Cementoblast response to low- and high-intensity ultrasound

Objective: It has been shown that ultrasound stimulation accelerates repair of orthodontically induced root resorption. However, the mechanism of such adaptive change is still unclear. The purpose of this study was to evaluate pulsed ultrasound on the differentiation-potential and cementoblast-mediated osteoclastogenesis using a cementoblastic cell line. Design: Cultured cementoblasts (murine cementoblastic cell line, OCCM-30) were subjected to ultrasound exposure (frequency = 1 MHz; pulsed 1:4; spatial average temporal average intensities = 30 or 150 mW/cm(2)) or sham exposure for 15 min per day. Expression levels of alkaline phosphatase (ALP), type I Collagen (COL-I), osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL) mRNAs were analysed by a real-time PCR analysis. Furthermore, ALP activity, collagen synthesis, and protein levels of OPG and RANKL were examined after 6-day ultrasound exposure. Results: Real-time PCR analysis indicated that, irrespective of the intensity, single ultrasound exposure increased the expression of transcripts for COL-I and ALP after 24 h; the expression of OPG and RANKL also increased after 1 and 4 h, respectively. Cultured cementoblasts receiving ultrasound stimulation for 6 days showed a significant (p < 0.05 or 0.01) increase in cell number and collagen synthesis. ALP activity and OPG synthesis were also significantly (p < 0.05) upregulated by ultrasound stimulation with 150 mW/cm(2). Conclusions: These results demonstrated that ultrasound stimulation especially with 150 mW/cm(2) might be a better candidate as a medical remedy to protect against root resorption and/or accelerate its repair. (C) 2007 Elsevier Ltd. All rights reserved.