Rigid internal fixation and the effects on the temporomandibular joint and masticatory system: a prospective study.

A prospective study of 22 patients who underwent a bilateral sagittal osteotomy to advance the mandible and subsequent rigid internal fixation, were examined for signs and symptoms of temporomandibular joint (TMJ) pain and masticatory dysfunction. A modified Helkimo index was used to analyze the anamnestic, clinical, and occlusal data. In addition, 12 of the cases chosen at random were mounted on a semiadjustable (SAM2) articulator and analyzed with the mandibular position indicator (MPI) to determine the amount and the direction of condylar displacement postoperatively. Anamnestic dysfunction decreased because of a reported decrease in muscular pain, joint noise, headache frequency, and parafunctional habits postoperatively. Clinical dysfunction remained unchanged, with a decrease in muscular soreness but with an increased incidence of joint clicking of 7%. The increased incidence of temporomandibular joint pain postoperatively was 4%. Increase in clinical dysfunction was most often seen in women and older patients. Occlusal dysfunction decreased, with the majority of interferences remaining after surgery as a result of insufficient lingual crown torque of the maxillary buccal segments. Occlusion is thought to have played only a minor role in temporomandibular joint and masticatory dysfunction. Reduction in range of motion was 10%, indicating the added benefit of early mobilization with rigid internal fixation procedures. The MPI study found the condyles inferiorly or inferoposteriorly displaced less than 1 mm from their preoperative position. These findings suggest that rigid internal fixation had no adverse effects on the temporomandibular and masticatory system. The variable responses and results can be attributed, at least in part, to the heterogenous population of patients studied and the variations in surgical techniques employed.