(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.
- 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.
Figure 4-20. - Curve of Spee.
Figure 4-21. - Curve of Wilson.
Figure 4-22. - Occlusal plane.
- 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.
- 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.
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.
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