,17 We have previously demonstrated that the 5-lipoxygenase inhibitor is able to regulate RANK/RANKL/OPG in apical periodontitis;18 however, studies showing the effects of a COX-2 selective inhibitor and a non-selective COX-2 inhibitor on the regulation of RANK, RANKL, OPG and other genes involved in bone metabolism following root canal inoculation with LPS has not been reported. Here, PTGER2 is linked to periapical periodontitis.