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Chapter 7 • Head

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in clinical (dental) practice, the mesial surface of a tooth is directed toward the median plane of the facial part of the cra- nium. The distal surface is directed away from this plane; both mesial and distal surfaces are contact surfaces —that is, surfaces that contact adjacent teeth. The masticatory surface is the occlusal surface. PARTS AND STRUCTURE OF TEETH A tooth has a crown, neck, and root (Fig. 7.82). The crown projects from the gingiva. The neck is between the crown and root. The root is fixed in the tooth socket by the peri- odontium (connective tissue surrounding roots) ; the number of roots varies. Most of the tooth is composed of dentine (L. dentinium ), which is covered by enamel over the crown

or permanent (secondary), the type of tooth, and its prox- imity to the midline or front of the mouth (e.g., medial and lateral incisors; the 1st molar is anterior to the 2nd). Children have 20 deciduous teeth; adults normally have 32 permanent teeth (Fig. 7.80A & C). The usual ages of the eruption (“cutting”) of these teeth are demonstrated in Figure 7.81 and listed in Table 7.13. Before eruption, the developing teeth reside in the alveolar arches as tooth buds (Fig. 7.80B). The types of teeth are identified by their characteristics: incisors, thin cutting edges; canines, single prominent cones; premolars (bicuspids), two cusps; and molars, three or more cusps (Fig. 7.80A & C). The vestibular surface (labial or buccal) of each tooth is directed outwardly, and the lingual surface is directed inwardly (Fig. 7.79B). As used

Maxillary alveolar process

PM

*

I

I

C

PM M1

M3

M2 M1 PM PM

I

C

I

M3

I

I

C

PM

M2

PM PM M1

PM

M2 M1

M3

M1 PM PMCI I

M2

M3

PM PM M1

Mandibular alveolar process

(A) Right anterolateral view

(B) Left anterolateral view

M3 M2 M1 PM PM C I I M3 M2 M1 PM PM C I I 1 2 3 4 5 6 7 8

16

9 10 11 12 13 14 15

18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

(C) Panoramic view

FIGURE 7.80. Secondary dentition. A. The teeth are shown in occlusion. There is a supernumerary midline tooth (mesiodens) in this specimen (*). B. Maxillary and mandibular jaws of a child acquiring secondary dentition are shown. The alveolar processes are carved to reveal the roots of the teeth and tooth buds. C. A pantomographic radiograph of an adult mandible and maxilla is shown. The left lower 3rd molar is not present. I, incisor; C, canine; PM, premolar; M1, M2, and M3, 1st, 2nd, and 3rd molars. (Part C courtesy of M. J. Pharoah, Associate Professor of Dental Radiology, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.)

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11/15/2012 8:27:53 PM