Contribution of jaw muscle size and craniofacial morphology to human bite force magnitude

The existence of an interaction among bite force magnitude, jaw muscle size (e.g., cross-sectional area, thickness), and craniofacial morphology is wi dely accepted. Bite force magnitude depends on the size of the jaw muscles and the lever arm lengths of bite force and muscle forces, which in turn ar e dictated by craniofacial morphology. In this study, the relative contribu tions of craniofacial morphology and jaw muscle thickness to the bite force magnitude were studied. In 121 adult individuals, both magnitude and direc tion of the maximal voluntary bite force were registered. Craniofacial dime nsions were measured by anthropometrics and from lateral radiographs. The t hicknesses of the masseter, temporal, and digastric muscles were registered by ultrasonography. After a factor analysis was applied to the anthropomet ric and cephalometric dimensions, the correlation between bite force magnit ude, on the one hand, and the "craniofacial factors" and jaw muscle thickne sses, on the other, was assessed by stepwise multiple regression. Fifty-eig ht percent of the bite force variance could be explained. From the jaw musc les, only the thickness of the masseter muscle correlated significantly wit h bite force magnitude. Bite force magnitude also correlated significantly positively with vertical and transverse facial dimensions and the inclinati on of the midface, and significantly negatively with mandibular inclination and occlusal plane inclination. The contribution of the masseter muscle to the variation in bite force magnitude was higher than that of the craniofa cial factors.