. In this way, pulp chamber is very narrow in the incisal region and wider in the mesiodistal dimension than in the labiolingual dimension ¹⁰⁹.

Morphological aspects of the root and root canal anatomy of this tooth group are detailed in Table 6.1, while illustrate this tooth in variousaspects.

MAXILLARY LATERAL INCISOR

The maxillary lateral incisor supplements the central incisor in function, and the crowns bear a close resemblance; however, lateral incisor is smaller in all dimensions except root length. The pulp chamber is narrow in the incisal region and may become very wide at the cervical level of the tooth, while pulp horns are usually prominent ¹⁰⁹. Morphological aspects of the root and root canal anatomy of this tooth group are detailed in Table 6.2, while illustrate this tooth in various aspects.size of the pulp chamber of this tooth may also be the largest in the mouth ¹⁰⁹. Morphological aspects of the root and root canal anatomy of this tooth group are detailed in Table 6.3, while Figs. illustrate this tooth in various aspects.

MAXILLARY CANINES

Maxillary canines are the longest teeth in the mouth; the crowns are usually as long as those of the maxillary central incisors, and the single roots are longer than those of any of the other teeth. Therefore, maxillary canine has the larg- est buccolingual root dimension of any tooth in the mouth, and because the pulp cavity corre- sponds closely to the outline of the tooth, the size of the pulp chamber of this tooth may also be the largest in the mouth ¹⁰⁹. Morphological aspects of the root and root canal anatomy of this tooth group are detailed in Table 6.3, while illustrate this tooth in various aspects.

MAXILLARY FIRST PREMOLARS

The premolars are so named because they are anterior to the molars in the permanent dentition. The maxillary first premolar has two cusps, a buccal and a lingual, each being sharply defined. The buccal cusp is usually about 1 mm longer than the lingual cusp, and, because of that, the pulp horn usually extends further incisally under the buccal cusp than the lingual cusp. The maxillary first premolar may have two well- developed roots, two root projections that are not fully separated, or one broad root. The majority of maxillary first premolars have two root canals, but a small percentage of teeth may have three roots that sometimes are undetectable radio- graphically. The pulp chamber floor is below the cervical level of all the variations found in this tooth group ¹⁰⁹. Morphological aspects of the root and root canal anatomy of this tooth group are detailed in Table 6.4 and , while , and illustrate maxil- lary premolars in various aspects.

MAXILLARY SECOND PREMOLARS

The maxillary second premolar supplements the maxillary first premolar in function and closely resembles maxillary first premolar. The maxil- lary second premolar may have a crown that is noticeably smaller cervico-occlusally and also mesiodistally; however, it may also be larger in those dimensions. Usually the root of the sec- ond premolar is as long as, if not a millimeter or so longer than, that of the first premolar. Most maxillary second premolars have only one root and canal. Two roots are possible, although two canals within a single root may also be found. The pulp cavity may demonstrate well-devel- oped pulp horns; others may have blunted or nonexistent pulp horns. The pulp chamber and root canal are very broad in the buccolingual aspect of teeth with single canals ¹⁰⁹. Morphological aspects of the root and root canal anatomy of this tooth group are detailed in Table 6.5 and illustrate maxillary premolars in various aspects.

MAXILLARY FIRST MOLARS

The maxillary molars are the largest and strongest maxillary teeth, by virtue both of their bulk and of their anchorage in the jaws. The crown of this tooth is wider buccolingually than mesiodistally. The maxillary first molar is normally the largest tooth in the maxillary arch. It has four well- developed functioning cusps and one supple- mental cusp of little practical use. The maxillary first molar usually has three roots and four canals. The palatal root usually has the largest dimensions, followed by the mesiobuccal and distobuccal roots, respectively. The mesiobuccal root is often very wide buccolingually and usu- ally possesses an accessory canal commonly called MB2, which usually is the smallest of all the canals in this tooth ¹⁰⁹. Maxillary molars present the greatest clinical challenge for end- odontic treatment. This is because the complex- ity of the root canal system surpasses that of all other teeth within the human dentition. More extensive use of the clinical microscope has con- tributed to the discovery that not only a fourth canal but other additional canals also exist. Morphological aspects of the root and root canal anatomy of this tooth group are detailed in Table 6.6 .

MAXILLARY SECOND MOLARS

The maxillary second molar supplements the first molar in function. The roots of this tooth are as long as, if not somewhat longer than, those of the first molar. The tendency for root fusion is greater in the second maxillary molar than in the first maxillary molar, but the palatal root is usually separate. Most often maxillary second molars possess three roots and three canals. The mesio- buccal root of the maxillary second molar is not as complex as that formed in the maxillary first molar. The tendency for a very wide mesiobuccal canal is not present in the maxillary second molar ¹⁰⁹. Morphological aspects of the root and root canal anatomy of this tooth group are detailed in Table 6.7 . Mandibular TeethThe term mandibular refers to the lower jaw, or mandible

ROOT CANAL ANATOMY OF DECIDUOUS TEETH

The deciduous incisor teeth are functional in the mouth for approximately five years, while the deciduous molars are functional for approximately nine years. They therefore have considerable functional significance.- When second deciduous molars are lost prematurely, this can be very detrimental to the alignment of the permanent teeth.- Premature loss of deciduous teeth because of dental caries is preventable and is to be avoided The primary teeth are 20 in number -10 in each jaw- They are classified as follows: -four incisors, -two canines, and -four molars in each jaw as numbered with the universal system of notation

PRIMARY MAXILLARY CENTRAL INCISOR

Consist of 3 slight projections on incisal border i.e 3pulp horns- Chamber tapers in M- D diameter cervically, widest at cervical region Labiolingually- Pulp chamber and Canal are larger than perm’ ones,- No distinct demarcation betw canal &chamber- Pulp canal tapers evenly untill ending in apical foramen

PRIMARY MAXILLARY LATERAL INCISOR

The contour of the tooth, as does the canal- The root has similar shape, but is longer, thinner & tapering.

PRIMARY MAXILLARY CANINE

There is a little demarcation between pulp chamber and the canal.

- The canal tapers as it approaches the apex.
- Pulp chamber follows the external contour of teeth.
- Central pulpal horn is projecting incisally.

PRIMARY MAXILLARY FIRST MOLAR

Consists of a chamber & 3 pulpal canals corresponding to 3 roots

- Variations from this basic design may be present as anastomoses & branchings
- 3-4 pulp horns
- Pulp horn sizes MB>ML>DB

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MAXILLARY SECOND MOLAR

The pulp cavity consist of a pulp chamber & 3 pulp canals corresponding to three roots.

- These canals leave floor of chamber at the mesiobuccal & distobuccal corners & from lingual area.
- Pulp chamber has 4 pulpal horns, a fifth horn projecting from lingual aspect of mesiolingual horn may be present.
- The mesiobuccal pulp horn is largest, pointed & extends occlusally.⁷

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GERIATRIC ENDODONTICS AGE CHANGES IN THE TEETH

Macroscopic Changes

- Changes in form and color
- Wear and attrition of teeth.
- Causes for change in color of teeth:
– Decrease in thickness of dentin
– General loss of translucency
– Pigmentation of anatomical defects
– Corrosion products
– Inadequate oral hygiene.

AGE CHANGES IN ENAMEL

- All changes in enamel are based on ionic exchange mechanism
- Decrease in permeability of enamel
- Enamel becomes more brittle with age
- Enamel exhibits attrition, abrasion and erosion (Fig. 35.3).

AGE CHANGES IN CEMENTUM

- Cementum increases gradually in thickness with age
- Cementum becomes more susceptible to resorption
- There is increased fluoride and magnesium content of cementum with age.

AGE CHANGES IN DENTIN

- Physiologic secondary dentin formation
- Gradual obliteration of dentinal tubules
- Dentin sclerosis
- Size of the pulp chamber reduces with age
- Occlusion of dentinal tubules by a gradual deposition of the peritubular dentin.

CLINICAL IMPLICATIONS OF AGE CHANGES IN DENTIN

- Obliteration of the tubules leads to reduction in sensitivity of the tissue
- Reduction in dentin permeability prevents the ingress of toxic agents
- Addition of more bulk to the dentin reduces pulpal reactions and chances of pulp exposures.

AGE CHANGES IN PULP (Fig. 35.4)

- The difference between dental pulp of old individuals and young teeth is due to more fibers and less cells
- Blood supply to the tooth decreases with age
- The prevalence of pulp stones increases with age.

AGE CHANGES IN ORAL MUCOSA

The oral cavity is lined by stratified squamous epithelium which forms a barrier between internal and external environment thus providing protection against the entry of noxious substances and organisms, mechanical damage, and fluid exchange.⁸

CLINICAL CHANGES IN EPITHELIUM WITH AGE,

Oral mucosa has been reported to become increasingly thin, smooth, and dry to have a stain like, edematous appearance with loss of elasticity and stippling and thus becomes more susceptible to injury.

Tongue exhibits loss of filliform papillae, and deteriorating taste sensation with occasional burning sensation.

Histological Changes in Oral Mucosa

- Epithelial changes
- Connective tissue changes.

Epithelial Changes These are:

- Decreased thickness of epithelial cell layer
- Reduced keratinization
- Alteration in the morphology of epithelial-connective tissue interface
- Decrease in the length of retepegs of oral epithelium have been reported with age
- Rate of cell renewal in human oral epithelia decreases with aging. ⁹

Connective Tissue Change

- There is increase in number and density of elastin fibers.

Cellular changes are also reported, which include:

– Cells becoming shrunken
– Cells becoming inactive
– Reduction in number of cells.

Age Changes in Periodontal Connective Tissue Structural Changes

- Gingival connective tissue becomes denser and coarsely textured upon aging
- Decrease in the number of fibroblasts
- Decrease in the fiber content
- Increase in the size of interstitial compartments containing blood vessels
- Evidence of calcification on and between the collagen fibers.

Age Changes in Salivary Glands

A common generalized association with aging oral cavity is the diminished function of salivary glands which further results in reduced salivation or xerostomia. The main consequences of xerostomia include dry mouth, generalized mouth soreness, burning or painful tongue, taste changes, chewing difficulty, problems with swallowing, talking, and reduced denture retention.

Age Changes in Bone Tissue

- Cortical thinning: The cortex thins and porosity increases from about an age of 40 to 80 - Loss of trabeculae
- Cellular atrophy
- Sclerosis of bone.⁹¹

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Fig. 35.1 Physiological wear of teeth

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Fig. 35.2 Attrition of teeth resulting in multiple pulp exposure

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Fig. 35.4 Age changes in enamel, pulp, dentin and cementum

ENDODONTICS IN GERIATRIC PATIENTS

The primary function of teeth is mastication; thus, the loss of teeth leads to detrimental food changes and reduction in health. The needs, expectations, desire, demands of older patients thus exceeds for those of any age group (Fig. 35.5). The quality of life for older patients can be improved by preventing the loss of teeth through endodontic treatment and can add a large and impressive value to their overall dental, physical and mental health. The desire for root canal treatment is increasing considerably amongst aging patients. Root canal treatment can be offered as a favorable alternative to the terms of extraction and cost of replacement. Medical History Dentists should recognize that the biologic or functional age of an individual is far more important than chronological age. As most of the old aged people suffer from one or the other medical problems, a medical history should be taken prior to starting any treatment for geriatric patients. A standardized form should be used to identify any disease or therapy that would alter treatment plan or its outcome. Aging usually causes changes in cardiovascular, respiratory, central nervous system that result in most drug therapy needs. The renal and liver function of the patients should be considered while prescribing drugs as they have some action on these organs. Chief Complaint of Geriatric Patients Most common reason for pain in old age patients is pulpal or periapical problem that requires either root canal treatment or extraction. Older patients are more likely to have already had root canal treatment and have a more realistic perception about treatment comfort. Usually the pain associated with vital pulps seems to be reduced with aging, and severity seems to diminish overtime suggesting a reduced pulp volume.

Past Dental History The dentist should ask the patients past dental history so as to access the patient’s dental status and plan future treatment accordingly. Patient can give history as recent pulp exposure and restoration, or it may be as subtle as a routine crown preparation 15 to 20 years ago. From dental history, the clinician can assess the patient’s knowledge about dental treatment and his psychological attitude, expectations from dental treatment. Subjective Symptoms Subjective symptoms are described by patient. Patient explains regarding their complaint, stimulus or irritant that causes pain, nature of pain, its relationship to the stimulus or irritant. This information is useful in determining whether the source is pulpal or periapical and if these problems are reversible or not. Objective Symptoms Objective symptoms are the one diagnosed by the dentist by clinical examination. Extraoral and intraoral clinical examination provides dentist useful information regarding the disease and previous treatment done. Common Observations in Geriatric Patients - Missing teeth: In older patients, usually some of teeth get extracted.Missing teeth indicate the decrease in functional ability, resulting in loss of chewing ability. This reduced chewing ability leads to a higher intake of more refined soft carbohydrate diet and sugar intake to compensate for loss of taste and xerostomia. All these lead to increased susceptibility to dental decay. - Gingival recession: It results in exposure of cementum and dentin and thus making them more prone to decay and sensitivity (Figs 35.6A to C).

- Root caries (Figs 35.7A and B): It is very common in older patients and is difficult to treat; the caries excavation is irritating to the pulp and often results in pulp exposures or reparative dentin formation that might affect the negotiation of canal, if root canal treatment is needed.
- Attrition, abrasion, and erosion expose the dentin and allows the pulp to respond with dentinal sclerosis and reparative dentin which may completely obliterate the pulp (Figs 35.8A and B).
- With the increasing age, the pulp cavity size decreases. This decrease in volume can be due to formation of reparative dentin resulting from recurrent caries, restorative procedures, and trauma.
- Continued cementum deposition is seen with increasing age thus moving cementodentinal junction (CDJ) farther from the radiographic apex (Figs 35.9A to C).
- Calcifications are observed in the pulp cavity which can be due to caries, pulpotomy or trauma and is more of linear type. The lateral and accessory canals can be calcified, thus decreasing their clinical significance.
- Reduced tubular permeability is seen as the dentinal tubules become occluded with advancing age.
- The missing and titled teeth in older patients result in change in the molar relationship, biting pattern in older patients which can cause TMJ disorders.
- Reduced mouth opening in older patients increases working time and decreases the space needed for instrumentation.

CHAPTER 7 – ROOT CANAL ANATOMY OF MANDIBULAR TEETH

Table 7.1 Morphological aspects of the root and root canal anatomy of mandibular incisors

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Table 7.2 Morphological aspects of the root and root canal anatomy of mandibular canines

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Table7.3. Morphological aspects of the root and root canal anatomy of mandibular first premolars

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Table 7.4 Morphological aspects of the root and root canal anatomy of mandibular second premolars

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Table 7.5 Morphological aspects of the root and root canal anatomy of mandibular second molars

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Table 7.6 Combined data from CBCT studies on root and root canal morphology of mandibular permanent teeth

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MANDIBULAR INCISORS

The mandibular central incisors are centered in the mandible, one on either side of the median line, with the mesial surface of each one in con- tact with the mesial surface of the other. The right and left mandibular lateral incisors are dis-tal to the central incisors. The mandibular inci- sors have smaller mesiodistal dimensions than any of the other teeth. The central incisor is somewhat smaller than the lateral incisor, which is the reverse of the situation in the maxilla. These teeth are similar in form and have smooth crown surfaces that show few traces of develop- mental lines. The mandibular central incisor is the smallest tooth in the mouth, but the bucco- lingual dimension of its root is very large. This tooth usually has one canal; two canals may be found, but not very frequently. The pulp horn is well developed in this tooth. The mandibular lateral incisor tends to be a little larger than the mandibular central incisor in all dimensions, and the pulp chamber is also larger. The pulp canal may taper gently from the apex or narrow abruptly in the last 3–4 mm of the canal ¹⁰⁹. Morphological aspects of the root and root canal anatomy of this tooth group are detailed in Table 6.8.

MANDIBULAR CANINES

The mandibular canine crown is narrower mesio- distally than that of the maxillary canine, although it is just as long in most instances and, in many instances, is longer by 0.5–1 mm. The root may be as long as that of the maxillary canine, but usually it is somewhat shorter. The pulp cavity of the mandibular canine tends to be a little shorter to that of the maxillary canine. A not rare varia- tion in the form of the mandibular canine is bifur- cated roots, and it is also not uncommon to find two roots or at least two canals. Because the pres- ence of two canals cannot be easily detected radiographically, their presence must be ruled out clinically as well. Some mandibular canines demonstrate an abrupt narrowing of the pulp cav- ity when passing from the region of the pulp chamber to the region of the pulp canal. Other mandibular canines demonstrate an abrupt nar- rowing of the pulp canal in the apical region ¹⁰⁹. Morphological aspects of the root and root canal anatomy of this tooth group are detailed in Table 6.9.

MANDIBULAR FIRST PREMOLARS

The first premolar is always the smaller of the two mandibular premolars, whereas the opposite is true, in many cases, of the maxillary premo- lars. Most of these teeth have one canal, but two or three canals are possible. The pulp chamber is usually very large, and the pulp cavity may taper gently toward the apex or abruptly as the root canal starts. The root of the first premolar usually shows a deep developmental groove which has been associated with complex anatomical fea- tures including C-shaped and extra root canals ¹⁰⁹. Morphological aspects of the root and root canal anatomy of this tooth group are detailed in Table 6.10 .

MANDIBULAR SECOND PREMOLARS

The second premolar has three well-formed cusps in most cases, one large buccal cusp and two smaller lingual cusps. It usually has one root and canal that may be curved, but usually in the distal direction. The pulp horns are prominent, and the pulp chamber and root canal gently taper toward the apex. The single root of the second premolar is larger and longer than that of the first premolar. The root is seldom, if ever, bifurcated, although some specimens show a deep developmental groove buccally ¹⁰⁹. Morphological aspects of the root and root canal anatomy of this tooth group are detailed in Table 6.11.

Mandibular First Molars

The mandibular first molar is usually the largest tooth in the mandibular arch. It has five well- developed cusps and two well-developed roots, one mesial and one distal, which are very broad buccolingually. These roots are widely separated at the apices. The buccolingual cross section of the mandibular first molar demonstrates a large pulp chamber that may extend well down into the root formation. The mesial root usually has a more complicated root canal system because of the presence of two canals. The distal root usu- ally has one large canal, but two canals are often present. Occasionally, a fourth canal is present that has its own separate root ¹⁰⁹. Morphological aspects of the root and root canal anatomy of this tooth group are detailed in Table 6.12 .

MANDIBULAR SECOND MOLARS

Normally, the second molar has four well- developed cusps, two buccal and two lingual, of nearly equal development. The tooth has two well- developed roots, one mesial and one distal. These roots are broad buccolingually, but they are not as broad as those of the first molar, nor are they as widely separated. The buccolingual section of the mandibular second molar demonstrates a pulp chamber and pulp canals that tend to be more vari- able and complex than those found in the mandib- ular first molar ¹⁰⁹. Morphological aspects of the root and root canal anatomy of this tooth group are detailed in Table 6.13 .

ROOT CANAL SYSTEM IN MANDIBULAR DECIDIOUS TEETH PRIMARY MANDIBULAR CENTRAL AND LATERAL INCISOR

Oval in appearance, tapers as it reaches apex- No demarcation betw’n chamber and canal

MANDIBULAR CANINE

Wide mesiodistally as labiolingually

- No diff’ between canal &chamber
- Ends in marked constriction at the apex

PRIMARY MANDIBULAR FIRST MOLAR

The pulp cavity contains a chamber & 3 canals

- Mesiobuccal & mesiolingual canals are confluent & leave the chamber in the form of a ribbon.- The distal pulp canal projects in ribbon fashion from floor of chamber in distal aspect.

MANDIBULAR SECOND MOLAR

Pulp cavity is made up of a chamber & usually 3 pulp canals

- The two mesial pulp canals are confluent as they leave floor of pulp chamber through a common orifice.
- Distal canal is constricted in the center.

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CHAPTER – 8 THE COMPLEXITY OF THE APICAL ANATOMY

There is general agreement that the root canal sys- tem anatomy in the apical region, with its physio- logical and pathological variations, can rarely be fully anticipated on the basis of conventional peri- apical radiographs or cone beam computed tomog- raphy (CBCT). This includes ramifications and lateral canals, frequently present in the apical third, the fine variations in the topography of their foram- ina, and also the sequelae of infection/inflamma- tion, such as resorption and calcification. The complexity of the root canal anatomy in the apical third and the preoperative histologic and microbiologic conditions of the pulp tissue can be regarded as the two major factors affecting resorption of the apical root structure and canal calcification, may make it difficult to establish an adequate working length for end- odontic procedures.

In the light of the histo- logical and microbiological conditions of the apical pulp tissue, the apical patency concept seems justified in cases with pulp necrosis/ infection. the success rate of the endodontic treatment ¹¹⁰. Inflammation—up to necrosis—of the pulp tissue consequent to caries, trauma, or periodon- tal disease may considerably alter the apical den- tin and cementum, resulting in morphological changes that may have an impact on root canal instrumentation and obturation procedures.

The root canal usually narrows toward the apex and then expands to form the apical foramen. The narrowest part of the canal forms the apical constriction, which is located just short of the apical foramen. Its distance to the apical fora-men varies from 0.5 to 1 mm in teeth from indi- viduals with different ages ¹¹¹. The configuration of exclusively a single canal, with no ramifications, terminating at the geometrical top of the root (Fig. 7.1) is relatively uncommon. In more than 60% of the teeth, the apical fora- men is not located at the root apex, and the dis- tance between the apical foramen and the radiographic apex ranges from 0 to 3 mm ¹¹¹. Kuttler observed that the mean apex-to-fora- men distance was 0.48 mm for young individu- als and 0.6 mm for older ones, while Dummer et al. ¹¹² reported a mean apex-to-foramen dis- tance in anterior teeth of 0.36 mm. The fact that the main foramen frequently ends at a location short of the root apex (Fig. 7.2) represents a problem for the endodontist, because this condi- tion can only be recognized in the radiographs when the foramen exits on the mesial or distal aspect of the root ¹¹³. D. Ricucci et al. The analysis of the mineralized tissue topog- raphy (dentin and cementum) forming the apical structure and their interrelationship deserves par- ticular attention. The cementum layering the external apical surface folds into the foraminal opening extending to varying distances in coro- nal direction. The area where the cementum ends in the apical canal is called cementum-dentin junction (CDJ). In the past, it was believed that the CDJ coincided with the smaller diameter or “apical constriction” . Thus, it was recom- mended that this point be the apical limit of root canal instrumentation and obturation procedures . However, histologic observations show that the CDJ rarely coincides with the apical constric- tion. In longitudinal sections cut through the api- cal canal, the CDJ is frequently observed to be several millimeters higher on one wall than on the opposite wall¹¹⁰. It is also salient to address the characteristics of the soft tissue present in the apical canal. Odontoblasts are absent in the funnel-shaped foraminal area. Therefore, in the very end of the

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Fig. 8.1 Examples of single root canals ending approximately at the geometrical top of the root. (a) Single-rooted maxillary third molar. (b) Distal root of a mandibular first molar (hematoxylin-eosin, original magnification ×16) 8 The Complexity of the Apical Anatomy

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Fig. 8.2 (a, b) Mesial roots of mandibular first molars. Sections show foramens ending at a location short of the radio- graphic apices (hematoxylin-eosin, original magnification ×16)

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Fig. 8.3 Maxillary premolar with apical periodontitis. The CDJ is located at different levels on opposite walls, and it does not coincide with the apical constriction (hematoxylin-eosin, original magnification ×16) canal, the tissue should not be called pulp tissue, as it is indistinguishable from the adjacent peri- odontal ligament. In fact, it is constituted mainly by fibroblasts and collagen bundles, and it is crossed by numerous vessels and nerves entering the pulp space. It has to be kept in mind, however, that the discussion on the combination of tissues present in the apical end of the canal may be purely aca- demic, with little or no practical impact on the clinic. In fact, it is a common occurrence that the main canal in the apical third divides into two or more branches, each ending on the external root surface with a distinct foramen. The anatomical complexity of the root canal system, and particularly of the apical third, has been discussed in the dental literature since the beginning of the last century. Several studies have been published describing the varying anas- tomosing canal system [¹¹⁵,¹¹⁴ ]. Kuttler ¹¹¹ provided a deep morphological analysis of the apical root region. In the past, the most commonly used methods for studying the root canal anatomy and to ascer- tain the presence of ramifications of the main canal, as well as localization and number of foramina, were based on tooth clearing [¹¹⁶,¹¹⁷ ]. Images were obtained showing that in some instances the apical anatomy of all teeth were 244 D. Ricucci et al. Fig. 7.4 Cleared roots of teeth whose canals were injected with a dye. (a) Maxillary canine. An apical delta with several branches is present in the apical root end. (b) Mesial root of a mandibular first molar showing a very complex apical anatomy (Courtesy of Dr. G. Riitano. From collection of Dr. F. Riitano) very complex, with the main canal dividing into two or more branches that give rise to an intricate system (Fig. 7.4).

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These observations raised the concern that, from a clinical point of view, there could not be correspondence between the shape of endodontic files and the apical canal morphol- ogy (Fig. 7.4). Scanning electron microscopy (SEM) has also been widely used in the study of morphology, location, and number of foraminal openings ¹¹⁷.

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The limitation of this methodology is that it allows exclusively for the observation of the external surface of the structure under investi- gation. Therefore, only the external apical sur- face can be analyzed, together with the outer morphology of foramina. The advent of three- dimensional (3D) imag- ing, specifically the micro-computed tomography (micro-CT), has overcome most limitations of previous investigation techniques. This technology is nondestructive and has the great advantage that the internal anatomy of teeth can be recon- structed and observed from various angles [18–20]. The frequency of ramifications deserves par- ticular attention. Ricucci and Siqueira in a sample of 493 human teeth investigated with light microscopy found that the overall prevalence Fig. 8.5 Apex of the distal root of a mandibular first molar examined with SEM. Four foraminal openings are present (Courtesy of Dr. Pablo Ensinas) of lateral canals and/or apical ramifications was approximately 75%. Ramifications were reported to occur more commonly in the apical portion and in posterior teeth ¹¹⁶. Vertucci reported that ramifications are found in the apical third of the root in 73.5% of the cases, while in the mid- dle third and in the coronal third, they are observed in 11% and in 15%, respectively. Using a micro-CT approach that involved centerline-fitting algorithm, Xu et al. assessed the morphologic features of lateral canals in the apical 3 mm of 204 permanent 8 The Complexity of the Apical Anatomy 245 teeth. They found lateral canals (total number 178) in 93 apical root segments. The number of lateral canals varied from 1 to 7 per root. Interestingly the median diameter of the ramifi- cations was 67.0 μm (data ranging from 16.7 to 238.4 μm). A distinction is made between lateral canals and apical deltas. Lateral canals are those branching from the main canal, which is still dis- tinguishable up to its exit. On the other hand, the morphological pattern observed when a root canal divides into three or more ramifications near the root apex, with the main canal becoming indistinguishable, is referred to as “apical delta” ¹¹⁹. The apical delta can be defined as an intri- cate system of spaces within the root canal that allows free passage of blood vessels and nerves from the periapical compartment to the pulp tis- sue ¹¹⁹. Using a large sample from a native Chinese population (1400 permanent teeth; 100 teeth for each tooth type except for the third molar), Gao et al. ¹¹⁹ investigated the frequency and the mor- phologic features of apical deltas in human teeth with micro-CT and a centerline-fitting algorithm. A total of 136 apical deltas were detected, and the prevalence of the apical delta was 9.7% (6.3%, 8.8%, and 15.8% in anterior, premolars, and molars, respectively). Of the 136 apical deltas, 634 apical delta branches, ranging from 3 to 18, were detected. Data concerning vertical exten- sion of the apical deltas is especially relevant from a clinical perspective. The median vertical distance from the beginning of the first apical delta branch to the apex was 1.87 mm (ranging from 0.62 to 5.08 mm), and 13% (18/136) were more than 3 mm long. According to this numbers, if 3 mm of the apical structure are resected during surgical procedures, in 87% of the cases, the api- cal deltas with infecting bacterial biofilms will be fully removed. However, the other 13% of the apical deltas with longer vertical extensions would harbor exposed biofilm-infected ramifica- tions. Therefore, a valid practical recommenda- tion is to meticulously observe the resected surface under surgical microscope with dyes for remaining ramifications and eventually extend the resection length accordingly ¹¹⁹. The reported prevalence of apical deltas in human permanent teeth may vary considerably and is likely dependent on the geographical areas where the studies were conducted, the tooth type, and the analytical methods. In a Turkish popula- tion, the prevalence of apical deltas was found to be as high as 23.5% in mandibular lateral inci- sors, while it was 9.8% in mandibular central incisors and 7.8% in mandibular canines ¹²⁰. Histopathologic Facts Affecting the Apical Dentin- Pulp Complex Establishment of pulp necrosis and bacterial col- onization in the root canal has a profound impact on the condition of the apical canal system, which may adversely affect the outcome of endodontic treatment procedures. The successive events tak- ing place in the progress of pulp degeneration are discussed next. When the pulp is exposed by caries, acute inflammation usually takes place and conse- quently leads to the establishment of necrotic areas in the coronal pulp. Bacteria from the caries biofilm usually invade and colonize the necrotic compartments of tissue. The advance of inflam- mation, necrosis, and infection through the pulp tissue in an apical direction is usually a slow pro- cess. In early stages, tissue areas involved by necrosis are minimal. Bacteria are observed in the necrotic tissue, surrounded by a concentration of polymorphonuclear leukocytes (PMNs). An accumulation of chronic inflammatory cells sur- rounds the area with acute inflammation, while the rest of the pulp can be vital and free from sig- nificant pathological changes. With passage of time, successively larger areas of the coronal pulp become involved by necrosis and infection, and the process trespasses the root canal orifices to reach the radicular pulp tissue, gradually advancing toward the apical part of the root canal. Contrary to a widely held opinion, it is not necessary that the entire pulp becomes necrotic and the frontline of infection reaches the apical foramen for apical periodontitis to develop. Early inflammatory changes can be observed in the 246 apical periodontal tissues even when necrosis is still confined to the pulp chamber. In many teeth, widening of the periodontal ligament space can be radiographically discernible at this stage. From a clinical perspective, it is important to point out that most of the tissue present in lat- eral canals and apical ramifications is vital and free from bacterial colonization (Figs. 7.6 and 7.7). These ramifications are unlikely to be debrided with contemporary instrumentation devices and protocols. On the contrary, maintaining the vitality of the tissue in these spaces is advantageous (Fig. 7.8). Thus, in all cases where vital tissue is observed in the root canals, after working length is established at or near the apical constriction with an elec- tronic apex locator and confirmed with radio- graphs, it is advised that instrumentation be performed without the use of high concentra- tions of sodium hypochlorite, and no attempts should be taken to force obturation materials D. Ricucci et al. into ramifications with the intention “of filling them.” In fact, this might create an unnecessary larger wound. In later stages, as necrosis and bacterial infection are progressing in an apical direction, a distinct area of transition between necrotic and viable pulp tissue is often observed. This is characterized by the following gradient of tis- sue reactions: necrosis/infection–acute inflam- mation–chronic inflammation–uninflamed tissue. Vital, although inflamed, tissue can be observed in the apical canal also in a certain number of cases where a frank periapical radio- lucency is observed (Fig. 7.9). In a histological study based on serial sections of 50 apices with apical periodontitis lesions, Ricucci et al. ¹²¹ observed the presence of vital tissue with vary- ing degrees of inflammation in the apical por- tion of the canal in 18 cases, which is in about one-third of the specimens. Explanation for this

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Fig. 8.6 (a, b) Apex of the mesial root of a mandibular first molar with the clinical diagnosis of irreversible pulpi- tis.

Vital tissue is present in the main canal and in the apical ramification (hematoxylin-eosin, original magnifi- cation ×25 and ×50) 8 The Complexity of the Apical Anatomy Fig. 7.7 (a) Maxillary second premolar with caries pen- etrating the pulp chamber and the clinical diagnosis of irreversible pulpitis. The radiograph shows widening of the PDL space around the apex. (b) Section cut at the center of the main canal, displaying a large apical ramifica- tion. Vital pulp tissue can be observed. Note the thickened periodontal tissue remaining attached to the root at extrac- tion (hematoxylin-eosin, original magnification ×16) is simple in terms of inflammation and immu- nology. As the frontline of infection advances in an apical direction, the inflamed tissue also retreats. The extent of the inflamed tissue will vary from case to case, but it is not restricted to a small area adjacent to the frontline of infec- tion. Bacterial virulence factors may diffuse through the tissues and cause inflammation in a large area, not only restricted to the narrow area immediately in contact with the most advanced bacteria. From a clinical viewpoint, the important fact is that the most advanced front of bacterial infection is in many cases confined to a more coronal position in the main canal lumen (Fig. 7.9b). Therefore, the inflamed connective tissue remaining in the most apical portion may not be colonized by bacteria, which is similar to the periradicular inflammatory tissue. This con- dition is referred to as “partial necrosis” and helps explain the high rate of success in treat- ment of teeth with apical periodontitis with instrumentation limited to 1 mm short of the apex ¹²². The explanation for the resistance of this apical pulp tissue to necrosis likely resides in the circulatory system present in the apical region of the root canal system. The apical third is the area where ramifications of the main canal are abundant, and neurovascular bundles enter from the rich circulatory network of the periodontal ligament. This allows for the con- tinuous arrival of nutrients and oxygen, as well as defense cells and molecules in that most api- cal area that guarantee survival and oppose bac- terial advance. However, if no treatment is provided, it is highly likely that, with passage of time, the last portion of apical tissue, including the tissue in ramifications, will be inevitably affected by 248 D. Ricucci et al. Fig. 7.8 Buccal root of a maxillary first premolar that was extracted because the tooth was non-restorable. The pulp was vital and the canals were instrumented with NiTi files before extraction. Working length was established 1.5 mm short of the radiographic apex. The section shows that short instrumen- tation respected the tissue present in the apical delta, which appears vital and continuous with a widened periodontal liga- ment (hematoxylin-eosin, original magnification ×25) necrosis and infection (Fig. 7.10). When infec- tion reaches the entire extent of the root canal system up to the apical foramen (and some- times slightly beyond), possibly affecting api- cal ramifications, complete disinfection becomes a significant challenge for clinicians. This is confirmed by histopathologic and histo- bacteriologic analyses of tissue biopsies con- sisting of apex and periapical pathologic tissues, which were obtained by surgical proce- dures. They displayed that biofilms residing in apical intricacies of the canal system were not affected by chemomechanical preparation fol- lowed by long-term calcium hydroxide medica- tion ¹²³. Persistent infection was also observed even when different irrigants were used in the same canals and each of them activated by ultrasonics . Histologic research also did not lend credit to the common belief that “fill- ing” the ramifications with obturation materials would kill bacteria . An in vivo study con- ducted in human teeth demonstrated that obtu- ration materials squeezed into lateral canals and ramifications do not exert significant anti- bacterial effects, and bacterial biofilms were observed to remain undisturbed into those spaces .

Fig. 8.9 Mandibular premolar with the diagnosis of necrotic pulp, extracted with an apical periodontitis lesion attached.

Abbildung in dieser Leseprobe nicht enthalten

(a) Section showing that the canal ends on the left side and a ramification is present on the opposite site. Vital tissue is present in the apical canal (hematoxylin-eosin, origi- nal magnification ×25). (b) Section proximal to that in (a). The vital tissue in the apical canal is free from bacteria. Bacterial biofilms can be observed in the necrotic portion of the canal, located more coronally (arrow) (Taylor’s modified Brown & Brenn, original magnification ×16). (c) Section taken approximately 50 sections away from those in (a, b), displaying a third foramen (original magnification ×16) 8 The Complexity of the Apical Anatomy Fig. 7.10 Mandibular premolar with necrotic pulp. (a) Section cut at the center of the canal showing a delta. Necrotic tissue and bacterial aggregation can be observed in ramifications (Taylor’s modified Brown & Brenn, origi- nal magnification ×16). (b) Magnification of the area of ramification indicated by the lower arrow in (a). Biofilms are present in the irregularities of the canal walls. Concentrations of PMNs in the lumen, intermixed with scattered bacterial cells (original magnification ×400). (c) Magnification of the area indicated by the upper arrow in (a). Large biofilm surrounded by PMNs (original magnifi- cation ×400) Changes in the Apical Structure as a Result of Pathologic Conditions Two opposite phenomena may take place conse- quent to inflammation/infection of the pulp tis- sue, namely, resorption and apposition of mineralized tissue, i.e., calcification. Odontoclasts are the cells responsible for tooth resorption. They are motile, multinucleated giant cells and are formed by the fusion of mono- nuclear precursor cells of the monocyte- macrophage lineage. Their morphology is similar to that of osteoclasts. These cells are attracted to the site of injury by bacterial products or by the release of pro-inflammatory cytokines produced by host cells. Odontoclasts adhere to the root sur- face, dissolve the mineralized tissue, degrade the organic matrix, and create resorption depressions underneath them on the tooth surface, called Howship’s lacunae. Histologically, resorption lacunae may be observed on the apical root canal walls of teeth with partial pulp necrosis, when the apical tissue is still vital. When necrosis reaches the most apical canal, areas of previous resorp- tion can be seen as irregularities of the walls, often colonized by bacterial biofilms ¹¹⁰. In teeth with apical periodontitis, both cemen- tum and dentin may be resorbed to varying extents, up to the point that resorption can be appreciated on the radiograph. Histologic sec- tions show loss of hard tissue, enlargement of the foraminal region (Fig. 7.11a), and shortening of the apical structure with loss of the apical con- striction (Fig. 7.11b). Dystrophic calcifications can also be observed in the apical canal third as pulp stones embedded in the apical canal walls or free in the canal lumen. In addi- tion, cementum may sometimes show considerable thickness, in a condition known as hypercementosis. Both resorption and calcifications may interfere with proper apical instrumentation, including difficulties to establish an adequate working length and to debride/disinfect the apical canal segment. Apical Limit of Root Canal Instrumentation and Obturation: Still a Controversial Issue Precise working length determination is an essen- tial step in root canal treatment. The length of canal preparation and obturation is a significant D. Ricucci et al. Fig. 7.11 (a) Maxillary second premolar with necrotic pulp and a large apical periodontitis lesion. Section cut through the canal shows resorption of the foraminal walls. Note the biofilms in the canal lumen (Taylor’s modified Brown & Brenn, original magnification ×16). (b) Mandibular second premolar with necrotic pulp and a large apical periodontitis lesion. Section cut through the foramen. Resorption has removed mineralized tissue, to the point that the root end appears blunt (hematoxylin- eosin, original magnification ×25) predictor of successful outcome in endodontics ¹²². However, in the light of the dis- cussed variations in the normal anatomy in “healthy” teeth and the morphological changes occurring as a consequence of pulp inflamma- tion/necrosis, the problem of the apical limit of endodontic procedures is far from reaching con- sensus. Gluskin stated that the only thing we can say “…is that the anatomy is unpredictable… and the positions we choose to fill out root canals are inconsistent.” There seems to be general agreement that the original Schilder’s recommendation of using the radiographic apex as the practical apical limit of endodontic instrumentation and obturation] is in contrast to any biological concepts and evidence. In fact, Schilder’s recommendation invariably results in instrumentation beyond the root canal limit, inside the adjacent periodontal ligament ¹¹⁴. The vast majority of endodon- tic schools teach to restrict the operative proce- dures within the root canal limits, which is short of the radiographic apex . Although inconsistent (Fig. 7.3), the CDJ is still indicated by many as the ideal point for termination of the endodontic procedures . Although it is admitted that the position and anatomy of the CDJ may vary considerably from tooth to tooth, from root to root, and from wall to wall in each canal, it continues to be erroneously believed that this point coincides with the apical constriction . The apical constriction is the narrowest part of the root canal with the smallest diameter of blood supply, and preparation to this point results in a small wound site and optimal healing conditions . The apical constriction is advocated by many authors as the ideal and practical point where the endodontic procedures should end ¹²⁴ regardless of the type of tissue present on opposite walls (Fig. 7.3). However, it has to be taken into consideration that the apical constric- tion may be absent in cases with pulp necrosis and apical periodontitis lesions, because root apical resorption of varying severity may have taken place (Fig. 7.11). Still, in such circum- stances an effort must be made to confine end- odontic procedures within the root canal limits. Locating the apical constriction or, in its absence, the endpoint of the root canal space is not always an easy task using common clinical means. To determine the length of each root canal, a careful study of properly exposed radio- graphs, tactile sensation, and knowledge of api- cal anatomy, supplemented with the use of an electronic apex locator, will assist the clinician in establishing the correct working length. After the first electronic apex locator (EAL) was intro- duced in 1962 ¹²⁵, the first two generations of EALs were found to be unreliable when com- pared with radiographs, with many of the read- ings being significantly longer or shorter than the accepted working length , and this was par- ticularly frequent in the presence of conductive 8 The Complexity of the Apical Anatomy 251 fluids in the canal. The main shortcoming of early apex locators was overcome by the adoption of multiple frequencies to determine the distance from the end of the canal and with the introduc- tion of the “ratio method” . Most modern EALs are capable of recording the point where the tissues of the periodontal ligament begin outside the root canal . However, it must be kept in mind that, although modern EALs are reported to have more than 90% accuracy, they still have some limitations. On the other hand, no individual technique is truly satisfactory in determining endodontic working length . From a wound-healing perspective, very good results are observed when root canal treat- ment procedures are restricted to the confines of the root canal system, i.e., at or near the apical constriction (Fig. 8.12a, b), and infection is effectively controlled. In most cases, the tissue in the very apical segment of the canal and in contact with the filling material can remain vital

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Fig. 8.12 Mandibular second premolar with vital pulp at the moment it was endodontically treated, 13 years earlier.

(a) The radiograph shows caries destruction of the crown and the coronal portion of the root. Periapical conditions are normal. The tooth was extracted and pro- cessed for histologic evaluation. (b) Photograph of the apical third at the end of the demineralization process, while the specimen is immersed in the clearing agent. The obturated apical canal can be seen, but apical rami- fications, apparently not injected with obturation materi- als, can also be distinguished. (c) Section cut approximately at the center of the canal, encompassing the apical end of the filling (almost entirely removed by histological processing). Soft tissue is present apically. The foramen appears completely closed by mineralized tissue in this section, but the presence of vital tissue in the foramen indicates that there must be an opening for vessels in the neighboring section (hematoxylin- eosin, original magnification ×100). (d) Magnification of the area indicated by the arrow in (c). Uninflamed connec- tive tissue in contact with the obturation material (origi- nal magnification ×400). (e) Section cut through the exit of the ramification running horizontally in (b) (original magnification ×100). (f) High power view of the area indicated by the arrow in (e). Uninflamed connective tis- sue with fibroblasts and collagen fibers, adjacent to small masses of obturation materials (original magnifi- cation ×400) 252 and uninflamed (Fig. 7.12c, d). This tissue strand is continuous with the periodontal tissue, and its origin can be either a tissue remaining in the apical end after instrumentation or a peri- odontal tissue ingrowing into the apical canal. The apical foramen may be narrowed by the deposition of concentric layers of cementum, but total closure is seldom if ever observed ¹²⁶. The fate of the tissue present in apical ramifi- cations or deltas is relevant to the clinical out- come. In cases with vital noninfected tissue in ramifications at the time of treatment, if the pulp tissue is severed to a level that mechanical instrumentation does not interfere with the tissue present in ramifications (Fig. 7.8), and no filling materials are pushed into these spaces, the vitality of the tissue will be maintained by the vessels entering from the rich circulatory network present in the peri- odontal ligament, the result being a healthy con- nective tissue with fibroblasts and collagen bundles . This picture is totally different from cases with long-standing pulp necrosis, in which necrosis and bacterial colonization are established in the apical ramifi- cations . Instruments and irrigants cannot effectively reach and disinfect these areas. Intracanal medication can sometimes fail to significantly improve disinfection in these regions. Therefore, infection spread to lateral or apical ramifications can result in apical peri- odontitis lesions that are recalcitrant to treat- ment in the short term, with occurrence of persistent symptoms ¹²³,or in the long term, with lesions that become larger at follow-ups . In such cases, histobacteriologic analysis of biopsies consisting of the apex with sur- rounding pathologic tissue obtained during sur- gical endodontic procedures demonstrated the presence of bacteria/bacterial biofilms, which were not affected by the root canal treatment procedures ¹²³. On the other hand, the long heralded idea that filling lateral canals and api- cal ramifications with thermally softened gutta- percha and sealer would kill infecting bacteria has been proven untrue . D. Ricucci et al. The Complexity of the Apical Anatomy and the Concept of Apical Patency The apical patency concept is another reason of controversy in endodontics. In its original defini- tion, “patency” means the use of “a small flexible K-file, which will passively move through the apical constricture without widening it” . The intention is to keep the very apical portion of the canal free from debris accumulation and to allow antibacterial irrigants to penetrate the full length of the canal. The concept gained popularity among clinicians and dental schools , to the point that it was included in the Glossary of Endodontic Terms by the American Association of Endodontists . In general, the discussion on advantages and disadvantages of “apical patency” does not seem to consider the different histological and micro- biological conditions of the apical pulp tissue. In fact, in teeth with pulp necrosis, where the possi- bility that the frontline of infection has reached the apical foraminal area, the use of a patency file may theoretically favor mechanical disruption of the biofilms and help diffusion of irrigants in the most apical canal . However, histobacterio- logic analysis of failed cases showed that, despite the use of a patency file, all apical ramifications, including those with a straight course, harbored a biofilm . On the other hand, a patency file might potentially cause extrusion of debris and irrigants into the periapical area leading to post- operative pain. From the analysis of the literature, it is not clear whether the use of a patency file has an influence on debris extrusion through the fora- men. Clinical studies showed that maintaining apical patency did not increase the occurrence of postoperative pain and flare-up ¹²⁸. In all cases with apical ramifications or deltas, the important aspect to be considered is that a patency file will follow just one of the branches (the one with the straightest route), with no effects on the remaining branches . Needless to say, the clinician is not aware of this occurrence, as ramifications and deltas are seldom visible in the periapical radiographs.

The Complexity of the Apical Anatomy A study reported that the achievement of patency of the canal terminus resulted in better outcomes for both treatment and retreatment cases ¹²⁷. In all cases with vital pulp preoperatively, the use of a patency file is biologically contraindi- cated ¹¹³. After having obtained a clean apical pulp wound like that illustrated in , mov- ing a file through randomly one of the two ramifications invariably means cutting into undis- turbed tissue, causing a larger wound.

CHAPTER 9 – VARIOUS TYPES OF ROOT CANAL SYSTEM

Historically, and as of this date, the C-shaped root/ canal configuration was identified in 12.5% from the remains of a group of 17 individuals from the El Mirador cave in the Sierra de Atapuerca (Spain) near the city of Burgos ¹²⁹. The remains were dated to 4400 years ago (the Bronze Age) and represent one of the first, if not the first, record of this anatomical configuration in Europe. In recent centuries, there were suggestions of C-shaped root/canal anatomies in 1743 according to Malpighii , John Hunter in 1778 , and Thomas Bell in 1831 . Keith and Knowles provided a description of the C-shaped canal anatomy in 1911 , with Keith providing greater clarity in 1913 in what was being character- ized as a molar of the Brelade dentition (Fig. 9.1).

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FIGURE 9.1

Further evidence for this anatomical occurrence can be seen in the publications of Hess in 1917 ¹³⁰, Keller in 1928 , and Nespoulos in 1929 , with morphological reconstructions by Mayer in 1960

Initially, Keith described this anatomical variation as a form of taurodontism. According to Kato et al. , Nakayama and Toda in their analysis of the C-shaped variant in 1941 referred to this anatomy as a “gutter-shaped root canal,” while Tratman in 1950 referred to the morphology as “horseshoe reduction form.” Contemporarily, the clinical perspective on the C-shaped canal was highlighted and amplified by Cooke and Cox in 1979 , although descrip- tions were provided a few years earlier by Piñeda and Kuttler and Waikai . Cumulatively, these papers set in motion a renewed interest in all phases of the clinical management of the C-shaped canal system[131,132] .

C-SHAPED CANAL MORPHOLOGIES

Due to the high incidence of C-shaped canal mor- phologies found in the mandibular second molars, the features that they present are primarily used for the classification purposes. The resultant ana- tomical characteristics are due to incomplete root separation that is speculated to be caused by the failure of Hertwig’s epithelial root sheath to fuse on the lingual or buccal surface ¹³³. This results in a ribbon-shaped canal space that is often eccentric to the lingual side of the C-shaped radic- ular dentin (Fig. 8.3g). The concept of a C-shaped morphology is based on the cross section of the root and the canal. The floor of the pulp chamber in C-shaped root often displays a single, ribbon-shaped orifice with an arc of 180° or more, which may begin at the mesial-lingual line angle and move around the buccal to the end at the distal aspect of the chamber (Fig. 8.3g). Similar to an iceberg where 7/8 its anatomy and shape lies below the surface of the water, the anatomy of the C-shaped root canal can display a wide range of variations over the length of the root that have been seen historically through sections and contemporarily through the use of the micro-CT. In the last 10 years, there have been few trea- tises that have provided a thorough assessment of the C- shaped root canal configurations ¹³⁴.However, the initial attempt to classify this unusual anatomical finding and its particular irregularities was addressed by Melton in 1991 and was characterized as follows ¹³⁵:

Category I: A continuous C-shaped canal that flows from the pulp chamber to the apex delineates a C-shaped outline without any separation.

Category II: A semicolon-shaped orifice in which dentin separates the main C-shaped canal from one distinct mesial canal.

Category III: Those anatomies with two or more discrete and separate canals with a:

FIGURE 9.2 (1) subdivision I, C-shaped orifice in the coro- nal third that divides into two or more dis- crete and separate canals joining apically;

(2) subdivision II, C-shaped orifice in the coronal third that divides into two or more discrete and separate canals in the mid-root to the apex; and

(3) subdivision III, C-shaped orifice that divides into two or more discrete and separate canals in the coronal third. In Melton’s classification, only three arbitrary section levels were chosen, therein abandoning all the information on how the anatomy of the canals may change over their length from orifice to apex. Needless to say, the micro- CT was not available at this time to provide better clarifica- tion of the anatomical variances.

The next major classification system pre- sented took advantage of the newer technology with the application of extensive micro-CT sections. Accordingly, and bolstered with new ana- tomical information, Fan et al. ¹³⁶ modified Melton’s classification as follows (Fig. 8.4b):

Category I: The shape of the canal was an interrupted “C” with no separation or division.

Category II: The canal shape resembled a semicolon resulting from a discontinuation of the “C” outline; however, either angle created should be no less than 60°.

Category III: Two or three separate canals were present and both angles created were less than 60°.

Category IV: Only one round or oval canal was present in that cross section.

Category V: No canal lumen could be observed (usually seen near the apex only) in this variant

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FIGURE 9.3

Fan and co-investigators felt that although the C-type orifice may have looked like two or three separate orifices, an isthmus linking them was often discernible. The single, round, or oval canal that may be found near the apex should be considered as a variation because other parts of the canal have shown the “C” configuration. Furthermore, they noted that “C” shape often varies along the root length so the clinical crown morphology or the appearance of the orifice may not be good predictors of the actual canal anatomy (Fig. 8.4c). In this classification, one of the canals in the C2 category would appear as an arc (i.e., the C2 canal would be more likely to extend into the fused area of the root where the dentin wall may be quite thin) ¹³⁷. To establish more clinical relevancy, Fan et al. ¹³⁸ classified the C- shaped root canals radio- graphically into three types):

FIGURE 9.4

Abbildung in dieser Leseprobe nicht enthalten

- Type I: conical or square root with a vague, radiolucent longitudinal line separating the root into distal and mesial parts. There was a mesial and a distal canal that merged into one before exiting at the apical foramen (foram- ina) .
- Type II: conical or square root with a vague, radiolucent longitudinal line separating the root into distal and mesial parts. There was a mesial and a distal canal, and the two canals appeared to continue on their own pathway to the apex.
- Type III: conical or square root with a vague, radiolucent longitudinal line separating the root into distal and mesial parts. There was a mesial and a distal canal, one canal curved to and superimposed on this radiolucent line when running toward the apex, and the other canal appeared to continue on its own path- way to the apex.

While two-dimensional radiograph imaging has given us a reasonable assessment of the presence of a C-shaped canal system (Figs. 9.3b–d), bone image superimposition could significantly decrease the accuracy of canal recognition ¹³⁹. Therefore, to enhance this recognition with in-depth anatomical details, Fan et al. , using an intraradicular contrast medium and micro-CT assessment (Figs. 9.7 and 9.8), pro- vided a better delineation of this classification. Additionally, and more recently, Amoroso-Silva and colleagues provided a greater analysis of the C1–C4 configurations (Figs. 8.9 and 8.10) with the C1 configuration and the distal aspect of the C2 configuration exhibiting the highest area values, low roundness values, and large apical diameters.

Furthermore, the analysis of the prevalence of the different cross-section configurations showed that these were predomi- nantly of the C4 and C3 varieties (1 mm from the apex) and the C1 and C2 varieties in the cer- vical third. In an attempt to assess the three- dimensional (3-D) morphology of the C-shaped root canal, Gao and associates used micro- CT and 3-D reconstruction to classify the canals into three types (Figs. 8.11 and 8.12).

- Type I (Merging): canals merged into one major canal before exiting at the apical fora- men; partial dentin fusion area may appear in the coronal and/or middle portion of the canal system.
- Type II (Symmetrical): separated mesial canal and distal can be located at the mesial part and distal part of the root, respectively. From the buccal- lingual view, symmetry of the mesial canal and distal canal was evident along the longitudinal axis of the root.
- Type III (Asymmetrical): separate mesial and distal canals were evident. From a buccal- lingual view, the distal canal may have a large isthmus across the furcation area, which com- monly made the mesial and distal canal asymmetrical.

ANATOMICAL CHARACTERIZATION OF C-SHAPED CANALS IN MOLARS FLOOR OF THE CHAMBER

Min et al. ¹⁴⁰ provided a detailed description of the morphology of the pulp chamber floor approximately 3 mm above the orifices (Fig. 9.13a). Scanned cross sections were reconstructed, and the images generated were assessed and assigned to one of the following four types (Fig. 8.14):

- Type I: a peninsula-like floor with a continu- ous C-shaped orifice.
- Type II: a buccal, strip-like dentin connection that exists between the peninsula-like floor and the buccal wall of the pulp chamber that separates the C-shaped groove into mesial and distal orifices. Sometimes the mesial orifice was separated into a mesiobuccal (MB) and a mesiolingual (ML) orifice by another strip- like dentin between the peninsula-like floor and the M wall of the pulp chamber.
- Type III: only one mesial strip-like dentin connection between the peninsula-like floor and the mesial wall that separates the C-shaped groove in a small ML orifice and a large MB 265 distal orifice. The MB distal orifice was formed by the merging of the MB orifice and the distal orifice.
- Type IV: Non-C-shaped floors. One distal canal orifice and one oval or two round M canal orifices are present.

Descending Canal Morphology To determine the canal morphology from orifice to a point 3.0 mm from the root apex, Min et al. ¹⁴⁰ made sections, 2 mm below the orifice (C1), one- third the distance between the orifice and the anatomical apex (C2), the midpoint from the ori- fice to the apex (C3a and C3b), and a point 3 mm from the apex. Configurations were analyzed and classified as follows (Figs. 8.13b and 8.15):

- C1: continuous C-shaped canal
- C2: MB distal and an ML canal
- C3a: mesial and distal canals
- C3b: MB, ML, and distal canals
- C4: single round or oval canal

Amoroso-Silva and colleagues ¹⁴¹ provided a further detailed delineation of the coursing of the C-shaped canal systems in mandibular sec- ond molars as seen in Figs. 8.9 and 8.10.

Detailed measurements, along with specific shapes, help to clarify the exact nature of this anatomy from orifice to apex in the different classifications. Apical Termination The apical termination of C-shaped canals has been characterized by many authors to a level approximately 1.0 mm from the apex. However, a view from the apex may afford a different interpretation, as many canals break into deltas, multiple accessory canals, and exit points well coronal to the apical termination of the root and have cementodentinal junctions that are placed deeply inside the root structure (Fig. 8.16). the C-shaped canal systems in mandibular sec- ond molars as seen in Figs. 8.9 and 8.10. Detailed measurements, along with specific shapes, help to clarify the exact nature of this anatomy from orifice to apex in the different classifications. Apical Termination The apical termination of C-shaped canals has been characterized by many authors to a level approximately 1.0 mm from the apex . However, a view from the apex may afford a different interpretation, as many canals break into deltas, multiple accessory canals, and exit points well coronal to the apical termination of the root and have cementodentinal junctions that are placed deeply inside the root structure (Fig. 8.16).

ANATOMICAL CHARACTERIZATION OF C-SHAPED CANALS IN PREMOLARS RADICULAR GROOVE

The presence of C-shaped root canals in premo- lars has also received attention in multiple studies (Table 8.1), with percentages ranging from 10.7% to 24%, the highest percentages being reported in Mongoloid populations. Along with the internal canal anatomical variations, which vary significantly from the orifice to apical terminus (Fig. 8.17), unique external anat- J. L. Gutmann omy has also been identified in the form of mesi- ally placed radicular grooves (Fig. 8.18) that extended from 3 mm below the cementoe- namel junction to the root apex (Fig. 8.19). While not always present, these grooves may pose sig nificant clinical concerns: (1) during root canal enlarging and shaping procedures, due to the thinness of the root wall adjacent to the groove, (2) during tooth restoration if the place- ment of a post is anticipated, and (3) as the groove may predispose to the accumulation of dental plaque and calculus, creating a periodontal prob- lem. However, when the groove was not identi- fied, there was no C-shaped canal system in the tooth ¹⁴². (Note: only the anatomy of the man- dibular premolar is being addressed, as this tooth presents with the most irregularities in its appear- ance and is the specific focus of most studies.)

CANAL ANATOMY AND APICAL TERMINATION

As seen in Fig. 8.20, there is a highly variable course of the canal anatomy longitudinally in mandibular first premolars , with the for- mation of the actual C-shape occurring at multi- ple levels and not in all canals that may be present. Fan et al. ¹⁴² classified these shapes as (1) a continuous C-shape only, (2) semilunar shape in the buccal canal only, (3) a combination of continuous C-shape and buccal semilunar, and (4) a C-shaped canal interrupted by a non-C- shaped canal. Accessory canals that originated in furcation areas of the semilunar buccal canal were also noted in 57 of the 327 reconstructed canal system models’ close furcation, which exited into mesial groove (Fig. 8.21). This finding may further com- plicate treatment procedures both endodontically and periodontally. Finally, Yang et al. addressed the canal termination apically in these complex premolars and found that most had a termination of 0–2 mm from the root apex. However, within the popula- tion studied (335 teeth), 72 teeth had a distance of 0–1 mm; 192 teeth, 2 mm; 61 teeth, 3 mm; 5 teeth, 4 mm; and 5 teeth, 5 mm. Furthermore, these findings are supported by Fan et al. ¹⁴² when reviewing the apical anatomical variables as seen in Fig. 8.20.

CLINICAL MANAGEMENT PROBLEMS

Key problems encountered during cleaning and shaping C-shaped canals include difficulty in removing pulp tissue and necrotic debris, exces- sive hemorrhage, working length determination, and persistent discomfort during instrumentation. Because of the large volumetric capacity of the C- shaped canal system, housing transverse anas- tomoses, and irregularities , many techniques have been advocated for the enlarging, shaping, cleaning, disinfecting, and filling of these canal systems ¹⁴³.

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Fig. 9.4 Classification of radiographic images after contrast medium introduction. (a) Type I; (b) Type II; (c) Type III (Reproduced by permission from Fan et al. )

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MIDDLE MESIAL CANALS IN MANDIBULAR MOLARS

The aim of root canal therapy is to eliminate all irritants from the root canal system. These irritants include necrotic pulp tissue, microorganisms, and their byproducts. A detailed knowledge of the pulp canal anatomy is necessary to effectively clean and shape the root canal system. Mandibular molars are the most frequent tooth type to be endodontically treated. Traditionally, mandibular molars are described as 2- rooted teeth with 2 canals in the mesial root and 1 or 2 canals in the distal root . However, studies have shown several variations in the anatomy of mandibular molars that are thought to be determined by race and genetics . These variations include a separate distolingual root , C-shaped anatomy of the roots and/or canals , an isthmus between the mesiobuccal (MB) and mesiolingual (ML) canals , and a third canal in the mesial root known as the middle mesial (MM) canal . The reported prevalence of the MM canal in mandibular molars varies among studies. Methods of detection include plastic casts , clearing, scanning electron microscopy , micro–computed tomographic (mCT) imaging , and use of a file under magnification . Based on the method used, the prevalence of the MM canal ranged from 0% (2)to 36% . Clinical studies on negotiable MM canals show results different from studies involving extracted teeth. Two older clinical studies reported an incidence of 2.6% and 12% for negotiable MM canals . Pomeranz et al described the anatomy of MM canals as follows: fin: The file passes freely between the main mesial canal (ML or MB) and the MM canal (transverse anatomies), confluent: The MM canal originates as a separate orifice but apically joins the MB or ML canal, and independent: The MM canal originates as a separate orifice and terminates as a separate apical foramen. Clinical studies show that magnification significantly increases the probability of locating and negotiating a second MB canal in maxillary molars . Compared with the dental operating microscope, there was no significant difference when loupes were used . In an attempt to locate and negotiate MM canals in mandibular molars, investigators showed in vitro that using the dental operating microscope can increase the number of located and negotiated canals . To date, there are no studies that report the incidence of negotiable MM canals in mandibular first and second molars using the dental operating microscope. The primary aim of this study was to evaluate the incidence of negotiable MM canals in mandibular first and second molars using the dental operating microscope for magnification. The secondary aim was to correlate the incidence of MM canals with variables including molar type (first or second mandibular molar), sex, age, ethnicity, and the presence of a second distal canal.

Failure of root canal treatment is related to the presence of bacterial biofilm in the root canal system (16). If 1 aim of root canal treatment is to remove all irritants from the root canal system, a missed canal or an unclean root canal system can be a cause for treatment failure. Persistent endodontic infection can be attributed to difficulties in removing a bacterial biofilm from root canal ramifications, including isthmuses (17). The presence of isthmuses in the mesial root of mandibular molars has been studied using different techniques. One in vitro study examined the apical 6 mm of the mesial root of 50 mandibular molars (18). These roots showed isthmuses in 33% of the specimens at 3–5 mm from the apex (18). However, none of the sections showed more than the 2 main canals. Using mCT reconstructions, Fan et al(19)investigated isthmuses in the apical 5 mm of 126 mesial roots of mandibular first and second molars. Isthmuses with different anatomies were present in 107 of 126 (85%) specimens. Some specimens had more than 1 isthmus in the apical 5 mm. Harris et al (10) studied the internal anatomy of 22 mandibular molars using mCT reconstructions. An isthmus was present in 100% of the specimens, and 36% had more than 2 canals. A systematic review, which included both in vitro and in vivo studies of the internal anatomy of mandibular first molars, showed isthmuses present in 54.8% of the mesial roots(20). Fifteen studies were included in this review with a collective sample size of 1615 teeth. However, none of these studies reported whether isthmuses were clinically negotiable. Nevertheless, they provide sufficient evidence to show that there is a high probability of having uncleaned areas in the mesial root of mandibular molars after root canal treatment. Using an endoscope to examine resected root ends, von Arx et al (21) studied 144 failed root canal–treated teeth that subsequently .

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FIGURE 1. (A) A preoperative view of tooth #30 in a 20-year-old black man. (B) A distal angle radiograph after obturation. The orifice of the MM canal is located close to the MB canal orifice. The MM canal showed ‘‘confluent’’ anatomy and joined the ML canal in the apical third. (C) A straight-on view of the tooth after obturation. (D) A magnified view (!8) of the 3 mesial canals.

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FIGURE 2. (A) A preoperative radiograph of tooth #30 in a 16-year-old black man. (B) A distal angle radiograph after obturation. The MM canal orifice is located close to the orifice of the MB canal. The MM canal showed a separate apical foramen (‘‘independent’’ anatomy). (C) A mesial angle radiograph after obturation. (D) A magnified view (!8) of the 3 mesial canals.

In removing bacterial biofilm from the mesial root of mandibular molars, no difference between Self Adjusting Files and other rotary files was found . The negotiation of MM canals with hand/rotary files provides access for irrigating solutions into the otherwise inaccessible isthmus. We hypothesize that negotiation and chemomechanical preparation of the isthmus area can substantially reduce the bacterial biofilm and bacterial load. We also hypothesize that this reduction in bacterial biofilm may improve the outcome of nonsurgical root canal treatment in mandibular molars. Clinical outcomes studies with long-term follow- ups are needed to test these hypotheses. Anatomic variations of mandibular molars such as the distolingual root/canal and C-shaped root/canal anatomy are well recognized by endodontic clinicians. Studies have shown an overall prevalence of 13% for distolingual root in mandibular first molars (20) with a higher prevalence of 22% to 28.5% in Asian ethnic groups. Studies have shown a prevalence of 10%–31.5% for C-shaped anatomy in mandibular second molars in different Asian populations . However, in this study, the prevalence of a distolingual root and C-shaped anatomy was less than other reports. This may be related to the fact that no patients of Asian heritage were included in the patient sample. In contrast, data on the incidence/prevalence of MM canals are limited. Clinical studies on the incidence of negotiable MM canals are limited to those performed in the 1980s without using magnification . Pomeranz et al reported the highest incidence (12%). It is now well documented that using magnification enhances the clinician’s ability to visualize the anatomy of the pulp chamber . Our study is the first in vivo evaluation of the incidence of MM canals using the dental operating microscope. The high incidence (20%) of MM canals in this study is likely attributable to the use of the microscope. Several of our anatomic findings regarding MM canals are consistent with other studies. Pomeranz et al reported that the orifice of the MM canal was always located close to the ML canal. Our findings were similar for the majority of teeth with a separate MM orifice . Only 2 of 10 (20%) of teeth had the orifice of the MM canal located near the MB canal (Figs. 1 and 2). Our findings were also consistent with the observations made under magnification in a recent ex vivo study on extracted mandibular molars .. A separate apical foramen for an MM canal was a rare finding.. Nevertheless, in the present study, 20% (3/15) of the MM canals had a separate apical foramen (‘‘independent’’ anatomy). Pomeranz et al reported that the most prevalent anatomy was a ‘‘fin’’ (67%). Karapinar-Kazandag et al found that all MM canals showed a ‘‘confluent’’ anatomy. No ‘‘independent’’ or ‘‘fin’’ anatomy was found. In our study, the most prevalent (46.7%) anatomy was ‘‘confluent.’’ In conclusion, using magnification and careful tactile search techniques, the incidence of MM canals in mandibular molars was found to be higher than previously reported. The probability of finding and negotiating an MM canal in younger patients is significantly higher than in older individuals. Using the operating microscope is key to locating and negotiating MM canals. Clinical studies with long-term follow-ups are needed to determine the effect of preparation of MM canals on the outcome of nonsurgical endodontic treatment in mandibular first and second molars.⁹¹

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FIGURE 3. (A) A preoperative view of tooth #31 in an 18-year-old white man. (B) A distal angle view of the gutta-percha cone fit. There are 2 ‘‘fins’’ in the mesial root adjacent to the MB and ML canals. (C) A mesial angle radiograph after obturation. (D) A magnified view (!8) of the access cavity. Note the presence of fins adjacent to the MB and ML canals.

CONCLUSION

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CHAPTER 10 - CONCLUSION

The fundamental basis of the endodontic spe- cialty is the knowledge of root canal anatomy. Thus, a thorough understanding of the canal morphology and its variations in all groups of teeth is a basic requirement to improve the out- come of the endodontic therapy.

Knowledge of root canal anatomy is essential in order to explain the treatment plan to a patient, to properly examine radiological imaging of teeth and surrounding structures, and, most important, to perform invasive procedures. Root canal treatment is indicated when the pulp tissue of a tooth is damaged or infected because of decay, trauma, iatrogenic operative procedures, or deep fillings. Different bacteria from the oral cavity can adhere to dentinal surfaces, invade the dentinal tubules and produce pulpal inflammation that, lately, may spread throughout the complexities of the root canal system, compromising the periradicular tissues.

So thor- ough knowledge of root canal morphology should be required to properly access the root canal system and remove microorganisms and pulp tissue from the canal for Successful root canal treatment.

The complexity of the root canal anatomy in the apical third and the preoperative histologic and microbiologic conditions of the pulp tissue can be regarded as the two major factors affecting for the success of the root canal system.

Awareness of canal configuration, adequate clinical skills, use of specialized techniques of diagnosis, debridement and obturation will pave the way for successful treatment outcomes.

INDEX

1. INTRODUCTION

2. BASIC STRUCTURE OF TOOTH: ENAMEL, DENTIN, PULP

3. ROOT CANAL COMPONENT

4. MORPHOLOGY OF ROOT CANAL SYSTEM

5. CLASSIFICATION OF ROOT CANAL MORPHOLOGY

6. ROOT CANAL ANATOMY OF MAXILLARY TEETH

7. ROOT CANAL ANATOMY OF MANDIBULAR TEETH

8. COMPLEX ROOT CANAL SYSTEM

9. VARIOUS TYPES OF ROOT CANAL SYSTEM

10. CONCLUSION

Frequently asked questions about Root Canal Anatomy

What is root canal anatomy and why is it important?

Root canal anatomy is the study of the internal structure of teeth, specifically the pulp chamber and root canals. A thorough understanding of this anatomy is crucial for successful endodontic (root canal) therapy, allowing dentists to effectively clean, shape, and obturate the entire root canal system.

What are the basic components of a tooth's structure?

The basic components include: Enamel (the hard outer layer), Dentin (the main body of the tooth), and Pulp (the living tissue containing nerves and blood vessels).

What are the main parts of the root canal system?

The root canal system consists of the pulp chamber (located within the crown) and the root canal (located within the root). It also includes components like isthmuses, accessory canals, and apical deltas.

How is the root canal system classified?

Several classification systems exist to categorize root canal configurations, including Weine's and Vertucci's classifications. More recently, a new classification system aimed at better codifying root and canal configurations using alphanumeric notation has been proposed.

What is the significance of isthmuses in root canal anatomy?

An isthmus is a narrow connection between two root canals, which can harbor bacteria and debris. Complete debridement of isthmuses is difficult, making them potential sites for endodontic failure.

What are accessory canals and how do they affect endodontic treatment?

Accessory canals are branches of the main root canal that communicate with the periodontal ligament. They can allow bacteria to reach the periradicular tissues, potentially causing inflammation and lesions. They can also cause issues if the canal is not well obturated.

What is the apical foramen?

The apical foramen is the opening at or near the root apex through which the main root canal communicates with the periapical tissues. Its location and morphology can vary significantly.

What is the apical constriction?

The apical constriction is the narrowest part of the root canal, typically located just short of the apical foramen. Many endodontists consider it the ideal termination point for root canal preparation and obturation.

What is the significance of root canal curvature in endodontic treatment?

Root canal curvature, particularly in the apical third, can complicate cleaning and shaping procedures. Preoperative recognition of canal curvature is essential to minimize iatrogenic errors.

What are the key anatomical features of maxillary incisors and how do they affect treatment?

Maxillary incisors typically have a single root and canal. They are characterized by their straight canal and apical termination but can also exhibit accessory canals and apical deltas. Knowing how to locate and obturate the root canal system can improve treatment success and prognosis.

What are the key anatomical features of maxillary canines and how do they affect treatment?

Maxillary canines are longer teeth and have larger buccolingual dimensions. The tooth generally exhibits only a single root and canal system. However, it is important to understand any possible anatomical anomolies to guarantee successful treatment.

What are the key anatomical features of maxillary premolars and how do they affect treatment?

Maxillary premolars, particularly the first premolar, exhibit a large degree of anatomical variance. They often have bifurcated root systems or have greater than one root canal in a root. Knowing these possibilities is key to finding the correct root canal system.

What are the key anatomical features of maxillary molars and how do they affect treatment?

Maxillary molars, particularly the mesial buccal root, are very large and strong teeth with well-developed pulpal and periodontal features. However, because they are complicated to treat, with an increase in anomolous presentations, it is important to understand as much about root and root canal system morphology as possible.

What are the key anatomical features of mandibular incisors and how do they affect treatment?

Mandibular incisors are narrow mesiodistally but often have a broader buccolingual face. They are also easily able to be bifurcated. Knowing these traits can be key in successfully obturating root canal systems.

What are the key anatomical features of mandibular canines and how do they affect treatment?

Mandibular canines have shorter roots than maxillary canines with narrow mesiodistally but broad buccolingually.

What are the key anatomical features of mandibular premolars and how do they affect treatment?

The two mandibular premolars exhibit one or two pulpal canals, but are otherwise usually a single-rooted tooth.

What are the key anatomical features of mandibular molars and how do they affect treatment?

The most commonly presented tooth is a two-rooted molar with three canals. However, variations like an additional distal lingual and C-shaped morphologies should be considered when planning out treatment.

What is a C-shaped canal and how is it classified?

A C-shaped canal results from the failure of Hertwig’s epithelial root sheath to fuse properly, leading to a C-shaped or ribbon-shaped canal space. These are categorized based on canal dimensions (Min et al) and axial orientation (Gao et al)

What are some age-related changes that affect root canal anatomy and endodontic treatment?

Age-related changes include: decreased pulp chamber size, dentin sclerosis, increased cementum deposition, pulpal calcifications, reduced tubular permeability and also are due to environmental trauma.