Comparative in vitro evaluation of sonic, passive ultrasonic, and Er: YAG laser-activated irrigation on Enterococcus faecalis reduction and smear layer/debris removal in root canals

BACKGROUND: Persistent intraradicular infection remains a major cause of endodontic treatment failure because conventional syringe irrigation may not adequately reach the apical third, dentinal tubules, and canal irregularities. The aim of this in vitro study was to compare the antimicrobial efficacy and smear layer/debris removal ability of sonic activation, passive ultrasonic irrigation, and Er: YAG laser-activated irrigation using photon-induced photoacoustic streaming (PIPS), relative to conventional syringe irrigation, in prepared root canals infected with a mono-species Enterococcus faecalis biofilm. METHODS: Sixty extracted single-rooted mandibular second premolars were prepared, sterilized, inoculated with E. faecalis, and randomly allocated to conventional syringe irrigation, sonic activation, passive ultrasonic irrigation, or Er: YAG/PIPS activation (n = 15). All groups received 2.5% sodium hypochlorite. Post-irrigation bacterial load was quantified as log10 CFU/mL, and smear layer/debris removal in the apical, middle, and coronal thirds was assessed by scanning electron microscopy using a five-point score. CFU values were analysed by one-way ANOVA with Tukey's post hoc test, and SEM scores by the Kruskal-Wallis test with Dunn's multiple-comparison test. Inter-examiner agreement was assessed using Cohen's kappa. Statistical significance was set at p < 0.05. RESULTS: Bacterial load differed significantly among groups (F(3, 56) = 85.11, p < 0.001). Mean log10 CFU/mL values were 6.41 ± 0.30 for conventional irrigation, 5.37 ± 0.26 for sonic activation, 4.12 ± 0.24 for passive ultrasonic irrigation, and 4.28 ± 0.27 for Er: YAG/PIPS activation. Passive ultrasonic and Er: YAG/PIPS activation produced significantly lower bacterial loads than sonic activation and conventional irrigation, with no significant difference between the ultrasonic and laser groups (p = 0.452). SEM scores also differed significantly (H = 38.9, p < 0.001). Overall median scores were 4.5 (IQR 4-5), 3 (IQR 3-4), and 2 (IQR 2-3) for conventional, sonic, and both ultrasonic and laser activation, respectively. CONCLUSIONS: All tested activation methods improved root canal disinfection and smear layer/debris removal compared with conventional syringe irrigation. Passive ultrasonic irrigation and Er: YAG/PIPS activation were more effective than sonic activation and showed comparable performance. These methods may be useful adjuncts to sodium hypochlorite irrigation, although clinical studies are needed to confirm their clinical effectiveness.