Chapter 7
•
Head
932
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
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
(C) Panoramic view
(A) Right anterolateral view
(B) Left anterolateral view
PM
PM M1
M3
I
I
C
PM PM M1
M2
M2
M1
PM PMCI I
PM PM M1
M3
M3 M2 M1 PM PM C I
I
M3 M2 M1 PM PM C I I
M3
M2 M1 PM PM
PM
PM
M3
M2 M1
C
C
I
I
I
I
*
Maxillary alveolar process
Mandibular alveolar process
1 2 3 4 5 6 7 8
9 10
11 12 13 14 15
16
18
19 20 21 22
23
24 25 26 27 28 29 30 31 32
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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