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First premolar - upper teeth
The crown of the first premolar has a grinding surface which is somewhat quadrilateral in outline, longer on the labial than on the lingual border, and has two cusps, of which the labial is much larger. The cusps or tubercles are separated by a pit, but are connected by a narrow ridge along the median and distal borders; the median-border is nearly straight, the distal is convex. The root may be single or bifurcated near the apex. In some cases the root is marked merely by a longitudinal depression. In other cases it is double throughout the greater part of its length and it may even present three distinct roots, like a molar.