Inubushi T, Tanaka E, Rego EB, Ohtani J, Kawazoe A, Tanne K, et al. Ultrasound stimulation attenuates resorption of tooth root induced by experimental force application. Bone 2013:53:497-506

The authors of this study evaluated the in-vivo effects of low-intensity pulsed ultrasound (LIPUS) on root resorption caused by excessive orthodontic forces and its role in the RANKL/OPG mechanism in vitro. The maxillary first molars of 24 Wistar rats were subjected to 50 g of mesial traction force for 1, 2, or 3 weeks. Each rat received LIPUS for 15 minutes per day for 1, 2, or 3 weeks on 1 molar; the contralateral side served as the control. At the end of 3 weeks, the LIPUS group showed significantly shorter root resorption lacunae and smaller root resorption areas with histomorphometric analyses. Fewer odontoclast and osteoclast numbers through TRAP staining were also observed in the LIPUS group. The amount of tooth movement was significantly greater at the end of 2 weeks with LIPUS, but not different at the end of 3 weeks. In-vitro experiments with no compressive forces and no LIPUS showed that osteoblastic cells (MC3R3-E1) continuously expressed higher levels of the osteoclastic/cementoclastic remodeling markers RANKL and RANTES mRNA compared with the cementoblastic cells (OCCM-30). The cementoblastic cells expressed much higher levels of the antiosteoclastic/cementoclastic remodeling markers OPG mRNA. LIPUS without compressive forces significantly increased RANKL mRNA expression at 4 and 12 hours in the osteoblastic cells, whereas OPG mRNA was not affected. Expressions of RANKL and OPG mRNAs were both significantly increased by LIPUS in the cementoblastic cells at 12 hours. LIPUS with compressive forces suppressed the up-regulation of RANKL mRNA in the cementoblastic cells; no similar effect on the osteoblastic cells was observed. The authors concluded that LIPUS significantly reduces root resorption by suppression of cementoclastogenesis by altering the OPG/RANKL ratio without interrupting bone remodeling and tooth movement.

Reviewed by Catherine Woo