[Kinematic analysis of limitation of mouth opening of temporomandibular disorders by rotation and translation of the condyle].

PURPOSE The purpose of this study was to determine whether rotation and translation of the condyle were useful parameters for identifying causes of limitation of mouth opening in patients with temporomandibular disorders (TMD). METHODS In 7 healthy volunteers and 55 patients with TMD, rotation and translation of the condyle were measured using a 6 degree-of-freedom jaw movement tracking device. Patients were divided into two groups: those who could open their mouth 40 mm or greater, and those who could not open their mouth 40 mm. In each group, the relationship of rotation and translation of the condyle to maximum mouth opening, condition of the articular disc, and pain was determined. RESULTS Both correlations between maximum mouth opening and rotation and translation of the condyle were strong, especially the former correlation. There was no marked difference in the distribution of range of mouth opening, and rotation and translation of the condyle with respect to condition of the artticular disc. Muscle pain was associated with reduced mouth opening. Even in patients without limited mouth opening, their range of mouth opening was actually reduced when they had muscle pain. Among the patients with limited mouth opening, joint pain correlated to limited translation of the condyle. However, in patients with Wo-Wo condition of articular disc, their translation of the condyle was not limited even with joint pain, but it was limited with muscle pain. CONCLUSIONS Rotation of the condyle indicated strong correlation with muscle pain, and so is a useful parameter for estimating treatment methods by a surgical approach. On the other hand, translation of the condyle showed variations in correspondence with combinations of several factors such as opening limitation, condition of the articular disc, and pain.