Effect of physical factors on osseointegration

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It is well known that appropriate occlusal force promotes bone formation around implants, whereas bone atorophy and bone resorption develop under no mechanical stress or overstressing. It has been reported that when shear stress loads to osteoblasts, increase of intracellular Ca^<2+> concentration, activation of protein kinase A, and upregulation of cyclooxygenase 2 (Cox-2) gene result in differentiation of osteoblasts. The purpose of this study was to clarify appropriate levels of stress for the bone remodeling and mechanotransduction signaling at molecular levels.We examined pattern of gene expression when compressing force was directly loaded to a mouse osteoblast like cell line (MC3T3-E1) for 24 hours by reverse transcription polymerase chain reaction and cDNA macroarray. Furthermore, we examined change of gene expression under its stress by cDNA microarray.Cox-2, c-fos, and alkaline phosphatase mRNAs were upregulated in proportion to the stress value when compressing force was loaded. The analysis of cDNA macroarray showed that expression of bone morphogenetic protein 4 (BMP4) and BMP7, which promote differentiation of osteoblasts, was upregulated. No differences of survival of MC3T3-E1 cells were observed between loading and unloading of stress. Furthermore, the analysis of cDNA microarray showed that compressing force upregulated expression of heat shock protein 25kDa (Hsp25). And when MC3T3-E1 cells were cultured in magnetic field and micro pulse magnetic field, Cox-2, c-fos, and alkaline phosphatase mRNAs were upregulated.The present study indicates that the compression force promotes differentiation of MC3T3-E1 cells through the signaling pathway upregulating Hsp25.In the study of immune reaction of dendritic cells to titaniumtitanium could not induce the immune reactions easily. It may be caused by the interface of Ti and immune cells which are ‘static' environment.