Abstract:

Objective

To evaluate the bactericidal effect of nano-silver against E.faecalis biofilm. This provides experimental evidence for seeking a novel effective root canal disinfectant.

Methods

309 dentin slices were inoculated with E.faecalis suspension for 24 h to form biofilms on the surfaces of dentin slices. Thereafter， all specimens were randomly divided into 3 groups of 103 each， and treated with 0.1% nano-silver solution， 1.313% sodium hypochlorite solution and 0.9% physiological saline， respectively. After treated for 0， 1， 6， 12 and 24 h， specimens of each group were taken to investigate the viable count of E.faecalis biofilms by colony-forming unit（CFU） counts， and to detect the viable/dead bacteria spatial distribution of E.faecalis biofilms by confocal laser scanning microscopy（CLSM）. Biofilm scanned images were analyzed and the viable percentages of each layer of biofilms were calculated by Fluoview.

Results

The viable counts of E.faecalis biofilm decreased with the extending of treatment time， and E.faecalis biofilm was eliminated after treated by 0.1% nano-silver for 24 h. CLSM observation showed that the average thicknesses of E.faecalis biofilm and viable cells percentages of the outer， middle and inner layers reduced with the treatment time. After treated by 0.1% nano-silver solution for 1 h， E.faecalis biofilm was not completely destroyed. However， the percentages of viable cells of the middle（27.4% ± 5.6%） and inner （20.8% ± 4.5%） layers decreased. These rapidly reduced to （2.0% ±0.9%） and （1.8% ± 0.9%） when treated for 6 h. There were no statistical differences of the percentages of viable cells in each layer between the 0.1% nano-silver solution group and the 1.313% sodium hypochlorite solution group when treated for 12 h and 24 h （P ＞ 0.05）.

Conclusions

0.1 % nano silver solution might penetrate E.faecalis biofilm easily and have a strong bactericidal effect against E.faecalis biofilm formed on dentin slices. The bactericidal effect was enhanced with the time of treatment， and the treatment time should be over 24 h for a better effect of root canal disinfection.

Key words: Nano-silver, Enterococcus faecalis, Biofilm, Root canal disinfection