A 26-year-old woman was referred to our clinic on December 22, 1993, because of limited mandibular movement. Minor restriction of mouth opening was first noticed at 10 years of age, during a dental health examination. The patient became aware of pain and swelling of the right masseter region with decreased jaw movement at the end of November 1993.
Clinically, the patient had a square face with prominent masseter muscles and mandibular angles. The interincisal opening was 22mm, with limitated lateral and anteroposterior mobility. A dense band of tissue, which became taut on maximal opening, was palpable along the anterior border of each masseter muscle.
The clinical diagnosis was restricted mouth opening due to bilateral hyperplasia of the masseter muscle aponeuorses. Masseter muscle myotomy with aponeurectomy was performed bilaterally by an intraoral approach on May 18, 1995. The aponeuroses extended for three quarters of the length of the masseter muscles, down to the inferior borders of the mandible. The mouth opening improved to 46mm on incision of the aponeuroses.
An examination of the patient 3 years after surgery revealed an interincisal opening of 38mm without strain.