Effect of ultrasonic instrumentation on dental plaque microflora in vitro

The aim of the present study was to investigate in vitro the effects of an ultrasonic scaler on the composition of dental plaque and selected bacterial isolates. Plaque samples obtained from patients with periodontitis were submitted for 10 s, 20 s, 30 s and 60 s to ultrasonication. Bacterial suspensions were then examined by dark field microscopy and cultured on solid medium to evaluate bacterial growth. Dark field microscopic counts showed that percentages of spirochetes and motile rods decreased sharply after 10 s of sonication and could no longer be detected after 60 s. Conversely, a relative increase in the percentage of coccoid cells as well as others was observed. Cultures of plaque samples following ultrasonication demonstrated a marked increase in CFU between 0 and 10 s to reach a maximum at 30 s. When bacterial suspensions containing Treponema vincentii LA-1 and Streptococcus mutans OMZ 176 were submitted to ultrasonication, a net decline in the percentage of spirochetes and a concomitant increase in cocci were observed by dark field. After 30 s there were exclusively cocci in the suspensions and spirochetes were virtually undetectable. The effect of ultrasonication on spirochetes viability was also evaluated using pure cultures of T. vincentii LA-1 and T. denticola CD-1. The data indicated that 10 s or 30 s of sonication had an adverse effect on both species because no growth could be observed in these cultures. It can be concluded that vibrations generated by an ultrasonic scaler have the potential to alter the composition of dental plaque and to kill spirochetes in vitro.