A preliminary study of the effects of low-intensity pulsed ultrasound exposure on the stability of orthodontic miniscrews in growing rats.

BACKGROUND: Orthodontic miniscrews placed in growing subjects often loosen during orthodontic treatment. The ability to place miniscrews, regardless of age, would be clinically beneficial. OBJECTIVES: To assess the effects of low-intensity pulsed ultrasound (LIPUS) on the stability of orthodontic miniscrews in growing rats. MATERIALS/METHODS: The mobility of miniscrews after placement was recorded and the miniscrew-bone interface was examined histomorphometrically using tibiae of seven male Sprague-Dawley rats (aged 6 weeks). Field-emission scanning electron microscopic images were used to evaluate the bone-miniscrew interface, and a mobility test device was used to assess the stiffness of miniscrew placement. Fourteen custom-made miniscrews with 1.4mm diameters and 4.0mm lengths were placed in the right and left tibiae. LIPUS was used to stimulate right tibiae at the sites of miniscrew placement, and left tibiae were left untreated as controls. RESULTS: Significantly lower mobility was observed in the LIPUS-treated group compared with the control group (P < 0.05). Histomorphometric evaluation indicated that bone-miniscrew adhesion was significantly better in the LIPUS-treated group than in the control group (P < 0.05). LIMITATIONS: This in vivo study used tibiae rather than jaw bones because the jaw bones of 6-week-old rats were too small to allow miniscrew placement. CONCLUSIONS: LIPUS was able to increase the bone-miniscrew contact and reduce the mobility of miniscrews in growing subjects. IMPLICATIONS: LIPUS may accelerate the bone healing process after miniscrew placement in growing subjects and can reduce the latent period.