Morphometric analysis of the cranial base in Asians.

This study tested the hypothesis that developmental heterogeneity in cranial base morphology increases the prevalence of Class III malocclusion and mandibular prognathism in Asians. Thin-plate spline (TPS) graphical analysis of lateral cephalometric radiographs of the cranial base and the upper midface configuration were compared between a European-American group (24 females and 31 males) and four Asian ethnic groups (100 Chinese, 100 Japanese, 100 Korean and 100 Taiwanese; 50 females and 50 males per group) of young adults with clinically acceptable occlusion and facial profiles. Procrustes analysis was performed to identify statistically significant differences in each configuration of landmarks (P < 0.001). The TPS graphical analysis revealed that the greatest differences of Asians were the horizontal compression and vertical expansion in the anterior portion of the cranial base and upper midface region. The most posterior cranial base region also showed horizontal compression between the basion and Bolton point, with forward displacement of the articulare. Facial flatness and anterior displacement of the temporomandibular joint, resulting from a relative retrusion of the nasomaxillary complex and a relative forward position of the mandible were also noted. These features that tend to cause a prognathic mandible and/or retruded midface indicate a morphologic predisposition of Asian populations for Class III malocclusion.