Electromyographic and ultrasonographic evaluation of the masseter muscle individuals with unilateral peripheral facial paralysis

Introduction:Individuals with peripheral Facial Paralysis (FP) show conditions that lead to unilateral mastication, performed by the non-affected side, mainly due to the difficulty of action of the buccinator muscle. Objectives: characterize the motor control and morphology of the masseter muscle in individuals with unilateral peripheral FP through electromyographic and ultrasonographic evaluation. Method: 16 participants, of both sexes, with ages superior to 18 years old. The study group (SG) consisted of 8 individuals who'd had idiopathic unilateral peripheral FP for more than 6 months; the control group (CG) consisted of 8 normal individuals. All the subjects were submitted to the masseter muscle evaluation through surface electromyography (sEMG) and ultrasonography (USG) during the following tasks: rest, clenching with cotton roller between the teeth (CT) and clenching with maximum intercuspation (MIC). Results: There was no statistically significant difference in comparisons within and between the groups concerning the hemifacial asymmetry, both for the sEMG and for the USG. Also there were no significant differences in the activation of the masticatory muscles (masseter and temporal) in the sEMG. Conclusions: Both the motor control and the morphology of the masseter muscles in individuals with unilateral peripheral FP were similar to those of normal individuals. Although literature suggests that the demand of functional adaptations made by FP individuals could exceed the structural and functional tolerance of the temporomandibular joints, the results indicate that the length of analyzed patient's FP was not enough to generate anatomical and physiological differences in the masticatory muscles.