The purpose of this study was to investigate the fundamental property and time coordination of the superior head (SLpt) and inferior head (ILpt) of the human lateral pterygoid muscle.
EMGs were recorded and analysed during mastication, together with the condylar and incisal movements in five subjects with normal jaw function. EMG recordings were taken at SLpt, ILpt, the anterior belly of the digastric muscle (Da), the posterior part of the temporal muscle (Tp) and the masseter muscle (Mm).
SLpt appears to have two phasic functions. In the first phase it controls the position and speed of the disk and condyle as it returns posteriorly to centric position. In the second phase, it functions mainly during the final closing phase on the working side to direct the orientation of masticatory forces toward the articular eminence in response to increases in these forces. These functions are completed by the supplementary activity of ILpt.