| ObjectiveThe objective of this study was establishment differential orthodontic force for orthodontic tooth movement in a rat model,to study the distance of orthodontic tooth movement,the expression and distribution of BMP-2 and RANKL during orthodontic tooth movement and the periodontal tissue remodeling in normal group and periodontitis group,And to study the effect of different orthodontic force on the rebuilding of inflammatory periodontal tissue and the relationship between alveolar bone remodeling and stress under different orthodontic force in periodontitis rats.To texploration the suitable orthodontic force and limitation of treatment of tooth movement in periodontitis,which can offer the basis of the theory and experiment for the clinical application of doctor.Material and MethodsEighty and four Wistar rats(Age:7weeks)were randomly divided into control group A and experimental group B(n=42 in each group).The rats of group A without any treatment.The experimental periodontitis model of group B was established after four weeeks using wire ligation method on the maxillary first molar.The rats of group A and group B were given general food,high-sugar soft food respectively. Two rats were executed randomly in two group respectively after 4 weeks, Histomorphometric analysis was performed in group B to determine that the experimental periodontitis model was successfully established. and then group A and B were randomly divided into 4 subgroups(n=10 in each group),orthodontic force of 0 g, 30 g,50 g, 80 g were loaded on the bilateral maxillary first molar in each subgroup and established the orthodontic tooth movement model. The distance of orthodontic tooth movement were recorded after adding the forces for 1d, 3d, 7d, 14 d, 21 d,respectively. The rats were executed to observe the change in periodontal ligament, alveolar bone, osteoclasts of bilateral maxiallary first molars by HE stain. And to detect the expression of BMP-2 in the tension side and RANKL in the pressure side of periodontal tissue using immunohistochemistry by Biosens Digital Imaging Systen(Shanghai Shanfu Scientific Instrument Co, Ltd).The average integral optical density was recorded. All the data was analyzed using SPSS17.0 software package.Results1. General observation in group B : Weight loss. Intra-oral observation of periodontal tissue in group B: localized inflammation, bleeding on probing, attachment loss and periodontal pockets were evident. Histological observation:gingival epithelial spikes hyperplasia, infiltration of inflammatory cells, resorption of alveolar bone surface and osteoclast. Hence, the establishment of animal model with periodontitis was observed.2.The speed of orthodontic tooth movement was accelerated after adding the force from 1d to 7d, slowed down from 7d to 14 d,then accelerated again from 14 d to 21 d in each subgroup. Among the subgroups in group A, the speed of orthodontic tooth movement of subgroup A3 was the fastest and subgroup A4 was the slowest.The average distance under the same orthodontic force was analysised using T-test between group A and B,finding that the average distance of orthodontic tooth movement in group B was significantly higher when comparing with group A. There were statistically significant difference(p﹤0.05).3.There were no obvious changes in periodontal tissue in group A1 by HE stain at different time.There was active remodeling of periodontal tissue with occurrence of new osteoblasts in the tension side and osteoclast along with the resorption in the pressure side of alveolar bone.The periodontal ligament fibers were disordered and irregularly arranged with root resorption in a small area in group A2 and A3. There was attachment loss, periodontal pocket formation, disordered and irregularly arranged periodontal ligament, infiltration with large number of inflammatory cells, resorption of alveolar bone and osteoclast in the pressure side of periodontal tissue in group B1. There was severe resorption of alveolar bone in the pressure side and occurrence of osteoblasts with widening of periodontal ligament in the tension side of periodontal tissue in group B2 and B3.There was resorption of alveolar bone, osteoclast cells with disordered and broken periodontal ligament present in the pressure side and scarce population of osteoblast in the tension side of periodontal tissue in group B4.4. In group A, as the orthodontic force was increased, the average integral optical density of BMP-2 increased, and there were statistically significant difference between other subgroups and A1(p﹤0.05).There were no statistically significant difference between group A3 and A4. The expression of BMP-2 in the tension side of periodontal tissue for both group A and B had the same tendency but the time of reaching the peak was different with 7d in group A and 14 d in group B which then declined gradually. Under the same orthodontic force,the average integral optical density of BMP-2 in group B was higher than group A, and there was no statistically significant difference.5. In group A and B, as the orthodontic force increased, RANKL expression increased and reaching the peak on 7d. Orthodontic force is positively related to RANKL expression. Under the same orthodontic force, RANKL expression in group B was positively higher than group A, and there was no statistically significant difference between group A and B.Conclusion1.Experimental periodontitis model can be established using high-sugar soft food and wire ligation method.2. Under the same orthodontic force, the distance of orthodontic tooth movement in experimental periodontitis group was greater than control group.3. As the orthodontic force increased, RANKL expression in the pressure side and the expression of BMP-2 in the tension side of periodontal tissue was increased, the expression of BMP-2 and RANKL was positively related to the orthodontic force.RANKL and BMP-2 play an important role in remodeling of periodontal tissue of orthodontic tooth.4.BMP-2 expression in the tension side of periodontal tissue in control group reached the peak on 7d, whereas reaching the peak on 14 d in experimental periodontitis group. It was evident that the speed of alveolar bone rebuilding was delayed in experimental periodontitis group.5.Under the different orthodontic force, there was no statistically significant difference in alveolar bone rebuilding between the control group and experimental periodontitis group. It was apparent that orthodontic therapy could not aggravate the destruction of alveolar bone.6. RANKL expression in the pressure side and the expression of BMP-2 in the tension side of periodontal tissue were active during 50 g force. And 50 g is the best force in promoting alveolar bone rebuilding. |
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