Ultrasound enhances the healing of orthodontically induced root resorption in rats

To examine the effect of low-intensity pulsed ultrasound (LIPUS) on orthodontically induced root resorption in rats.

Sixty-four male Wistar rats were divided randomly and equally into four groups (n  =  16 rats each). The rats were untreated (negative control) or treated with orthodontic tooth movement without (positive control) or with LIPUS at 100 or 150 MW/cm(2) (LIPUS-treated groups). An initial force of 100 g was applied to the areas between the upper right central incisors and the first molars of the rats for 10 days. Eight rats were randomly chosen from each group, and the root resorption index (RRI) was determined with scanning electron microscopy (SEM). Upper first molar-centered mesial-distal tissue slices were generated from the upper first molars and peridentium of the remaining eight rats from each group. Specimen slices were analyzed with hematoxylin-eosin and tartrate-resistant acid phosphatase staining, osteoprotegerin (OPG) and receptor activator of nuclear factor kappa-B ligand (RANKL) immunohistochemistry, and optical microscopy. Analyses of cell number, densitometry, and one-way analysis of variance were performed.

The LIPUS-treated groups displayed decreased RRI values, decreased osteoclast numbers and activity levels, and increased OPG/RANKL expression ratios. High-power SEM revealed reparative cementum in the LIPUS-treated samples.

LIPUS regulates osteoclast differentiation via the OPG/RANKL ratio, evoking a reparative effect on orthodontically induced root resorption in rats.