Effects of chemomechanical preparation with 2.5% sodium hypochlorite and intracanal medication with calcium hydroxide on cultivable bacteria in infected root canals.

This clinical study was conducted to assess the bacterial reduction after chemomechanical preparation with 2.5% NaOCl as an irrigant and the additive antibacterial effect of intracanal dressing with calcium hydroxide. According to stringent inclusion criteria, 11 teeth with primary intraradicular infections and chronic apical periodontitis were selected and monitored in the study. Bacterial samples were taken at the baseline (before treatment) (S1), after chemomechanical preparation with 2.5% NaOCl as an irrigant (S2), and after a 7-day dressing with a calcium hydroxide paste in glycerin (S3). Cultivable bacteria recovered from infected root canals at the 3 stages were counted and identified by means of 16S rRNA gene sequencing analysis. At S1, all canals were positive for bacteria, with the mean number of 2.8 taxa per canal (range, 1-6). At S2, 5 cases (45.5%) still harbored cultivable bacteria, with 1 or 2 species per canal. At S3, bacteria were cultured from 2 cases (18.2%), with 1 species per positive case. There was no indication that any specific bacterial taxon was more resistant to treatment. A significant reduction in bacterial counts was observed between S1 and S2, and S1 and S3. However, no statistically significant difference was observed for comparisons involving S2 and S3 samples with regard to the number of cases yielding negative cultures (P = .18) or quantitative bacterial reduction (P = .19). It was concluded that the whole antibacterial protocol used in this study significantly reduced the number of bacteria in the canal and rendered most canals free of cultivable bacteria.