Effect of ultrasonic instrumentation on Bacteroides intermedius

Two physical mechanisms of ultrasound, cavitation and acoustic streaming, were investigated in an ultrasonic endodontic unit. In addition, the potential of ultrasonic instrumentation for disruption of Bacteroides intermedius was examined at various time intervals. The ultrasonic file could not generate cavitation within the recommended power settings indicated for endodontic purposes. However, there was evidence of acoustic streaming. The latter phenomenon resulted in destruction of 21.6%, 30.4% and 92.9% of test bacteria after 1, 5 and 15 min sonication respectively. It appears that ultrasonic instrumentation of root canals has little bactericidal effect.