Thin-plate spline analysis of the cranial base in African, Asian and European populations and its relationship with different malocclusions.

OBJECTIVES

To test the hypothesis that midline basicranial orientation and posterior cranial base length are discriminating factors between adults of different populations and its potential maxillo/mandibular disharmonies.

DESIGN

Twenty-nine 2D landmarks of the midline cranial base, the face and the mandible of dry skull X-rays from three major populations (45 Asians, 34 Africans, 64 Europeans) were digitized and analysed by geometric morphometrics. We used, first, MANOVA to test for mean shape differences between populations; then, principal components analysis (PCA) to assess the overall variation in the sample and finally, canonical variate analysis (CVA) with jack-knife validations (N=1000) to analyse the anatomical features that best distinguished among populations.

RESULTS

Significant mean shapes differences were shown between populations (P<0.001). CVA revealed two significant axes of discrimination (P<0.001). Jack-knife validation correctly identified 92% of 15,000 unknowns. In Africans the whole cranial base is rotated into a forward-downward position, while in Asians it is rotated in the opposite way. The Europeans occupied an intermediate position. African and Asian samples showed a maxillo/mandibular prognathism. African prognathism was produced by an anterior positioned maxilla, Asian prognathism by retruded anterior cranial base and increase of the posterior cranial base length. Europeans showed a trend towards retracted mandibles with relatively shorter posterior cranial bases.

CONCLUSIONS

The results supported the hypothesis that basicranial orientation and posterior cranial base length are valid factors to distinguish between geographic groups. The whole craniofacial configuration underlying a particular maxillo-facial disharmony must be considered in diagnosis, growth predictions and resulting treatment planning.