ADAPTATIONS OF THE MASTICATORY SYSTEM AFTER BILATERAL FRACTURES OF THE MANDIBULAR CONDYLAR PROCESS

Purpose: The objective of this investigation was to evaluate the adapt ations that occur in the masticatory system after treatment of bilater al 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 fixatio n (n = 6), closed therapy (n = 14), or a combination of these techniqu es (n = 2) were compared with 22 sex-and age-matched controls. Measure s of mandibular range of motion, bite force, muscle activity, estimate d 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 patient s and controls. Results: There was no significant difference in the pa tients' morphologic measures for the open and closed reduction procedu res; therefore, all of these patients were tested as a single group. A fter treatment, patients had significantly increased mandibular plane and genial angles and decreased facial axis angles. They also showed a significant reduction in posterior facial height and moment arm lengt h for the masseter and pterygoid muscles. Anterior and posterior tempo ralis muscle direction also was significantly different between patien ts and controls. Patients had significantly limited mobility during th e first year after fracture. Bite forces were lower for patients at al l 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 differe nces were not statistically significant, probably because of the small sample size. The estimated joint force magnitudes were essentially id entical between patients and controls; however, the direction of the p atients' joint forces were more posteriorly directed for both incisor and molar bites. Conclusion: The results of this study suggest that ea rly reduction in mandibular range of motion, bite force, and the distr ibution of masticatory muscle activity assist in preventing overloadin g of the bilaterally fractured mandibular condylar processes.