Three-dimensional imaging and molecular analysis of the effects of photobiomodulation and mechanical vibration on orthodontic retention treatment in rats

Purpose We aimed to evaluate and compare effects of photobiomodulation (PBM) and low-magnitude high-frequencymechanical vibration (HFMV) on orthodontic retention.Methods Sixty-four female Wistar albino rats were divided into 9 groups (2 negative and positive controls each, 3 PBMand 2 HFMV groups) and studied for 25 days. In the experimental groups, closed nickel–titanium closed coil springswith a 50 cN force were placed for 10 days between the maxillary incisor and molar. PBM and HFMV were applieddaily over long- (15 days) and short-term (7 days) retention periods. The PBM groups received PBM with a singlewavelength (650 nm) or higher wavelengths (532, 650, 940 nm) for 9min per day. HFMV groups received HFMV of10, 20, and 30 Hz for 10min per day. Right and left maxilla were assessed using micro-computed tomography imagingand real-time polymerase chain reaction. The amount of tooth movement during the retention period, expression levelsof cyclooxygenase-2 (COX-2), osteoprotegerin (OPG), and receptor activator of nuclear factor-kappa B ligand (RANKL)mRNA gene expression levels, OPG/RANKL ratios, alveolar bone trabecular thickness (Tb.Th), trabecular number (Tb.N),and structure model index were analyzed. Kruskal–Wallis and Mann–Whitney U tests were used for multiple comparisonsof the nonparametric distributed data and binary comparisons, respectively.Results When using the long-term retention protocol, PBM and HFMV treatment increased Tb.N (p< 0.05) and decreasedCOX-2 mRNA gene expression levels (p< 0.05) and Tb.Th (p< 0.05) compared to controls. For short-term retention, PBMand HFMV decreased the amount of relapse tooth movement compared to controls. In addition, Tb.Th (p< 0.05) and themRNA gene expression levels of COX-2 and RANKL (p< 0.05) were decreased.Conclusion PBM and HFMV might be able to support retention after orthodontic tooth movement by reducing boneresorption and increasing bone quality