Animal Experimental Study On Rapid Tooth Movement Through Reducing Resistance And Distraction

Objective To set up the animal model of rapid tooth movement through Reducing Resistance and Distraction. Tooth movement was measured with a sliding caliper and root surface was observed with scanning electronic microscope(SEM). Different means of morphology, histology, immunity histochemistry were applied to make clear the tissue rebuilding of the moved teeth, evaluate the feasibility and safety of rapid tooth movement through Reducing Resistance and Distraction, explore the biological mechanism of tooth movement, and provide theoretical basis for orthodontic clinical research.Methods 8 native healthy hybrid dogs were selected and randomly divided into 4 groups, each group contained 2 dogs,The mandibular second premolars on both sides were extracted and one side was randomly selected as experimental side while the other as control side. The mandibular first premoalrs were distalized respectively using the method of Reducing Resistance and Distraction on the experimental side and traditional method on the control side. X-ray examination was performed and the distance of tooth movement was measured respectively at the end of 1st,2nd,4th and 12th week after the activation. Then the 2 dogs of each group were sacrificed. The moved teeth of the one dog were extracted to examine the surface of the cementum by using SEM. The moved teeth of the other dog together with gums, alveolar bone were completely cut to make the histological specimen. The histological changes of the root and periodontal tissue were observed by HE staining and expression of osteoprotegerin (OPG) in periodontal ligament (PDL) was also inspected by using immunohistochemistry.Results1. The average distal movements of moved teeth on the experimental side and the control side were 4.66mm and 0.68mm respectively (p<0.05) after 2 weeks.2. X-ray observation:Root absorption, alveolar bone height reduction were not found during the experiment in both sides.3. SEM observation:In the 1-week group, there was clear absorption in the root surface of the experimental pressure side compared with that on the control side, and the scope and depth of root absorption were significantly increased in the 2-week group and the 4-week group; while the control side showed no significant change in the 1-week group, the scope and depth of root absorption became heaver in the 2-week group and the 4-week group. However, root absorption was lighter after the 1st,2nd, and 4th week on control side than on experimental side. While in the 12-week group, the experimental side and the control side showed the similar root absorption performance, the surfaces of lacunas became lower, smoother and evener.4. Histological observation:The tension side of experimental group and control group showed widened PDL, The bone formation was activity, and new bone formated on alveolar bone surface in the 1st,2nd, and 4th week group; while the pressure side showed narrowing of PDL, osteoclast activity, and the alveolar was absorbed significantly, even cementum showed absorption; However, the experimental side osteoblasts and osteoclasts appeared earlier than the control side, the alveolar bone and cementum absorption were serious on experimental side than control side. There was no significantly difference between the pressure side and the tension side of experimental moved teeth and control moved teeth in the-12 week group.5. Immunohistochemical observation:In the 1-week group, the positive expression of OPG on the experimental side was significantly stronger than the control side. And the positive expression of OPG in PDL increased gradually in both group after 2 weeks, especially the experimental side showed stronger positive expression. With the time went on, the expression of OPG weakened gradually in both group after 4 weeks.Until the 12 weeks, expression of OPG declined to normal.Conclusions1. The method of Reducing Resistance and Distraction can speed up the tooth movement.2. Compared with the traditional method of orthodontic tooth movement, the method of rapid tooth movement through Reducing Resistance and Distraction can increase the root absorption of moved teeth in the pressure side. However, the cementum would repair after unloading of force if time extends.3. There was no difference in quality but in quantity on the histological reactions and the root absorption of the teeth moved by traditional method and by the method of Reducing Resistance and Distraction, the latter could accelerated tooth movement than the former.4. OPG participated in PDL remodeling process and maintained a dynamic balance of bone resorption and bone formation. The method of rapid tooth movement through Reducing Resistance and Distraction accelerated PDL remodeling and enriched the PDL cells.