| Background:Occlusion trauma is caused by abnormal contact of teeth,dysfunction of chewing,and occlusal interference due to iatrogenic causes.Abnormal occlusion may be one of the causes of temporomandibular disorder(TMD).In recent years,studies have found that PPAR-?(peroxisome proliferators-activated receptor-?)is closely related to the development of inflammation during the abnormal reconstruction of joints.Purpose:In our study,an animal model of occlusal trauma was established.The distribution of PPAR-y,MMP-13(matrix metalloproteinase-13),IL-1?(interleukin-1?)and IL-6(interleukin-6)in TMJ was observed and analysed at different time points.To explore the possible etiology of temporomandibular arthritis caused by occlusal trauma,the related role of PPAR-y in rat condylar inflammation and abnormal reconstruction,and to provide a new way to further explore the etiology of temporomandibular joint disorders and the new target of the treatment of the mandibular joint.Materials and Methods:48 8-week-old male Wistar rats(weight:180-220 g)were divided into experimental group?(EG I),experimental group ?(EG ?)and control group(CG)randomly.On the right lowerjaw first molar of EG I and EG II group was bonded with a 3/4 cobalt-chromium metal crown with a thickness of 1.0 mm.The EG I group was the experimental group with the occlusion trauma,which was randomly divided into occlusal trauma at 1 week,4 weeks,and 8 weeks,with 5 rats in each group.The 3/4 cobalt-chromium metal crown of the EG II group was removed at 1,4,and 8 weeks,and they were sacrificed after 2 weeks.So the EG II group was divided into 1 + 2 weeks,4 + 2 weeks and 8 + 2 weeks group,5 rats in each group;the CG group was divided into 1 week,3 weeks,4 weeks,6 weeks,8 weeks,10 weeks group with 3 rats in each group.These time points were sacrificed.The temporomandibular joint slices were prepared for hematoxylin-eosin staining(HE staining)at the corresponding time points in order to observe morphological changes of temporomandibular condylar cartilage.Immunohistochemical staining(IHC staining)was used to compare the expression of PPAR-?,IL-1L,IL-6 and MMP-13 in condylar cartilage.Results:Part I The establishment of traumatic occlusal rat modelThis study and the previous study have verified that the 3/4 cobalt-chromium metal crown has good retention and maneuverability,good metal crown adhesion,obvious pathological damage to the temporomandibularjoint.And occlusal trauma could induce temporomandibular arthritis.The model was successfully established and could be used for further research on temporomandibular joint inflammation.Part ? Histology observation of traumatic occlusal TMJThe hematoxylin-eosin staining showed that:The morphology of TMJ in the control group showed no significant changes.In the EG I group,the number of condylar cartilage chondrocytes decreased,and the cells in each layer were disordered with inflammatory behavior.It can be seen that the thickness of the proliferative layer and the hypertrophic layer of the 4w and 8w groups are thinner,the cells of the hypertrophic layer are obviously swollen with"island-like" shapes,and some areas had a cell-free zone.The inflammatory condition of EG II group was less than that of EG I group.The arrangement of cells in each layer became normal,and the hypertrophic layer and proliferative layer were thinner than the control group.Part III Expression changes of PPAR-?,IL-1p,IL-6 and MMP-13 in rat temporomandibular jointThe immunohistochemical staining showed that:1.In the CG group,IL-1?,IL-6 and MMP13 were weakly positively expressed;PPAR-y was strongly expressed(p<0.05).2.In the EG I group,when compared with 1-week group,the positive expression of IL-6,MMP13 and IL-1? was concentrated in the mast cell layer and enhanced in the 4-week group(p<0.01).The Chondrocytes between the mast cell layer and the proliferating layer cells also showed positive expression in a small amount.Besides,the expression of IL-6,MMP13 and IL-1?decreased in the 8w group(p<0.01);PPAR-? was mainly expressed in the mast cell laye.The expression of PPAR-y in the EG I group was lower than that of CG group(p<0.05),and the positive expression of PPAR-y in 4 weeks group was the lowest among all the EG I groups(p<0.05).3.EG II group:As for IL-1?,MMP13 and IL-6,each group of EG II showed positive expression,statistically different from the control group(p<0.05).Compared with the EG I group,the expression of IL-1?,MMP13 and IL-6 lessened in EG? group(p<0.05).However,EG group showed positive expression of PPAR-y,increasing after the mental crown was removed(p<0.05).4.There is no obvious inflammatory expression in the junction between temporomandibular joint and the olfactory fossa and the temporomandibular joint fossa in this experiment group,which may be related to the time of the model of occlusion trauma.Further experimental research is still needed.Conclusion:Bonding a 3/4 cobalt-chromium metal crown is a stable and reliable method of occlusal trauma,which is suitable for the investigation of occlusal trauma and temporomandibular joint.In the early stage of occlusal trauma,the TMJ inflammation in rats is obvious.In the late stage of occlusion trauma,the inflammatory reaction weakens,and the inflammatory reaction of the occlusion trauma after removing the crown weakens,which is beneficial to the tissue healing of the temporomandibularjoint.In the occlusal trauma environment,PPAR-y may be involved in the regulation of the temporomandibular joint inflamation.The down-regulation of PPAR-y may be related to the up-regulation of IL-1?,IL-6 and MMP-13 factors,which promotes the inflammatory response of the temporomandibular joint in occlusal trauma model. |
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