An electromyographic investigation of masticatory muscles symmetry in normo-occlusion subjects

The influence of occlusal conditions on stomatognathic function can be asse ssed by electromyography. Electromyographic activity of left and right temp oral and masseter muscles was recorded in 30 young healthy adults with a no rmal occlusion during: (1) a 3-s maximum voluntary clench on cotton rolls p ositioned on the posterior teeth (standardization recording); (2) a 3-s max imum voluntary clench in intercuspal position; and (3) a 3-s alternate 'max imum' voluntary contraction and relaxation with a 1 Hz frequency. All poten tials were standardized as a percentage of the maximum potential of test 1. Waveforms of paired muscles were compared by computing a percentage overla pping coefficient (ratio between each 50-ms overlapped areas and the total areas, up to 100% for symmetric muscles). Waveforms were also analysed for a laterodeviating effect on the mandible given by unbalanced muscular coupl es, and a torque coefficient (up to 100% for a significant laterodeviating couple on the mandible) was computed. In all subjects, both tests were perf ormed with symmetric muscular patterns (more than 88%) and with negligible laterodeviating couples on the mandible (lower than 10%). The two coefficie nts allow an assessment of muscular asymmetry during static and dynamic cle nching tests, and, together with the standardization of the potentials, cou ld be a useful tool to detect functionally altered occlusal conditions, i.e . conditions where an apparent good morphological situation is not related to a correct neuromuscular status.