Antibacterial efficacy of Er: YAG laser-activated irrigation using PIPS and SWEEPS against Enterococcus faecalis in dentinal tubules: a confocal laser scanning microscopy study

The SWEEPS modality using an Er: YAG laser has been developed to enhance debridement and disinfection during endodontic treatment. This study aimed to compare the bactericidal efficacy of sodium hypochlorite (NaOCl) at different concentrations activated by SWEEPS versus PIPS against Enterococcus faecalis within infected dentinal tubules using confocal laser scanning microscopy (CLSM). Fifty-two root canal specimens were longitudinally sectioned into 104 semicylindrical dentin slices and inoculated with Enterococcus faecalis . A total of 90 dentin segments were randomly selected and assigned to nine experimental groups. Each group received irrigation with NaOCl at different concentrations (1%, 2.5%, and 5.25%) combined with conventional needle irrigation, PIPS, or SWEEPS activation. Each specimen received 6 mL of NaOCl solution at the designated concentration throughout the irrigation protocol, with activation performed for 3 × 30s. The percentages of dead and live bacteria within the dentinal tubules were quantitatively assessed using LIVE/DEAD bacterial viability staining coupled with CLSM. The data were natural-log-transformed and analyzed using a linear mixed-effects model (LMM), with Bonferroni correction applied for pairwise intergroup comparisons. Bacterial reduction was significantly greater in all PIPS-activated NaOCl groups (51%-78%) and SWEEPS-activated NaOCl groups (52%-81%) than in the conventional irrigation (CI) + NaOCl groups (25%-37%) ( P < 0.05). Bacterial reduction increased with increasing NaOCl concentration across all irrigation modalities ( P < 0.05). Bacterial reduction with 1% NaOCl activated by PIPS (51%) and SWEEPS (52%) was significantly greater than that achieved with conventional irrigation using 5.25% NaOCl (37%) ( P < 0.05). No significant difference in bacterial reduction was observed between the PIPS and SWEEPS modalities ( P > 0.05). Under the experimental conditions of this study, Er: YAG laser activation (SWEEPS/PIPS) enabled the use of lower NaOCl concentrations without compromising intratubular antibacterial efficacy. Furthermore, SWEEPS and PIPS exhibited comparable antimicrobial efficacy against intradentinal bacterial biofilms.