Influence of Laser-Activated and Conventional Irrigation Protocols on Smear Layer Removal and Sealer–Dentin Interfacial Bond Strength in the Apical Third of Curved Canals: An In Vitro Study

This study evaluated and compared four irrigation activation protocols—conventional syringe irrigation (CSI), passive ultrasonic irrigation (PUI), photon-induced photoacoustic streaming (PIPS), and shock wave-enhanced emission photoacoustic streaming (SWEEPS)—with 17% EDTA as a final irrigant, with respect to smear layer (SL) removal and push-out bond strength (PBS) of root canal sealer in the apical third of curved root canals. One hundred and twenty extracted single-rooted human premolars with oval canals and moderate curvature (20–40°, Schneider’s method) were allocated into four groups randomly (n = 30 each). Canals were prepared crown-down under 2.5% NaOCl irrigation, followed by final 17% EDTA irrigation per the assigned protocol: CSI, PUI, PIPS, and SWEEPS. 10 specimens per group underwent SEM evaluation of SL removal using Hülsmann’s criteria; remaining specimens were obturated. In 10 samples, apical sealer adaptation was assessed via SEM. PBS of ten samples were evaluated using a universal testing machine, followed by failure mode assessment. Data were statistically evaluated using two-way mixed ANOVA, followed by Tukey’s post hoc test for PBS and Kruskal–Wallis test with Dunn’s multiple-comparison test with Bonferroni correction for SL scores (p < 0.05). Minimum SL removal was exhibited by the apical third of Group 1 (CSI-EDTA) samples. PIPS-EDTA and SWEEPS-EDTA presented comparable SL elimination outcomes in the cervical and middle thirds (p > 0.05). SL elimination between these two groups was significantly different in the apical third. The cervical section of Group 4 displayed the highest bond integrity. However, the lowest bond strength was exhibited by the apical third of Group 1 (CSI-EDTA). SWEEPS combined with EDTA demonstrated superior smear layer removal throughout curved root canals, including the apical third, and yielded the highest push-out bond strength among all tested irrigation protocols.