Relationships between jaw muscle cross-sections and craniofacial morphology in normal adults, studied with magnetic resonance imaging.

In 32 Caucasian adult males serial MRI scans of the jaw muscles were taken approximately perpendicular to the mean fibre direction of the jaw muscles to determine their cross-sectional areas. These areas are proportional to the maximal isometric strength of a muscle. To describe facial skeletal variation, nine angular and 21 linear cephalometric measurements were recorded, and statistically reduced by means of multiple regression and principal component analysis. Six components were extracted, rotated, and subsequently correlated with the maximal cross-sectional areas of the jaw elevators and anterior digastric muscle. Positive significant correlations were found between a linear combination of several transversal skull dimensions on the one hand, and the maximal temporalis and masseter cross-sections on the other. A negative significant correlation was found between the flexure of the cranial base and the temporalis cross-section. Surprisingly, no significant correlations were found between either anterior facial height or posterior facial height and any of the jaw muscles cross-sections. It was concluded that, in adult males with normal skull shape, relationships exist to a limited extent between craniofacial morphology and the cross-sectional areas of the jaw muscles.