Oral Structure & Biology E-Book

Ralf J. Radlanski

• Herausgeber: Quintessence Publishing Co, Inc
• Kategorie: Fachliteratur
• Sprache: Englisch
• Veröffentlichungsjahr: 2019

Seitenzahl: 1076

Beschreibung

Knowledge of the structures of the orofacial region from the macroscopic scale to the molecular level and pathologic changes to those structures enables practitioners to successfully treat patients or seek treatment options. This book presents the structural biologic foundations underpinning dental and oral medicine. Beginning with an overview of the anatomy of the mouth and moving on to the evolution of the oral structures and pre- and postnatal development of the oral cavity, related facial structures, and the teeth, this book describes each part of the orofacial region in terms of its morphology, tissue structure, cellular properties, and development. Functioning as both a textbook for dental students and a reference manual for experienced clinicians, this compendium of the structural biologic foundations of clinical work in dental and oral medicine allows practitioners to integrate current research in molecular biology into a solid framework of knowledge.

Leseprobe

Oral Structure and Biology

Dedication

This book is dedicated to all those who seek to preserve knowledge, to critically review and expand it, and to use it to treat their patients responsibly.

This book was originally published in German under the title Orale Struktur- und Entwicklungsbiologie.

Library of Congress Cataloging-in-Publication Data

Names: Radlanski, Ralf Johannes, author.

Title: Oral structure and biology / Ralf J. Radlanski.

Other titles: Orale Struktur und Entwicklungsbiologie. English

Description: Hanover Park, IL : Quintessence Publishing Co., Inc., [2018] | Translation of: Orale Struktur und Entwicklungsbiologie / Ralf J. Radlanski. Berlin : Quintessenz-Verlag, 2011. | Includes bibliographical references.

Identifiers: LCCN 2018011274 | ISBN 9780867157468 | eISBN 9780867159059

Subjects: | MESH: Stomatognathic System--embryology | Stomatognathic System--growth & development

Classification: LCC QM311 | NLM WU 101 | DDC 612.3/11--dc23

LC record available at https://lccn.loc.gov/2018011274

© 2018 Quintessence Publishing Co, Inc

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All rights reserved. This book or any part thereof may not be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, or otherwise, without prior written permission of the publisher.

Editor: Dojna Shearer

Design and Production: Angelina Schmelter

Contents

Preface

1Definitions, Objectives, and Clinical Relevance

2The Mouth and Its Parts

3Evolution

4Morphogenesis

5Development of the Oral Cavity in Relation to Facial Development

6Tooth Development

7Dental Enamel

8Dentin

9Pulp and Root

10Periodontium

11Cementum

12Periodontal Ligament

13Alveolar Bone and Jawbone

14Oral Mucosa

15Salivary Glands

16Immune System

17Development of the Dentition and Teeth Eruption

18Temporomandibular Joint

Index

Preface

It has been more than 10 years since Hubert E. Schroeder, Professor of Oral Structural Biology in Zürich and author of the book of the same name, asked me to produce a new textbook that would maintain and expand on the basic knowledge he had assembled.

When he retired, he entrusted to me a large proportion of his original illustrations so that they could be retained in the new book. As a student, I used his textbook as a study tool. At the time, I naturally had no idea I would one day be in a position to continue his legacy.

Over the intervening years, not only has our knowledge of morphology and developmental biology in the orofacial region greatly expanded, but our reading and learning habits have changed considerably. This change affects the structure of thought processes and sentence structure as well as the visual presentation of text and illustrations. A new book titled Oral Structural and Developmental Biology emerged from the experiences I gained during many years of lecturing on these topics at Göttingen University and the Free University of Berlin as well as the University of California at San Francisco and the University of Turku.

It is very important to be able to hold in our hands a compendium of the structural biologic foundations of clinical work in dental and oral medicine, especially today, as it is difficult to keep track of the growth in knowledge and molecular medicine is constantly growing in importance.

As the author, I am solely responsible for the content of this book, but a large number of highly committed colleagues have constantly given me valuable help over the years. First and foremost, I would like to thank Dr Herbert Renz, Dipl-Biol, for lots of in-depth discussions in which he saved me from making many a mistake. In addition, he prepared numerous specimens and laboriously photographed them under light and electron microscopes. I also wish to thank Dr Christine Knabe und Prof Dr Andrea-Maria Schmidt-Westhausen for checking some of the chapters. I am grateful to my secretary, Beate Lion, for doing the legwork on the literature search and maintaining the literature database as well as doing preparatory work on some of the illustrations. I would also like to thank medical technicians Barbara Danielowski, Irene Schwarz, and Karin Schulze-Dirksen for preparing many of the histologic specimens, photographs, and 3D reconstructions based on serial histologic sections.

Many students trial-read various passages and passed on their comments. Representative of all these students, I would like to thank Anne Schöler and Saskia Preisner, as well as my children Jana, Kalinka, and Philip Radlanski. As one of my peers, Prof Dr Birte Steiniger from Marburg University gave me numerous explanatory notes on the chapter dealing with the immune system, for which I sincerely thank her. Prof Dr Werner Götz of Bonn University rigorously worked through large parts of the manuscript and gave me valuable notes, for which I am extremely grateful.

My thanks to Johannes Wolters, the Publishing Director of Quintessenz in Berlin, for the patience he showed despite the delays. He recognized a real need for this unique book on the subject of oral structural and developmental biology. I thank him especially for his willingness to produce many of the illustrations in expensive color print.

This book was written primarily for students of dental and oral medicine. Students tackling the book in their first term will undoubtedly find the sheer amount of material and the high level of detail rather overwhelming. However, as they expand their horizons during the course of their studies and whenever clinical necessity calls for knowledge of the fundamentals of structural biology, I hope they will be able to find the correct answers in this book. I also hope this will prove a helpful reference work after readers have completed their studies. Furthermore, this book may provide the foundation for further study in related fields, such as anthropology, forensic medicine, or veterinary medicine.

I always found working on the text to be extremely instructive, fascinating, and at times more exciting than a Sunday evening crime thriller on the TV. I hope everyone working through this book has the same experience!

CHAPTER1

Definitions, Objectives, and Clinical Relevance

The difference between health and sickness can be seen even in the mouth, based on changes in form and structure from the macroscopic to the microstructural. Knowledge of the structures and pathologic changes to those structures enables practitioners to successfully treat patients or seek treatment options. This book presents the structural biologic foundations underpinning dental and oral medicine.

The mouth encompasses the area between the lips and the throat. All the parts are described in terms of their form, composition, tissue structure, and cellular properties. In many cases, the structural makeup only becomes comprehensible once its origins are understood. This is why aspects of development are described, ranging from embryonic development to changes in old age.

Clinical examination and treatment are influenced by patient morphology as understood through visual and haptic impressions. However, these aspects are based on the microstructure of the organs and tissues. Because this structure is not visible to the naked eye in most cases, our knowledge relies on rigorous examination using radiology, light microscopy, and electron microscopy. Knowledge is also gained through objective experiments. However, patience and sometimes substantial investment in laboratory equipment are needed to bring patterns and connections to light.

When dealing with a patient, the full range of knowledge and all available facts may not be needed. Nevertheless, the more fundamental knowledge practitioners have on which to base their work, the more successful they will be. People should not be frustrated if the odd fact escapes them every now and then. Understanding the connections between the facts is what matters most. However, these connections are only revealed after a thorough study of the facts. It is our duty to our patients to know exactly what we are doing. Patients will rarely go along with suppositions and a trial-and-error approach.

A large proportion of the material presented in this book is based on knowledge that was gained using human subjects. However, some experiments can only be done in animals. Not all findings are transferable to humans; where statements in the text apply only to a specific experimental animal, a note is given to that effect. To show links between fundamental knowledge about structural biology and patients, clinical notes are given where appropriate. Because our knowledge is still incomplete, reference is made in several places to unanswered questions.

Nevertheless, most morphologic and microstructural knowledge can be regarded as accepted fact. New findings in this sphere are rare. While modern research focuses on questions of molecular biology, structural biology remains the foundation. Furthermore, we can only meaningfully integrate biochemical knowledge if we know where the reactions take place, the physical distances that promote or inhibit a reaction, and the structural settings nature has provided for this purpose.

At present, we are witnessing a virtual explosion of knowledge about the signaling molecules cells use to communicate with each other during embryologic development and postnatal remodeling and healing. The same transcription and growth factors crop up time and again in relation to diverse tasks in different tissues and organs and at different phases of development. Table 4-1 presents a selection of these factors. Though research in the field of molecular developmental biology is very much in a state of flux, it seemed necessary to incorporate this aspect of structural development into this textbook, despite its potential to soon be outdated and deemed incorrect because of more recent findings. However, at least a fundamental understanding of molecular-oriented medicine has been established and is already being applied to some extent in dental and oral medicine on questions of bone formation, osseointegration of implants, and regeneration of the periodontium.

The more we intervene in the biology of the cell at the molecular level, however, the more side effects and difficult-to-manage repercussions come to light. Therefore, everyone who works in this area must act responsibly. The content of the individual chapters sometimes overlaps with that of other chapters, and in places cross references to other chapters are given. The chapters describing the individual structures in detail are preceded by a few introductory overview chapters.

Chapter 2 first explains the macroscopic anatomy of the mouth and its surrounding cranial structures and deals with orientation in the oral cavity. Each individual tooth is described here. Chapter 3 presents a brief assessment of the importance of evolutionary theory to explain the orofacial structures. Chapter 4, which explores general principles of morphogenesis, should be regarded as an introductory overview. Chapter 5 describes in detail the prenatal and postnatal development of the orofacial region. Tooth development is the subject of chapter 6. The reader will discover here that much more is known about the formation of the dental crown than about the formation of the roots. These gaps in knowledge are only partially filled by current research.

The structural makeup of dental enamel, dentin, root, and pulp is described in chapters 7, 8, and 9. Although dentin and pulp are structurally connected, each is assigned its own chapter because the structural similarity mainly relates to the odontoblasts as the outermost layer of the pulp and to the apposition of predentin as the innermost layer of dentin. Innervation of the dentin also involves a structural overlap with the pulp because the nerves extend from the pulp into the dentinal tubules and the content of the dentinal tubules may transmit stimuli from the periphery of the dentin into the pulp. Apart from these overlapping aspects, dentin and pulp are such different tissues that separate chapters were preferable. Chapter 10 is another introductory overview, dealing with the different structures of the periodontium that functionally form a unit, but they are discussed in their own chapters (chapters 11 to 13 on the cementum, periodontal ligament, and alveolar bone) because of their specific composition.

Chapter 14, concerning the oral mucosa, inevitably became a sizeable chapter; this shows how differently structured the various regions of the lining of the oral cavity are. The gingiva, as part of the marginal periodontium, is discussed in this chapter because it is part of the lining of the mouth. The salivary glands are given their own chapter 15. Because the mouth region is an extensive opening of the body to the outside world, the immune system has particular importance in this region, as is reflected structurally in the tissues. This is why a detailed description of the immune system warrants its own chapter, 16. In chapter 17 on the development of the dentition and eruption of the teeth, aspects of tooth development are picked up again from chapter 6. However, because aspects of the periodontium, jawbone, and oral mucosa play roles in eruption of the teeth, it makes sense to describe these toward the end of the book. Chapter 18, about the temporomandibular joint (TMJ), stands alone in terms of the description of its structure, but in terms of its formation the TMJ can only be understood in connection with the development of the face. Functionally, it is closely connected to development of the dentition and occlusion, so this chapter usefully concludes the description of oral structural and developmental biology.

CHAPTER2

The Mouth and Its Parts

This chapter provides a brief introductory guide. References in the text direct the reader to other chapters in the book that contain detailed descriptions. In addition, reference is made to textbooks for further reading and to atlases of anatomy. It can also be helpful when reading this chapter to hold a mirror in your hand and look at the structures being described in your own mouth.

Directional Terms

The nomenclature used in medicine and dentistry primarily has a Latin/Greek origin. Before embarking on an anatomical description, it is important to explain the positional and directional terms as well as the fundamental concepts (Fig 2-1 and Table 2-1). These positional and directional terms are clear and unambiguous because they pertain to the body and apply regardless of whether the patient is standing, sitting, or lying down.

Fig 2-1 Oral cavity with the most important directional terms identified (see Table 2-1).

Table 2-1Positional and directional terms

Face and Mouth

The human face has general characteristics that are common among all members of the species. Nonetheless, there is so much variation in facial features among individuals that we are able to recognize people purely from their faces. The interaction of anatomical structures and the extent to which they vary contribute to this individuality.

The bony structures form the facial skeleton that supports the overlying soft tissue. The contour and sturdiness of the masticatory and facial muscles and the distribution of the subcutaneous fatty tissue make a huge contribution to the shape of the face. The teeth also have a significant influence on the human face. The lips lie against the anterior teeth, while the posterior teeth support the mandible against the maxilla and, in so doing, determine the height of the lower face.

Sizeable deviations in tooth position and tooth loss can thus have an adverse effect on facial esthetics. The increased wrinkling of the facial skin in old age is due not merely to the aging of the skin itself but also to age-related changes affecting the teeth, including positional changes, abrasion, and tooth and bone loss.

Externally, the mouth is bounded by the lips. Anatomically, the lips are the area above and below (cranial and caudal to) the vermilion border. The vermilion border itself appears red because there is no thick horny layer of skin in this area and thin blood vessels are able to show through the thin epithelium (see chapter 14). A vertical furrow known as the philtrum runs down the middle of the upper lip below the nose. At its lower edge, the margin of the lip describes a curve known as the Cupid’s bow. The angles of the mouth are indented to varying degrees depending on muscle tension.

To the right and left of the wings of the nose, the nasolabial groove (or sulcus) forms the border between the cheeks and the top lip. The labiomental groove runs crosswise, usually in a slightly sweeping curve, between the lower lip and the chin. How pronounced these grooves are differs from one individual to another and varies with soft tissue thickness, muscle tension, and age.

Oral Cavity

Oral vestibule

The dental arches with their alveolar processes delineate the oral vestibule (vestibulum) from the actual oral cavity (Figs 2-1 and 2-2). Roughly level with the premolars, a buccal (cheek) frenum spans each quadrant. In the maxilla and mandible, a corresponding labial frenum runs from the area between the two central incisors to the inside of the corresponding lip. The formation of the oral vestibule is described in chapter 6.

Fig 2-2 View of the occluding dental arches with the adjacent soft tissue parts of the oral cavity: anterior view (a) and right lateral view (b).

Clinical note

Orthodontic plate appliances, which extend into the vestibule, and full and partial dentures have to be adapted to the contour of the buccal and labial frena to avoid limiting movement and causing ulceration of the mucosa.

Palate

The palate (palatum) separates the oral cavity from the nasal cavity (Fig 2-3). The larger area of the palate between the anterior teeth and the second molars is formed by the hard palate (palatum durum). In this area, the mucosa is horny (keratinized or at least parakeratinized). Especially in the middle area, no submucosa is present and the palatal mucosa lies almost immovable with a tight lamina propria directly on the bone. However, there are many small individual salivary glands closely packed over the whole of the palate. Raised ridges (palatine rugae; plicae palatinae) run transversally in the anterior part of the palate. They can be touched with the tongue and play a significant role in correct pronunciation of S sounds. Anterior to that, palatal to the maxillary central incisors, the incisive papilla lies in the middle. It covers the incisive foramen, the opening of the nasopalatine canal through which the nerves and vessels run to the floor of the nose. The posterior margin of the hard palate lies transversally between the third molars in adults, and the smaller soft palate (palatum molle) extends as a strong, sheetlike connective tissue framework of tendons. As a result of the muscles radiating into the soft palate (velum palatinum), this framework is highly mobile and helps to tightly seal the posterior part of the oral cavity from the nose and throat. This is extremely important with regard to speech. The uvula is located at the posterior end in the middle of the soft palate.

Fig 2-3(a) Frontal view of reconstruction of the bone and the teeth calculated from the data set of cone beam volumetric imaging. Parts b through e correlate with the sectional planes labeled. (Courtesy of Dr Christian Scheifele, Berlin, Germany.) (b) Sectional view of a in the paramedian sagittal plane. (c) Sectional view of a in the transverse-vertical plane (frontal plane) at the level of the second molars (M2 and M2). (d) Sectional view of a in the transverse-sagittal plane (horizontal plane) at the level of the tooth roots in the maxilla. The upper edge of the image points anteriorly. (e) Sectional view of a in the transverse-sagittal plane (horizontal plane) at the level of the tooth roots in the mandible. The lower edge of the image points anteriorly.

The oral cavity ends posteriorly at the palatoglossal arch, a fold of mucosa forming an arch on both sides that stretches between the lateral margins of the soft palate and the tongue-side area distal to the mandibular molars. The palatine tonsils lie behind the palatoglossal arch (see chapter 16).

The development of the palate is described in chapter 5 in the section “Formation of the palate,” and the specific regions of the oral mucosa are described in chapter 14.

Cheeks

The cheeks (buccae) form the lateral closure of the oral cavity. On the inside, they are lined with a nonkeratinized, mobile mucosa. Small, isolated salivary glands lie in the submucosa, and the excretory duct of the parotid gland opens into the mouth opposite the maxillary second molar. The buccinator muscle, following a horizontal course, makes the cheeks highly mobile. An individually variable amount of fat is deposited in the cheeks, and blood vessels and fibers of the facial nerve and branches of the trigeminal nerve pass through here.

Toward the lip, the cheeks merge into the inner surfaces of the upper lip and the lower lip. The fibers of the buccinator muscle also pass into the circular fibers of the orbicular muscle of the mouth (orbicularis oris), which gives the lips their familiar mobility.

Tongue

The tongue is extremely mobile and can completely fill the oral cavity when the mouth is closed. At the same time, the tip of the tongue is able to slip over nearly all areas of the inner lining of the oral cavity, again with the mouth closed. Muscle fibers run transversally, sagittally, and vertically through the inside of the tongue. The motor and sensory innervation of the tongue is intensive.

The surface of the tongue is covered with a diversity of fine elevations in different forms: the fungiform, filiform, and foliate papillae, as well as the vallate papillae, which are arranged in a row in front of the base of the tongue. The papillae together with the embedded taste buds serve the purpose of taste perception.

The development of the tongue is described in chapter 5, and the specific regions of the oral mucosa and the tongue are described in chapter 14.

Floor of the mouth

When the tongue is raised, the floor of the mouth and the lingual frenum, which is stretched between the lower margin of the tongue and the mucosa covering the floor of the mouth, become visible. The blood vessels can easily be seen through the thin mucosa of the underside of the tongue and the floor of the mouth. The ducts of the paired submandibular glands open to the left and right of the lingual frenum. The small, individual excretory ducts of the sublingual glands emerge on the surface here, arranged in a row and running further laterally and dorsally in the floor of the mouth.

Oral mucosa

The mucous membrane of the mouth (oral mucosa) is specialized and structured differently depending on the region of the oral cavity. Three layers—epithelium, partly keratinized, and lamina propria and submucosa—can be structurally distinguished in the oral mucosa. The epithelium, the uppermost layer, can be further divided into four layers (stratum germinativum/ basal cell layer, stratum spinosum/prickle cell layer, stratum granulosum/granular layer, and stratum corneum/keratinized layer).

The oral mucosa is kept constantly moist by the three major salivary glands (parotid, submandibular, and sublingual glands) and by a large number of minor salivary glands distributed throughout it. Owing to its mineral content, saliva is extremely important in remineralization of the teeth. It also contains digestive enzymes and has buffering, antimicrobial, and irrigating effects. The oral mucosa is intensively innervated, highly mobile, and adequately tear resistant. At the alveolar process it is immovably fixed, and toward the teeth it merges into the gingiva, which surrounds the teeth in a collarlike fashion.

The specific regions of the oral mucosa are described in chapter 14.

Skeleton and Masticatory Musculature

Maxilla

The maxilla is a paired bone. From the anterior view, its greatest width is at the level of the zygomatic arches. From here, its upper margin runs medially and forms the inferior edge of the orbits. Medially, the frontal process of the maxilla projects up to the frontal bone and makes contact with the nasal bone. Caudal to the orbits lies the infraorbital foramen, the opening through which the infraorbital nerve exits. This nerve branches off the maxillary nerve, and in the maxilla it runs in a canal caudal to the orbits. Finer branches of this nerve divide further and radiate into the teeth of the maxilla. The maxillary sinus (sinus maxillaris) lies in the maxillary body, opening toward the nasal cavity at the middle concha through the maxillary hiatus. In early childhood, the maxillary sinus is only about the size of a cherry. Over a person’s lifetime, it gets wider and even forms deep offshoots between the roots of the teeth into the alveolar process. In the middle of the face, the maxilla surrounds the bony opening of the nose, the piriform aperture. In the alveolar process, the two halves of the maxilla meet in the middle of the face at the intermaxillary suture. Directly below the bridge of the nose lies the anterior nasal spine, a tip of bone that is usually distinctly palpable. The maxilla forms the roof of the palate (palatal vault), separating the nasal cavity from the oral cavity (see Figs 2-3b and 2-3c). Thus, the largest part of the hard palate is formed from rooflike parts of the maxilla. The palatine bone is a separate bone that lies dorsal to the maxilla and merely forms a posterior part of the hard palate. The separating line (transverse palatine suture) runs transversally at the level of the second molars in adults. At the level of the third molars, through the lesser and greater palatine foramina, emerge the palatine nerves; fitting close to the bone, they spread out over the palatal surface. The posterior end of the palatine bone tapers to a point at the middle known as the posterior nasal spine.

The posterior edges of the bodies of the maxilla are in contact with the cranially extending offshoots of the palatine bone and the sphenoid bone as well as the pterygopalatine fossa.

Clinical note

A maxillary sinus greatly extended in the direction of the alveolar process can lead to opening of the sinus (oroantral perforation) when dental extractions are carried out. This can prevent or make difficult orthodontic tooth movements or preclude the use of implants without preparatory measures because of the lack of available bone mass.

The bone structure is less dense (more spongy) in the maxilla than in the mandible. As a result, orthodontically or spontaneously induced tooth movements take place more quickly in the maxilla, while anesthetics diffuse faster and infections are able to spread more quickly.

Mandible

The mandible also originates as a paired bone and at birth still displays a medial symphysis. However, this rapidly ossifies so that by adulthood not even a bone suture can be detected. The mandible is differentiated into the alveolar process, in which the teeth are anchored; the mandibular body; and the ascending ramus. The prominence of the bony chin is variable. Here the chin musculature inserts from the facial onto the mental protuberance; a small mental spine projects in an oral direction, from which the genioglossus muscle arises. On the inside of the mandibular body, the mylohyoid line is discernible as a bony edge from which the mylohyoid muscle originates. It extends from the inside of the chin area through to the last molar and spans the mandible. Posteriorly, it is fused in the middle with the hyoid bone.

The mandibular body is connected to the chin on the left and right in a gently curved arch. The mental foramen is located roughly level with the first premolar. This is where the inferior alveolar nerve emerges, which from this point is called the mental nerve and conducts the sensory sensations of the lower lip. The inferior alveolar nerve, together with the artery and vein of the same name, are contained in the inferior alveolar canal. From there it gives off branches to each tooth root. The dorsal entry to this canal is the mandibular foramen. It lies on the medial side of the mandible, where the mandibular body merges into the ascending ramus.

The ascending ramus extends distally, forming a flattened, slightly outward curve, and points cranially with respect to the mandibular body. This forms the angle of the mandible, which is almost a right angle in some cases and in others slopes more in the dorsal-cranial direction, depending on the individual manifestation and growth pattern. At the angle of the mandible, the masseter muscle attaches to the outside and the medial pterygoid muscle to the inside. The ascending ramus ends anteriorly in a pointed coronoid process and posteriorly in a condylar process with a flattened condyle that slopes down toward the middle. The semilunar hiatus lies in between. The fibers of the temporal muscle attach to the coronoid process.

As a paired unit, the mandible has two temporomandibular joints. These have to function together during every movement of the mandible because of the join in the chin region.

The structural and cellular features of the bone of the alveolar process are described in chapter 13, while the temporomandibular joint is described in more detail in chapter 18.

Teeth

Every normal human tooth is made up of enamel, dentin, cementum, and pulp. The part of the dentin core covered with enamel is called the anatomical crown, and the part covered with cementum is called the anatomical root. Enamel and cementum meet at the cementoenamel junction, which is a curved line running around the neck of the tooth.

These anatomically defined boundaries are not always clinically visible. In young adults, the cervical enamel is still covered by the gingiva, while in elderly people a portion of the root close to the crown is often exposed as a result of atrophic processes. Therefore, a distinction is made between the anatomical crown and the clinical crown (the clinically visible portion) and also between the anatomical root and the clinical root (the portion of the root that is surrounded by the tissues supporting the teeth). The anatomy and structure of the tissues supporting the teeth is described in chapters 10, 11, 12, and 14. The largest horizontal circumference of the dental crown is known as the height of contour. Owing to the specific shape of the dental crown, the height of contour follows a curved path in such a way that it runs closer to the neck of the tooth vestibularly and orally than it does approximally, where it lies closer to the occlusal surface.

The dental pulp, made of gelatinous connective tissue permeated by collagen fibers and containing specially differentiated cells (odontoblasts, fibrocytes, fibroblasts, connective tissue cells, lymphocytes, macrophages), blood vessels, lymph vessels, and nerves, lies in the area of the crown (coronal pulp) and in the tooth roots. Individual tooth roots may contain several root canals (Table 2-2; see also Fig 2-7i). The vessels and nerves pass through the apical foramen at the root apex into the tooth. At the apex of the root there is often a division into several separate ramifications; root canals emerging at the sides of the root are also found in many cases. The structural and cellular features of the pulp are described in chapter 9.

Humans have two generations (dentitions) of teeth. This is known as a diphyodont dentition. The teeth are also differently shaped, which is known as a heterodont dentition.

They are divided into incisors, canines, premolars (only found in the permanent dentition), and molars. The teeth are usually numbered distinctively with two digits (Fig 2-4).

According to the Fédération Dentaire Internationale (FDI) system, the first digit refers to the quadrant (1 to 4), with the maxillary right quadrant (from the viewpoint of the patient) bearing the number 1.

Counting of the quadrants continues in the primary dentition from 5 to 8, starting with the maxillary right quadrant as quadrant 5. The second digit denotes the tooth, starting with the central incisor, which bears the number 1. The third molar is numbered 8. This system clearly identifies each tooth and has become established partly because it is easy to record using a computer keyboard.

However, this system is not applied worldwide. In the United States, a different method is used. In this method, counting starts with the maxillary right third molar, which is assigned number 1. From there, the numbering continues until the mandibular right third molar is reached as number 32. For the primary teeth, capital letters are used, and counting starts in the maxillary right quadrant with the second molar, designated A, and continues to T for the second molar in the mandibular right quadrant (see Fig 2-4).

Old tooth notations employed Arabic numerals for the permanent teeth, with a cross or the appropriate parts of the cross to identify the quadrant.3 Roman numerals were used in a similar way for the primary teeth (see Fig 2-4).

Because the teeth are arranged along a curved dental arch, the tooth surfaces cannot be named according to the usual anatomical system in the same way throughout the dentition. For instance, the vestibular surface of a molar shows laterally, but the vestibular surface of an incisor shows anteriorly. This is why the nomenclature drawn up by Zuckerkandl4 still applies today: The positional names are related to the curved dental arch (which can be visualized as stretched out for the purpose of naming). Accordingly, mesial means pointing along the dental arch toward the middle of the arch, while distal points in the posterior direction following the course of the dental arch. Mesial and medial are only identical in the anterior region of the dental arch. The other terms refer to the adjacent soft tissues (see Table 2-1).

Table 2-2Number of roots and root canals of the permanent teeth and their variations

Fig 2-4 Tooth notations for the primary and secondary dentition.

Each individual tooth has a typical form, so its position in the dental arch can usually be clearly identified. The teeth in the right and left halves of the mouth are identically shaped in a mirror image fashion, with a few exceptions.5 Irrespective of the individual tooth form, the teeth generally display a characteristic of mass, which means that the mesial portion of the tooth is more voluminous than the distal part (Fig 2-5). In line with this is the curvature characteristic, which means that the transverse convexity of the mesial half of the crown follows a more curved course than the distal half (see Fig 2-5). In addition, the angle characteristic of the incisors shows that the mesial proximal surface with the incisal margin forms a more acute angle than the distal proximal surface. This characteristic can be identified only from the labial or oral view (see Fig 2-5). The root characteristic indicates that the tooth axis, which is related to the total volume of the tooth, is not vertical to the occlusal surface but follows a distally inclined path, and the root apex bends in the distal direction.1 This distal bend is related to migration of the tooth in a mesial direction: If a tooth is still migrating mesially during the formation of its root apex, the nerves and vessels entering at the apex cannot take part as quickly in this migration. This leads to a distally bent root apex, which is observed particularly in incisors and first molars. However, this does not always occur and is extremely variable in all types of teeth. Another characteristic is the lingual inclination of the dental crowns in the mandible, which is known as the tooth inclination. This mainly involves the molars and premolars. The crown of a canine may have a slight lingual inclination; the crowns of the anterior teeth do not display this characteristic.

Fig 2-5(a) Characteristic of mass using a comparison of the maxillary central incisors and canines in occlusal view. The curvature radius is larger mesially (M) than distally (D), in the sense that the tooth has more mass mesially. (b) Root characteristic and angle characteristic using maxillary left central and lateral incisors in labial view. As a result of the slight distal bend in the root (root characteristic), the tooth axis deviates distally by a few degrees. The angle characteristic can be seen from the incisal margin, which shows a more acute angle to the lateral surface of the tooth mesially (M) than distally (D). (Modified from Schumacher1 with permission.)

Overall, clinical experience shows that the manifestation of the tooth form can be highly variable among individuals; similarly, not all of the characteristics described here are necessarily found in each individual.

The color of the permanent teeth can be different shades of white tending toward yellow, blue, or gray. It is partly determined by the transparency of the enamel, through which the dentin—itself rather yellow—shows. The variable thickness of the enamel and its intrinsic optical properties that cause it to reflect, refract, and absorb light in different ways contribute to the variable shading of the teeth. Tooth color changes with age.6 The enamel becomes more transparent with increasing mineralization,7 and as a result, the yellow dentin shows through more. The dentin itself loses a lot of its red tones and becomes more yellow-gray because the dentinal tubules narrow with age and some completely close up. As a result, the well-perfused pulp shows through less. The pulp cavity itself becomes smaller because of the prolonged deposition of secondary dentin and contributes less to the coloring of the dentin.

Clinical note

Discolorations of the teeth can be caused by chronic caries, exposed cementum (brown), extreme formation of secondary dentin (gray-yellow), nonvital pulp tissue (gray to black), mineralization disorders (white, yellow, brown), fluorosis (yellow-brown), or tetracycline administration (gray, yellow, brown). If oral hygiene is poor, pigment-containing bacteria can stain the teeth a greenish color, among others. As a result of the constant demineralization and remineralization by the saliva and due to the fact that dental enamel is permeable to a limited extent, all kinds of small colored particles can migrate into the enamel. Pigments from tea and red wine become deposited on the enamel. Tobacco smoking understandably stains the teeth because of tar deposits.

Primary teeth

The primary dentition (often referred to as milk teeth or deciduous teeth) comprises five teeth in each quadrant: two incisors (dentes decidui incisivi), one canine (caninus deciduous), and two molar teeth (dentes decidui molares).

The primary dentition is covered in chapter 17, where intraoral images of the primary dentition are also presented (see Figs 17-2 and 17-3).

The primary teeth differ from the permanent teeth in general terms. They are mostly smaller than the teeth that succeed them—with the exception of the primary molars, which are usually larger than the succedaneous premolars. The crowns are less yellowish and more white-bluish as a result of the optical properties of the enamel, which is thinner and less well mineralized.8 This is also why the enamel of primary teeth is worn away more quickly. The cervical enamel margin is raised to form a bulge and does not taper flatly as it does in the permanent teeth. The roots of the primary teeth are shorter, although the incisor and canine roots are longer relative to the crown than in the permanent teeth. The roots of the molars follow a highly divergent course. All the pulp cavities are relatively voluminous (Fig 2-6).

Fig 2-6(a) Shape of the teeth of the primary dentition in the right half of the dentition. (b) Shape of the teeth of the primary dentition in vestibulo-oral cross section through the roots, showing the extent of the pulp (red). (Modified from Schroeder8 with permission.)

Maxillary primary incisors

The maxillary primary incisors have a distinct angle characteristic, the crown is roughly as high as it is wide, and the incisal margin is centered on the volume of the crown. From the distal or mesial view, these teeth have a distinct shovel shape. The labial surface of the crown is very rounded, while the oral surface displays distinctly bulging marginal ridges. The roots are conical and round, and the pulp cavities have a large lumen. The primary lateral incisor is smaller than the central incisor, but its shape is similar. In fact, it can easily be mistaken for the permanent lateral incisor. Its root is shorter than that of the primary central incisor (see Fig 2-6).

Maxillary primary canine

The crown of the maxillary primary canine is almost symmetric in the mesiodistal direction and markedly convex at the neck of the tooth. The mesial edge can be longer and steeper and the distal edge shorter and flatter. The crown is roughly as tall as it is wide and deep, and the palatal surface is indented and has longitudinal and marginal ridges, between which vertical grooves run. The canine has a substantial dental tubercle. The root is triangular in cross section, and the pulp chamber is voluminous.

Maxillary primary first molar

The maxillary primary first molar has an idiosyncratic form. As the smallest primary molar, it is not comparable with any other tooth. It can take on a premolar or molar shape.1,9 Its masticatory surface is trapezoidal, and its mesiodistal fissure is bordered by mesial and distal marginal ridges. The buccal and oral cusps can be divided into main and accessory cusps by a lateral fissure. The mesiobuccal edge of the crown is highly developed and bulges buccally. Buccal and oral surfaces project obliquely, and the cervical convexity is highly developed on both sides. Regarding the three roots, the mesiobuccal is broad, the distobuccal is short, and the palatal is round. All the roots diverge considerably; their apices can be bent forceps-like toward the interradicular space. The pulp chamber and the root canals are relatively broad.

Maxillary primary second molar

The maxillary primary second molar looks like a scaled-down copy of the permanent first molar. It is larger than the primary first molar and has a fissure system that resembles a tilted H. It has four cusps, the largest of which is the mesiopalatal cusp. Palatally, a Carabelli tubercle may be formed here. Its three roots are highly divergent, and its pulp cavity has a large lumen (see Fig 2-6; see also Figs 17-2 and 17-3).

Mandibular primary incisors

The mandibular primary incisors show the angle characteristic like the maxillary primary incisors. The lateral incisor is larger than the central incisor, and they both resemble their two permanent successors. The roots are short and round, and the pulp cavities are large (see Fig 2-6; see also Figs 17-2 and 17-3).

Mandibular primary canine

The mandibular primary canine is smaller and slimmer than that in the maxilla. The crown is asymmetric with a slightly mesially displaced cusp. The oral longitudinal ridge on the lingual surface of the crown is unremarkable. Its root is rather triangular in cross section, and its pulp cavity is large (see Fig 2-6).

Mandibular primary first molar

The mandibular primary first molar has an elongated occlusal surface that is extended in the mesiodistal direction. It can have four or five cusps (usually two buccal and two or three lingual). The mesiobuccal cusp is the largest and most bulbous. The main developmental groove running in the mesiodistal direction has several bends and is bordered mesially and distally by marginal ridges. The vestibular (buccal) surface of the crown projects obliquely and shows a pronounced enamel convexity cervically. The lingual surface, by contrast, runs rather vertically. This primary molar has two roots that sharply diverge. The mesial root is broader and longer than the distal, and both roots may be bent at their apex toward the interradicular space. The pulp cavity has a large lumen (see Fig 2-6; see also Figs 17-2 and 17-3).

Mandibular primary second molar

As in the maxilla, the primary second molar in the mandible resembles the permanent first molar in its form. It is the largest primary molar and has five cusps (three buccal and two lingual). Its buccal surface projects obliquely with a well-developed cervical marginal ridge. Transverse fissures branch off from the mesiodistal central developmental groove in the buccal and oral directions. The crown tapers sharply toward the trunk of the root, from which two wide roots follow a sharply divergent course. The root apices bend toward the interradicular space like curved forceps. The pulp cavity displays well-developed pulp horns and is extremely voluminous. The root canals, by contrast, are relatively narrow (see Fig 2-6; see also Figs 17-2 and 17-3).

Permanent teeth

Permanent teeth replace the primary teeth. A distinction is made between five succedaneous or successional teeth (incisors, canines, and premolars) that replace primary teeth and accessional teeth (first, second, and third molars) that have no primary predecessors. The permanent teeth are also known as the second dentition. Although there are numerous characteristics that are typical of each individual tooth,10 the permanent teeth can be highly variable in terms of their form, size, and individual manifestation of separate traits and features. The distinction between variation in form and anomaly or malformation is fluid and cannot always be clearly ascertained.11,12 The teeth are normally slightly larger in men than in women, but sex cannot always be detected with certainty from the teeth alone.

Many of the morphologic characteristics of the occlusal and incisal enamel surface apply to a lesser and more simplified extent to the relief of the dentin core underlying the enamel crown (see Fig 7-1). The form of the coronal pulp can also be matched to the occlusal relief, so that a pulp horn can be expected under each cusp, at least in young people.

The teeth in the maxilla receive sensory innervation from the maxillary nerve (trigeminal nerve II), which passes through the infraorbital canal as the infraorbital nerve and gives off a superior alveolar nerve to each tooth. These individual nerves branch further several times and together form the dental plexus. The blood supply to the teeth comes from the maxillary artery, which divides into the anterior and posterior alveolar arteries, from which the dental and peridental branches originate. The veins follow the same course as the arteries.

The sensory innervation of the teeth in the mandible comes from the inferior alveolar nerve (trigeminal nerve III), which passes through the inferior alveolar canal in the mandible and branches further to the teeth as the dental plexus.

The arterial supply to the teeth in the mandible comes from the maxillary artery, from which the inferior alveolar artery branches off to the mandible and, like the nerve, continues to pass through the inferior alveolar canal of the mandible, where it gives off dental and peridental branches. The course of the veins matches the arrangement and course of the arteries.

All the nerves and vessels pass through the apical foramen at the apices of the roots into the teeth. Depending on the degree of individual branching of the vessels, a wide variety exists of smaller accessory foramina and accessory canals, which connect the pulp cavities to the periodontal space.

Clinical note

Individual nerve branches can extend across from one half of the face to the other over the midline. This possibility must be borne in mind when performing a nerve block in the anterior region.

Maxillary central incisor

The maxillary central incisor (Fig 2-7a) is often broad and shovel-shaped. Shortly after eruption, the incisal margin has three or four flat protuberances known as mamelons (see Fig 17-3). Between these protuberances, vertically tapering grooves can merge into the labial enamel surface and extend cervically to a varying extent. However, the mamelons are subject to abrasion as the teeth are used and therefore cannot always be found in adults. The angle characteristic is highly developed in most cases. The labial surface is not highly curved close to the incisal margin, where it is usually flat, but it follows a convex course down toward the neck of the tooth.

Fig 2-7 Morphology of maxillary and mandibular teeth. The distal view shows a section in the vestibulo-oral direction. The pulp chamber of the tooth in a young person is shown in light red and is larger than in an adult, which is superimposed in dark red. B, buccal; D, distal; La, labial; Li, lingual; M, mesial; P, palatal. (a) Maxillary right central incisor.

The curvature characteristic is often highly developed. The oral tooth surface is concave and often bears a dental tubercle that may be split or may have three vertical ridges. Mesial and distal marginal ridges are developed to varying degrees. A vertical section through the middle of the tooth often reveals a palatal concavity and a subsequent palatal convexity corresponding to the dental tubercle. Because the tooth has a round contour toward the cervix, the mesial and distal lateral surfaces are almost triangular; however, the palatal contour of the tooth follows a curved course. The root is cone-shaped and often has a prominent root characteristic. In cross section it is round, and mesially and distally it has lateral longitudinal grooves. The juvenile pulp cavity has a pointed shape, and in young people it has three pulp horns corresponding to the mamelons; it is round in cross section. In old age, the pulp cavity shrinks because of dentin growth; it gets thinner and only extends to the level of the labiopalatal cementoenamel junction.

Clinical note

A deep fold of enamel may run through the dental tubercle, which is known as the foramen caecum. It is very susceptible to caries. In rare cases, more deep-lying invaginations may originate from this point through to a dens in dente, where a tooth in miniature form is folded inward.

Maxillary lateral incisor

The maxillary lateral incisor (Fig 2-7b) closely resembles the central incisor, but it is smaller and narrower overall. The crown form can vary considerably. Mamelons are less pronounced on the juvenile incisal margin; two are usually visible. The labial surface is smoother and has fewer depressions than on the central incisor. The oral surface is variably concave, and the dental tubercle is developed to a highly variable degree. In most cases, the angle characteristic is pronounced. The root is slender and compressed in the mesiodistal direction, making it rather oval in cross section, often with a prominent root characteristic. The pulp cavity is smaller than in the central incisor and becomes narrower and shorter with advancing age.

Fig 2-7(b) Maxillary right lateral incisor.

Clinical note

Particularly in the case of the maxillary lateral incisor, extremely narrow crowns may be present, or peg-shaped teeth may exist, which taper off to a point instead of having an incisal margin. The maxillary lateral incisor is frequently affected by complete aplasia (see Table 2-3).

Maxillary canine

The maxillary canine (Fig 2-7c) is the sturdiest tooth in the permanent dentition. Relatively, it has the most consistent form. A typical feature is the cusp tip, from which a longer masticatory edge extends mesially and a shorter one distally, both merging into lateral edges. The mesial lateral edge is longer than the distal, which gives the canine an asymmetric appearance. The result is that the distal contact point with the adjacent premolar lies more cervically than the mesial contact point. The labial surface is convex, more markedly in the mesiodistal than the coronocervical direction, with a well-developed curvature characteristic. On the labial surface, a flat central ridge runs vertically to the cusp tip. The lingual surface is slightly concave, but a sturdy tubercle usually dominates, with a central ridge that runs up to the cusp. A shallow depression lies mesially and distally from here, and further outward substantial marginal ridges run along both sides. The lateral surfaces are roughly triangular and lower distally than mesially. The root is the longest of all the permanent teeth; in cross section it is oval to triangular and shows longitudinal grooves mesially and distally. The root characteristic is often very pronounced. The pulp cavity matches the tooth shape with a cusp; it is slightly compressed mesially and distally and broader at the neck of the tooth. With age, the pulp cavity becomes far shorter and thinner, especially in the root area.

Fig 2-7(c) Maxillary right canine.

Maxillary first premolar

Premolars are bicuspid teeth. The maxillary first premolar (Fig 2-7d) has an oval, almost trapezoidal occlusal surface because the buccal cusp is larger, more voluminous, taller, and more pointed than the palatal cusp, which is nevertheless well developed. The distal lateral surface converges more palatally than the mesial surface does, so that the palatal cusp appears slightly mesially displaced. The occlusal surfaces of the cusps fall away sharply in the palatal direction. The deeply incisive central developmental groove runs between them in the mesiodistal direction. Mesially and distally, the groove forks and is bounded by marginal ridges that connect the cusps mesially and distally in the buccopalatal direction. The buccal surface closely resembles the surface of the canine. The palatal surface is narrower and more curved than the buccal. The proximal surfaces tend to be trapezoidal and slightly concave in terms of outline. The contact point lies fairly close to the marginal ridges. This tooth is single-rooted in roughly half of all cases and double-rooted in 41% of cases, with the buccal root always being the larger of the two. In rare cases, this tooth has three roots. The two main roots are separated by a mesiodistal groove of variable depth. The pulp cavity in adolescents has a large coronal cavity with two pulp horns and two root canals; the buccal canal may again split into two often interconnected mesiodistal canal portions. Even if the premolars appear single-rooted from the outside, a buccal and a palatal canal are often present (80% of cases). They may be joined together toward the apex. With age, the pulp cavity becomes smaller but retains its basic form.

Fig 2-7(d) Maxillary right first premolar.

Maxillary second premolar

The maxillary second premolar (Fig 2-7e) is smaller than the first premolar but has roughly the same form. However, the cusp relief differs because the buccal and palatal cusps are about the same size. The central developmental groove running mesiodistally is shorter. In most cases (91%), the root is undivided and has distinct vertical grooves mesially and even more so distally. The pulp cavity resembles that of the first premolar, and two canals are frequently present. This tooth, like the mandibular second premolar, is more frequently absent compared with the other teeth (see Table 2-3).

Fig 2-7(e) Maxillary right second premolar.

Maxillary first molar

The maxillary first molar (Fig 2-7f) is the largest molar in the dental arch. Viewed from the occlusal, its crown has a rhomboid outline with the longest diameter from mesiobuccal to distopalatal. The occlusal surface has four cusps, the largest being the mesiopalatal cusp. As it engages in the central developmental groove of the mandibular first molar, it is also described as a bearing cusp. The two buccal cusps are smaller and roughly the same size as each other, while the distopalatal cusp is the smallest of all. From the the mesiopalatal cusp, a marginal ridge runs mesially to the mesiobuccal cusp, which mesially borders the occlusal surface. A second marginal ridge runs from the mesiopalatal cusp diagonally over the occlusal surface to the distobuccal cusp. It is referred to as the transverse crest. In gnathology, significance is attached to this crest in securing the occlusal arrangement of the first molar in the maxilla and mandible. As a result of the dominance of this diagonal transverse crest, the distopalatal cusp appears rather separated from the occlusal surface, an impression that is further reinforced by the fissure tapering far onto the palatal surface. As a result of this separating fissure, the diagonal central developmental groove, and the transverse fissure between the two buccal cusps, the overall fissure system looks like a tilted H. The occlusal relief is also bordered distally by a marginal ridge. On its curvature, overhanging far palatally, the mesiopalatal cusp bears another small cusp, the Carabelli tubercle, in about 10% to 40% of cases.13–16 It never extends as far as the occlusal surface, a corresponding underlying dentin cusp may be absent, and in 20% to 50% of cases there is only a hint of a pit.1 The proximal surfaces are convex, while the distal surface is more curved than the mesial. Its crests, which form the contact points, lie roughly in the middle of the masticatory edges.

Fig 2-7(f) Maxillary right first molar.

This tooth normally (90% of cases) has three roots. They originate not directly from the crown but from a root trunk that also can be differentiated based on the size of the tooth. Of the two buccal roots, the mesial is sturdier and wider than the distal and often shows the root characteristic. The palatal root is the longest and most voluminous root and lies opposite the distal root. It is rather flattened and is usually inclined palatally; its root apex, on the other hand, often points into the interradicular space. The pulp cavity is very voluminous and has four pulp horns corresponding to the number of cusps. The coronal cavity lies with its largest volume in the root trunk. The floor of the pulp cavity lies apical to the cementoenamel junction. The root canals vary in width, and the palatal root has the widest and longest canal, in keeping with its size. Although maxillary first molars do not have four roots, they still have four root canals in more than half of cases (53%), where the distal root has two canals. With advancing age and corresponding dentin growth, the pulp cavity becomes smaller but retains its characteristic form.

Maxillary second molar

The maxillary second molar (Fig 2-7g) can have three different crown forms. First, it can appear like a scaled-down copy of the first molar, though without the Carabelli tubercle. Furthermore, the distopalatal cusp is often reduced in size, and the fissure pattern is more variable. Second, a crown form may be present in which the distopalatal cusp is missing and only one large palatal cusp exists. In these cases, the fissure pattern comprises a mesiodistal longitudinal fissure and a buccal transverse fissure, which meet in a central fossa. This crown form is found in about 50% of cases.4 Third, the crown may appear compressed overall from the mesiopalatal to distobuccal direction and have three to five cusps. In terms of the root trunk and the root, the morphology greatly resembles that of the first molar. This also applies to the pulp cavity, which is adapted to the different crown forms.

Fig 2-7(g) Maxillary right second molar.

Maxillary third molar

The maxillary third molar can be very variable in shape or entirely absent, so it cannot be characteristically described at this point. Its manifestations range from fairly typical molars, with all the form characteristics resembling those of the first and second molars, to an apparently random arrangement of cusps, to more simplified and merged shape variations with only one cusp. The roots can also be highly variable and have bizarrely splayed root apices or be simple taproots. The third molars are referred to as wisdom teeth.

Mandibular central incisor

The mandibular central incisor (Fig 2-7h) is a very slender tooth. Its crown is roughly twice as tall as it is wide. The incisal margin, like that of the maxillary central incisor, has three eminences referred to as mamelons (see Fig 17-3). The corners to the mesial and distal lateral surfaces are almost right-angled. The labial surface is only slightly convex, and the lingual surface is a shallow concave shape. Marginal ridges are usually absent or only superficially suggested. However, the base of the crown at the cementoenamel junction is relatively voluminous, which is mainly apparent when viewed from the mesial or distal; the largest dimension of the tooth is at this level in the vestibulo-oral direction. Accordingly, the root has a flat oval shape and is greatly compressed in the mesiodistal direction. It shows pronounced longitudinal grooves, especially distally. Even though this tooth always occurs as a single-rooted tooth, two root canals are formed in more than one-third of cases because of the broad spread of the root in the vestibulo-oral direction. The pulp cavity in young people is correspondingly flat and is widest at the level of the cementoenamel junction. With age, the pulp cavity becomes thinner and in most people retracts out of the coronal area.

Fig 2-7(h) Mandibular right central incisor.

Mandibular lateral incisor

The mandibular lateral incisor (Fig 2-7i) is larger and broader than the mandibular central incisor. Viewed from the labial, its crown looks asymmetric because the distal coronal edge tapers slightly more. This is why the mesial and distal lateral surfaces are not parallel but converge markedly in the apical direction. The root has a flat oval shape and is greatly compressed in the mesiodistal direction. In very rare cases (0.2%), the lateral incisor in the mandible may be double-rooted; the pulp cavity is shaped accordingly and not uncommonly (37% of cases) divides down toward the root into a labial and a lingual canal.

Fig 2-7(i) Mandibular right central incisor.

Mandibular canine

The mandibular canine (