Simultaneous mandibular movement and EMG analysis during habitual masticatory movement in patients with mandibular protrusion and deviation

Purpose: This study compared the incisal paths and masseter and anterior temporal muscle activity of patients with and without mandibular deviation. Subjects and methods: Fourteen adult patients with mandibular protrusion with or without mandibular deviation were subjected to simultaneous measurements of their incisal paths and masseter and anterior temporal muscle activity during masticatory movements. Results: The incisal paths of the deviation group (DG) were significantly more unstable than those of the non-deviation group (NDG) in the vertical direction in all sections of the mouth-opening path and from the initial to middle sections of the mouth-closing path. Horizontally, the incisal paths of the DG were also significantly more unstable than those of the NDG in all sections of the mouth-opening path and the initial and end sections of the mouth-closing path. The onset of masseter and temporal muscle activity on the working and nonworking sides occurred significantly earlier in the DG than in the NDG. Conclusion: The DG exhibited more unstable incisal paths than the NDG, and the early onset of masseter and temporal muscle activity observed in the DG patients during mouth closing might have been an attempt to compensate for their unstable incisal paths. This strategy might have been initiated based on information regarding the instability of the terminal position of the closing horizontal incisal path provided by periodontal sensory receptors. (C) 2015 Elsevier Ltd and the Japanese Orthodontic Society. All rights reserved.