Midfacial morphology of Koreans with class III malocclusions investigated with finite-element scaling analysis

The spheno-ethmoidal model of midfacial retrognathia suggests that deficient chondrocytic proliferation in the anterior cranial base is associated with inadequate anterior translation of the midfacial complex resulting, for example, in Class III malocclusions. The purpose of this study was to determine whether the morphology of the midface differed in subjects of diverse ethnic origin exhibiting features associated with Class III malocclusions. Lateral cephalographs of 142 children of Korean or European American descent aged between 5 and 11 years were compared. The cephalographs were traced and subdivided into seven age- and sex-matched groups. Average geometries, scaled to an equivalent size, were generated using Procrustes superimposition and subjected to analysis of variance (ANOVA). Graphical analysis using a color-coded finite-element scaling analysis (FESA) program was used to localize differences in morphology. Results indicated that the mean Korean and European American midfacial configurations differed statistically (P < 0.01), and this difference was maintained at most, but not all, age-wise comparisons. Comparing Korean and European American Class III midfacial configurations for local size-change, FESA analysis revealed that while local increases in size were apparent in the posterior palatal regions, the Korean anterior nasal spine regions were generally smaller. For shape-change, the Korean and European American midfacial configurations were predominantly isotropic. Therefore, heterogeneity in appearance may be influenced by morphological variation of the midfacial complex in subjects of diverse ethnic origin, but features of the anterior cranial base may contribute also to the prevalence and severity of Class III malocclusions in Koreans. Moreover, perturbations in endochondral mechanisms of cranio-mandibular growth, and not maxillary intramembranous methods, may be implicated in the etiology of Class III malocclusions in South East Asians.