Low-intensity Low-frequency Ultrasound Promotes Proliferation and Differentiation of Odontoblast-like Cells

Introduction: Ultrasound is a potential therapeutic tool for dental tissue repair, but its biological effects on odontoblasts have not been well characterized. In this study, the effects of low-intensity low-frequency ultrasound on the viability, proliferation, and differentiation of odontoblast-like cells were investigated. Methods: Cell viability and proliferation were assessed after the treatment of adherent clonal MDPC-23 odontoblast-like cells with a 25-mW/cm(2) 45-kHz ultrasound. An in vitro scratch wound healing assay was used to investigate the ultrasound effects on cell migration. Long-term cultures were used to study odontogenic differentiation and extracellular mineralization. Results: Ultrasound exposure for up to 30 minutes did not significantly affect odontoblast-like cell viability but significantly increased cell numbers after 2 days in culture. Ultrasound did not influence the scratch wound closure rate in the absence or presence of the mitogen inhibitor mitomycin C, indicating that ultrasound did not influence cellular migration. Single and consecutive exposures to ultrasound resulted in the enhancement of in vitro mineralization after 14 days in culture with an osteogenic differentiation medium. This coincided with the up-regulation of gene expression of collagen type I, osteoadherin, dentine matrix protein 1, and osteocalcin as well as the expression of cell markers alkaline phosphatase and nestin. Conclusions: These findings indicate that low-frequency ultrasound is able to influence proliferation and differentiation of odontoblast-like cells and may potentially be considered as a therapeutic tool for dental pulp and dentine repair. (J Endod 2012;38:608-613)