e. Occlusal Surface. The occlusal surface is characterized by the presence of
a fifth cusp called the distal cusp. This cusp is smaller than the other cusps. It forms
part of the masticating surface of the tooth. The presence of this cusp is accompanied
by the presence of additional developmental grooves. Three grooves--facial, distofacial,
and lingual--have been mentioned in descriptions of the facial and lingual surfaces.
Other grooves are a central groove and mesial and distal developmental grooves. The
mesial developmental groove runs from the central fossa over the mesial marginal
ridge. The distal developmental groove runs from the central fossa over the distal
f. Roots. The roots are divided into a mesial and a distal root. The bifurcation
is located closer to the crown than the bifurcation of any of the other teeth. Both roots
are wide faciolingually and narrow mesiodistally. The mesial root is larger than the distal
root. The mesial root commonly has a distal inclination in its apical portion. The distal
root may have a similar curvature but usually is straight.
4-24. MANDIBULAR SECOND MOLAR
The mandibular second molar (figure 4-34) is smaller than the mandibular first
molar but is similar in general appearance. Cusps are usually four in number, but
occasionally there are five. They are arranged similarly to those of the mandibular first
molar. Because of the age at which they erupt, they are sometimes called the "twelve-
Figure 4-34. Mandibular right second molar.