Antibacterial properties of silver nanoparticles as a root canal irrigant against Enterococcus faecalis biofilm and infected dentinal tubules

AimTo evaluate the antimicrobial action of an irrigant containing silver nanoparticles in an aqueous vehicle (AgNp), sodium hypochlorite and chlorhexidine against Enterococcus faecalis biofilm and infected dentinal tubules. MethodologyBovine dentine blocks were used for E.faecalis biofilm development for 21days and irrigated with 94ppm AgNp solution, 2.5% NaOCl and 2% chlorhexidine for 5, 15 and 30min. For infection of dentinal tubules with E.faecalis, dentine specimens from bovine incisors were submitted to a contamination protocol over 5days, with eight centrifugation cycles on every alternate day, and irrigated with the same solutions and time intervals used for the biofilm. The specimens were stained with the Live/Dead technique and evaluated using a confocal laser scanning microscope (CLSM). The bioImage_L software was used for measurement of the total biovolume of biofilm in m(3) and percentage of viable bacteria (green cells) in biofilm and in dentinal tubules found after the irrigation. Statistical analyses were performed using Kruskal-Wallis and Dunn's tests for quantification of viable cells in biofilm, the Friedman test for comparisons of viable bacteria in dentinal tubules in different areas of the root canal and the Mann-Whitney U-test to compare the action of the irrigants between the two methods (P<0.05). ResultsThe AgNp solution eliminated fewer bacteria, but was able to dissolve more biofilm compared with chlorhexidine (P<0.05). NaOCl had the greatest antimicrobial activity and biofilm dissolution capacity. AgNp solution had less antimicrobial action in infected dentinal tubules compared with NaOCl (P<0.05). The AgNp solution after 5min was more effective in eliminating planktonic bacteria in dentinal tubules than in biofilm, but at 30min fewer viable bacteria were observed in the biofilm compared with intratubular dentine (P<0.05). ConclusionsAgNp irrigant was not as effective against E.faecalis compared to solutions commonly used in root canal treatment. NaOCl is appropriate as an irrigant because it was effective in disrupting biofilm and in eliminating bacteria in biofilms and in dentinal tubules.