Antimicrobial effect of 2% chlorhexidine as a chemical adjuvant in different endodontic protocols: an in vitro study

Aim: To analyze the antimicrobial effect of different protocols using 2% chlorhexidine as an irrigating substance, and 2.5% sodium hypochlorite to decontaminate lower molars infected with Enterococcus faecalis.

Methodology: 72 mesial roots were sectioned and contaminated with E. faecalis. The samples were randomly distributed into 4 groups (n=14) according to the protocols: 2 ml of 2% chlorhexidine gel and 10 ml of 9% saline solution (CHX G + SS); 2 ml of 2% chlorhexidine gel and 10 ml of 2% liquid chlorhexidine (CHX G + CHX L); 12 ml of 2% liquid chlorhexidine (CHX L); 12 ml of 2.5% liquid sodium hypochlorite (HIP L) (positive control). Bacteriological samples were collected before preparation and irrigation (S1), and after instrumentation and irrigation with different protocols (S2), for the ultimate purpose of quantifying the reduction in planktonic bacteria and intracanal biofilm. The samples were evaluated by using scanning electronic microscopy (SEM) to confirm the presence of biofilm. Bacterial quantification was performed using qPCR and the colony forming unit (CFU)/mL count. Statistical analysis was performed using the Kruskal-Wallis and Wilcoxon tests to compare the protocols of use for chlorhexidine as a according to the time points tested. The Student-Newman-Keuls test was used for multiple comparisons, with a significance level of 5%.

Results: The SEM analysis allowed visualizing the biofilm structure. At S1, there was a significant difference among the teeth that made up each group (p<0.001) regarding the CFU count. At S2, there was no difference among the HIP L, CHX G + CHX L and only CHX L groups, but the CFU count was significantly higher in the CHX G + SS group (p<0.001). Significantly lower CFU counts were found after S2, for all the groups (p=0.010).

Conclusion: The application of different 2% chlorhexidine protocols was effective in reducing bacterial contamination by E. faecalis. The 2% chlorhexidine application protocols proved to be good alternatives to 2.5% sodium hypochlorite, given the excellent antimicrobial efficacy.