Adaption Of Masseter Muscle After Mandibular Angle Ostectomy In Rabbits

Objective To study the changes of masseter muscle after ostectomy of the mandibular angle along arc line in rabbits.Methods Left mandibular angle ostectomy was performed on New Zealand female rabbits aged three months.The right was not operated as control. Five rabbits were examined at the following intervals:2,4,8,12 and 24weeks.The changes of masseter were investigated in postoperative morphology, histology,histochemistry and expression of myosin heavy chains mRNA.Results There were remarkable decreases in the experimented masseter muscle masses and the same type muscle fiber areas compared with the control group(p<0.05).As for the fiber types,a decrease in type I fibers and an increase in type II fibers were noticed on operative side masseters(p<0.05). Sarcomere lengths in the operative side muscles were significantly reduced and showed statistical significance during first 4 weeks(p<0.05),but there was no difference between the operative group and the contral group after 8 weeks (p>0.05). The amount of MHCI mRNA on the left masseter significantly decreased at the first 8 weeks(p<0.05).The amount of MHCII mRNA was significantly different at 2nd week(p<0.05),and then recovered to no statistic value after 4th week(p>0.05). MHCII/MHCI on the operative masseter was more than that of control group at 2,4,8 weeks(p<0.05) and then showed no statistical significance.Conclusion The changes of masseter fibres show reconstruction of masseter muscle after mandibular angle ostectomy.