Osteoblast viability and detachment following exposure to ultrasound in vitro

Ultrasound has been used in dentistry for over 40 years and has recently been proposed for cutting bone. The purpose of this study was to establish the effects of ultrasonic instruments on osteoblasts. A 25 kHz magnetostrictive ultrasound generator and a TFI-1 tip (Dentsply, UK) were used as the ultrasound generating instruments. Primary osteoblast cultures were established from the parietal bones of two-day-old Albino Wistar rats grown on tissue culture (TC) petri dishes (Corning, UK) in alphaMEM (Sigma, UK). Once confluent, the osteoblasts were harvested using 0.05% trypsin in 0.02% EDTA then 1.7 x 10(5) cells in 2.5 ml of alphaMEM were either re-seeded immediately onto TC dishes and allowed to adhere for 24 h or kept in suspension before application of ultrasound with different tip displacements prior to re-seeding the cells. Osteoblast viability was assessed using 0.4% Trypan Blue following the initial dose of ultrasound then periodically over a 20 h period for both adherent and suspension osteoblasts. This study demonstrated that ultrasound caused osteoblast detachment and loss of viability in vitro, both when adherent to a substrate or in suspension. Loss of osteoblast viability was related to the maximum displacement of the ultrasonic tip and continued throughout the 20 h period observed for osteoblasts adherent to TC dishes.