VERTICAL AND HORIZONTAL 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

Figure 4-20.\Curve of Spee.

Figure 4-21.\Curve of Wilson.

Figure 4-22.\Occlusal plane.

(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.

PERMANENT DENTITION

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.