Mechanisms involved in enhancement of osteoclast formation and function by periodontal cells obtained from sever orthodontic root resorption.

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The mechanism of root resorption that occurs during and after orthodontic treatment has not been clarified. We investigated the production of inflammatory cytokines and osteoclast formation after stimulus with substance P(SP) and compression force(CF) that are expressed in dental pulp and periodontal ligament(PDL) during orthodontic tooth movement. Pulp cells were obtained from 5 patients with root resorption due to orthodontic treatment, and SP (10^<-4>-10^<-12> mol/L) was added and cultured. Similarly, PDL cells were exposed compression force (0-3.0 g/cm^2). The levels of prostaglandin E_2(PGE_2), interleukin(IL)-1β,IL-6, and tumor necrosis factor(TNF)-α were determined after 24 hours. Further, culture supernatants were added to cultured rat osteoclasts, and osteoclast formation was observed after formation of resorption cavities. SP and CF stimulus increased the levels of PGE_2, IL-1β, IL-6, and TNF-α though the increase was greater in the root resorption group than in the control group, in a time- and concentration- dependent manner in pulp cells and PDL cells. As for osteoclast formation, the resorptive pits were significantly increased in the root resorption group as compared to the control. Human pulp and PDL cells obtained from patients with severe root resorption produced large amounts of inflammatory cytokines following neuropeptide and mechanical stimulus. Our results suggest that SP and CF may be highly involved in the progress of inflammation in pulp and PDL tissue and the occurrence of root resorption during orthodontic treatment.