[Changes in the fine structure of the masseter muscle as affected by unilateral occlusal disorders]

Biopsy specimens from the masseter muscle of the miniature pig "Mini-LEWE" were analysed histochemically before and after unilateral occlusal disturbances. The percentages of different fibre types and the cross-sectional area of fibres were determined with the myosin-ATPase reaction after acid preincubation. The capillary membranes were visualized by means of modified PAS-reaction. There was demonstrated a significant increase from the percentage portion of ST-fibre types, especially of the side of occlusal disturbance, under experimental conditions. This indicates an increased isometric contraction of the masseter muscle. The size of FT-fibre types and the capillarity increase significantly on the side without occlusal disturbances, due to the dislocation of the masticatory efforts to this side. The masseter muscle fine structure is shown to be adapted good to the disturbed functional conditions. No significant side differences were found in the dry mass of the masticatory muscles, at the end of experiments.