Activity of jaw-opening and jaw-closing muscles and their influence on dentofacial morphological features in normal adults.

The purpose of this study was to determine the relationship between the dentofacial morphology and the function of masticatory muscles estimated by kinesiological measurements during isotonic jaw-opening (O) and closing (C) muscle contractions. We examined 26 male adult subjects who had no history of masticatory dysfunction. Three kinesiological parameters, the maximum force (F(max)), maximum velocity (V(max)) and maximum power (P(max)) were measured in both O and C muscles. Correlation analysis was performed between these parameters and dentofacial morphological features determined on lateral roentgenographic cephalograms. The F(max) (C), V(max) (O), log O/C of V(max), and P(max) (O) significantly correlated with anterior overbite. P(max) (C) significantly and negatively correlated with SN-ArG. Furthermore, log O/C of P(max) significantly and negatively correlated with SNA, SNB and ArG/GMe, and positively with SN-ArG. These results, combined with our previous findings that electromyographic muscle activity during isometric contraction correlated significantly with mandibular morphology, indicate that the dentofacial morphology is influenced by the function of both O and C muscles.