Purpose We aimed to evaluate and compare effects of photobiomodulation (PBM) and low-magnitude high-frequency
mechanical vibration (HFMV) on orthodontic retention.
Methods Sixty-four female Wistar albino rats were divided into 9 groups (2 negative and positive controls each, 3 PBM
and 2 HFMV groups) and studied for 25 days. In the experimental groups, closed nickel–titanium closed coil springs
with a 50 cN force were placed for 10 days between the maxillary incisor and molar. PBM and HFMV were applied
daily over long- (15 days) and short-term (7 days) retention periods. The PBM groups received PBM with a single
wavelength (650 nm) or higher wavelengths (532, 650, 940 nm) for 9min per day. HFMV groups received HFMV of
10, 20, and 30 Hz for 10min per day. Right and left maxilla were assessed using micro-computed tomography imaging
and real-time polymerase chain reaction. The amount of tooth movement during the retention period, expression levels
of 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 comparisons
of 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 decreased
COX-2 mRNA gene expression levels (p< 0.05) and Tb.Th (p< 0.05) compared to controls. For short-term retention, PBM
and HFMV decreased the amount of relapse tooth movement compared to controls. In addition, Tb.Th (p< 0.05) and the
mRNA 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 bone
resorption and increasing bone quality