Visualization and quantitative analysis using normalized electromyographic linear envelopes of muscle contraction patterns during gum chewing.

Surface electromyography (EMG) has been widely used in clinical dentistry, although interpretation of the raw data is difficult owing to its low reproducibility. Linear EMG envelopes, also known as EMG profiles, which are normalized with respect to raw EMG amplitudes and stride, have been developed to analyze the time course of gait stride. Normalized EMG contraction patterns can be used for comparing individuals or recording sessions on the same individual made at different times. We made EMG profiles during unilateral gum chewing for the masticatory muscles of five asymptomatic volunteers. EMG signals were recorded from the anterior temporal (Ta), masseter (M) and anterior belly of the digastric (Da) muscles on the subject's preferred chewing side. The mandibular kinesiograph was used for tracking incisal point movement during chewing. EMGs and kinesiometric data were simultaneously recorded for 90 seconds. Ensemble averages of EMG profiles were made from 10 stable strokes after 60 seconds of initiation of chewing. Phasic characteristics of the EMG profiles were evaluated by product-moment correlation and intraclass correlation coefficients. Although the EMG profiles for Ta and M were very similar, those for Da were different from the elevator muscles.