The Structural And Metabolic Changes In The Rat's Temporomandibular Joints Under Emotional Stress

Temporomandibular disorders(TMD) is an often disease in over a century. It is documented that the abnormal occlusions and mental influence affected TMD[1-2]. Though many studies was made on the relation between abnormal occlusions and TMD, the effect of mental influence was seldom reported. Few reports has shown that the mental influence could lead to symptoms, such like abnormal mandibular movements, pains and tiresome in facial muscle. The factor of emotional stress was concerned in the study of TMD, for the higher mental pressure of humans with the development of the society. 3 facial muscles with close relation with temporomandibular joint(TMJ) were chosen in this study, including messator, external pterygoid muscle and temporal muscle. SD rat emotional stress was simulated with the communication box model. The microstructural and ultrastructural pathological change in the TMJ and external pterygoid muscle was observed to show the emotional stress influence to TMJ structure and metabolism.90 SD rats were randomly divided into control group, emotional stress group and foot-shocked group in average. The communication box was applied in the emotional stress group. All the specimen of TMJ and external pterygoid muscle were taken after 1, 3 and 5 weeks. The microstructural and ultrastructural pathological change in the disc surface, condylar surface and external pterygoid muscle was observed with HE staining, scan electon microscropy (SEM) and transmission electon microscropy (TEM). The results showed that the collage was exposed and broken in TMJ disc and condyle, especially in the specimen of 3 weeks. At 5 weeks, the condylar cartilage started to recover. The mitochondria edema in the external pterygoind muscle was found after 1 week, even vacuolar degeneration with scan electon microscropy.To study the relationship between emotional stress and TMD, the SP and CGRP expression in the temporomandibular joints(TMJ) of the rats undergone emotional stress was observed. The results showed that the CGRP and SP postive nerve fibers could be found in the TMJ. The image analysis showed that the number of CGRP postive nerve fibers rised from the 1st week to the 3rd week and then falled down at the 5th week. The CGRP postive nerve fibers in the experimental group were more than that in the control(P <0.05). There was apparent difference in the number of SP positive nerve fibers between the experimental group and control(P <0.01). The number of SP fibers in 0 week differed to the number at 1st week(P<0.05), but did not differ to that at the 3rd and 5th week.The electromyogram(EMG) of facial muscles was examined at the first day, 1st, 3rd and 5th week for further research on the mechanism of the influence of metal stress to TMJ. The results showed the potential of temporal and messator muscles in metal stress affected rats were higher than that in the non-affected ones. There was no difference between both sides of the animals. The rest period of EMG in the both sides of temporal and messator muscles of in metal stress group were longer than that in the control group.Conclusion:1 Long term emotional stress could lead to pathological changes of the temporalmandibular system. The TMJ could be partly recovered after a certain time of adaption.2 the number of SP and CGRP energy nerve fibers in TMJ changed under emotional stress, suggesting that they might have taken part in the TMJ pathological process undergone emotional stress.3 there were changes in the EMG of mastication muscles under mental stress, which might be one of the factors of TMJ pathology and etiology.