Answer:
D. (broader facially than lingually), (usually free of marked distal curvature) and (frequently seen with slight concave areas on mesial and distal surfaces)
Explanation:
From the diagram below, we can different aspects of Mandibular first premolars. A. Buccal, B. Lingual, C. Mesial, D. Distal, E. Occlusal.
The Buccal aspect of mandibular first premolars have buccolingual measurement as a canine and has a sharp buccal cusp.The crown is inclined lingually but is broader facially than lingual, and therefore, the tip of the buccal cusp is situated on the vertical axis of the root.
The lingual cusp is smaller and shorter than buccal cusp.
The distal contact area is wider than the mesial contact area, since the contact tooth is second premolar offering it a free of marked distal curvature.
In addition, the outline is concave from the contact area is broader than the mesial contact area, thus it is frequently seen with slight concave areas on mesial and distal surfaces.
