Evaluation of the Antibacterial Activity of Mentha Longifolia Essential Oil against Enterococcus faecalis and its Chemical Composition.

Background: Enterococcus faecalis (E. faecalis) is a multidrug resistant pathogen that can cause persistent infections within the root canal system, which poses major challenges in dentistry and is involved in the majority of endodontic failures.

Purpose: This investigation was conducted to evaluate the antibacterial properties of Mentha Longifolia (M. longifolia) essential oil as a root canal irrigant against E. faecalis and its compounds.

Materials and method: In this in vitro study, 60 primary canines were divided into five groups: G1: Normal saline (negative control), G2: Normal saline, G3: 2.5% sodium hypochlorite (NaOCl), G4: 2% Chlorhexidine (CHX), and G5: M. longifolia essential oil based on minimum inhibitory concentration (MIC). The standard strain suspension of E. faecalis (ATCC 29212) was injected into the canal of all groups, except for the negative control group. After four weeks, the groups were washed with 2 ml of the introduced solutions and sampled by paper point to compare the antibacterial effect of these solutions. Broth microdilution method was used to determine the MIC, while Gas chromatography-mass spectrometry (GC/MS) was used to evaluate the chemical compositions of the essential oil. Data were analyzed based on one-way analysis of variance (ANOVA). Then, pairwise comparisons of groups were performed using Tukey's test.

Results: The MIC of M. longifolia against E. faecalis was 10%. As a root canal irrigant, its highest antibacterial impact was associated with 2.5% NaOCl, 2% CHX, 10% essential oil, and normal saline. The difference was not statistically significant in antibacterial effect between 2.5% NaOCl and 2% CHX (p Value=0.64). However, the difference was statistically significant in antibacterial effect between 2.5% NaOCl and 10% M. longifolia, 2.5% NaOCl and normal saline, 2% CHX and 10% M. longifolia, 2% CHX and normal saline, and 10% M. longifolia and normal saline (p< 0.001). Nineteen compounds were identified in the chemical analysis of M. longifolia, among which Piperitenone oxide (64.68%) and Piperitone oxide (23.68%) were the major compounds.

Conclusion: M. longifolia essential oil (10%) was effective against E. faecalis. The highest antibacterial effect of root canal irrigants was observed in 2.5% NaOCl, 2% CHX, 10% essential oil, and normal saline, respectively.