658
UNIT FIVE
teeth are anchored in each jaw from the midline toward the
sides in the following sequence: central incisor, lateral inci-
sor, canine (cuspid), F
rst molar, and second molar.
The primary teeth are usually shed in the same order they
erupted, after their roots are resorbed. Then, the
secondary
(permanent)
teeth
push the primary teeth out of their sock-
ets. This secondary set consists of thirty-two teeth—sixteen in
each jaw—and they are arranged from the midline as follows:
central incisor, lateral incisor, canine (cuspid), F
rst premolar
(bicuspid), second premolar (bicuspid), F
rst molar, second
molar, and third molar
(f g. 17.9)
.
Table 17.2
summarizes
the types and numbers of primary and secondary teeth.
The secondary teeth usually begin to erupt at six years,
but the set may not be completed until the third molars
emerge between seventeen and twenty-F
ve years. Sometimes
these third molars, also called wisdom teeth, become wedged
in abnormal positions in the jaws and fail to erupt. Such
impacted
wisdom teeth must be removed to alleviate pain.
The teeth break food into smaller pieces, which begins
mechanical digestion. Chewing increases the surface area
PRACTICE
6
What are the functions of the mouth?
7
How does the tongue function as part of the digestive system?
8
What is the role of the soft palate in swallowing?
9
Where are the tonsils located?
Teeth
The
teeth
are the hardest structures in the body. They are
not considered part of the skeletal system because they have
at least two types of proteins that are not also found in bone,
and their structure is different.
Teeth develop in sockets in the alveolar processes of the
mandibular and maxillary bones. Teeth are unique structures
in that two sets form during development
(f
g. 17.8)
. The
F
rst set, the
primary teeth
(deciduous teeth), usually erupt
through the gums (gingiva) at regular intervals between the
ages of six months and two to four years. The ten primary
Frontal sinus
Nasal cavity
Hard palate
Vestibule
Tongue
Hyoid bone
Trachea
Esophagus
Laryngopharynx
Epiglottis
Lingual tonsil
Oropharynx
Palatine tonsil
Uvula
Oral cavity
Nasopharynx
Soft palate
Opening of auditory tube
Pharyngeal tonsil
Sphenoidal sinus
Lip
Tooth
Larynx
FIGURE 17.7
Sagittal section of the mouth, nasal cavity, and pharynx.
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