HISTOPATHOLOGIC AND BIOCHEMICAL-CHANGES IN THE MUSCLES AFFECTED BY DISTRACTION OSTEOGENESIS OF THE MANDIBLE

Lengthening of the canine mandible using an intraoral distraction devi ce was performed in order to study the effects of distraction on the a ssociated muscles of mastication. Biopsies of the masse ter and digast ric muscles were taken after lengthening at four different time interv als to assess tile temporal changes in the masticatory muscles of 10 d ogs. Biopsies of the muscles on the contralateral side also were taken from 6 of these dogs before lengthening to establish a control group. Each biopsy was analyzed histologically and spectophotomerically for RNA, DNA, and protein content. The digastric muscle underwent transien t atrophy with initiation of distraction but regenerated completely af ter 48 days of fixation. The masseter muscle was unchanged initially b ut showed evidence of atrophy only after 20 mm of distraction; it cont inued to exhibit evidence of atrophy during fixation. Protein synthesi s was decreased significantly during periods of atrophy in the massete r; no such change was noted in the digastric. Unlike the masseter, the digastric fibers lie in a plane parallel to the vector of distraction . These findings suggest that any muscle affected by skeletal distract ion in the same plane or vector (e.g., digastric) adapts with compensa tory regeneration and hypertrophy. Moreover, those muscles lying in a different plane (e.g., masseter) show persistent evidence of atrophy w ith decreased protein synthesis.