Functional Analysis of the human masticatory muscles by means of the muscular sound measured with the displacement sensor, and relation to the dentofacial morphology

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The purpose of the present study is estimate the mechanism of muscle contraction and the condition of the muscle fatigue by means of the muscular sound (MS), the microvibration of the muscle.First, the characteristics of displacement-output voltage of the Amorphous Magnetic Sensor picked the MS up were measured. Secondly, the MS and electromyogram (EMG) of the right masseter muscle in 16 healthy male were recorded, when the eight different contraction forces (%MVC) were exerted and four %MVC after fatigue. And the amplitudes (Amp) and frequencies (Freq) of both records were analyzed. The following is the results.1. On the range of 3.0±0.1mm, the relation of displacement-output voltage of this sensor is linear.2. The Amp of the MS has been increased until 20 %MVC. Beyond its %MVC, it has been decreased.3. As the %MVC has been bigger, the power in the higher Freq band of MS has increased. However, the median Freq of power spectrum of the MS has not changed.4. After fatigue, the Amp of EMG recordings have been increased, but those of the MS have not been changed.5. The conversion efficiency (the Amp of MS / the Amp of EMG) has tended to decrease in 10 and 20 %MVC after fatigue.6. After fatigue, it became small that the powers of the higher Freq band of MS tend to increase.It is suggested that the recordings and analysis of MS is useful diagnostic tool in clinical dentistry, because the assessment of MS is get the more information of the muscle condition than EMG and muscle power.