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

Malocclusion is the one of the three major stomatological diseases which confirmed by WHO (The World Health Organization) and affects physical and psychological health seriously. By traditional technique, the general rate of orthodontic tooth movement was 1 mm/month. Therefore, the process of orthodontic treatment was usually about 2 years or longer. Because of these, scholars all over the world focused how to accelerate the tooth movement and shorten treatment period. Recently, they proposed some new methods to accelerate the tooth movement based on the same principal. Such as: selected the adapt force and timing, reducing resistance of periodontal tissue, local stimulation by electromagnetic force and using medications etc. Although these methods did improve the speed of tooth movement, but most of them were still in the experimental and study stage and seldom used in clinic practice. In 1998, foreign scholars had put forward the technique of distraction osteogenesis (DO) in clinical study for rapid canine distal movement and worked out 6.5mm in three weeks without any side effect. The new technique which we called Periodontal Ligament Distraction accelerated tooth movement rapidly. Currently, the molecular biology mechanism of tissue remodeling under mechanical strength is not clear that progressive study should be carried out to clarify how the mechanical signal transform to biological signal. Meanwhile, there only few reports which establishing animal experimental models for molecular biology mechanism study have been published. It is necessary to investigate the difference between new andtraditional technique and open up a new view for mechanism study of tooth movement.This study will set up reducing resistance and distraction experimentalanimal models firstly. The periodontal ligament histological changes of moving tooth will be observed by light microscope and transmission-microscope to investigate the difference between new technique force and traditional way. Further more, the BMP-2 and TGF-β1 in periodontal ligament will measured by using well- known immunohistochemistry and in situ hybridization techniques. It is first time to explore the BMP-2 and TGF-β1 changes in protein and molecular level which help us understand deeply about PDL remodeling and molecular biology mechanism of moved tooth.1. The Feasibility Research of Animal Model (Dogs) in Rapid Tooth Movement Through Reducing Resistance and Distraction (RRAD)Objective: We use self-made device for study group and traditional device forcontrol group. Animal models which are scientific, feasible and repeatable are established for study. Provide the basic theory for progressive study and clinic practice. Methods:9 male dogs were divided by 5 groups randomly as 6w group, 4w group, 2w group, 1w group (each group has two dogs) and other one for control (1 dog). The second premolars were extracted in both sides of dogs. We selected one side for study and the other side for control. After that, the following work processed: such as preparing tooth, making device, trimming alveolar bone and fixing the device etc. The experimental side was activated 0.25mm/d, twice a day for 2 weeks and followed by retention period. The control side activated 100g force for 2 weeks and followed by retention period. The anchorage loss, regular X-ray and pulp vitality were evaluated byresearcher. Results: After 4 weeks retention period, the mobility of moved tooth less than I degree. On the experimental side, 2 weeks activation made 3.95mm distal movement compared with 1.13mm distal movement in control side.(P<0.001). The anchorage loss in experimental side was 0.43mm averagely compare with 0.41mm in control (P>0.05). There were 3 tooth showed blunting root resorption(l degree) in experimental side from X-ray view and 1 tooth had the same resorption in control side. There were no evidence of anchor tooth root resorption and alveolar bone loss in both sides. For the moved tooth, the pulp vitality was no significant difference after distraction and 4 weeks retention. Conclusions: The animal model of rapid tooth movement through RRAD was feasible. This method accelerated the tooth movement with out root resorption, pulp lesions, bone loss, tooth mobility and anchorage loss etc.2. Histological Study of Periodontal Ligament (PDL)Remodeling Through RRADObjective: Biological characteristic of periodontal ligament changes which affected by two methods were observed by light microscope. This new technique provide the theory foundation for clinic practice. Methods: Sacrificed the dogs followed by the above individual group time frame and decalcified. Sections were stained with hematoxylin and Mallory's trichrome methods for observation and photograph. Results: The periodontal ligaments on tension side widened significantly in experimental side which compared with traditional method from initiation distraction to complete. Fibroblasts enriched in PDL (Periodontal Ligament, PDL) and new bone spicules formed actively with the same direction of distraction. New bone grew inactively incontrol side. However, PDL narrowed after initiating the distraction and then widened with the fibroblast enriching during mid-term on the pressure side. The hyalinization zone was disappeared early on the experimental side than control side. The interseptal bone which have undermined was absorbed gradually after initiating distraction and completed the alveolar bone remodeling after 1 week retention. 6 weeks later, the PDL recovered both in experimental side and control side. Conclusions: Reducing resistance and distraction method has the same mechanism as traditional way. There is no quality difference except quantity. The new method accelerated the PDL remodeling and alveolar bone absorbing (pressure side), new born growing (tension side). There was no evidence showing pulp and PDL lesions on the moved tooth.3. Ultramicrostructure Study of PDL Remodeling ThroughRRADObjective: Observing the PDL cells ultra-microstructure changes of moved tooth and revealing the affects of RRAD in PDL remodeling. That will provide the theories for further clinical practice. Methods: Making normal transmission-microscope section, stained with toluidine blue and selected the sections by normal light microscope and then make the transmission microscopy sections by LKB-5 microtome machine, all the sections will be observed by H-600 transmission microscope and photograph. Results: During the distraction, we found the cells which effect the remodeling of PDL are the similar between study side and control side (cells included osteoblasts, mesenchymal cells, osteoclasts, macrophagocyte etc). However, the number of the cells was different. Observed by transmission-microscope, we found theultra-microstructure and size of osteoblasts have significant different between experimental side and control side. During the retention period, the components of PDL cells changed back to normal as time went on. Conclusions: RRAD stimulated PDL cells growing and enlarged the size of osteoblasts and activated the function. However, the ultramicrostructure of cells was not effect significantly.4. The Expressions of BMP- 2 Protein and mRNA in PDLThrough RRADObjective: Evaluating the BMP-2 protein and mRNA expressions under the PDL remodeling after distraction by using immunohistochemical and in situhybridization techniques. This study will provide the theories for further clinic practice. Methods: Making the sections on different period of time and processing by immunohistochemical and in situhybridization as well as analyzing diagram. Results: The expression of BMP-2 protein and mRNA was more active in PDL through dental distraction than traditional method. It increased as distraction time went on and then reduced as retention time went on. On the moved tooth, the tension side expression of BMP-2 protein and mRNA was more active than pressure side. BMP-2 expressed mainly in osteoblasts near alveolar bone, cementoblasts near cementum, fibroblasts and few osteoclasts. In addition, BMP-2 expressed mainly in fibroblasts, osteoblasts and cementoblasts. Conclusions: BMP-2 took part in the remodeling of PDL. Dental distraction enriched the PDL cells and accelerated the new born growing so that the PDL remodeling and recovery become faster than traditional method. But there wasn't quality different between two methods.