Effects Of Repeated+Gz Forces On Temporomandibular Joints And Masticatory Muscles

The evolution of high performance combat aircraft has resulted hi ever increasing physiological stressors being imposed on the pilots of these vehicles. Many studies have shown that repeated high sustained +Gz stresses can cause injury of cerebrum, heart and kidney as well as skeleton and muscles in experimental animals by its high footwards centrifugal force, no study have demonstrated that +Gz force can induce injury of temporoman餴bular johit(TMJ) and masticatory muscles. This research aims to study the changes of repeated +Gz forces on TMJ and masticatory muscles. The effects of tea polyphenols(TP) on TMJ under +Gz condition was also observed. 1. Changes of temporoman餴bular joint(TMJ) under +Gz stresses.60 male Wistar rats were randomly divided into 5 groups (n =12). Group A was normally fed. Group B was only fixed with rat-kept devices for 5 minutes. Group C was borne +lGz for 5 minutes. Group D was repeatedly exposed +10Gz (each for 30s, onset rate about O.SG/s, 3 times/d witii +lGz l minute intervals, 3d/wk, 3 weeks in total). In group E 5 times/d and 4d/wk, other variables is the same as group D. TMJs from each group were respectively taken out and observed under optical microscope, scanning electron-microscope(SEM) and transmission electron-microscope(TEM). Results: No abnormal changes were observed in group A. B. and C. But in Group D and E pathologic injuries were seen m TMJs in different degrees. In group D, it can be seen that the arrangement disorder disruption of collagenfibers, the breakdown of primitive collagen fibers and the deformation of mitochondria cristae of flbroblast cells. The gel-like substances become very thin but roughly integrated. In group E, because most gel-like substances disappeared, the dispose and breakdovvn of collagen fibers of condyles of mandible and joint discs were found. Some flbroblast cells were taken from the condyle. The disappearance and deformation of mitochondria cristae and the abundance of rough endoplasmic reticulum(RER) in cartilage cells could be seen. Conclusion: The TMJs were induced pathologic changes in different degrees under various experimental variables. The increashig +Gz exposure could lead to the heavier damage of Rat's TMJ.2. Masticatory Muscles Injured by Repeated +Gz Forces and Its Possible Principles48 male Wistar rats vvere randomly divided into 4 groups. Group A was normally fed. Group B was only fixed with rat-kept devices for 5 minutes. Group C was borne +1GZ for 5 minutes. Group D was repeatedly exposed -1-lOGz (each for 30s, onset rate about 0.5G/S, 5 times/d with -1-lGz l minute intervals, 4d/wk, 3 weeks in total). The histological changes of themasseter muscles , temporalis and lateral pterygoid muscles were observed. The content of endothelin(ET), nitric oxide(NO) , malondiabdehy-de(MDA) and superoxide dismutase (SOD) hi masseter muscles homogenate of group A and D were determined. The fiber type composition of the masseter and temporalis muscles were analysed NADH-TR and adenosinetriphosphosphatase(ATPase) enzyme histochemical stain analysis. Results: No abnormal changes were observed in Group A B and C. But histological changes could be found hi group D. The wrench and deformationof muscular fibers, the dissolution of partial myofibril, the svvelling of mitochondria, the reduce of hepatin from the masseter muscles and lateral ptervgoid muscles could be found. Compared with the group A, in group D the levels of ET hi masseter were increased, but NO were not changed, both the levels of ET and NO in plasma didn't changed. The content of MDA in masseter vvere increased, but SOD were not changed. Both the cross-section area and distribution of type n fibers in the masseter and temporalis muscles vvere decreased in group D rats. ConclusionsiRepeated +Gz stress could induce the damage of masticatorv muscles in different degrees. The damage was related with too much release of ET and free radicals in muscles.