Role of the masseter, anterior temporalis, and sternocleidomastoid muscles in myofascial temporomandibular disorder pain: evaluation of thickness and stiffness by ultrasonography.

OBJECTIVES: This study aimed to compare the thickness and stiffness of the masseter, anterior temporalis, and sternocleidomastoid muscles of patients diagnosed with myofascial temporomandibular disorders (TMD) pain to those of a control group. METHODS: This was a cross-sectional study conducted at a single center. Twenty-five patients diagnosed with myofascial TMD pain and 29 asymptomatic controls (Control Group) matched by age and sex were recruited. B-mode ultrasonography and shear wave elastography were used to measure the thickness and stiffness of the bilateral masseter, temporalis, and sternocleidomastoid muscles. All measurements were performed while resting and clenching. Patients were systematically evaluated for pain intensity and maximum mouth opening. RESULTS: There were no differences between groups in the resting and clenching thickness of any muscles (p > 0.05). There were no differences in the stiffness of the measured muscles at rest and clench between the groups, except for the masseter (p > 0.05). Individuals with myofascial TMD pain showed higher median stiffness in the right (p < 0.001) and left (p = 0.003) masseter muscles during clenching (but not during resting) compared with controls. CONCLUSIONS: Clenching masseter stiffness was greater in individuals with myofascial TMD pain than in asymptomatic controls. These findings might help to understand the jaw biomechanics and dysfunction of individuals with myofascial TMD pain.