| The oral maxillofacial system is composed of occlusion, temporomandibular joint(TMJ), masiticatory muscles and central neural system. They affect and restrict each other, that is to say, the movement of the masticatory muscles will arouse corresponding movement of the mandible with the adaptive position of the condyle and occlusal condition. Therefore, the changes of the occlusal vertical dimension will result in the changes of the condylar position which may arouse the masticatory muscles and TMJ to remodel adaptively. It is known that weaker masticatory activity can decrease the formation of the condyle and height of the mandibular ramus which may come out a high angle pattern. Evidences have indicated that patients with high angle pattern are more liable to temporomadibular disorder(TMD) and malocclusions of vertical discrepancy and the TMJ synovium is involved initially. However, researches at present are mainly forced on condylar cartilage and fewer researches on synival tissue. Generally, it is difficult to correct the vertical discrepancy on patients with high angle pattern and required for increase of occlusal vertical dimension to relieve the lock relationship of the teeth occasionly. Unfortunately, during the orthodontic treatment, those patients often suffer from TMJ discomforts especially pain.Sixteen 6-week-old male Spraque-Dawley rats were classified into four goups. The first group served as control, and rats in the second group were adhered composite resin to their maxillary molars in order to increase the occlusal vertical dimension when they were 9-week-old. Rats in the third group were cut off their bilateral masseter when they were 6-week-old. In the last group, rats experienced bilateral masseter resection and increase of occlusal vertical dimension. All rats were sacrificed at their 10 weeks old. TMJ samples were prepared for histology and evaluated for cyclooxygenase-2(COX-2) and inducible nitric oxide synthase(iNOS) expressions by immunohistochemistry to examine the inflammatory changes in the synovial membrane. In this study, we simulate the condition as we mentioned above to investigate the changes on the TMJ synvium in adolescent rats to discuss the effects of masiticatory muscles and changes of occlusal vertical dimension on formation of TMD which may offer the experimental basis for the clinical prevention and therapy. The study consists of two sections:1 Establishment of animal model of temporomandibular joint synivitis and its histological investigationResults: The control group showed non-inflammatory changes. The occlusal dimension increase group and the masseter resection group showed vascular dilation and synovial lining proliferation, but there were no statistically significant differences between the two groups(P>0.05). Compared to the two disposed groups, the last group showed significant inflammatory changes(P<0.05), including synival lining proliferation, vascular dilation and fibrin deposit which were common features of synovitis.2 Weaker masseter affects expressions of C0X-2 and iNOS induced by occlusal vertical rise on temporomandibular joint synovium of adolescent ratsResults: The control group showed rarely expression of C0X-2 or iNOS. The occlusal dimension increase group and the masseter resection group showed some expression of COX-2 and iNOS, there were no significant differences on the expression of COX-2 between the two groups(P>0.05), but the occlusal vertical rising group existed higher expression of iNOS(P<0.05). The last group came up with more significant expressions of COX-2 and iNOS than the other two disposed groups(P<0.05)Conclusions:The rats experienced bilateral masseter resection following with increase of occlusal vertical dimension existed obvious inflammatory reactions. Therefore, we may conclude that masticatory activity plays an important role in mandibular growth and weaker masticatory can not induce temporomandibular disease alone. However, when it cooperates with increase of occlusal vertical dimension it can deteriorate the temporomandibular disease. |
