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.

The contact areas are broad from this aspect; they are almost at the same level mesially and distally, this level being a little more than half the distance from cervical line to cusp tip. The measurement mesiodistally at the cervical line is small compared with the measurement at the contact areas.

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 crown exhibits little curvature at the cervical line buccally, because of the slight curvature of the cervical line on the mesial and distal surfaces of the tooth. The crest of curvature of the cervical line buccally approaches the center of the root buccally.

The mesial outline of the crown is straight or slightly concave above the cervical line to a point where it joins the curvature of the mesial contact area. The center of the contact area mesially is occlusal to the cervical line, a distance equal to a little more than half the crown length. The outline of the mesial slope of the buccal cusp usually shows some concavity unless wear has obliterated the original form.

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 distal outline of the crown is slightly concave above the cervical line to a point where it is confluent with the curvature describing the distal contact area. This curvature is broader than that describing the curvature of the mesial contact area. The distal slope of the buccal cusp usually exhibits some concavity.

The cervix of the mandibular first premolar crown is narrow mesiodistally when compared with the crown width at the contact areas.

The root of this tooth is 3 or 4 mm shorter than that of the mandibular canine, although the outline of the buccal portion of the root bears a close resemblance to that of the canine.

The buccal surface of the crown is more convex than in the maxillary premolars, especially at the cervical and middle thirds.

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.

In general, the enamel of the buccal surface of the crown is smooth and shows no developmental grooves and few developmental lines. If the latter are present, they are seen as very fine horizontal cross lines at the cervical portion.

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.

The crown and the root taper markedly toward the lingual so that most of the mesial and distal surfaces of both may be seen from the lingual aspect.

The occlusal surface slopes greatly toward the lingual in a cervical direction down to the short lingual cusp. Most of the occlusal surface of this tooth can therefore be seen from this aspect.

The cervical portion of the crown lingually is narrow and convex, with concavities in evidence between the cervical line and the contact areas on the lingual portion of mesial and distal surfaces. The contact areas and marginal ridges are pronounced and extend out above the narrow cervical portion of the crown.

Although the lingual cusp is short and less developed (resembling a strongly developed cingulum at times), it usually shows a pointed tip. This cusp tip is in alignment with the buccal triangular ridge of t/>