Antibacterial and dissolution ability of sodium hypochlorite in different pHs on multi-species biofilms

The aim of this study was to investigate whether variation in pH of sodium hypochlorite (NaOCl) increased its antibacterial and dissolution ability on polymicrobial biofilms formed in situ.

Fifty-six dentin blocks (eight/group) were intraorally infected for 48 h and incubated in BHI for 48 h to standardize the biofilm growth. The specimens were irrigated with 1 and 2.5% NaOCl with pH levels of 5, 7, and 12 for 20 min. The control group was irrigated with distilled water. The cell viability and the bacterial volume were measured at the pre- and post-irrigation procedures. Five random areas of each sample were chosen and analyzed with confocal laser scanning microscopy (CLSM). Statistical analysis was performed using the non-parametric Kruskal-Wallis and Dunn's tests (p < 0.05).

All the experimental solutions were able to decrease the biomass (p < 0.05) except for the 1% NaOCl-pH 5 group. The antibacterial ability of the NaOCl was dependent on the concentration and acidification of the solution.

The acidification of NaOCl improves its antibacterial ability, but the dissolution effect of the irrigant is decreased.

Bacteria and their products are the main factors in development of apical periodontitis. The pH reduction in the NaOCl could enhance the reduction or elimination of the root canal bacterial colonies in comparison with the unaltered solution.