Zinc oxide nanoparticles and blue light enhance sodium hypochlorite disinfection against Enterococcus faecalis: an in vitro study

Aim: This study aimed to evaluate the antimicrobial efficacy of zinc oxide nanoparticles (ZnO NPs) and blue light, both individually and in combination, against Enterococcus faecalis (E. faecalis) in vitro. Their performance was compared to 1% sodium hypochlorite (NaOCl) to determine whether these adjuncts could enhance root canal disinfection.

Materials and Methods: A laboratory investigation was conducted using eight experimental groups: E. faecalis with phosphate-buffered saline (control), 1% NaOCl, ZnO NPs, blue light, 1% NaOCl/ZnO NPs, 1% NaOCl/blue light, ZnO NPs/blue light, and 1% NaOCl/ZnO NPs/blue light. Standardized E. faecalis inocula were exposed to each treatment under controlled conditions. Bacterial cells were then recovered, serially diluted, and plated on agar to determine colony-forming units (CFU). Reductions in CFU, compared to the control, were analyzed using Mann-Whitney tests. Statistical significance was set at p<0.05.

Results: Most experimental groups exhibited significantly lower bacterial counts than the control (p=0.000), except for the blue light–only group, which was not statistically different. Among the single-agent treatments that reached significance, 1% NaOCl produced the greatest bacterial reduction, followed by ZnO NPs. When combined, dual treatments reduced bacterial counts more than single agents. The triple combination achieved the highest reduction overall.

Conclusions: This study highlights the potential of ZnO NPs and blue light as adjuncts to 1% NaOCl for more effective elimination of E. faecalis in planktonic cultures. The enhanced antimicrobial activity observed with combined treatments suggests that incorporating nanoparticles and photodisinfection could reduce the need for higher NaOCl concentrations while maintaining robust antibacterial efficacy.