| Clinically, occlusal disorders including tooth loss, malocclusion are often found to be coexisted with TMD patients. However, controversies still exist concerning the occlusal etiology of TMD. Because of the tooth eruption, attrition, tooth loss, orthodontic and prosthetic treatment, orthognathic surgery and so on, the occlusion is believed to be taking changes during one's life time, and has obviously individually characterized. For the reason of multi-appearance and changes of occlusion and the complicated structure and movement of TMJ. it is impossible to investigate relationships between all kinds of occli.~ions and TMJ. The more practicable and effective way of research might be to choose a particular type of mal-occlusion and to detect the role it may play in the histo-pathological alterations of condylar cartilage. Our past experiments showed that the gradual occlusal disorders led to degenerative changes of TMJ. But, the pathogenesis is kept unclear. The main purpose of the present experimental study was to establish a stable animal model of degenerative changes of TMJ result from gradually induced occlusal disorders in New Zealand white rabbit, and to investigate the process and mechanism of the pathogeneses. Part I: To establish the animal mode of gradually induced occlusal disorders (GIOD) to TMJ degenerative changes, the upper first premolar at one side and the lower premolar at the other side of three New Zealand Rabbits were pulled by the orthodontic string, making them inclined medially to the anterior intrinsic space, inducing a convex to convex occlusal contact relationship. Four control groups, three rabbits in each group, were converted among them as extraction of first premolars referred above, supe.filling the related premolar by light-cure resin, merely ligation them with orthodontic wire (method control), and the blank control. Histology observation and histometric study were carried out, the results showed as followings. I. Condyles of blank controls from the age of 5 to 8 months showed the typical aging appea~ences: declination of the full thickness of cartilage as well as hypertrophic layer. and the cellular density. The thickness of the proliferative layer also declined though unevenly distributed. 2. Two months after super-filling, the thickness of fibrous and hypertrophic layers, and the whole cartilage of anterior intermediate parts of condyles decreased significantly. The layer-border became indistinct. However, the thickness of all the whole cartilage. fibrous layers and proliferative layers increased while that of hypertrophic layers decresed. Most subchondral bone trabecula became parallel to the articular face instead of perpendicular like those in controls. In contrast to the single super-filling group. the thickness of hypertropic layers and proliferative layers of multi-super-filling animals increased significantly. Moreover, the changes of the latter became more obvious as the experiment time getting longer. 3. One month after extraction of the first premolars, the opposite tooth became over-errupt comparing to the occlusal plane and the adjacent teeth inclined to the space, occluding with opposite in-coordinately, wthat led to secondary occlusal disorders. Degenerative changes appeared in their condylar-cartilage significant. But 2 and 3 months later, enhanced tissue-repairing response were observed. 4. No obvious difference was found between the merely ligation group and blank control group, both of which showed normal characteristics. But for the GIOD group the condylar car... |
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