Time-dependent antibacterial effects of the self-adjusting file used with two sodium hypochlorite concentrations

This in vitro study evaluated the time-dependent ability of the self-adjusting file (SAF) used with either of two NaOCl concentrations to reduce bacterial populations in long oval root canals.

Oval-shaped canals from extracted teeth were infected with Enterococcus faecalis for 30 days and subjected to preparation with the SAF system using continuous irrigation with either 2.5% NaOCl (n = 11) or 6% NaOCl (n = 11). Bacteriological samples were taken before preparation (baseline) and after 2, 4, and 6 minutes of SAF operation.

Intragroup quantitative analyses revealed that the SAF operating for 2, 4, or 6 minutes yielded a highly significant bacterial reduction when compared with counts at baseline (P < .001) irrespective of the NaOCl concentration. No significant differences were found for intragroup analyses comparing the three time periods (P > .05). Likewise, intergroup quantitative analysis showed no significant difference for the SAF with 2.5% NaOCl or 6% NaOCl during 2, 4, or 6 minutes (P > .05). The incidence of positive cultures in the 2.5% NaOCl group was 6 of 11, 5 of 11, and 2 of 11 after 2, 4, and 6 minutes, respectively. Corresponding figures in the 6% NaOCl group were 4 of 11, 2 of 11, and 1 of 11. When all samples were gathered together, overall findings revealed that using the SAF for 6 minutes significantly reduced both the bacterial counts (P = .02) and the incidence of positive cultures (P = .04) when compared with 2 minutes.

Findings revealed that the SAF promoted a significant reduction in bacterial populations even after only 2 minutes regardless of the NaOCl concentration. The most impressive results were obtained after a 6-minute operation.