[Frequency spectra of EMG activities and mastication muscular development]

The purpose of this study was to investigate the change of frequency components of EMG (electromyograph) signals obtained from masticatory muscles in term of the development from deciduous mixed and permanent dentition using FFT (Fast Fourie Transform) algolism. A total of one hundred and fourty subjects who had no oral dysfunction were subjected. The subjects were divided into four groups: deciduous dentition (designated as G1), early mixed dentition (designated as G2), late mixed dentition (as G3) and permanent dentition (as G4). EMG signals were taken from the right masseter and temporal muscles using bipolar surface electrodes during tooth tapping, clenching in the intercupsal position and maximum biting and EMG were recorded on magnetic tape (FM data recorder). Three parameters on the surface EMGs were chosen for the measuring points such as 1) frequency range, 2) frequency of maximum peak (peak frequency), 3) strength of maximum peak (peak magnitude). The results obtained in the present studies were summarized as follows; 1) In the frequency range, temporalis showed a higher range than masseter muscle among every group and it decreased with the dentitional development. 2) As to the peak frequency and peak magnitude, the clenching has higher frequency than tooth tapping and maximum biting, and the those differences between each group were clarified with the development. 3) Cross-powerspectrum showed that the main frequency harmonized into high frequency at every movement, while the strength of the harmony maintained a high frequency and increased with the development of the muscles. As aforementioned, EMG spectra may also reflect on to muscle activities associated with dentitional development.