Effect of ultrasonic power settings on intracanal biofilm reduction

This study evaluated the effect of different power settings in ultrasonic activation, combined with antimicrobial and non-antimicrobial irrigants, on Enterococcus faecalis biofilm reduction and cell viability. A total of 150 root canals of human uniradicular teeth were prepared to size #50.05 and inoculated with E. faecalis for 21 days. Specimens were assigned to groups according to ultrasonic activation protocols (activation at lower or intermediate power and no activation) and irrigant (2.5% NaOCl or phosphate-buffered saline) used in ultrasonically activated irrigation. Biofilm reduction was assessed by colony-forming unit (CFU) counts and data were analyzed using two-way ANOVA and Tukey’s post hoc test (p < 0.05). Biofilm structure and bacterial cell viability were qualitatively evaluated by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Significant differences in CFU counts were observed between irrigants, ultrasonic power settings, and their interaction (p < 0.001). NaOCl 2.5% promoted greater microbial reduction regardless of the activation protocol (p < 0.05). Intermediate power resulted in the lowest CFU counts (p < 0.05), and showed greater qualitative biofilm disruption and reduced cell viability with both irrigants, particularly in the middle and apical thirds. Intermediate ultrasonic power improves root canal cleaning by enhancing biofilm disruption and reducing bacterial cell viability, even without antimicrobial irrigants. Precise adjustment of ultrasonic power should be regarded as a critical parameter to maximize cleaning and disinfection efficacy. Adjusting ultrasonic power to an intermediate level improves biofilm removal and reduces bacterial viability, enhancing root canal cleaning even when non-antimicrobial irrigants are used.