Human occlusofacial form commonality: race-related traits, ontogeny, paedomorphism, and functional correlates

Previous cephalometric studies of occlusofacial angular and metric data show small variability within and between population samples of Caucasian children and adults. Comparable results were obtained by use of standardized X-ray cephalometry and direct craniometric measurements of skulls of mature specimens of Alouatta caraya and Cebus capucinus. These data measure facial and occlusofacial form and form relationships. Identical measuring techniques are applied to compare data derived from headplates of 19 young adult American Caucasians and 19 articulated Hindu skulls of mature individuals. The data are expanded to include measurements that relate symphyseal form to occlusal and nasomaxillary structure. The facial plane and an "internal" facial plane (nasion to a point tangential to the superior genial tubercles) straddle the mandibular symphysis. The angles they form at nasion and at their intersections with the maxillary occlusal plane were derived and statistically analyzed. The occlusal plane intersect angles show small absolute variability and are not significantly different (P greater than .05) in the two groups. The nasion plane angles are significantly different (P less than .025), reflecting sample differences in facial height. Linear measurements confirm a considerably larger dentoalveolar prognathism in the Hindu group. Data derived from the geometrically averaged tracings of Bjork, Broadbent, Sassouni, and Solow provide further evidence of occlusofacial form commonality. These shared phyletically conservative traits are evidence of highly integrated morphological adaptations for the attainment, maintenance, and functioning of the species-wide pattern of precisely fitting complementary crowns and crown parts that constitute the dental occlusion.