The effect of mechanical vibration on orthodontically induced root resorption

Objective: To investigate the effect of low-frequency mechanical vibration (LFMV) on orthodontically induced root resorption. Materials and Methods: Forty male CD1, 12-week-old mice were used for the study. The mice were randomly divided into five groups: group 1 (baseline) no spring and no mechanical vibration, group 2 orthodontic spring but no vibration, group 3 orthodontic spring and 5 Hz of vibration applied to the maxillary first molar, group 4 orthodontic spring and 10 Hz of vibration applied to maxillary first molar, and group 5 orthodontic spring and 20 Hz of vibration applied to maxillary first molar. In the different experimental groups, the first molar was moved mesially for 2 weeks using a nickel-titanium coil spring delivering 10 g of force. LFMVs were applied at 5 Hz, 10 Hz, and 20 Hz. Microfocus X-ray computed tomography imaging was used to analyze root resorption. Additionally, to understand the mechanism, we applied LFMV to MC3T3 cells, and gene expression analyses were done for receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG). Results: Orthodontic tooth movement leads to decreased root volume (increased root resorption craters). Our in vivo experiments showed a trend toward increase in root volume with different frequencies of mechanical vibration. In vitro gene expression analyses showed that with 20 Hz of mechanical vibration, there was a significant decrease in RANKL and a significant increase in OPG expression. Conclusion: There was a trend toward decreased root resorption with different LFMVs (5 Hz, 10 Hz, and 20 Hz); however, it was not more statistically significant than the orthodontic-spring only group.