Protuberance or fossa on the lateral surface of the mandible in primates.

In order to clarify the morphological characteristics and function of the protuberance and/or fossa on the lateral surface of the mandible, we examined 778 mandibles of 9 genera, 19 species of non-human primates. Both protuberance and fossa were found in Macaca, Chlorocebus, and Cercocebus at frequencies ranging from 0% to 60%. The protuberance was composed of compact bone and was similar to the mandibular torus in humans. A well-developed protuberance extended from the fourth premolar to third molar region, and was situated at the central part of the mandibular body, or continued on the oblique line. Sometimes the protuberance localized on the mandibular base. A deep and large fossa was found in all individuals of Papio, Theropithecus, and Mandrillus, and the bone width was thin in the center of the fossa. The fossa extended from the third premolar to the second molar region, and the deepest area was the first molar region. In Macaca, Chlorocebus, and Cercocebus, the curvature of the external table of the mandible created a fossa. In Colobus, and Hylobates, the external surface of the mandible looked concave because of the thickened mandibular base. These concavo-convex structures have some biological functions and represent an adaptive change for mastication.

Comparative study of craniofacial morphology and bite force in Fijians and Japanese.

An anthropological survey was conducted in Fiji in 1994 and 1995 to study dental arch form, craniofacial morphology, and bite force of Fijians. Measurements were obtained from dental casts, cephalograms, and thin pressure-sensitive sheets (Dental Prescale®) for bite force analysis. Results were compared with those of Japanese. In every direction, the size of the dental arch in Fijians was larger than in Japanese. Fijians displayed longer palates, longer mandibles, and bimaxillary protrusion. There was no significant difference in upper and lower facial heights. FH to lower incisor angle in Fijians was significantly larger than in Japanese. Fijians were characterized by a small palatal plane angle, occlusal plane angle and mandibular plane angle, and were thus brachyfacial. The Japanese tended to be more dolichofacial. The distances from the Cd line to the pterygoid muscles, masseter muscles, and teeth in Fijians were significantly longer than in Japanese. Occlusal contact areas of Fijians were also greater than those of Japanese. The results indicate that the masticatory muscles and craniofacial morphologies supporting them would be better integrated in Fijians than in Japanese. Am. J. Hum. Biol. 10:63-72, 1998. © 1998 Wiley-Liss, Inc.

Mandibular permanent second molar with four roots and root canals: a case report.

Although four-rooted mandibular first molars have been observed on a few occasions in the literature, to the best of our knowledge, four-rooted second molars have not been reported. Here, we describe a mandibular second molar with four roots and canals: two mesial and two distal. Mesial roots were separated in the cervical one-third near the cervical margin, while distal roots were divided at a lower level in the middle one-third of the root. We discuss the possibility of different root and canal variations of the mandibular second molar from a developmental point of view.