Abstract
It has been recognized that clarifying the masticatory function of the elderly is important because of their remarkable increase in population and QOL. The purpose of this study was to investigate the usefulness of the normalized EMG linear envelope analysis to compare masticatory muscle activity patterns of the elderly with young. We applied EMG linear envelope analysis to the elderly who were different in oral conditions with the young. Four elderly complete denture wearers (one male and three females; mean age, 71.0 years; range, 68-75 years) and eight young dentate volunteers (four males and four females; mean age, 25.3 years; range, 23-28 years) participated in this experiment. EMG signals were recorded from the bilateral masseter and anterior temporal muscles during gum chewing on the preferred chewing side for 90 seconds. The Rower incisal point movement was tracked by the Mandibular Kinesioguraph (MKG) simultaneously. Root mean square values were calculated from the raw EMG signals. Each rectified EMG signal was smoothed by weighted moving average method to produce a linear envelope. These data were divided into individual chewing strokes and each stroke was divided into 3 phases using the data for vertical displacement of the MKG: closing, compressive, and opening phases. The time base average for each phase was then normalized to 100 points representation, 300 points in total, for each stroke period. 10 stable strokes were selected and each stroke was normalized by setting the mean ensemble value over a single stroke to 100%. Ten normalized EMG amplitudes were averaged. It was possible to compare each volunteer's masticatory muscle activity patterns because the activity patterns were reduced inter- and intra- volunteer variability.
The results were obtained as follows;
1. Normalized EMG linear envelopes of the elderly complete denture wearers showed plane curves on both sides. Their peaks of the activities were not clear and their amplitudes were low.
2. Normalized EMG linear envelopes of the young dentate volunteers showed sharp curves on the working side and smooth on the non-working side. Their peaks of the activities were near the 100 points of the stroke.
3. Masticatory muscle activity patterns of the elderly complete denture wearers and young dentate volunteers were different.
The normalized EMG linear envelope analysis was useful to compare masticatory muscle activity patterns of the elderly population with the young.
