| Orthodontic tooth movement is mediated by interactions between PDL cells and those of the alveolus. One protein---the receptor activator nuclear factor kappa B ligand (RANKL)---is critical for osteoclastogenesis, and osteoprotegerin (OPG) is a decoy ligand that competitively inhibits RANKL. A higher RANKL/OPG ratio is associated with areas of bone resorption, while a lower ratio occurs in areas of bone deposition and homeostasis. There has been almost no clinical study of RANKL and OPG expression in patients undergoing orthodontic tooth movement.;The purpose of this study was to quantify changes in the levels of RANKL and of OPG in response to orthodontic forces. Untreated adolescents had a calibrated force applied across a left-right pair of maxillary premolars with a transpalatal spring (TPS). RANKL and OPG was measured in gingival crevicular fluid (GCF) sampled serially from the pressure and tension sides of maxillary premolars at 5 time points: before placement of transpalatal spring, 2 days after TPS placement, 5 days after TPS placement, 10 days after TPS placement (TPS was then removed), and 7 days after TPS removal. RANKL and OPG expression was measured by ELISA assay. Expectations were that (1) force would raise RANKL and diminish OPG, (2) force removal would reverse the RANKL-OPG levels, (3) strength and duration of force are associated with RANKL-OPG levels, and (4) responses would exhibit considerable inter-individual variation.;Gingival crevicular fluid (GCF) volume increased significantly after applying force with the nickel-titanium coil spring. The volume remained elevated until the force was removed, and had returned to baseline by one week. Low detectability of RANKL and OPG in the samples, which can be partially attributed to low volumes of GCF, made it impossible to assess the effects of orthodontically induced changes in their concentrations. The levels of these molecules present in the GCF collected, as well as their changes over time, were, more than likely, too small to be measured with current commercially available ELISA assay kits. It is also possible that a large change in RANKL or OPG expression could have occurred after spring placement and before the first sample of GCF was collected (between 0 and 48 hours). Further research is needed to determine what effect variations in individual RANKL and OPG expression have on orthodontic tooth movement. |
