Functional subdivision of the human masseter and temporalis muscles as shown by the condylar movement response to electrical muscle stimulation

In previous studies from our laboratory, a functional subdivision of the hu man temporalis and masseter muscles was demonstrated by means of opto-elect ronic recordings of the lower incisal point movement responses to electrica l muscle stimulation. In the present study, it was examined whether this su bdivision was also reflected in different movement responses of the mandibu lar condyle. To that end, the condylar movement responses to unilateral sti mulation of four masseter muscle parts and three temporalis muscle parts we re studied in four different jaw positions. The kinematic centre was used f or condylar reference point. For both the amplitude and the direction of th e movement responses, the effects of stimulation location and jaw position were studied using multivariate ANOVA and contrast analyses. It was found t hat for both outcome variables, the functional subdivision of the masseter and temporalis muscles was also reflected in some, but not all, of the move ment responses of the mandibular condyles. The deep masseter muscle part an d the (anterior) temporalis muscle part responded similarly to electrical s timulation.