Characterization of brux-like movements in the laboratory rat by optoelectronic mandibular tracking and electromyographic techniques

High-resolution optoelectronic mandibular tracking and fine-wire electromyographic (EMG) data from the anterior temporalis muscles of laboratory rats (Rattus norvegicus) were collected during mastication (chewing) and bruxing/thegosis (grinding/sharpening of teeth) in order to test for task-related activity patterns of the anterior temporalis. Analyses of the collected data revealed that masticatory and bruxing/thegosis cycles displayed significantly different patterns of movement trajectories, displacement, duration, velocity, and acceleration in all three spatial dimensions (frontal vertical, frontal horizontal and sagittal horizontal). Activity patterns in the anterior temporalis during masticatory and bruxing/thegosis behaviours were also significantly different from each other. High-resolution analyses revealed that the masticatory cycle had both opening-burst and closing-burst phasic patterns of anterior temporalis activity while the bruxing/thegosis cycle displayed only opening-burst phasic patterns. The opening- and closing-burst attributes of anterior temporalis phasic activity patterns in relation to physiological centric occlusion also revealed significant differences between masticatory and bruxing/thegosis behaviours. These data demonstrate that the anterior temporalis muscle of the laboratory rat does indeed display task-related activity patterns depending upon the manifested oral behaviour. The task-related shifts of EMG patterns in the anterior temporalis between masticatory bruxing/thegosis behaviours 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 anterior temporalis suggest the possible existence of a bruxing/thegosis pattern generator in addition to the masticatorys 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.