The Effect Of Occlusal Trauma On The Remodling Of Condyle And Subchondral Bone Of Rats

Purpose:To evaluate the effect of occlusal trauma(OT)on changes of histomorphology and biomechanical characteristics of rat mandibular condyle and subchondral bone remodeling.And we attempt to elucidate the influence mechanism of occlusal trauma to the temporomandibular joint,so that we can provide a theoretical basis for clinical methods.Materials and Methods:8-week-old Wistar rats(45)are randomly divided into three groups:,occlusal trauma group(experimental group A),removing of OT for 2 weeks(experimental group B)and control group(group C).In order to establish the occlusal trauma rat model,we bonded th:ree-quarter cobalt-chromium metal crown on the first right mandibular molar,which is about 1.0 mm higher than occlusal plane.The experimental groups were further divided three times points,The experimental groups A:TMJ were harvested at 1,2 and 4 weeks post-OT(n=5).The experimental groups B:removing of UOT for 2 weeks after OT for 1,2 and 4 weeks(n=5).For the rats in control groups nothingwasdone for theocclusion and raised in the same environment 15 rats were positioned in the control group and rats were sacrificed at the end of 1,2,3,4,6week respectively.The animals from all groups were killed and we collectted the TMJ as specimens to make tissue slice.HE staining and Masson trichrome staining to observe thechanges of morphology in the condyle and subchondral bone.Osteoclast activities were analyzed by tartrate-resistant acid phosphatase(TRAP)staining and cathepsin K(CK)immunohistochemistry staining.And the number and activity of osteoblast were analyzed by alkaline phosphatase(ALP)staining.We calculated the average optical density value of ALP,CK and the number of TRAP cells by the ImagePro-Plus6.0 software.And we used the statistical software,Graphpad Prism.6.0 for the corresponding statistical analysis.Results:(1)Establishing animal model:Compared with the control group,the rats in the experimental group were thinner,didn't care the diet,and the casting crown was stable.(2)the results of HE staining showed that:The control group;the layer of cells in the control group arranged orderly,clear boundaries,with prolonged observation time,condylar cartilage showed age-related changes for cartilage thickness,the thickness of articular cartilage is negatively correlated with age of rats.The experimental group:experimental group A showed a typical degenerative changes of the condylar cartilage thickness,corresponding with the same old rats than in the control group(P<0.05),and condylar cartilage degenerated gradually.However,in the experimental group B,there was no significant difference in B1 group,B2 group with control group,and the B3 group had the characteristics of hierarchical fuzzy and cell arrangement disorder.(3)the expression of Masson trichrome staining in subchondral bone:The control group:the structure of cancellous bone was regular,the mature mature cancellous bone(red)and the new bone(blue)were axisted,and the proportion of mineralized mature cancellous bone was more than the new bone.The experimental group:experimental group A showed irregular and disordered cancellous bone structures,in experimental group A?B,the proportion of immature bone(blue)is higher than that of C group(COL/TV)(P<0.01).And in the experimental group B,there was the dyed blue non mineralized cancellous bone near cartilage increasedsignificantly.(4)The immunohistochemical analysis of ALP showed that:The control group:ALP was mainly expressed in the condylar subchondral trabecular bone.The experimental group:experimental group A:the positive area percentage was significantly higher than that of the control group(P<0.01).Compared with the control group,the experimental group B was also showed an increasing trend(P<0.01).(5)The TRAP staining and theimmunohistochemical analysis of CKshowed that:The control group:there were few TRAP staining in the subchondral bone,and CK positive cells were very few.The experimental group:TRAP?CK positive cells were mainly expressed in the fibrocatilaginous zone and subchondral bone,In the experimental A group,the percentage of positive area compared with the same age control group increased significantly(P<0.05).In the experimental B group:had more TRAP.CK positive cells than that of the control group,and the expression in experimental B group was significantly higher than that of the control group in the same age group(P<0.05).Conclusion:(1)The way of adhesive easting crowns can establish a stable and reliable model of occlusal trauma.(2)traumatic occlusion can lead to degenerative changes of the condylar cartilage in rats,and the degree of histological changes is more obvious with the increase of the occlusion timeand is associated with proliferative response.(3)removal of local stimulation factors,the condylar cartilage and subchondral bone morphology tended to normal.