Effect Of Locally Inject Ursolic Acid On Orthodontic Tooth Movement And Root Resorption In Rats

For the past few years, with the improvement of people’s living standard, orthodontics also got vigorous development. More and more people resorted to accept orthodontic treatment for a confident and beautiful smile. However, under the influences of personal factors and environmental factors, a part of patients suffered from tooth root resorption, which was a common side effect of orthodontic treatment. Therefore, to explore a medicine that can prevent or treat root resorption, has become an urgent problem to be solved by orthodontists.The mechanism of root resorption is similar with the mechanism of bone absorption. The cementoclast plays an important role during this process. In the pressure side, ischemia happened in the periodontal tissue, resorption pits were found on tooth root surface. With the continuous expansion of the scope of absorption, eventually leading to root resorption. Protein-tyrosine phosphatases(PTPs) has always been one of the research hotpots in the field of molecular biology. There were studies showed that osteoclastic protein-tyrosine phosphatase(PTP-oc), a member of PTPs family, was specially expressed in osteoclasts and had a positive regulatory effect on osteoclasts.At present, researchers have found efficient inhibitors of PTP-oc, that is ursolic acid(UA). Since ursolic acid can inhibit the activity of osteoclasts by inhibit the activity of PTP-oc, does it also play an important role as inhibitor during the process of tooth movement distance and tooth root resorption caused by orthodontic treatment? Under the above research background, the authors designed the following experiments, hoping to provide some scientific basis for the prevention or treatment of tooth root resorption.Objective: To investigate the effect of local injection different doses of ursolic acid both on orthodontic tooth movement distance and tooth root resorption in rats.Method: 1.To establish a modle of orthodontic tooth movement in Wistar rats. 96 male model rats were randomly divided into 4 groups, 24 rats in each group. After the successful establishment of the orthodontic tooth movement model, locally injecting different doses of ursolic acid into the buccal submucosal area adjacent to the right upper first molar, the dosages of ursolic acid in each group were: 0 mmol·L-1(control group), 0.5 mmol·L-1, 1.0 mmol·L-1 and 2.0 mmol·L-1 respectively, once per 3 days, each time 50 μL. Then the animals were respectively sacrificed on the 1 d, 3 d, 5 d, 7 d, 10 d, 14 d, 21 d and 28 d, 3 rats in each group.2.We made precise plaster model of rat maxiliary, then used vernier caliper to measure and calculate the moving distance of the right maxillary first molars of rats.3.After the preparation of tissue slices, we used hematoxylin-eosin(HE) staining to observe the morphological changes of rat root tissue.Result: 1.The tooth movement distances of rats in these 4 groups were all increased with the extension of time. Compared with the control group, the tooth movement distance of rats in 0.5 mmol·L-1 ursolic acid group after forcing 3 d, 7 d, 14 d, 21 d and 28 d had statistical significance(P<0.05 or P<0.01); compared with the control group, the tooth movement distance of rats in 1.0 mmol· L-1 and 2.0 mmol· L-1 ursolic acid group after forcing 1 d had no statistical significance(P>0.05), at any other time points, the tooth movement distance of rats had statistical significance(P< 0.01). Pairwise comparison among 0.5 mmol·L- 1, 1.0 mmol·L-1 and 2.0 mmol·L-1 ursolic acid group, after forcing 5 d, 7 d, 10 d, 14 d, 21 d and 28 d, the tooth movement distance of rats were all had statistical significance(P<0.05 or P<0.01).2.The morphological changes of rats root tissue: with the extension of the forcing time we found resorption pits on the surface of tooth root; in addition, with the increase of the dose of ursolic acid, the situation of root resorption was alleviated.Conclusion: 1. Locally inject ursolic acid could reduce the distance of orthodontic tooth movement in rats.2. The distance of tooth movement in rats were reduced with the increase of the dosages of ursolic acid.3. Ursolic acid had the tendency to eased tooth root resorption caused by orthodontic treatment on a certain extant.