The EMG Activity of Masticatory Muscles During Different Chewing Tasks

Mastication is a highly coordinated neuromuscular function that involves fast effective movements of the jaw and continuous modulation of muscle force. To understand the relationship between muscles during mastication it is necessary to know the position and direction of movement of the mandible. MATERIAL AND METHODS: Twenty-four young healthy adults, age ranged 17 to 27, participated in this study. They were chosen among dental students of School of Dental Medicine University in Zagreb and had to be free of sign and symptoms of TMD. Surface EMG recordings were obtained from left and right anterior temporal muscle, left and right masseter muscle and from left and right digastric muscle on the 8 channel PC based EMGA-1, apparatus for simultaneous recording of myoelectrical activity (6 differential EMG channels, input impedance 100 MW, CMRR> 95 dB at 50 Hz, bandwidth 2 Hz-1 kHz, programmable input sensitivity from 100mVpp to 20 mVpp, an 8 bit resolution A/D conversion, 2 kHz sampling rate) - occlusal sound (2 audio channels), specially designed and developed for the purpose of kinesyological examinations of stomatognathic system’s function. The disc electrodes (Ag/AgCl, diameter 10 mm) were placed 2 cm apart in the main direction of the muscle fibres. RESULTS: 1. Main effect of factor "functional movement" was significant at p<0.01, and values were the highest for gum chewing, and the lowest for empty chewing except fordigastric muscle which had lowest values at continuous isometric contraction. 2. Main effect of factor “muscles” was significant at p<0.01 for all muscles involved, values were similar for the same muscles on left and right side. 3. Main effect of factor “time” was statistically significant p<0.05 for all cases showing decreasing trends except in last minute during functional movements. 4. Interactions between factors “functional movement” and “time” were present at significance p<0.01