Circumscribed Myositis Ossificans of the Masseter Muscle.

The authors report a case of myositis ossificans traumatica of the masseter muscles. A 21-year-old man developed masseter myositis after orthognathic surgery to treat facial asymmetry. The myositis may have been triggered by factors such as calcification of a hematoma, periosteum implantation after surgical trauma, and local soft tissue injury. An intraoral incision was made to excise the ectopic bone, resulting in resolution of the patient's symptoms including limited oral opening.