Reference Values of Electromyography Studies of the Masseter and Temporalis Muscles

Abstract

The masseter and temporalis muscles are very relevant in the process of mastication; they are also often affected by myoarticular and neurological diseases,among others.This study aims to present the results of electromyography with needle electrodes of the masseter and temporalis muscles at the time of mastication, evaluating the parameters in amplitude and duration of the potentials obtained. Twenty-six individuals were taken with a previous dental evaluation that ruled out congenital alterations, masticatory defects, and with normal dynamometry at the moment of maximum occlusion, to whom needle electromyography was performed in the masseter and temporalis muscles at maximum occlusion; the results were analyzed under the study of the maximum and minimum amplitude values,as well as duration located in percentiles and quadrilles, seeking to determine values that could be considered normal in this sample. When studying the temporal muscle, it was found that the normal duration is between 4.75 and 6.487 msec, while the amplitude would be between 1572.05 uV and 1038.03 uV; in the case of the masseter muscle, it was evidenced that the normal duration is between 4.03 and 6.767 msec, while the amplitude would be between 2838.43 uV and 1864.635 uV. This study reveals values specific to our population in terms of duration and amplitude of the motor unit action potentials of the temporalis and masseter muscles, which agree with those previously established as normal. In previous studies performed in other parts of the world, it was found that the duration is shorter than in the extremities. Still, the amplitude is similar, although with a tendency to lower values than the average.