PTGS2 and periapical periodontitis: ,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.