Histochemical Study of the Masseter Muscle in Patients with Maxillofacial Deformity

Abstract

This study was designed to examine the histochemical characteristics of the masseter muscle in patients with maxillofacial deformity.Biopsies of the deep surface of the anterior aspects of the superficial masseter were obtained in 21 male patients (18 with mandibular prognathism., 2 with open bite, 1 with maxillo-facial asymmetry) at the time of corrective surgery by sagittal splitting rami osteotomies of the mandible. Controls were 6 normal subjects with normal occlusion.Individual muscle fibers were classified as type 1 (slow twitch-oxidative), type 2A (fast twitch-oxidative glycolytic) and type 2B (fast twitch-glycolytic) based on ATPase staining.The normal human masseter muscles had a unique fiber profile compared to that of normal limb and trunk muscles, and type 1 fibers were the largest and type 2 fibers were the smallest in normal subjects. These findings suggest that the masseter muscle is highly adapted to the special and complicated functions of the stomatognathic system.In patients with maxillofacial deformity, type 1 fibers were the largest and most prevalent type of fiber and type 2 fibers were much smaller than those in normal subjects with statistical significance. Some cases demonstrated evidence of myopathic disorders: type 2 group atrophy, small angulated fibers and type 1 grouping. Targetoid fibers were recognized in one patient. The pattern of type 1 predominance and type 2 atrophy observed in these patients was different from the distribution in a person free of jaw deformities.It is a very interesting problem on whether the pathologic abnormalities observed in this study represent an underlying neuromuscular problem or a secondary manifestation of muscle stress is caused by a abnormal bone growth.