Experimental Study Of The Osteoprotegerin And The Ovariectomized Rat Model Of Experimental Periodontitis

Objective:To establish experimental periodontitis model in SD rats by bilateral overiectomized and ligatured their first maxillary molars with steelwire in order to evaluate the effects of estrogen-deficiency and estrogen replacement therapy upon alveolar bone height. Meanwhile to observe local molecule expressions of OPG in periodontium and compare the content of OPG in alveolar bone of relevant groups, then clarify the role of OPG in alveolar bone absorbion. Methods:Fifty -three female healthy SD rats were randomly divided into three groups, group Sham(n=17): sham operated;group OVX (n=18): ovariectomized;group OVX+E2 (n=18): ovariectomized and estrogen administrated. All of the rats were fed 7 days to adapt the environment before ovariectomy or sham operation. The rats of group OVX+E2 were prescribed benzyl estradiol one day after ovariectomy. Half of the rats of every group (8 of group Sham, 9 of group OVX and 10 of group OVX+E₂ ) were ligatured with steelwire on the upper first molars to induce periodontitis respectively two after ovariectomy or sham operation. The remainder were ligatured two weeks later. Four weeks after ligature, all of the animals were sacrificed and the specimens routinely processed. The right maxillary molar was choosed to be evaluated in this study and their digital photos and X-ray were taken, the periodontal bone loss and the periodontal bone support was measured with Photoshop 7.0 software. Immunohistochemistry were used to observe the expression of osteoprotegerin in periodontium, and the mean optical density and integrated optical density of OPG positive expression was measured with digital image analysis system.Results:1. Compared with group Sham and group OVX+E2, the PBL of group OVX ishigher and the PBS is lower (PO.05 ), there is no significant difference between group Sham and group OVX+E2 ( P>0.05 ) . In the same group , the PBL and PBS at different weeks(6w and 8w after ovariectomy or sham operation) were compared, the PBL of 8w is higher and the PBS is lower than that of 6w (P<0.05 ) .2. The OPG positive expression in rat periodontium are situated in the cementum, alveolar bone and periodontal membrane, positive cells include osteocytes, osteoblasts, mesenchymal cells in bone marrow, cementoblasts, cementocytes and fibroblasts. The expression of OPG at dentino-cemental junction and the bone around marrow cavity were intense and their distribution was polar.3. The semi-quantitative analysis of IOD revealed that the IOD of group OVX is lower than that of group Sham and group OVX+E2 (PO.05 ) .There is no significant difference between group Sham and group OVX+E2 (P>0.05 ). In the same group , the IOD at 8w after ovariectomy or sham operation were lower than that of 6w (PO.05 ) .4. The number of osteoclasts in periodontium and osteoblast on the surface of alveolar bone of group OVX were higher than that of group Sham and group OVX+E2 (PO.05) .In the same group, there is no significant difference betweenthe number of 6w or that of 8w (P>0.05) . Conclusions: 1. Estrogen deficiency accelerates alveolar bone absorption. Estrogen replacementtherapy can help prevent alveolar bone height reduction due to estrogen deficiency. It's prompted that the female should recruit extra estrogen at the beginning of menopause to improve their resistance to alveolar bone absorption.2. The expression of OPG in periodontium imply that OPG is concerned with the remodelling of alveolar bone and part of the regulation of estrogen to alveolar remodelling is via OPG.3. Estrogen deficiency decreased the expression of OPG in alveolar bone, weaken the protective function of OPG in bone tissue .