The purpose of this study was to investigate the effect of cytokine-induced osteoclastogenesis on tooth movement related to orthodontic force. We evaluated the cytotoxicity as well as the expression of OPG and RANKL, which influence the homeostasis of bone metabolism. Titanium particles were applied to human periodontal ligament cells and subcultured fourth generation cells. The ALP assay and the MTT assay were used to assess changes in cytotoxicity. After 48 hours, cytotoxicity increased proportionally with the concentration of titanium. With 20 mg, the cytotoxicity was the lowest. R T-PCR was u sed for assessing m R NA l evels of O PG a nd R ANKL; after 96 hours, t he m R NAs of O PG a nd R ANKL increased steeply. A western blot analysis showed that with 20 mg of titanium, the protein expression of OPG increased linearly with time, especially a fter 96 hours, while t he p rotein e xpression o f RANKL d id n ot s how significant changes with titanium processing. Given the increase in OPG expression after the initial cytotoxicity, changes in cytotoxicity with titanium may be attributable to the antagonistic effect of OPG on cytotoxicity