The Effects Of Mechanotransduction Of Osteocyte On Orthodontic Tooth Movement Under Mechanical Stress

ObjectiveIn classic theories of orthodontic tooth movement, when we apply appropriate force to the teeth in orthodontic treatment, it will first cause reconstruction of periodontal tissues, then the bones, and eventually achieve movement of the correctional teeth. At present, it is generally believed that the activation and proliferation of periodontal ligament cells is the key to start the reconstruction of tissues, while the remodeling of bones is only a consequence accompanied by reactions of the periodontal tissues.However, a phenomenon in clinical orthodontic treatment caught our attention. Periodontal membranes are usually not involved in the traction of embedded teeth, and yet bone remodeling still happens; in addition,select the cases who implant micro-implants as anchorage, it was found through CT 3D registration technology that micro-implant will also move under stress. Does this suggest that that movement of embedded teeth and micro-implants is the result of the alveolar bone’s direct response to the mechanical stress, while periodontal ligament is not the key to the movement of embedded teeth (implants).So we turn our eyes to bone cells. Under stress stimulus, mature bone cells may secrete a kind of protein which inhibits osteogenesis-Sclerostin.More and more researches show that,sclerostin is an extracellular inhibitor of the Wnt/β-catenin signal path. Through competitively combining with Wnt protein, it assists receptor LRP5/6 in restraining differentiation and activity of osteoblast. In addition,Sclerostin through a competitive combination of BMP type land type II receptor inhibition of TGF-beta/BMP signaling pathways,thus inhibiting osteoblast differentiation and bone formation. In animal models of SOST gene knockout mice, where the inhibiting effect upon Wnt/β-catenin signal path from Sclerostin is removed, osteogenesis markedly increases. Thus, Sclerostin is very important negative regulatory protein in bone remodeling.Based on previous related researches, by simulating the stress environment of body cells by means of applying traction force to vitro cultured cells, combined with molecular biological detection, this experiment explores the influence and mechanism of Sclerostin in bone remodeling during orthodontic tooth movement at cellular level and from the angle of molecular biology and further provides theoretical and practice basis for orthodontic tooth movement.This research selects Saos2 cells to perform in vitro experiment. Saos2 cells are bone sarcoma cells and have the characteristics of bone cells, such as SOST and DMP1-marker genes of overexpression mature bone cells, as well as RUNX2 and COL1A1, marker genes of low expression osteoblast, and under mechanical force, they secrete Sclerostin, thus are ideal models to study bone cells in vitro.MethodsObserve the expression changes of SOST genes and Sclerostin of cells under mechanical forceWith Saos2 cell lines as the research objects, a torque meter is used to exert stretch stress to Saos2 cells. After 0,1,2,4,6,12,24 and 48 hours of stress, RT-PCR detects the expression changes of SOST genes of cells, and ELISA detects the concentration changes of Sclerostin in cell-culture medium.Results1.Changes of SOST gene expression in Saos2 cells after different loading timeOh loading group was the control group,Saos2 has SOST gene expression under no stress, and under mechanical stretch stress, Sclerostin concentration changes:after 1h of stress, it begins to reduce obviously, have statistical significance (p<0.05); after 6h of stress, it minimizes (p<0.01); after 12h of stress, the expression begins to rise, but still lower than the level of the control group (p<0.01); after 48h of stress, it is elevated to the level of the control group(p>0.05).2.Changes of Sclerostin concentration in Saos2 cell-culture medium after different loading timeOh loading group was the control group,Saos2 has SOST gene expression under no stress, and under mechanical stretch stress, Sclerostin concentration changes:after 1h of stress, it begins to reduce, but with no statistical significance (p>0.05); after 4h and 6h of stress, the concentration of Sclerostin is lower than other groups,have statistical significance (p<0.01),but no statistical significance (p>0.05) between them; after 12h of stress, the expression begins to rise, but still lower than the level of the control group (p<0.01); after 48h of stress, it is elevated to the level of the control group(p>0.05).Conclusion1.In Saos2 cells under mechanical stress, depending on different duration of time, the expression of SOST has obvious changes, which shows that bone cells are involved in the tooth movement in the process of bone remodeling, and is of great significance in the mechanism of orthodontic tooth movement.2.Mechanical stress can reduce the expression of SOST and protein, and the expression quantity minimizes from 4h to 6h, then gradually rises to normal levels; it shows that Osteocyte can make rapid and brief response of expression to mechanical stimulation. It proves from the cellular level that Osteocyte participates in the bone remodeling in the tooth movement process.3.This research helps to better understand the bone remodeling in the tooth movement process.