Objective: The association between cranial base morphology and greater tendency towards the prognathic mandibular and/or retrognathic midfacial profile associated with Class III malocclusion in Asians is poorly understood. Methods: Lateral cephalographs of 400 young adults with normal Class I molar occlusion of four Asian groups (Chinese, Japanese, Korean and Taiwanese) were compared to those of 55 European Americans. Fourteen landmarks on the cranial base and upper midface were identified and digitized. Resultant geometries were normalized, and the Procrustes analysis indicated that the cranial base and upper midface configuration differed statistically for all four comparisons (P < 0.0001). Finite element morphometry (FEM) was employed to localize morphological differences. Results: While the anterior-most region of the anterior cranial base and upper midface was the most anisotropic for FEM shape change, moderate anisotropy was evident in the posterior cranial base. For FEM size change, areas of negative allometry were located in the anterior-most region of the anterior cranial base, the upper midface, and in the posterior-most region of the posterior cranial base, but dilation in the mid-cranial base and around sella turcica was also apparent. Conclusions: Morphological alterations in the anterior-most region of the anterior cranial base and upper midface accompanied by changes in the posterior-most region of the posterior cranial base contribute to differences from European-American cranial base configuration. This presumably coincides with flat frontal and facial profile and the forward displacement of the temporomandibular joint in Asians. These deformations may induce a greater tendency towards the retrognathic midfacial and/or prognathic mandibular profile associated with Class III malocclusion in Asians. This work was supported by the National Science Council of Taiwan, NSC 90-2314-B-037-087; NSC 89-2314-B-037-058; NSC 89-2314-B-037-181.

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