The Correlation Between IL-17 Level In Gingival Crevicular Fluid And Orthodontically Induced Inflammatory Root Resorption In Rats

Objective To investigate gingival crevicular fluid (GCF) and serum levels of interleukin-17 before and after orthodontic treatment in rats with different forces, and observe the morphological alterations of periodontium on the pressure side of the orthodontic tooth and examine the levels of IL-17, RANKL, OPG and the quantity of osteoclasts at different time points. Furthermore, to assess the correlation between IL-17 level in GCF and the above-mentioned measurements related to root resorption. Then find out whether the level of IL-17 in GCF could remind the occurring of orthodontically induced inflammatory root resorption (OIIRR).Methods 65 male Wistar rats (aged 8-10 weeks) were randomly divided into 4 groups:Og group,20g group,60g group and control group. The experimental groups (0g,20g,60g) were subjected to different forces to induce a mesially tipping movement of the bilateral upper first molars with NiTi spring while the control group were subjected to no treatment. The rats were sacrificed after 1,3,5,7 and 14 days of orthodontic force application to simulate the occurring of OIIRR at different time points.IL-17 levels were measured by enzyme-linked immunosorbent assay in GCF and serum samples taken from the rats before and after orthodontic treatment. The morphological alterations of periodontium on the pressure side of the orthodontic tooth were observed by HE staining. The expression levels of IL-17, RANKL and OPG in periodontal ligament were determined by immunohistochemical analysis and were measured by Image-pro-plus6.0 image analysis system. The quantity of osteoclasts was examined by TRAP staining. Finally, all the data were analyzed by SPSS 16.0 statistical software.Results(1) The model of orthodontic tooth movement in rats with different forces was established successfully.(2) IL-17 was detected both in GCF and serum. The IL-17 levels in GCF and serum showed significant increases on the day 3,5,7,14 in different experimental groups after orthodontic force application (P<0.05) while the rate of increase was dependent on the force.(3) In the group of 20g, the most obvious changes of IL-17 levels in GCF and serum were on the day 3,5 respectively, while on the day 5,7 in the 60g group. The change of IL-17 level in GCF was moderately correlated with the change in serum (P<0.05).(4) In the group of 20g, the pressure area only had alveolar bone resorption but no root resorption. While the 60g force not only caused the alveolar bone resorption but also lead to the root resorption.(5) The expressions of IL-17, RANKL/OPG and the quantity of osteoclasts were consistent. All the most obvious expressions were on the day 3 in the 20g group while on the day 5 in the 60g group. There were high correlations among the above-mentioned measurements (P<0.05).(6) The change of IL-17 level in GCF was strongly correlated with the expressions of IL-17, RANKL/OPG and the quantity of osteoclasts in periodontal ligament (P<0.05). Once periodontium rebuilds or root resorption occurs during the orthodontic treatment, the IL-17 level in GCF would show a same trend.Conclusion During the orthodontic treatment, the expression of IL-17 in periodontium on the pressure side of orthodontic tooth will increase and then participate in root resorption through the function of osteoclasts by up-regulating the ratio of RANKL/OPG in rats. The change of IL-17 level in periodontium could express a same trend in the IL-17 level in GCF. The result indicated that the detection of IL-17 level in GCF could predict the degree of alveolar bone and root resorption availably during orthodontic treatment.