LAUSR

BACKGROUND Although vibration combined with orthodontic force may accelerate orthodontic tooth movement, little is known about the mechanisms that regulate the associated cellular responses. The goal of this study was to investigate whether mechanical vibration combined with compressive force regulates cyclooxygenase (COX)-2/prostaglandin E2 (PGE2 ) and interleukin (IL)-6 and IL-8 messenger RNA (mRNA) and protein expression in human periodontal ligament (hPDL) cells via the COX pathway. METHODS The primary cultured hPDL cells were exposed to mechanical vibration, compressive force or a combination of both mechanical vibration and compressive force at 24, 48, and 72 hours. The COX-2, IL-6, IL-8, receptor activator of nuclear factor kappa-Β ligand (RANKL), and osteoprotegrin (OPG) mRNA expressions were determined using quantitative real-time polymerase chain reaction (qPCR). The PGE2 , IL-6, and IL-8 protein expressions were quantified by enzyme-linked immunosorbent assay (ELISA). To demonstrate whether the expression of PGE2 , IL-6, and IL-8 was in the COX-dependent pathway, the hPDL cells were treated with indomethacin. To determine whether PGE2 stimulated the hPDL cells to express IL-6 and IL-8, exogenous PGE2 was added to the culture media. RESULTS The combination of mechanical vibration and compressive force synergistically upregulated RANKL/OPG, COX-2/PGE2 , IL-6 and IL-8 mRNA, and protein expression. The indomethacin significantly attenuated the increases of PGE2 , IL-6, and IL-8 expression in cells stimulated with compressive force or mechanical vibration combined with compressive force. In addition, exogenous PGE2 increased IL-6 and IL-8 mRNA and protein expressions in hPDL cells. CONCLUSION Mechanical vibration may enhance alveolar bone resorption at the compression side during orthodontic tooth movement via a mechanism involving the cyclooxygenase pathway.