The effect of hydrodynamic shear on sodium hypochlorite disinfection of Enterococcus faecalis biofilms in dentinal tubules

Objectives: Hydrodynamic shear, generated by fluid movement along surfaces, may enhance biofilm disruption and irrigant penetration into dentinal tubules. This study evaluated the influence of hydrodynamic shear on the antimicrobial efficacy of sodium hypochlorite (NaOCl) against intratubular Enterococcus faecalis biofilms. Methods: Three hundred dentine specimens infected with 3-week E. faecalis biofilms were randomly assigned to experimental groups (n = 20). Disinfection was performed in a Centers for Disease Control and Prevention (CDC) biofilm reactor under controlled hydrodynamic conditions. Specimens were treated with 2% or 5% NaOCl for 3 or 10 min at rotational speeds of 0, 130, and 260 rpm. Sterile water served as the control. Bacterial viability was assessed using LIVE/DEAD staining and confocal laser scanning microscopy. The percentage of dead bacteria was quantified using three-dimensional image analysis. Data were analysed using three-way analysis of variance and Tukey’s post hoc tests (α = 0.05). Results: NaOCl concentration, irrigation time, and rotational speed significantly affected bacterial killing ( p < 0.001). Significant two-way interactions were observed between concentration and time, concentration and speed, and time and speed ( p < 0.001), whereas the three-way interaction was not significant ( p = 0.055). Increasing NaOCl concentration, exposure time, and rotational speed enhanced antibacterial efficacy. The effect of hydrodynamic shear was most pronounced at short exposure time, particularly in the 3-min groups. Conclusions: Hydrodynamic shear significantly enhances the antimicrobial efficacy of NaOCl against intratubular E. faecalis biofilms. Clinical significance: Optimizing irrigant hydrodynamics may improve root canal disinfection and reduce reliance on higher NaOCl concentrations or longer irrigation times.