The upper canine tooth is the first tooth in the upper dental arch behind the suture between the premaxilla and the maxilla. The lower canine is less satisfactorily defined as the first tooth in the arch to articulate immediately in front of the upper canine. Tooth surfaces that face the anterior midline of the jaws are termed mesial and those that face away from it distal. Surfaces that face the tongue are lingual and surfaces on the outer aspect of the tooth arch are buccal. Canine teeth are single rooted but can, rarely, be double rooted in the lower jaw. Canine roots and crowns are longer (taller) than those of incisors. Modern human upper canines have two strong marginal ridges and a midline elevation running from the cingulum to the tip. These usually define two shallow lingual mesial and distal fossae but which are less well defined in lower canines. The mesial slope from the cusp tip is always shorter than the distal slope in both upper and lower canines. A lingual cingulum is present in great apes, which interestingly in Pongo, is bigger in female than male canines. When viewed occlusally, therefore, lower great ape canines are more or less triangular in outline but with more rounded, obtuse borders in Pan. Great ape canines are sexually dimorphic, extremely so in Pongo and Gorilla, and scale in a positively allometric manner with body size. In both sexes, canines project well below the occlusal plane of the other teeth creating a wide gap (diastema, pl. diastemata) in the opposing dental arches to accommodate them. Great ape canine crowns are basically conical with convex mesial and concave distal borders. The mesial borders of upper canines and distal borders of lower canines wear in a distinct way to produce sharp elongated blade-like facets.
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