Salivary Levels of Opg and Rankl During Orthodontic Tooth Movement—a Prospective Pilot Study

Abstract Background and objective: Receptor activator of nuclear factor-kappa ligand (RANKL) and Osteoprotegerin (OPG) perform functions in orthodontic tooth movement (OTM) by regulation of osteoblast and osteoclast activation. This novel approach aims to monitor continuous changes in OPG and RANKL levels in the saliva during two years of OTM. Material and methods: Nine healthy females (15-20 years of age) were included in this prospective longitudinal pilot study. All patients had crowding requiring four premolar extractions and fixed appliances in both jaws. In total, 134 stimulated and 134 unstimulated saliva samples were collected: before tooth extractions (baseline), and then every 6-8 weeks at follow-up appointments during the whole treatment period of two years. All saliva samples were analysed by enzyme-linked immunosorbent assay. The mean levels of OPG and RANKL were calculated according to the different orthodontic treatment stages: alignment, space closure and finishing. A mixed model analysis was used to compare the means of treatment stages. Results: RANKL was not detectable either in stimulated or unstimulated saliva. OPG levels were measured in stimulated saliva due to low levels in unstimulated saliva. A significant increase in OPG was observed at all treatment stages: alignment, space closure and finishing compared with baseline (p = 0.002, p = 0.039, p = < 0.001, respectively). A small non-significant decrease was seen in space closure compared with alignment. OPG reached peak levels during the finishing stage. Conclusions: The salivary levels of OPG increased gradually, except during space closure, reaching peak levels at the finishing stage. This novel approach shows the changes in the levels of OPG in OTM and indicates how and when to sample saliva during orthodontic treatment to analyse bone remodelling.