Repair Effects And Related Mechanism Of Ultrasound On Orthdontic Root Resorption In Rats

Objective: To examine the effect of ultrasound and the expressions of TNF-α andOPG/RANKL ratios on orthodontically induced root resorption in rats.Methods:64male Wistar rats were randomly divided into4equal groups:negativecontrol group, simple loading group,natural recovery group andultrasound-treated group (n=16, respectively). The animal models of orthodontic rootresorption were established except the contral group.An initial force of100g wasapplied to the areas between the upper central incisors and the right first molars of therats in two weeks.After that, removed the coils and killed the rats of the simple loadinggroup.The ultrasound-treated group were accepted the ultrasound irradiation(1.5MHz100MW/cm2)every day for two weeks. Eight rats were randomly chosen from eachgroup. Observed the microcosmic change of the root surfaceby scanning electronmicroscopy and measured the root resorption indexes. The experimental teeth-centeredsagittal tissue slices were generated from the experimental teeth and peridentium of theremaining8rats of each group. HE staining to obseve root absorption and repair, trapstaining for analyses of positive cell number, immunohistochemistryto detect theexpression of TNF-α,OPGand RANKL, image analysis system of Imagepro-Plus6.0was usedfor optical density. The experimental results were analysed with spss softwareby one-way analysis of variance.Results:1. The ultrasound-treated groups displayed significantly fewer cementoclastnumbers and lower root resorption indexthan the natural recovery group(p<0.01).Ultrasound-treated group also showed abundant new cementum formation.2. Theexpression of TNF-α were decreased and theOPG/RANKL ratios wereincreased in the ultrasound-treated groups. Compare to nature recovery group, thedifferences were statistically significant.Conclusion: Ultrasoundreduced the generation of cementoclastand conduced tocementum regenerationby reducing the expression of TNF-α and increasingOPG/RANKL ratios.