Mandibular Osteoradionecrosis Of SD Rat Bone Metabolism Mechanism Research

1.Establishment of animal model of mandible osteoradionecrosis in SD rats.Objective: To establish a convenient,efficient and stable animal model of mandible osteoradionecrosis in SD rats for further study of the pathogenesis of mandibular ORN.Methods: Twenty-four male Sprague-Dawley rats were randomly divided into 4 groups,6 in each group: group a(normal control group);group b(simple extraction group);group c(simple radiation group);group d(radiological extraction group).The right mandible of group c,d rats were exposed to 35 Gy 6MV-X-ray once.All molars of the right mandibular were extracted 15 days after irradiation by submandibular incision.The clinical manifestations were observed regularly.The right mandible was respectively taken from each group 90 days after irradiation for imaging examination of CBCT,Micro-CT and histomorphology observation of HE,Masson staining.Results: 1.Clinical manifestations: 90 days after irradiation,there was no obvious osteoradionecrosis of the mandible in a,b,and c groups.The tooth extraction wound in group b was healed normally two weeks after tooth extraction.In group d,it began to appear that the maxillofacial cutaneous fistula or penetrating defect and the death bone exposure one month after the radiation.There was a significant decrease in body weight in the d group compared with the other groups(p<0.05).2.CBCT and Micro-CT: CBCT observed bone destruction and cortical bone discontinuity.Micro-CT observed that not only the formation of dead bone,but also pathological fracture.The bone density of group d was significantly lower than that of a,b and c groups,which was statistically significant(p<0.05).3.Histomorphology observed lamellar bone fracture,osteocytes disappearance,late fibrosis repair.Conclusion: Using the 3D-CRT technique which commonly used in clinical radiotherapy,The right mandible of group c,d of rats which were exposed to 35 Gy 6MV-X-ray once combined with tooth extraction trauma once can set up an available and stable animal model,which can be used for the study of the pathogenesis of radiation osteonecrosis.2.Mandibular osteoradionecrosis of bone metabolism mechanism research in SD ratsObjective: Based on the establishment of animal model of mandible osteoradionecrosis in SD rats,the expressions of RUNX2,OPG,RAKNL and VEGF in bone metabolism at different time points were observed and morphological changes were observed to explore the possible mechanism of osteoradionecrosis of the mandible.Methods: 144 male Sprague-Dawley rats were randomly divided into 4 groups,36 in each group.Grouping method was the same as the first study.Using the same method of irradiation and tooth extraction,the specimens of bone tissue were obtained at the end of the 4th,9th,15 th,30th,45 th,90th day after the irradiation.Histopathological changes were observed by HE at the same time.The expression of bone metabolism related factors: VEGF,RUNX2,OPG,RAKNL were assessed by RT-q PCR and WB.Results: 1.HE staining: Osteogenesis and osteotomy coexisting phenomenon occurred in the early stage of irradiation,mainly osteogenesis reconstruction.Osseous poor inflammatory repaired in the later stage.Slow bone regeneration occurred in group c and osteogenic repair occurred in group b after tooth extraction at the same time.2.Expression of VEGF: There were no sighificant differences in expression of VEGF between group b and the normal control group.The expression of VEGF in group c and d was lower than that in normal control group.3.Expression of RUNX2.The expression level of RUNX2 in group d reached its peak at the 9th day.After a rapid decline,the expression reached the lowest point at the 45 th day.The expression appeared a bimodal state in the group c,increased obviously at the 9th,30 th day.The expression degree of RUNX2 increased significantly at the 45 th day.At the 4th,9th day,the degree of RUNX2 in group c,d was higher than group b.At the 45 th day,the expression in group d was lower than group a,b,c.4.The ratio of RANKL/OPG: The ratio of group d decreased at the 4th day,reached its peak at the 45 th day in group d.The change trend of the group c was similar to group d.The ratio of group b got a peak at the 30 th day,then decreased.There were no significant differences in the ratio of RANKL/OPG among groupb,c,d at the 4th,9th,and 15 th day.The ratio of groupb,c,d was statistical differences at the 45 th day.Among them,group d was the highest,group c was the second,and group b was the lowest.Conclusion: The expression of angiogenic factor VEGF was decreased.Vascular function damage and metabolic disorders throughout the whole radiation.New bone formation dominated in the first 15 days after radiation.Bone resorption was aggravated in the 15 days after radiation.The trauma after tooth extraction can aggravate the imbalance of ORN bone metabolism and promoted the occurrence of ORN.