This study was performed to investigate the effects of hand grip of dynamometer on the masticatory system, especially on the masticatory muscle activity(EMG) and mandibular position. For this study, healthy thirteen dental students, 9 male and 4 female, served as subjects. Subjects were asked to sit comfortably with upright position, without touching the ground with dynamometer on holding the instrument. Surface EMG electrodes were placed over the right and the left anterior temporalis(TA), the superficial masseter(MM). And magnet for mandibular tracking device was attached on the labial side of lower incisors. Movement distance from the rest position was recorded.
Three types of hand grip were applied, such as powerful single grip(single), sustained grip with medium power(sustained phase 0, and sustained grip with most powerful power(sustained phase 2). Data were recorded and the statistical analysis was performed using SPSS Windows?(ver. 10,0) program. The results of this study were as follows:
There were no difference between the right hand grip and the left hand grip for the mean value of EMG activity and grip power on all the types of grip, whereas slight difference were noticed for the distance of frontal height and sagittal slant on single grip, more with left hand.
There were no difference of EMG activity and grip power between the single grip and the sustained grip phase 2. However, difference was showed for the distance of mandibular movement between the two grip method, allowing slightly more with single grip with left hand.
The distance of mandibular movements without regard to the direction during entire period of grip was the most in the whole sustained grip covering phase I and phase 2, and the time reaching the highest position toward the maxilla from the rest position was 6.2~6.7sec. after phase I grip.
Positive correlation with grip power were appeared for the distance of mandibular movements on left hand single grip and physical height.
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