Adaptations of the masticatory system after bilateral fractures of the mandibular condylar process

Purpose: The objective of this investigation was to evaluate the adaptations that occur in the masticatory system after treatment of bilateral fractures of the mandibular condylar process. Patients and Methods: Twenty- two patients (15 men and seven women) with bilateral condylar process fractures treated by open reduction and rigid internal fixation (n = 6), closed therapy (n = 14), or a combination of these techniques (n = 2) were compared with 22 sex- and age-matched controls. Measures of mandibular range of motion, bite force, muscle activity, estimated joint forces, and skeletal morphology were determined at 6 weeks, 6 months, and 1, 2, and 3 years after treatment in all subjects. Various statistical tests were used for comparing differences between patients and controls. Results: There was no significant difference in the patients' morphologic measures for the open and closed reduction procedures; therefore, all of these patients were tested as a single group. After treatment, patients had significantly increased mandibular plane and gonial angles and decreased facial axis angles. They also showed a significant reduction in posterior facial height and moment arm length for the masseter and pterygoid muscles. Anterior and posterior temporalis muscle direction also was significantly different between patients and controls. Patients had significantly limited mobility during the first year after fracture. Bite forces were lower for patients at all times and tooth positions, with a significant difference at 6 weeks after treatment. Patients had a tendency to use proportionally higher temporalis muscle activity during maximum biting; however, the differences were not statistically significant, probably because of the small sample size. The estimated joint force magnitudes were essentially identical between patients and controls; however, the direction of the patients' joint forces were more posteriorly directed for both incisor and molar bites. Conclusion: The results of this study suggest that early reduction in mandibular range of motion, bite force, and the distribution of masticatory muscle activity assist in preventing overloading of the bilaterally fractured mandibular condylar processes.