9 The Permanent Maxillary Premolars
The maxillary premolars number four: two in the right maxilla and two in the left maxilla. They are posterior to the canines and immediately anterior to the molars.
When premolars have two roots, one is placed buccally and one lingually.
Maxillary First Premolar
Figures 9-1 through 9-16 illustrate the maxillary first premolar from all aspects. The maxillary first premolar has two cusps, a buccal and a lingual, each being sharply defined. The buccal cusp is usually about 1 mm longer than the lingual cusp. The crown is angular, and the buccal line angles are prominent.

Figure 9-1 Maxillary right first premolar, mesial and occlusal aspects. LR, Lingual root; CL, cervical line; MMDG, mesial marginal developmental groove; LC, lingual cusp; BC, buccal cusp; MCA, mesial contact area; BCR, buccal cervical ridge; MDD, mesial developmental depression; BR, buccal root; MBCR, mesiobuccal cusp ridge; MMR, mesial marginal ridge; MTF, mesial triangular fossa (shaded area); CDG, central developmental groove; MLCR, mesiolingual cusp ridge; DLCR, distolingual cusp ridge; DTF, distal triangular fossa; DMR, distal marginal ridge; DBCR, distobuccal cusp ridge.

Figure 9-7 Maxillary right first premolar. Graph outlines of five aspects are shown. (Grid = 1 sq mm.)


Figure 9-11 A, Mesial view of a maxillary right first premolar demonstrating single root and mesial crown concavity. B, Mesial view of a maxillary right second premolar demonstrating single root and no mesial crown concavity.

Figure 9-13 Maxillary first premolar. Ten specimens with uncommon variations are shown. 1, Constricted occlusal surface; short roots. 2, Single root of extreme length. 3, Constricted occlusal surface; mesial developmental groove indistinct on mesial surface of root. 4, Short root form, with two buccal roots fused. 5, Short root form, with two buccal roots showing bifurcation. 6, Short roots, with considerable separation. 7, Buccolingual calibration greater than usual. 8, Root extremely long; distal contact area high. 9, Twisted buccal root. 10, Three roots fused; roots are also uncommonly long.

Figure 9-15 Maxillary first premolar, occlusal aspect. A, Crest of buccal ridge; B, crest of lingual ridge; C, crest of mesial contact area; D, crest of distal contact area.

Figure 9-16 Maxillary first premolar, occlusal aspect. TBC, Tip of buccal cusp; MBCR, mesiobuccal cusp ridge; MBDG, mesiobuccal developmental groove; MTF, mesial triangular fossa; MMDG, mesial marginal developmental groove; MMR, mesial marginal ridge; MLCR, mesiolingual cusp ridge; LTR, lingual triangular ridge; TLC, tip of lingual cusp; CG, central groove; DLCR, distolingual cusp ridge; DMR, distal marginal ridge; DTF, distal triangular fossa; DBDG, distobuccal developmental groove; BTR, buccal triangular ridge; DBCR, distobuccal cusp ridge. (Compare with Figure 9-1.)
The crown is shorter than that of the canine by 1.5 to 2 mm on the average (Table 9-1). Although this tooth resembles the canine from the buccal aspect, it differs in that the contact areas mesially and distally are at about the same level. The root is shorter. If the buccal cusp form has not been changed by wear, the mesial slope of the cusp is longer than the distal slope. The opposite arrangement is true of the maxillary canine. Generally, the first premolar is not as wide in a mesiodistal direction as the canine.
Most maxillary first premolars have two roots (see Figure 9-10) and two pulp canals. When only one root is present, two pulp canals are usually found anyway.
DETAILED DESCRIPTION OF THE MAXILLARY FIRST PREMOLAR FROM ALL ASPECTS
Buccal Aspect
From the buccal aspect, the crown is roughly trapezoidal (see Figure 4-16, C). The crown exhibits little curvature at the cervical line. The crest of curvature of the cervical line buccally is near the center of the root buccally (see Figure 9-2 and Figures 9-7 through 9-9).
The mesial slope of the buccal cusp is rather straight and longer than the distal slope, which is shorter and more curved. This arrangement places the tip of the buccal cusp distal to a line bisecting the buccal surface of the crown. The mesial slope of the buccal cusp is sometimes notched; in other instances, a concave outline is noted at this point (see Figure 9-9, 7, 9, and 10).

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