Antimicrobial Efficacy of Calcium Hydroxide Nanoparticles Combined with Nisin Against Enterococcus faecalis in Root Canal Infections

Objective: This study aimed to evaluate the antimicrobial effects of calcium hydroxide (Ca(OH)2) nanoparticles combined with nisin against Enterococcus faecalis in infected root canals.
Methods: The Minimum Inhibitory Concentration (MIC50) and Fractional Inhibitory Concentration (FIC) index were determined to assess the potential synergistic effect of the combination. Root canal specimens infected with E. faecalis were divided into three treatment groups: Ca(OH)2 nanoparticles with nisin, Ca(OH)2 nanoparticles alone, and a control group with no treatment. Colony Forming Units (CFU) were quantified at different dentinal depths, and the relative gene expression of E. faecalis was analysed using quantitative PCR.
Result: MIC50 was not achieved by Ca(OH)2, while nisin had an MIC of 50 mg/mL. FIC analysis indicated no synergistic interaction between Ca(OH)2 and nisin. From the root canal specimen model, Ca(OH)2 nanoparticles alone and the combination of Ca(OH)2 nanoparticles and nisin disinfected dentinal tubules up to 1.3 mm, however, neither group achieved disinfection at a depth of 1.5 mm. Relative gene expression analysis showed that the combination treatment significantly reduced E. faecalis gene expression compared to Ca(OH)2 alone.
Conclusions: The combination of Ca(OH)2 nanoparticles and nisin does not improve the antimicrobial activity of Ca(OH)2 nanoparticles against E. faecalis, suggesting independent antimicrobial activity of both agents. (EEJ-2025-04-054)