Adaptations in the Temporalis Muscles of Rabbits after Masseter Muscle Removal

Masseter muscles were surgically removed in six youngfemale rabbits so that we could study adaptations of the superficial temporalis mus-cles (ST) to increasedfunctional requirements. Eight weeks following surgery, we used morphological measurements, histochemistry, con-tractile properties in situ, and occlusal force in vivo to compare the muscles in the experimental animals and six control rabbits. Analysis of the results demonstrated a decrease in fatigability of ST after mas-seter myectomy. Incisal occlusal force decreased by 65 % during the first two weeks, and no recovery was observed during the following six weeks. At eight weeks post-surgery, the mass, twitch tensions, and tetanic tensions of ST were not significantly different from those of the controls. An increase in the percent of the cross-sectional area composed offastfatigue-resistant fibers, a slower time-to-peak twitch tension, and a decrease infatigability suggest an increase in oxidative metabolism. Analysis of these results suggests that muscles used for highly repetitious activities with submaximal loadings adapt to in-creased functional requirements by increasing fatigue-resistant prop-erties