The bactericidal efficiency of various positively and negatively charged silver nanoparticles has been extensively evaluated in literature, but there is no report on efficacy of neutrally charged silver nanoparticles. The goal of this study is to evaluate the role of electrical charge at the surface of silver nanoparticles on antibacterial activity against a panel of microorganisms. Three different silver nanoparticles were synthesized by different methods, providing three different electrical surface charges (positive, neutral, and negative). The antibacterial activity of these nanoparticles was tested against gram-positive (i.e., Staphylococcus aureus, Streptococcus mutans, and Streptococcus pyogenes) and gram-negative (i.e., Escherichia coli and Proteus vulgaris) bacteria. Well diffusion and micro-dilution tests were used to evaluate the bactericidal activity of the nanoparticles. According to the obtained results, the positively-charged silver nanoparticles showed the highest bactericidal activity against all microorganisms tested. The negatively charged silver nanoparticles had the least and the neutral nanoparticles had intermediate antibacterial activity. The most resistant bacteria were Proteus vulgaris. We found that the surface charge of the silver nanoparticles was a significant factor affecting bactericidal activity on these surfaces. Although the positively charged nanoparticles showed the highest level of effectiveness against the organisms tested, the neutrally charged particles were also potent against most bacterial species.

Ag NP surface charge was important in bactericidal efficacy against E. faecalis. The positively charged imidazolium-based ionic liquid-protected Ag NPs showed promising antibacterial results against E. faecalis and exhibited a high level of cytocompatibility to L929 cells.

Background: Nanoparticles are made by different methodologies, which can affect the particle's features. Recently, imidazoliumcoated silver nanoparticles with a positive surface charge (PC Im-based AgNPs) have revealed favorable results as a root canal disinfectant. However, the antibacterial potency of these particles against biofilm form of Enterococcus faecalis, as the most resistant organism to eliminate in endodontic treatment, has not been investigated. It can be noted that removing this microorganism is associated with extremely effective disinfection. Objectives: This study investigated the antibacterial efficacy of PC Im-based AgNPs at 5.7 × 10-8 mol L-1 in comparison with 2.5% sodium hypochlorite (NaOCl) and 2% chlorhexidine as the two broadly used endodontic irrigation solutions against biofilm E. faecalis using quantitative real-time polymerase chain reaction. Methods: In total, 48 premolar teeth with a single root were infected with E. faecalis and then prepared with ProTaper rotary instruments. The samples were randomly allocated into 4 groups of 12 samples. Sterile saline, PC Im-based AgNPs, NaOCl, and chlorhexidine were used as irrigants. Sampling the root canals was implemented with paper points and Gates-Glidden drills. The reduction in E. faecalis counts was calculated and statistically analyzed by means of the Kruskal-Wallis and Mann-Whitney U tests. Results: Irrigation with PC Im-based AgNPs or NaOCl was significantly more effective in bacterial count reduction compared to irrigation with chlorhexidine or sterile saline (P < 0.05). There was no significant difference between PC Im-based AgNPs and NaOCl irrigants when either Gates-Glidden drills (P = 0.751) or paper points (P = 0.488) were employed. Chlorhexidine was significantly less efficient than PC Im-based AgNPs and NaOCl solutions (P < 0.001); however, it was significantly better than sterile saline in both sampling approaches (P > 0.001). Conclusions: The PC Im-based AgNP solution revealed promising results as a root canal irrigant. This solution at 5.7 × 10-8 mol L-1 was effectively able to eliminate biofilm E. faecalis and this was not significantly different from that of 2.5% NaOCl.

Introduction:This study compared the antifungal effect of Zataria multiflora essential oil (EO) with that of sodium hypochlorite (NaOCl) as an irrigant for root canals infected with Candida albicans.Materials and Methods:Sixty mandibular premolars were infected with C. albicans suspension. After 72 h of incubation, the samples were divided into four groups. Teeth in Group 1 were irrigated with minimum fungicidal concentration (MFC) of Z. multiflora EO, in Group 2 with twice the MFC of Z. multiflora, in Group 3 with MFC of NaOCl, and in Group 4 with distilled water (DW). Pre- and post-operative samples were cultured, and fungal colony count of each specimen was obtained. Data were analyzed using Kruskal-Wallis and Mann-Whitney tests (P < 0.05).Results:NaOCl at MFC and Z. multiflora EO at twice the MFC showed the highest antifungal efficacy, with no significant difference (P > 0.05). However, antifungal efficacies of these irrigants were significantly different from those of Z. multiflora EO at MFC and DW (P < 0.05).Conclusion:Our results showed that Z. multiflora EO at twice the MFC had the same antifungal efficacy as NaOCl at MFC.

This study was performed to validate the previous antimicrobial and cytotoxic data on the influence of ionic liquids as coatings of silver nanoparticles (AgNPs). The antibacterial and cytotoxicity assessments were carried out against different microorganisms and a cancerous cell line. AgNPs with two different ionic-liquid coatings and hydrocarbon chains were synthesized and characterized. We tested the antibacterial activity of these NPs against Salmonella typhi, Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Candida albicans in planktonic forms and against Enterococcus faecalis and Escherichia coli in biofilm forms. MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay was employed for toxicity evaluation. The antimicrobial activity of NPs with 12 carbons was significantly higher than those with 18 carbons. Furthermore, NPs with 12 carbons were also effective against bacterial biofilms. All of the NPs tested had good cell viability at different antimicrobial concentrations. The length of the hydrocarbon chain is an essential factor in determining the antimicrobial activity of ionic-liquid-coated AgNPs. The variation in ionic-liquid coatings was not as effective as other influencing factors. Evaluation of AgNPs using other alkyl chain lengths to find the optimal size is recommended.