Abstract
The mandibular arch width changes between the right and left first molars, incisal movements and electromyograms of the inferior head of the lateral pterygoid muscle (LPt) was analyzed during opening and protrusive jaw movement.The average maximum mandibular arch width decrease in five subjects was 397.7μm during opening and 585.0μm during protrusion. The width did not change much during the early stages of opening, although it decreased markedly in the later stages. During closing, the width rapidly returned to its original state. The decrease in width during static maintenance of a given opening position was smaller than the decrease at the same position during dynamic opening.There was an immidiate decrease in the mandibular arch width at the beginning of protrusion, a gradual decrease as the protrusion proceeded, and an accelerating decrease in the later stages. The width during static maintenance of a given protrusive or retrusive position was essentially the same as that during dynamic movement.There was a significant correlation between the decrease in mandibular arch width and the electromyographic activity of the LPt (p<0.001). The results suggest that the LPt is the primary cause of decreases in the mandibular arch width during opening and protrusion.
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