CHARACTERIZATION OF BRUX-LIKE MOVEMENTS IN THE LABORATORY RAT BY OPTOELECTRONIC MANDIBULAR TRACKING AND ELECTROMYOGRAPHIC TECHNIQUES

High-resolution optoelectronic mandibular tracking and fine-wire elect romyographic (EMG) data from the anterior temporalis muscles of labora tory rats (Rattus norvegicus) were collected during mastication (chewi ng) and bruxing/thegosis (grinding/sharpening of teeth) in order to te st for task-related activity patterns of the anterior temporalis. Anal yses of the collected data revealed that masticatory and bruxing/thego sis cycles displayed significantly different patterns of movement traj ectories, displacement, duration, velocity, and acceleration in all th ree spatial dimensions (frontal vertical, frontal horizontal and sagit tal horizontal). Activity patterns in the anterior temporalis during m asticatory and bruxing/thegosis behaviours were also significantly dif ferent from each other. High-resolution analyses revealed that the mas ticatory cycle had both opening-burst and closing-burst phasic pattern s of anterior temporalis activity while the bruxing/thegosis cycle dis played only opening-burst phasic patterns. The opening- and closing-bu rst attributes of anterior temporalis phasic activity patterns in rela tion to physiological centric occlusion also revealed significant diff erences between masticatory and bruxing/thegosis behaviours. These dat a demonstrate that the anterior temporalis muscle of the laboratory ra t does indeed display task-related activity patterns depending upon th e manifested oral behaviour. The task-related shifts of EMG patterns i n the anterior temporalis between masticatory bruxing/thegosis behavio urs in the same animal suggests a complex neurophysiological substrate that coordinates the three-dimensional expression of phasic activity patterns in the muscle. The radically different nature of masticatory and bruxing/thegosis cycles and their associated EMG patterns in the a nterior temporalis suggest the possible existence of a bruxing/thegosi s pattern generator in addition to the masticatory one. Careful, high- resolution analyses of these rat behaviours by combined optoelectronic /EMG techniques suggest that the rat model for human bruxism may prove useful in future studies. (C) 1997 Published by Elsevier Science Ltd.