Ultrasound stimulation attenuates root resorption of rat replanted molars and impairs tumor necrosis factor-α signaling in vitro

Background and Objective: A therapeutic protocol to minimize root resorption induced by tooth replantation has not yet been universally established. In this context, noninvasive modality such as ultrasound therapy have been a focus of increased interest. This study aimed to evaluate the inhibitory effect of ultrasound therapy on root resorption of replanted rat molars. In addition, the study aimed to promote insights into the mechanism through which ultrasound mediates the metabolism of periodontal cells in vitro. Material and Methods: An experimental model of tooth replantation in rats, involving luxation and immediate replacement of the maxillary first molars, was used to assess the inhibitory effect of an ultrasound-therapy regimen (15 min of exposure to ultrasound, each day for 21 d) on root resorption. Moreover, the effect of ultrasound on osteoclastogenesis/cementoclastogenesis was examined in vitro using a mouse osteoblastic stromal cell line (ST2) and a mouse cementoblastic cell line (OCCM-30). Results: The area of root resorption lacunae was statistically decreased (p < 0.01) in the ultrasound-treated sample. In addition, immunohistochemical staining, using murine TNF-alpha polyclonal antibody, failed to detect tumor necrosis factor-a (TNF-alpha) protein in the ultrasound-treated sample compared with the control. An in vitro study showed that the lipopolysaccharide (LPS)-induced expression of Tnfalpha mRNA was significantly reduced by ultrasound therapy in both osteoblastic and cementoblastic cells. Moreover, the TNF-alpha-induced up-regulation of Rankl mRNA was also inhibited by ultrasound. Conclusion: Ultrasound may contribute to the reduction of the trauma-induced inflammatory reaction through impairment of the TNF-alpha signaling pathway. It is therefore suggested that ultrasound shows potential as a therapeutic tool to optimize the regenerative potential of periodontal tissues on replanted teeth.