Pathohistological study on changes observed in the temporomandibular joint after experimental mutilation and shortening of the mandibular process with special reference to the changes under abnormal mandibular movement.

Abnormal mandibular movement continues to occur when fracture of the mandibular process has resulted in abnormal occlusion or abnormal mandibular movement. However, what changes might occur in the temporomandibular joint have not yet been fully clarified. In the present study, a fracture of the condylar process was experimentally induced in rats, and the resulting bone ends were wired in place. That is to say, the resulting displacement was fixed permanently. Histological studies were made on the changes of the temporomandibular joint at the postoperative third month in those rats which demonstrated abnormal occlusion and abnormal mandibular movement. Lack of uniformity of the fibrous layer and a shallowing of the mandibular fossa; proliferation of the fibrous connective tissue and reduction in size of the superior and inferior articular cavity; tylosis and irregularity in the articular disc; deformation and tylosis of the fibrous layer of the articular cartilage, tendency of the layer structure in the articular cartilage to disappear, and some effect on cartilaginous ossification in the condyle; flattening of the condyle and thinning of the layer structure in the condylar articular cartilage in the unaffected side of the mandibular joint. These changes were observed to be more marked as the displacement and occlusal abnormality of the mandible intensified, showing no morphological adaptation of the temporomandibular joint.