| In an age of information, we can obtain information through a variety of methods, which reinforced the understanding of malocclusion and enhanced awareness of dental aesthetic. There are more and more people require for orthodontic treatment. During the orthodontic treatment, due to various factors, different levels of root resorption usually occurs leading a disordered crown-to-root ratio, gomphiasis, loss of tooth and so on, which can impair the health and living quality of patients. Root resorption occurred frequently, thus, the resorption degree and its repair have always been the focus of orthodontist. However, the issues as to whether this kind of resorption can be repaired or not, to what extent can it be repaired and whether there is an effective measure to further the repair are still unclear at present.Our study built a tooth movement model of the left maxillary first molar of rats, a closed-coil spring had exerted 100 g of force for 14 days and then it was removed. Whereafter, the enamel matrix protein was injected into the flexure of mucosa of left maxillary first molar and a vivo Micro-CT scan was conducted. The changes in root resorption craters volume and its surrounding alveolar bone microstructure were observed. With the application of HE staining and TRAP staining and immunohistochemistry technology, the changes in cementoclast, BMP-2, BSP, OPG and RANKL in periodontal tissue were detected. The role of enamel matrix proteins in the root resorption repair process was explored in order to seek a feasible method to promote root repair and provide an experimental basis for the clinical application.Part one: Using Micro-CT to observe the effect of enamel matrix protein on the root resorption repair process.Objective: Using Micro-CT to evaluate the effect of Enamel matrix protein on the the root resorption craters volume and alveolar bone microstructure.Methods: Ten male Sprague-Dawley rats aging at 10 weeks-old were selected. The animals were stochastically divided into two groups(n=5 in each group). A nickel-titanium coil spring exerting 100 g was ligated between the ipsilateral first upper molar and upper central incisor with a 0.2-mm ligature wire for 14 days. As soon as it was removed a vivo Micro-CT scan was immediately conducted. The scan range included the left maxillary first and second molar, and the surrounding alveolar bone. The images obtained from the scan were processed by 3D measurement software, to assess the volume of root resorption lacuna and structural parameters of trabecular bone. Since the appliance was removed, 30μg/ml of enamel matrix protein was injected at the flexure of mucosa of left maxillary first molar in experimental group for once every three days with a dosage of 0.02 ml for each injection(five times in total), while the control group received no treatment. After the 14 days a vivo Micro-CT scan was taken again, the root resorption craters volume and trabecular parameters between the two scan time points were calculated.Results: on the day 0 of root repair process, the difference of root resorption craters volume between the two groups was not statistically significant(P>0.05).But on the day 14, the root resorption craters volume of experiment group was smaller than that of control group, the decrement of root resorption craters volume of experiment group was significantly greater than that of control group(P<0.05). The root resorption craters volume of both groups were smaller than that on the day 0, and the volume of resorption lacuna at dental root surface before the repair was significantly different from the one after the repair. On the day 0 of root repair process, the difference in BV/TV, Tb.Th, Tb.N, SMI, Tb.Sp between the experiment group and control group was not statistically significant(P>0.05).But on the day 14, both groups had an increase in BV/TV, Tb.Th and the experiment group had a greater increase than control group, the increment in BV/TV and Tb.Th of experiment group was significantly greater than that of control group(P<0.05), there was a decrease in SMI, Tb.Sp and an increase in Tb.N of both groups, but the difference in SMI, Tb.Sp, Tb.N between the experiment group and control group was not statistically significant(P>0.05).Conclusion: EMD can enhance the effect of the repair after root resorption was done to the orthodontic tooth movement in rats.Part two: The effect of enamel matrix protein on the expression of BMP-2, BSP, OPG and RANKL in root resorption repair process.Objective: Using HE staining and TRAP staining and immunohistochemistry technology to observe the effect of enamel matrix protein on cementoclasts and the expression of BMP-2, BSP, OPG and RANKL in root resorption repair process.Methods: the model was identical to the Part one. The rats were killed on the 14 th day since the remove of orthodontic appliance, the cementoclasts were counted by TRAP staining, the morphological change in periodontal tissue was observed by HE staining, the expression of BMP-2, BSP, OPG, RANKL was detected by immunohistochemical methods.Result:1. HE staining: on the day 14 of repair process, as for the control group, an obvious resorption lacuna can be seen in the the apical third of the mesial root and neck of the first molar, which reached deep dentin, the periodontal fibers were disordered in arrangement, the cementum was discontinuous. As for the experiment group, the periodontal interval of both sides was symmetrical, the periodontal fibers were relatively regular in arrangement and the surface of cementum was smooth and level.2. TRAP staining: in 14 days since repair process, the positive and stained multinucleate cell can be occasionally seen in the resorption lacuna for both groups, the staining was relatively light, the difference between both groups was not statistically significant.3. Immunohistochemistry: after 14 days since the removal of force, the positive expression quantity of BMP-2 and BSP of experiment group was greater than that of control group, their positive expressional level was clearly higher than that of control group. The positive expression quantity of OPG and RANKL of experiment group was close to that of control group, the difference in expressional level between both groups was not statistically significant.Conclusion: during the root resorption repair, EMD enhanced the expressional quantity of BMP-2 and BSP, from which it can be speculated that, EMD could induce the proliferation and differentiation of periodontal ligament cells and increase the expression of relevant mineralization factors and promote root resorption repair. |
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