Study Of The Expression Of RANKL In Periodontal Tissue Of Rat During The Orthodontic Tooth Movement

The growth and development of alveolar bone are influenced by biotic force. As Structural frames, the bone rebuild constantly in all the life of the people to form ideal structure to adapt mechanical environment. The biological mechanisms of tooth movement result from the cellular responses of periodontal connective tissues of exogenous mechanical forces.The orthodontic tooth movement is a bone remodeling process accompanied with the bone resorption on the compression side and the bone formation on the tension side .It was shown that receptor activator of NF-kB ligand (RANKL) has close relation with bone remodeling. The tumour-necrosis-factor-family molecule RANKL has been identified as a potential osteoclast differentiation factor. It is confirmed that RANKL can facilitate the bone resorption by osteoclast in vivo and induce the formation of osteoclast in vitro. RANKL is on the cell membrane of osteoblast. It is the key factor of signal transmission between osteoblast and osteoclast. RANK is the protein of the tumour necrosis factor receptor. RANK is on the osteoclast precursors and can be identified by RANKL.It is the only target signal receptor of facilitating osteoclast differentiation by RANKL. All kinds of factors of stimulating bone resorption act on the osteoblast and induce its membrane expressing RANKL. Then, RANKL combines with RANK which is on the precursors. Signal is introduced into precursors. This arose expanding reaction. Osteoclast is differentiated and mature. OPG combines with RANKL as the inducing fake receptor and restrains the formation and differentiation of osteoclast. So the OPG/RANKL/RANK cytokine system forms the key way of developing, mature and function of the osteoclast. RANKL is expressed in gingival, tooth follicle and periodontal ligament(PDL) fibroblasts.It plays an important role during the rebuilding of the periodontal tissues.It takes part in the tooth eruption, physiological root resorption of deciduous teeth and the orthodontic tooth movement. The purposes of our study are (1) to investigate the RANKL expression location and expression level changes in PDL during the experimental rat tooth movement process,(2)to explore the origination, mechanism of RANKL and the relation between RANKL and alveolar bone remodeling during the orthodontic tooth movement. Materials and methods:The male rats whose weights were almost 225±25 gram were chosen and they were divided into normal group and experimental( 1,3,5,7,14,21 day ) group randomly . Each group had 6 rats, and the total number was 42. A coil spring was deposited between the maxillary first molar and the maxillary central incisor, the first molar of rats was considered as the orthodontic tooth and the central incisor was the anchorage tooth. The first molar was moved to the mesial by 50g force.42 rats were sacrificed at 0 day,1 day, 3 day, 5 day, 7 day, 14 day and 21 day. All of tissue sections were processed, then proceeded with HE staining and RANKL immunohistochemical staining. Observing thehistological changes of periodontal tissue, the result was analyzed by the Computer Image Analyzing System and treated by statistics test. Results: There are RANKL expression in the compression and tension side of PDL in both non orthodontic treatment groups and orthodontic treatment groups. In the periodontal tissue of non orthodontic treatment groups, RANKL expressed lower. The localization of RANKL was marked in the cytoplasm of osteoblasts on the surface of alveolar bone and a few periodontal ligament fibroblasts., well-distributed. The expression of RANKL on the compression side is not lower than the tension side. In the 1 day group, no significant changes of RANKL expression was noted, except disturbing sequence of fibroblasts shapes. In the 3 days group, osteoclast activation was noted and strong RANKL expression exist in the compression side .The number of the cell which express RANKL increased . The localization of RANKL was marked in the cytoplasm of osteoblasts on the surface of alveolar bone and in the medullary cavity of bone and periodontal ligament fibroblasts near the alveolar bone. But in the periodontal ligament fibroblasts near the cementum RANKL expressed lower. In the 5 day group, the expression and distribution of RANKL were similar with the 3 day group. In the 7 day group, the osteoblasts on the surface of alveolar bone still express RANKL. The number of the cell which express RANKL near blood vessel decreased. In the 14 day group, the expression of RANKL became weaker. In 21 day group, RANKL expression level...