OBJECTIVETo study the changes of masseter muscle after reducing the mandibular by measuring some relative index after ostectomy of the mandibular angle along arch line.

METHODSLeft mandibular angle ostectomy was performed on New Zealand female rabbits aged three months. The right was not operated as control groups. Five rabbits were examined at the following intervals: 2, 4, 8, 12 and 24 weeks.

RESULTSThere 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 control group after 8 weeks (P > 0.05).

CONCLUSIONSThe changes of masseter fibres show reconstruction of masseter muscle after mandibular angle ostectomy.