Maintenance of the Body
Similarly, the permanent dentition [two incisors, one canine,
two premolars (PM), and three molars] is
Each tooth has two major regions: the crown and the root
. Te enamel-covered
is the exposed part
of the tooth above the
, which sur-
rounds the tooth like a tight collar.
, a brittle ceramic-
like material thick as a dime, directly bears the force of chewing.
Te hardest substance in the body, it is heavily mineralized with
calcium salts, and its densely packed hydroxyapatite (mineral)
crystals are oriented in force-resisting columns perpendicular
to the tooth’s surface. Te cells that produce enamel degenerate
when the tooth erupts; consequently, decayed or cracked areas
of enamel will not heal and must be artiﬁcially ﬁlled.
is the portion of the tooth embedded in the jaw-
bone. Canine teeth, incisors, and premolars have one root,
although the ﬁrst upper premolars commonly have two. Te
ﬁrst two upper molars have three roots, while the correspond-
pieces of food. Te conical or fanglike
(cuspids or eye-
teeth) tear and pierce. Te
have broad crowns with rounded cusps (tips) best suited for
grinding or crushing. Te molars, with four or ﬁve cusps, are
the best grinders. During chewing, the upper and lower molars
repeatedly lock together, an action that generates tremendous
is a shorthand way of indicating the
numbers and relative positions of the diﬀerent types of teeth.
Tis formula is written as a ratio, uppers over lowers, for
of the mouth. Since the other side is a mirror image, we
obtain total dentition by multiplying the dental formula by 2.
Te primary dentition consists of two incisors (I), one canine
(C), and two molars (M) on each side of each jaw, and its dental
formula is written as
Central (6–8 mo)
Central (7 yr)
First molar (6–7 yr)
Lateral (8–10 mo)
Lateral (8 yr)
(about 2 yr)
Teeth of the lower jaw: the
deciduous and permanent sets. Approximate age at which tooth
erupts is shown in parentheses. The shapes of individual teeth are
shown on the right.
2I, 1C, 2M (upper jaw)
2I, 1C, 2M (lower jaw)
2I, 1C, 2PM, 3M
2I, 1C, 2PM, 3M
Longitudinal section of a canine tooth within
its bony socket (alveolus).