Mandibular movements at maximum mouth opening and EMG activity of masticatory and neck muscles in patients rehabilitated after a mandibular condyle fracture

Objective. To assess rotation and translation movements of the mandible at maximum mouth opening in a group of patients successfully rehabilitated after condylar fractures. Materials and methods. Using a three-dimensional motion analyser, free movements of mouth opening were recorded in nine patients, and divided into their rotation and gliding components. Surface electromyography (EMG) of the masticatory and sternocleidomastoid (SCM) muscles was performed during maximum voluntary teeth clenching (MVC). Data were compared with those collected in healthy adults. Results. At maximum mouth opening, the total displacement of the mandibular interincisor point was 86% of reference value (p > 0.05, Student's t test), with a reduced vertical displacement (84% of reference value, p = 0.012). Percentage mandibular rotation was significantly larger in patients (82%) than in reference subjects (77%, p = 0.005). During MVC, patients had more asymmetric EMG potentials (p = 0.018), with greater mandibular torque (p < 0.001), and reduced co-contraction of SCM (p = 0.003). EMG indices were used to formulate an overall performance score that was related to the characteristics of mouth opening (r = 0.557). Conclusion. Notwithstanding a good recovery in the total mandibular movement, the rotation/translation components of mouth opening were modified. The overall EMG performance score could be used to predict the characteristics of mandibular motion.