A rare case of postoperative malocclusion with severe joint effusion due to mouth opening rehabilitation exercise after surgical correction of masticatory muscle tendon-aponeurosis hyperplasia

We reported a case of postoperative malocclusion with severe joint effusion due to mouth opening rehabilitation exercise after surgical correction of masticatory muscle tendon-aponeurosis hyperplasia (MMTAH). A 39-year-old female with gradually progressive trismus had been diagnosed with MMTAH. Panoramic imaging showed bilateral elongation of the coronoid process, square mandible with hyperplasia of the mandibular angle and left lower wisdom tooth pericoronitis. Computed tomography and magnetic resonance imaging (MRI) demonstrated hyperplasia of the masticatory muscle. MRI of the TMJ revealed no abnormal findings. Under general anesthesia, the patient underwent a coronoidectomy of the bilateral coronoid process. The maximum mouth opening increased to 53 mm immediately after the osteotomy. Five days after surgery, we began mouth opening exercises. The patient remained able to open her mouth wider than 41 mm. Then, malocclusion with posterior open bite occurred. Three weeks after surgery, an MRI revealed severe joint effusion of bilateral TMJ. Thus, we carried out pumping therapy on the bilateral TMJ. The malocclusion promptly disappeared. Prior to surgery, there had been no joint effusion in the MRI. However, we found severe joint effusion after surgery and mouth opening training. So, MRI examination is very important to check postoperative progress in the case of unusual signs or symptoms.