Combination of Intracanal Medicines with Zinc Oxide Nanoparticles for Effective Eradication of Enterococcus faecalis

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Background: Intracanal-resistant infections are the most important reason for root canal treatment failure. Therefore, cleaning the root canals is crucial. The efficiency of nanomedicines in eliminating intracanal contaminations and preventing bacterial attachment to surfaces are new strategies in this field. This study aimed to evaluate the effect of intracanal medicines, including calcium hydroxide (CH), zinc oxide nanoparticles (nZnO), pantoprazole (PP), and chlorhexidine (CHX) on Enterococcus faecalis (E. faecalis) in the individual and combinatorial form in an in vitro design in order to introduce an effective medicine for the eradication of E. faecalis. Sterilized water and sodium hypochlorite (NaOCl) 5.25% were used as the negative and positive control of antimicrobial activity, respectively. Methods: E. faecalis (ATCC 29212) was used for bacterial assays. The powder and the gel forms of the tested compounds were used in the analysis. The antibacterial and antibiofilm activities of the medicines were evaluated by the Minimum Inhibitory Concentration (MIC) determination using the broth microdilution method. The anti-biofilm effect of the tested compounds was assessed by Minimum Biofilm Inhibitory Concentration (MBIC). The antibacterial and antibiofilm effects of antimicrobial agent combinations were detected using the checkerboard assay and determination of the Fractional Inhibitory Concentration Index (FICI). Time-kill kinetics were conducted at zero, 2, 4, 6, 8, 10, 12, and 24 h. Results: Except for the MIC of the NaOCl, which was significantly lower than CH, there was no statistically significant difference between groups in MIC and MBIC. Only the mixture of CHX and nZnO and the mixture of PP and nZnO had a synergic effect against the planktonic and biofilm form of E. faecalis. Except for CHX and ZnO nanoparticles in gel form, other medicines did not show significant anti-biofilm effects against E. faecalis. Furthermore, the gel for CHX and nZnO showed stronger anti-biofilm effects. Conclusion: Combination therapy of common intracanal medicines with zinc oxide nanoparticles would lead to higher antibacterial and anti-biofilm effects against E. faecalis compared to conventional intracanal medicaments.