10 The Permanent Mandibular Premolars
The mandibular premolars number four: two are situated in the right side of the mandible and two in the left side. They are immediately posterior to the mandibular canines and anterior to the molars.
The first premolar has a large buccal cusp, which is long and well formed, with a small, nonfunctioning lingual cusp that in some specimens is no longer than the cingulum found on some maxillary canines (see Figure 10-10, 3 and 8; and Figure 10-12, 4 and 7). The second premolar has three well-formed cusps in most cases, one large buccal cusp and two smaller lingual cusps. The form of both mandibular premolars fails to conform to the implications of the term bicuspid, a term that implies two functioning cusps.
Mandibular First Premolar
Figures 10-1 through 10-12 illustrate the mandibular first premolar from all aspects. The mandibular first premolar is the fourth tooth from the median line and the first posterior tooth in the mandible. This tooth is situated between the canine and second premolar and has some characteristics common to each of them.

Figure 10-1 Mandibular right first premolar, mesial and occlusal aspects. BC, Buccal cusp; BTR, buccal triangular ridge; LC, lingual cusp; MLDG, mesiolingual developmental groove; CL, cervical line; BCR, buccal cervical ridge; MCA, mesial contact area; MMR, mesial marginal ridge; DBCR, distobuccal cusp ridge; DMR, distal marginal ridge; CDG, central developmental groove; MBCR, mesiobuccal cusp ridge.

Figure 10-2 Mandibular right first premolar, buccal aspect. The specimen in this photograph shows a mesial inclination of the root. Mandibular premolars and canines have this tendency, although most of the roots of these teeth will curve, if at all, in a distal direction. (Grid = 1 sq mm.)

Figure 10-7 Mandibular right first premolar. Graph outlines of five aspects are shown. (Grid = 1 sq mm.)

Figure 10-12 Mandibular first premolar. Ten specimens with uncommon variations are shown. 1, Crown oversized. 2, Crown and root diminutive. 3, Mesial and distal sides of crown straight; cervix wide mesiodistally; root extra long. 4, Unusual formation of lingual portion of crown; root with deep developmental groove mesially. 5, Bifurcated root. 6, Lingual cusp long; little lingual curvature; root of extra length. 7, No lingual cusp; root bifurcated. 8, Dwarfed root. 9, Crown poorly formed; root unusually long. 10, Very long curved root for crown so small.
The characteristics that resemble those of the mandibular canine are as follows:
The characteristics that resemble those of the second mandibular premolar are as follows:
Although the root of the mandibular first premolar is shorter generally than that of the mandibular second premolar, it is closer to the length of the second premolar root than it is to that of the mandibular canine (Table 10-1).
DETAILED DESCRIPTION OF THE MANDIBULAR FIRST PREMOLAR FROM ALL ASPECTS
Buccal Aspect
From the buccal aspect, the form of the mandibular first premolar crown is nearly symmetrical bilaterally (see Figures 10-2, 10-7, 10-8, and 10-9). The middle buccal lobe is well developed, which results in a large, pointed buccal cusp. The mesial cusp ridge is shorter than the distal cusp ridge.
From the buccal aspect, the crown is roughly trapezoidal (see Figure 4-16, C). The cervical margin is represented by the shortest of the uneven sides.
The tip of the buccal cusp is pointed and, in most cases, is located a little mesial to the center of the crown buccally (see Figure 10-9, 3, 7, 8, and 9). The mandibular canine has the same characteristic to a greater degree.
The development of the middle buccal lobe is outstanding, ending in a pointed buccal cusp. Developmental depressions are often seen between the three lobes (see Figure 10-9, 2, 3, 8, and 10).
The continuous ridge from the cervical margin to the cusp tip is called the buccal ridge.
Lingual Aspect
The crown of the mandibular first premolar tapers toward the lingual, since the lingual measurement mesiodistally is less than that buccally. The lingual cusp is always small (see Figures 10-3, 10-7, and 10-8). The major portion of the crown is made up of the middle buccal lobe (see Figure 10-11). This makes it resemble the canine.

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