Maxillary Second Premolar
Figures 9-17 through 9-25 illustrate the maxillary second premolar from all aspects. The maxillary second premolar supplements the maxillary first premolar in function. The two teeth resemble each other so closely that only a brief description of each aspect of the second premolar is necessary. Direct comparison is made between it and the first premolar, and variations are mentioned.
FIGURE 9-17 Maxillary left second premolar, buccal aspect. (Grid = 1 sq mm.)
FIGURE 9-18 Maxillary left second premolar, lingual aspect. (Grid = 1 sq mm.)
FIGURE 9-19 Maxillary left second premolar, mesial aspect. (Grid = 1 sq mm.)
The maxillary second premolar is less angular, giving a more rounded effect to the crown from all aspects. It has a single root.
Considerable variations in the relative sizes of the two teeth may be seen, because the second premolar does not appear true to form as often as does the first premolar (Table 9-2). The maxillary second premolar may have a crown that is noticeably smaller cervico-occlusally and also mesiodistally; however, it may also be larger in those dimensions. Usually the root of the second premolar is as long as, if not a millimeter or so longer than, that of the first premolar. The two teeth have about the same dimensions on the average, except for the tendency toward greater length of the second premolar root. Ten specimens with uncommon variations are shown in Figure 9-25.
DETAILED DESCRIPTION OF THE MAXILLARY SECOND PREMOLAR FROM ALL ASPECTS
From the buccal aspect, it may be noticed that the buccal cusp of the second premolar is not as long as that of the first premolar and it appears less pointed (see Figure 9-17). Also,the mesial slope of the buccal cusp ridge is usually shorter than the distal slope. The opposite is true of the first premolar.
FIGURE 9-20 Maxillary left second premolar, distal aspect. (Grid = 1 sq mm.)
FIGURE 9-21 Maxillary left second premolar, occlusal aspect. (Grid = 1 sq mm.)
Figure 9-22 Maxillary second premolar, buccal aspect. Ten typical specimens are shown.
Table 9-2 Maxillary Second Premolar
FIGURE 9-23 Maxillary second premolar, mesial aspect. Ten typical specimens are shown.
In many instances, the crown and root of the second premolar are thicker at their cervical portions. This is not the rule, however (see Figure 9-22, 5, 6, 7, and 9). The buccal ridge of the crown may not be as prominent as that of the first premolar.
From the lingual aspect, little variation may be seen except that the lingual cusp is longer, which makes the crown longer on the lingual side (see Figure 9-18).
The mesial aspect shows the difference in cusp length between the first and second premolars (see Figures 9-4 and 9-19). The cusps of the second premolar are shorter, with the buccal and lingual cusps more nearly the same length. Greater distance between cusp tips widens the occlusal surface buccolingually.
No developmental depression is evident on the mesial surface of the crown as on the first premolar; the crown surface is convex instead. A shallow developmental groove appears on the single tapered root.
No deep developmental groove crossing the mesial marginal ridge is evident, and except for the variation in root form, no outstanding variation is noted when viewed from the distal aspect.
The distal root depression is deeper than the mesial depression on the maxillary second premolar. This characteristic of the distal root surface is the opposite of that of the maxillary first premolar, in which the depression is on the mesial surface of the root. A knowledge of where these depressions are facilitates periodontal instrumentation, that is, scaling and root planing.
Figure 9-24 Maxillary second premolar, occlusal aspect. Ten typical specimens are shown.
Figure 9-25 Maxillary second premolar. Ten specimens with uncommon variations are shown. 1, Root dwarfed and malformed. 2, Broad occlusal surface; lingual outline of crown straight. 3, Malformed root. 4, Crown very broad mesiodistally; root dwarfed. 5, Root extremely long. 6, Root dwarfed and very pointed at apex. 7, Root extremely long; bifurcation at root end. 8, Crown wider than usual buccolingually, curvature at cervical third extreme. 9, Root malformed, thick at apical third. 10, Root unusually long, bifurcated at apical third.
From the occlusal aspect, some differences are to be noted between the two premolars. On the second premolar, the outline of the crown is more rounded or oval, rather than angular (see Figures 9-21 and 9-24). There are, of course, exceptions. The central developmental groove is shorter and more irregular, and there is a tendency toward multiple supplementary grooves radiating from the central groove. These supplementary grooves terminate in shallow depressions in the enamel that may extend out to the cusp ridges.
This arrangement makes for an irregular occlusal surface and gives the surface a very wrinkled appearance.