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Figure 4-23.—Vertical and horizontal overlap |
(fig. 4-20) in which the mandibular arch forms a
concave (a bowl-like upward curve). The lateral curve
is called the Curve of Wilson (fig. 4-21). The
composite (combination) of these curves form a line
called the occlusal plane, and is created by the contact
of the upper and lower teeth as shown in figure 4-22.
V E R T I C A L A N D H O R I Z O N T A L
OVERLAP.—Vertical overlap is the extension of the
maxillary teeth over the mandibular counterparts in a
vertical direction when the dentition is in centric
occlusion (fig. 4-23). Horizontal overlap is the
projection of maxillary teeth over antagonists
(something that opposes another) in a horizontal
direction.
ANGLES CLASSIFICATION.—Angle was a
dentist who developed a classification of normal and
abnormal ways teeth meet into centric occlusion.
Angle came up with three classes, Class I, II and III, as
illustrated by figure 4-24.
Class I—patient’s profile is characterized as
normal.
Class II—patient’s profile is deficient in chin
length and characterized as a retruded
(retrognathic) profile.
Class III—patient’s profile is excessive in chin
length and characterized as protruded
(prognathic) profile.
KEY TO OCCLUSION.—The occlusal surfaces
of opposing teeth bear a definite relationship to each
other (fig. 4-25). In normal jaw relations and when
teeth are of normal size and in the correct position, the
mesiofacial cusp of the maxillary first molar occludes
in the facial groove of the mandibular first molar. This
normal relationship (fig. 4-26) of these two teeth is
called the key to occlusion.
Figure 4-20.—Curve of Spee.
PERMANENT DENTITION
Figure 4-21.—Curve of Wilson.
Figure 4-22.—Occlusal plane.
The permanent dentition consists of 32 teeth. Each
tooth in the permanent dentition is described in this
section. It should be remembered that teeth show
considerable variation in size, shape, and other
characteristics from one person to another. Certain
teeth show a greater tendency than others to deviate
from the normal. The descriptions that follow are of
normal teeth.
MAXILLARY CENTRAL
INCISORS
The maxillary central incisor (tooth #8 or #9) is
illustrated in figures 4-27 and 4-28. Viewed mesially
or distally, a maxillary central incisor looks like a
wedge, with the point of the wedge at the incisal
(cutting) edge of the tooth.
Facial Surface-The facial surface resembles a
thumbnail in outline.
The mesial margin is nearly
straight and meets the incisal edge at almost a 90°
angle, but the distal margin meets the incisal edge in a
curve. The incisal edge is straight, but the cervical
margin is curved like a half moon. Two developmental
grooves are on the facial surface.
4-14
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