Quantitative analyses of microwear and honing on the sloping crest of the P3 in female Japanese monkeys (Macaca fuscata).

Female wild Japanese monkeys (Macaca fuscata), as with all male cercopithecoids, use the mesiobuccal surfaces or the elongated crests of the mandibular third premolars (P3s), as cutting blocks that wear against edges of maxillary canines during threat manifestation or food-eating. In other words, the crests of their P3s are honed with the maxillary canines. The crests become sloped during growth and more heavily striated with the advance of age. The number, directions, lengths, and widths of these striations have been analyzed quantitatively using scanning electron microscopy (SEM). Two samples showed two distinct types of parallel striations, one longer and thicker (171.5 microns long and 14.5 microns wide on average) than the other (114.8 microns long and 12.0 microns wide on average). These striations were caused by contact between the sharp edge of the upper canine and the P3 during honing (canine/premolar complex). The long and thick striations are asymmetrical with widened parts or pits on one end, and were easily distinguished from other thinner striations which may have been caused by fine particles. The third sample showed Hunter-Schreger bands with striae of Retzius on the sloping heavily worn mesiobuccal surface. The features of these thick parallel striations indicate that they result from closing movements of the jaw.