Time-related changes in salivary levels of the osteotropic factors sRANKL and OPG through orthodontic tooth movement

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In this study, we aimed to determine whether the variations in salivary concentrations of soluble receptor activator of nuclear factor kappa B ligand (sRANKL) and osteoprotegerin (OPG), and their ratios, might be linked with the different phases of orthodontic tooth movement.


Twenty healthy subjects who required fixed appliance therapy not involving tooth extractions or surgical procedures were selected. Unstimulated whole saliva samples were collected from each patient before fitting the orthodontic appliances, and at 24 to 48 hours, 2 weeks, 5 weeks, and 8 weeks after the activation. Salivary sRANKL and OPG concentrations were determined by enzyme-linked immunosorbent assays. The data were analyzed by using nonparametric statistics.


Overall, median values of sRANKL showed significant increases, median OPG salivary values showed a significant downward trend, and the sRANKL/OPG ratio tended to increase significantly over time after the activation visit. However, clear fluctuations in the immunoenzymatic findings were noted at the different sampling times, indicating nonlinear trends in the levels of the biomarkers through time. Post-hoc pairwise comparisons showed significant differences between (1) all sRANKL values relative to those of the 8-week sampling time; (2) baseline/8-week OPG salivary levels; and (3) baseline, 24 to 48 hours, and 2-week sRANKL/OPG ratios compared with those of the 8-week test.


The findings indicate that variations in salivary concentrations of sRANKL and OPG and their ratios might be linked to the different phases of orthodontic tooth movement. Hence, these analytes might serve in a panel of salivary functional biomarkers that could assist in the screening of orthodontic treatment in clinical practice.

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