Reduction of dual-species biofilm after sonic- or ultrasonic-activated irrigation protocols: A laboratory study.

Abstract

To evaluate the antibacterial effect of sonic- and ultrasonic-activated irrigation on bacterial reduction of a dual-species biofilm in root canals compared to nonactivated irrigation in a laboratory study. Two hundred and forty extracted human single-rooted maxillary anterior teeth were divided into two main groups (G, n=120) according to the initial preparation size of the root canal (G1: size 25, 0.06 taper, G2: size 40, 0.06 taper). Root canals were inoculated with Enterococcus faecalis and Streptococcus oralis. After 5days, G1 received combined instrumentation (up to size 40, 0.06 taper) and irrigation/activation, whereas G2 received solely irrigation/activation protocols. In both groups, irrigation was performed with sodium hypochlorite (NaOCl 1%) or physiological saline (NaCl 0.9%), using nonactivated syringe irrigation, sonic activation (2x30s) or ultrasonic activation (2x30s). Logarithmic reduction factors (LRFs) of colony-forming units were analysed separately for dentine-adherent and planktonic bacteria immediately after irrigation/activation protocols (time-point 1) or after 5days of further incubation (time-point 2) by analysis of variance (anova) and post hoc tests (Tukey's HSD, t-test). The significance level was set at 0.05. In G1subgroups (combined instrumentation with irrigation/activation), LRFs were significantly affected by the applied irrigation solution (p<.0001), but not by the activation method (p>.05; anova). In G2subgroups (solely irrigation/activation), both, irrigant solution and activation, significantly affected LRFs (p<.0001, anova). Sonic activation resulted in significantly higher LRFs than ultrasonic activation (p<.0001) which had significantly greater reductions than nonactivated irrigation (p<.05; Tukey's HSD). At T2, strong bacterial regrowth was observed in all groups; however, a significant bacterial reduction was detected for factors instrumentation, irrigant solution and activation (p<.0001; anova). Similar LRFs were found for dentine-adherent and planktonic bacterial cells in all groups (r=0.91 at T1, r=0.8 at T2). In this laboratory study on extracted maxillary anterior teeth high-frequency sonic activation resulted in a greater bacterial reduction compared to ultrasonic activation in groups receiving solely irrigation/activation protocols; however, irrigation using NaOCl and ultrasonic activation also contributed significantly to bacterial reduction compared to the control groups.