Finite element analysis of the cranial base in subjects with Class III malocclusion.

The association between cranial base morphology and Class III malocclusion is poorly understood. This study analyses local shape- and size differences in cranial base configurations of Class I and Class III subjects, employing finite element (FEM) analysis. Seventy-three prepubertal European-American children with Class III malocclusion were compared to their counterparts with a normal, Class I molar occlusion. Lateral cephalographs were traced, checked and subdivided into age- and sex-matched groups. Thirteen points on the cranial base were identified and digitized, providing a geometrical cranial base representation. Average cranial geometries were scaled to an equivalent size and a FEM analysis, capable of depicting and quantifying local shape- and size-change, employed to highlight regionalized, morphological differences. While the anterior cranial base was more homogeneous for shape-change, significant, localized anisotropy in the posterior regions of the cranial base and around sella turcica was evident. For size-change, areas of negative allometry were located posteriorly, but dilations in the mid- and anterior cranial base also were apparent. It is concluded that morphological alterations within the petro-occipital complex accompanied by changes in the sphenoidal and ethmoidal regions induce deviation from a normal cranial base configuration to one associated with deficient orthocephalization and an appearance of Class III malocclusion.