An electromyographic assessment of masticatory muscles asymmetry in normal occlusion subjects

Abstract

The aim of this study was to evaluate the existence of functional asymmetry in main masticatory muscles, masseter (m) and anterior temporal (t). For that were used a computerized instrument of eight channels and double surface electrodes in a 30 young adults subjects, aged between 17 and 25 years, all with complete and permanent healthy teeth, without prior trauma or craniofacial surgery and without temporomandibular disorders. The action of the masseter and temporal muscles was examined by electromyography (EMG) examination during: Test 1 - maximum voluntary clench (MVC) with cotton rolls (standartization test); Test 2 - MVC without cottons rolls in intercuspal position and Test 3 – alternating between MVC and relaxation. The electromyographic waves were analysed and compared both right and left sides of muscle pairs by computing the percentage overlapping coefficient (POC,%). Moreover, the torque coefficient (TC,%) was calculated, which assesses the component of laterodeviating effect on the jaw when there is unbalanced between contraction masseter and temporal contralaterals. The results, averages and standard deviation, were: POC t: 86.96 ± 3.20; POC m: 86.51 ± 3.33; POC Middle: 86.75 ± 2.48; TC: 8.60 ± 1.08. The results revealed that EMG index means were within the normal range. In conclusion, the values of muscles functional asymmetry were in accordance to those reported in the literature for healthy young adults established for other population.