In vitro evaluation of the antibiofilm activity of grapefruit seed extract against Enterococcus faecalis and its effect on dentin microhardness as a root canal irrigant

Abstract The study was conducted to evaluate the effect of grapefruit seed extract (GFSE) at different concentrations on Enterococcus faecalis biofilm and to compare its effect to sodium hypochlorite (NaOCl) on dentin microhardness over time. Thirty dentin samples were treated with NaOCl (2.5%) and grapefruit seed extract (0.5%, 1%, 2.5%, and 5%) with six samples per group. Microhardness was measured at three-time intervals: pre-irrigation, post-irrigation, and 2 weeks post-irrigation using Vicker’s microhardness tester. In vitro antibiofilm effect was assessed for a contact time of 6 min using Enterococcus faecalis biofilm dentin block model applied to thirty-six dentin block samples (six samples per group). Antibiofilm data was analyzed using Kruskall-wallis with follow-up Mann-Whitney U tests based on normality testing, while microhardness data were analyzed using two-way repeated measures ANOVA, Tukey post hoc test, and mixed-effect model analysis. GFSE demonstrated the best antibiofilm effect at the concentration of 2.5% while the best effect on preserving microhardness was achieved at 5% GFSE concentration. No significant difference was observed in the antibiofilm effect between 2.5% NaOCl and both 2.5% and 5% GFSE concentrations with the three groups demonstrating a large effect size ( r > 0.8). NaOCl showed a significant reduction in microhardness over time ( p = 0.002 ). In contrast, all GFSE groups demonstrated a more preserving effect on microhardness with no statistically significant change in all tested concentrations over time. Additionally, direct post hoc comparison contrasting change overtime showed significant mean differences between NaOCl and all GFSE tested groups. GFSE demonstrated less progressive reduction and a more preserving effect on dentin microhardness compared to NaOCl. The effect of GFSE against E. faecalis biofilm highly approached the antibacterial effect of NaOCl as a standard of practice, suggesting its potential as a biocompatible alternative irrigant in endodontics.