[Electromyographic study on lateral jaw movements].

This study aims to analyse how jaw-closing muscle activities are modulated during lateral jaw movement. Jaw movements were recorded by Sirognathograph (Siemens Co.) and electromyograms were simultaneously recorded from bilateral masseter, anterior temporal and posterior temporal muscles in 20 young adults without any stomatognathic dysfunction. Each subject sat upright in the chair with the head unsupported. The lateral jaw movements from the intercuspal position were guided three times for each lateral excurtion (right and left). The data were recorded on magnetic tape and later analysed by use of a computer. Following variables were analysed; the number of contacted teeth, the position of contacted teeth, the muscle activities during lateral jaw movement. The results can be summarised as follows; 1) The working-side posterior temporal muscle showed obvious activity in more than 90% subjects during lateral jaw movement. However, this muscle activity was not influence by the number or position of the contacted teeth. 2) The right side masseter muscle tended to show the obvious activity during both right and left lateral jaw movement. The results of this study suggest the difference in the activities between masseter and temporal muscle during lateral jaw movement.