Muscle thickness, bite force, and craniofacial dimensions in adolescents with signs and symptoms of temporomandibular dysfunction.

Ultrasonography has been used to determine the association between muscle thickness, temporomandibular dysfuntion (TMD), facial morphology, and bite force. The aim of this study was to evaluate signs and symptoms (SS) of TMD using the craniomandibular index (CMI), masseter and anterior temporalis thickness, facial dimensions, and bite force in adolescents (12-18 years of age): 20 (10 males and 10 females) with SSTMD and 20 without (control, matched for age and gender). Ultrasonography was carried out using Just-Vision 200, and bite force measured with a pressure transducer. The measurements undertaken on the cephalograms included anterior (n-gn, n-Me, sp-gn) and posterior (S-tgo) facial dimensions, jaw inclination (NSL/ML), vertical jaw relationship (NL/ML), gonial angle (ML/RL), and overbite and overjet. The data were analysed with analysis of variance, Pearson's and Spearman's correlation and multiple regression. The SSTMD group showed a smaller bite force than the controls (P < 0.05). In the control group, bite force was negatively correlated with jaw inclination and overbite. There were negative correlations between anterior temporalis thickness and anterior facial dimensions; and positive correlations for masseter and anterior temporalis and posterior dimensions. In the SSTMD group, there were positive correlations for masseter and bite force, and anterior and posterior dimensions. Negative correlations were found for the masseter and temporalis muscles and jaw inclination and vertical jaw relationship. Multiple regression analysis showed that in the control group the overjet and jaw inclination contributed 50 per cent to the variance in bite force. In the SSTMD group, the dimensions of the masseter muscles during contraction contributed 39 per cent to the variance. The correlations between CMI and the craniofacial variables were more significant in the SSTMD group. The findings indicate that muscle thickness influences facial dimensions and bite force in adolescents with SSTMD.