Abstract
The aim of this study was to disclose the variation in the surface EMGs recorded from electrodes put on different positions on the masseter and temporal muscles and read on different days.
Seven male subjects with normal tooth alignment and occlusion were studied. For the power spectrum analysis, digital correlator and spectrum analyzer were used.
1) On the relative power spectra, the electrode positioning on the corresponding muscles hardly affected the EMG spectral distribution.
2) Whereas the electrode positioning was found to manifestly affect the root mean square values (rms) of the voltage of the EMG activities.
3) When records were on different days, no great changes in spectral distribution were found. The rms voltage of EMG made a little difference, however, it was much smaller than the variation due to the electrode position.
4) Although significant difference was shown between individual subjects, the masseter and temporal muscles appeared to have respectively charactaristic spectral distributions, which were affected by the functional states of muscle contruction, i. e. chewing and clenching.
5) The EMG power spectra of masticatory muscles might be refrected in their quantitative changes, and could obtain more accurately reproducible result than other parameters.
