[Morphological feature and incidence of TMJ disorders in mandibular lateral displacement cases]

In the malocclusion with mandibular lateral displacement (MLD), it is difficult to establish the functional occlusion by orthodontic means. The careful diagnosis brings us to recognize that MLD condition is the rule rather than the exception. In order to examine the characteristics of the cranio-facial morphology in the cases with MLD, the posteroanterior cephalograms were analyzed. Furthermore, the incidence of temporomandibular joint (TMJ) disorders (joint sound and joint pain) were examined clinically. The results were as follows: 1) Occlusal plane and mandibular plane (the plane running through the anti-gonialnotch bilaterally) inclined superiorly toward the mandibular displaced side. 2) The position of mandibular head shifted to the opposite direction of the mandibular displaced side. 3) The symptoms of TMJ disorders were found in 65.0% of patients with MLD, and more frequently at the TMJ of mandibular displaced side. Considering the evidences, the symptoms of TMJ disorders were much detected and occlusal deviation was found in MLD, it is suggested that mandibular dysfunctions derived from occlusal problems relate to the appearance of MLD. Since both the mandibular plane and the occlusal plane revealed the similar changes in response to mandibular deviation, it is considered that the condition of MLD as skeletal problem may be induced by the functional lateral shift of mandibular position come from occlusal interference during growth period. The deviation of mandibular head may relate to the appearance of TMJ disorders in MLD. Therefore, it is important to recognize the adequate mandibular position prior to occlusal reconstruction, and the vertical dimension control of the occlusal plane is necessary for improving the condition of TMJ and establishing the functional occlusion in the cases with MLD.