Buccal Aspect

The crown is roughly trapezoidal, with cervical and occlusal outlines representing the uneven sides (see Figures 11-4, 11-13, 11-14, and 11-15). The cervical line is the shorter of the uneven sides (see Figure 4-16, D).

Figure 11-4 Maxillary right first molar, buccal aspect. (Grid = 1 sq mm.)

Figure 11-5 Maxillary right first molar, lingual aspect. DBR, Distobuccal root; LR, lingual root; CL, cervical line; LDG, lingual developmental groove; DLC, distolingual cusp; MLC, mesiolingual cusp; FC, fifth cusp; MBR, mesiobuccal root.

Figure 11-6 Maxillary right first molar, lingual aspect. (Grid = 1 sq mm.)

When the buccal aspect of this tooth is viewed with the line of vision at right angles to the buccal developmental groove of the crown, the distal side of the crown can be seen in perspective, which is possible because of the obtuse character of the distobuccal line angle (see Occlusal Aspect later in this chapter). Parts of four cusps are seen, the mesiobuccal, distobuccal, mesiolingual, and distolingual.

The mesiobuccal cusp is broader than the distobuccal cusp, and its mesial slope meets its distal slope at an obtuse angle. The mesial slope of the distobuccal cusp meets its distal slope at approximately a right angle. The distobuccal cusp is therefore sharper than the mesiobuccal cusp, and it is at least as long and often longer (see Figure 11-15, 4, 6, 7, 8, and 9).

Figure 11-7 Maxillary right first molar, mesial aspect. (Grid = 1 sq mm.)

Figure 11-8 Maxillary right first molar, mesial aspect. LR, Lingual root; FC, fifth cusp; MLC, mesiolingual cusp; MMR, mesial marginal ridge; MBC, mesiobuccal ridge; MCA, mesial contact area; CR, cervical ridge; MBR, mesiobuccal root.

Figure 11-9 Maxillary right first molar, distal aspect. DBR, Distobuccal root; MBR, mesiobuccal root; BDG, buccal developmental groove; DBC, distobuccal cusp; DMR, distal marginal ridge; DLC, distolingual cusp; DCA, distal contact area; CL, cervical line; LR, lingual root.

The buccal developmental groove that divides the two buccal cusps is approximately equidistant between the mesiobuccal and distolingual line angles. The groove slants occlusoapically in a line of direction parallel to the long axis of the distobuccal root. It terminates at a point approximately half the distance from its origin occlusally to the cervical line of the crown. Although the groove is not deep at any point, it becomes more shallow toward its termination, gradually fading out. Lateral to its terminus is a dip in the enamel of the crown that is developmental in character and extends for some distance mesially and distally.

The cervical line of the crown does not have much curvature from mesial to distal; however, it is not as smooth and regular as that found on some of the other teeth. The line is generally convex with the convexity toward the roots.

The mesial outline of the crown from this aspect follows a nearly straight path downward and mesially, curving occlusally as it reaches the crest of contour of the mesial surface, which is the contact area. This crest is approximately two thirds the distance from cervical line to tip of mesiobuccal cusp. The mesial outline continues downward and distally and becomes congruent with the outline of the mesial slope of the mesiobuccal cusp.

The distal outline of the crown is convex; the distal surface is spheroidal. The crest of curvature on the distal side of the crown is located at a level approximately half the distance from cervical line to tip of cusp. The distal contact area is in the middle of the middle third.

Often from this aspect, a flattened area or a concave area is seen on the distal surface immediately above the distobuccal cusp at the cervical third of the crown.

All three of the roots may be seen from the buccal aspect. The axes of the roots are inclined distally. The roots are not straight, although the buccal roots show an inclination to curvature halfway between the point of bifurcation and the apices. The mesiobuccal root curves distally, starting at the middle third. Its axis usually is at right angles to the cervical line. The distal root is straighter, with its long axis at an acute angle distally with the cervical line. It has a tendency toward curvature mesially at its middle third.

The point of bifurcation of the two buccal roots is located approximately 4 mm above the cervical line. This measurement varies somewhat, of course. Nevertheless, the point is much farther removed from the cervical line than in the deciduous molars. This relation is typical when all permanent molars are compared with all deciduous molars.

A deep developmental groove buccally on the root trunk of the maxillary first molar, which starts at the bifurcation and progresses downward, becoming more shallow until it terminates in a shallow depression at the cervical line. Sometimes this depression extends slightly onto the enamel at the cervix.

The reader must keep in mind the fact that molar roots originate as a single root on the base of the crown. They then are divided into three roots, as in the maxillary molars, or two roots, as in the mandibular molars. The common root base is called the root trunk (see Figures 11-3 and 11-8).

In judging the length of the roots and the direction of their axes, we must indicate the part of the root trunk that is congruent with each root as part of it, because they [i.e., the root trunk and the root] function as an entity. Usually, the lingual root is the longest, and the two buccal roots are approximately equal in length. Considerable variance is evident, although the difference is a matter of a millimeter or so only in the average first molars with normal development.

From the buccal aspect, a measurement of the roots inclusively at their greatest extremities mesiodistally is less than a calibration of the diameter of the crown mesiodistally.

No invariable rule covers the relative length of crown and root when the upper first molar is described. On the average, the roots are about twice as long as the crown.

Lingual Aspect

From the lingual aspect, the gross outline of the maxillary first molar is the reverse of that from the buccal aspect (see Figures 11-5, 11-6, 11-13, and 11-14). Photographs or drawings show this only approximately, because all teeth have breadth and thickness; consequently, the perspective of two dimensions plus the human element, which enters into the technique of posing specimens and making drawings and photographs, are bound to result in some error in graphic interpretation.

Figure 11-10 Maxillary right first molar, distal aspect. (Grid = 1 sq mm.)

Figure 11-11 Maxillary molar primary cusp triangle. The distolingual lobe, represented by shaded areas, becomes progressively smaller on maxillary molars, starting with the first molar, which presents the greatest development of the lobe. The plain areas, roughly triangular in outline, represent the maxillary molar primary cusp triangles.

Figure 11-12 Maxillary right first molar, occlusal aspect. (Grid = 1 sq mm.)

The variation between the outline of the mesial surface and that of the distal surface is apparent. Because of the roundness of the distolingual cusp, the smooth curvature of the distal outline of the crown becoming confluent with the curvature of the cusp creates an arc that is almost a semicircle. The line that describes the lingual developmental groove is also confluent with the outline of the distolingual cusp, progressing mesially and cervically and ending at a point at the approximate center of the lingual surface of the crown. A shallow depression in the surface extends from the terminus of the lingual groove to the center of the lingual surface of the lingual root at the cervical line and then continues in an apical direction on the lingual root, fading out at the middle third of the root.

The lingual cusps are the only ones to be seen from the lingual aspect. The mesiolingual cusp is much larger, and before occlusal wear, it is always the longest cusp the tooth possesses. Its mesiodistal width is about three fifths of the mesiodistal crown diameter, with the distolingual cusp making up the remaining two fifths. The angle formed by the mesial outline of the crown and the mesial slope of the mesiolingual cusp is almost 90 degrees. An obtuse angle describes the junction of the mesial and distal slopes of this cusp.

The distolingual cusp is so spheroidal and smooth that it is difficult to describe any angulation on the mesial and distal slopes.

The lingual developmental groove starts approximately in the center of the lingual surface mesiodistally, curves sharply to the distal as it crosses between the cusps, and continues on to the occlusal surface.

The fifth cusp appears attached to the mesiolingual surface of the mesiolingual cusp. It is outlined occlusally by an irregular developmental groove, which may be des/>