The Permanent Maxillary Molars (Dental Anatomy, Physiology and Occlusion) Part 4

Detailed Description of the Maxillary Second Molar From All Aspects

Buccal Aspect

From the buccal aspect the crown is a little shorter cervico-occlusally and narrower mesiodistally than is the maxillary first molar (see Figures 11-19 and 11-24). The distobuccal cusp is smaller and allows part of the distal marginal ridge and part of the distolingual cusp to be seen.

The buccal roots are about the same length. These roots are more nearly parallel and inclined distally more than those of the maxillary first molar, so that the end of the distobuccal root is slightly distal to the distal extremity of the crown. The apex of the mesiobuccal root is on a line with the buccal groove of the crown instead of the tip of the mesiobuccal cusp, as was found on the first molar.

Maxillary second molar, mesial aspect. Ten typical specimens are shown.

Figure 11-25 Maxillary second molar, mesial aspect. Ten typical specimens are shown.

Maxillary second molar, occlusal aspect. Ten typical specimens are shown.


Figure 11-26 Maxillary second molar, occlusal aspect. Ten typical specimens are shown.

Lingual Aspect

Ways in which the second molar differs from the first molar to be noted here, in addition to those mentioned earlier, are the following:

1. The distolingual cusp of the crown is smaller.

2. The distobuccal cusp may be seen through the sulcus between the mesiolingual and distolingual cusp.

3. No fifth cusp is evident.

4. The apex of the lingual root is in line with the distolingual cusp tip instead of the lingual groove as was found on the first molar (see Figure 11-20).

Maxillary second molar. Ten specimens with uncommon variations are shown. 1, Roots spread similar to those of first molar. 2, Bifurcated mesiobuccal root. 3, Roots very short and fused. 4, Mesiobuccal and lingual roots with complete fusion. 5, Crown similar to the typical third molar form. 6, Short roots with spread similar to that of first molar. 7, Roots extra long with abnormal curvatures. 8, Another variation similar to specimen 7. 9, Very long roots fused. 10, Crown with extreme rhomboidal form.

FIGURE 11-27 Maxillary second molar. Ten specimens with uncommon variations are shown. 1, Roots spread similar to those of first molar. 2, Bifurcated mesiobuccal root. 3, Roots very short and fused. 4, Mesiobuccal and lingual roots with complete fusion. 5, Crown similar to the typical third molar form. 6, Short roots with spread similar to that of first molar. 7, Roots extra long with abnormal curvatures. 8, Another variation similar to specimen 7. 9, Very long roots fused. 10, Crown with extreme rhomboidal form.

Mesial Aspect

The buccolingual dimension of the second molar is about the same as that of the first molar, but the crown length is less (see Figures 11-21 and 11-25). The roots do not spread as far buccolingually but are within the confines of the buc-colingual crown outline.

Distal Aspect

Because the distobuccal cusp is smaller in the maxillary second molar than in the first molar, more of the mesiobuccal cusp may be seen from this angle (see Figure 11-22). The mesiolingual cusp cannot be seen. The apex of the lingual root is in line with the distolingual cusp.

Occlusal Aspect

The rhomboidal type of second maxillary molar is most common, although in comparison with the first molar, the acute angles of the rhomboid are less and the obtuse angles greater (see Figures 11-23 and 11-26). The buccolingual diameter of the crown is about equal, but the mesiodistal diameter is approximately 1 mm less. The mesiobuccal and mesiolingual cusps are just as large and well developed as in the first molar, but the distobuccal and distolingual cusps are smaller and less well developed. Usually, a calibration made of the crown at the greatest diameter buccally and lingually of the distal portion is considerably less than one made at the greatest diameter buccally and lingually of the mesial portion, so that more convergence distally is seen than in the maxillary first molar.

It is not uncommon to find more supplemental grooves, accidental grooves, and pits on the occlusal surface of a maxillary second molar than are usually found on that of a maxillary first molar.


Maxillary Third Molar

Figures 11-28 through 11-36 illustrate the maxillary third molar from all aspects. The maxillary third molar often appears as a developmental anomaly. It can vary considerably in size, contour, and relative position to the other teeth (Table 11-3). It is seldom as well developed as the maxillary second molar, to which it often bears resemblance. The third molar supplements the second molar in function, and its fundamental design is similar. The crown is smaller, and the roots are shorter as a rule, with the inclination toward fusion with the resultant anchorage of one tapered root.

The predominating third molar design, when the occlusal surface is viewed, is that of a heart-shaped type of second molar. The distolingual cusp is very small and poorly developed in most cases, and it may be absent entirely.

All third molars, mandibular and maxillary, show more variation in development than any of the other teeth in the mouth. Occasionally they appear as anomalies bearing little or no resemblance to neighboring teeth. A few of the variations in form are shown in Figure 11-36.

Maxillary right third molar, buccal aspect. (Grid = 1 sq mm.)

Figure 11-28 Maxillary right third molar, buccal aspect. (Grid = 1 sq mm.)

Maxillary right third molar, lingual aspect. (Grid = 1 sq mm.)

Figure 11-29 Maxillary right third molar, lingual aspect. (Grid = 1 sq mm.)

Maxillary right third molar, mesial aspect. (Grid = 1 sq mm.)

Figure 11-30 Maxillary right third molar, mesial aspect. (Grid = 1 sq mm.)

It is necessary to give a short description of the third molar that is considered average in its development and one that would be in good proportion to the other maxillary molars and with an occlusal form considered normal. In describing the normal maxillary third molar, direct comparisons will be made with the maxillary second molar.

Maxillary right third molar, distal aspect. (Grid = 1 sq mm.)

Figure 11-31 Maxillary right third molar, distal aspect. (Grid = 1 sq mm.)

Maxillary right third molar, occlusal aspect. (Grid = 1 sq mm.)

Figure 11-32 Maxillary right third molar, occlusal aspect. (Grid = 1 sq mm.)

Detailed Description of the Maxillary Third Molar From All Aspects

Buccal Aspect

From the buccal aspect, the crown of the third molar is shorter cervico-occlusally and narrower mesiodistally than that of the second molar (see Figures 11-28 and 11-33). The roots are usually fused, functioning as one large root, and they are shorter cervicoapically. The fused roots end in a taper at the apex. The roots have a distinct slant to the distal, giving the apices of the fused root a more distal relation to the center of the crown.

Lingual Aspect

In addition to the differences just mentioned, in comparison with the maxillary second molar, only one large lingual cusp is present, and therefore no lingual groove is evident (see Figure 11-29). However, in many cases, a third molar with the same essential features has a poorly developed distolin-gual cusp with a developmental groove lingually (see Figure 11-35, 2).

Mesial Aspect

From the mesial aspect, aside from the differences in measurement, the main feature is the taper to the fused roots and a bifurcation, usually in the region of the apical third. Figure 11-30 does not show a bifurcation. See Figure 11-34, 1, 2, and 3. The root portion is considerably shorter in relation to the crown length. Both the crown and the root portions tend to be poorly developed, with irregular outlines.

Maxillary third molar, buccal aspect. Ten typical specimens are shown.

Figure 11-33 Maxillary third molar, buccal aspect. Ten typical specimens are shown.

Maxillary third molar, mesial aspect. Ten typical specimens are shown.

Figure 11-34 Maxillary third molar, mesial aspect. Ten typical specimens are shown.

Distal Aspect

From the distal aspect, most of the buccal surface of the crown is in view (see Figure 11-31). More of the occlusal surface may be seen than can be seen on the second molar from this aspect because of the more acute angulation of the occlusal surface in relation to the long axis of the root. The measurement from the cervical line to the marginal ridge is short.

Occlusal Aspect

The occlusal aspect of a typical maxillary third molar presents a heart-shaped outline (see Figures 11-32 and 11-35).

Maxillary third molar, occlusal aspect. Ten typical specimens are shown.

Figure 11-35 Maxillary third molar, occlusal aspect. Ten typical specimens are shown.

 Maxillary third molar. Twelve specimens with uncommon variations are shown. 1, Very short fused root form. 2, Extremely long roots with extreme distal angulation. 3, Complete fusion of roots with extreme distal angulation. 4, Three roots well separated; crown very wide at cervix. 5, Extreme rhomboidal outline to crown, with developmental grooves oddly placed. 6, Overdeveloped mesiobuccal cusp. 7, Crown wide at cervix, with roots perpendicular. 8, Very large crown; poorly developed root form. 9, Complete absence of typical design. 10, Specimen abnormally large, with four roots well separated. 11, Five well-developed cusps, atypical in form. 12, Small specimen, atypical cusp form.

Figure 11-36 Maxillary third molar. Twelve specimens with uncommon variations are shown. 1, Very short fused root form. 2, Extremely long roots with extreme distal angulation. 3, Complete fusion of roots with extreme distal angulation. 4, Three roots well separated; crown very wide at cervix. 5, Extreme rhomboidal outline to crown, with developmental grooves oddly placed. 6, Overdeveloped mesiobuccal cusp. 7, Crown wide at cervix, with roots perpendicular. 8, Very large crown; poorly developed root form. 9, Complete absence of typical design. 10, Specimen abnormally large, with four roots well separated. 11, Five well-developed cusps, atypical in form. 12, Small specimen, atypical cusp form.

The lingual cusp is large and well developed, and little or no distolingual cusp is evident, which gives a semicircular outline to the tooth from one contact area to the other. Three functioning cusps are seen on this type of tooth: two buccal and one lingual.

The occlusal aspect of this tooth usually presents many supplemental grooves and many accidental grooves unless the tooth is very much worn.

The third molar may show four distinct cusps. This type may have a strong oblique ridge, a central fossa and a distal fossa, with a lingual developmental groove similar to that of the rhomboidal type of second molar. In most instances, the crown converges more lingually from the buccal areas than in the second molar, losing its rhomboidal outline. This is not always true, however (compare 1 and 3 in Figure 11-35). 

Table 11-3 Maxillary Third Molar

First evidence of calcification

7-9 yr

Enamel completed

12-16 yr

Eruption

17-21 yr

Root completed

18-25 yr

Measurement Table

Cervico-occlusal Length of Crown

Length of Root

Mesiodistal Mesiodistal Diameter of Diameter Crown at of Crown Cervix

Labio- or Buccolingual Diameter of Crown

Labio- or Buccolingual Diameter of Crown at Cervix

Curvature of Cervical Line—Mesial

Curvature of Cervical Line—Distal

Dimensions* suggested for carving technique

6.5

11.0

8.5 6.5

10.0

9.5

1.0

0.0

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