Effect of working side interferences on mandibular movement in bruxers and non-bruxers.

The effect of working interference on 13 bruxers and 14 non-bruxers was studied by applying a metal overlay on the buccal cusps of the adjacent upper premolar and molar. The pattern and velocity of cyclic movement during gum chewing before and after overlay insertion were observed. EMG of the temporalis and masseter muscles were recorded bilaterally during the chewing movement. It was found that after insertion, one of the non-bruxers complained of pain in the muscles, while such a complaint was not found in bruxers. Bruxing habit was reported to be less or eliminated in 44% of the bruxers, but no non-bruxers became bruxers. The closing velocity was more often decreased immediately after overlay insertion, and the closing path near the occlusal phase was significantly narrower, with patterns of over-extension and avoidance before reaching the occlusal phase. The delayed effects were a more vertically oriented chewing cycle without over-extended closing movement, and an unretarded chewing velocity. It was concluded that within the experimental period a working side interference was tolerable in most of the subjects studied with or without a bruxing habit.