The effect of different irrigation activation methods used for the removal of residual filling materials during retreatment on bond strength

Objective: This study aimed to compare the effects of standard needle irrigation (SNI), sonic activation (EDDY), passive ultrasonic irrigation (PUI), photon-induced photoacoustic streaming (PIPS), and shock wave-enhanced emission photoacoustic streaming (SWEEPS) used during retreatment (RT) on the bond strength of a calcium silicate–based root canal sealer to radicular dentin. Methods: A total of 80 extracted human maxillary central incisors with single roots and canals were used. The crowns were removed to obtain root lengths of 18 ± 0.1 mm. Root canals were prepared up to size X3 using the ProTaper Next (Dentsply Maillefer, Ballaigues, Switzerland) system and an endomotor (VDW, Munich, Germany). All canals were filled with TotalFill BC Sealer HiFlow (FKG Dentaire, La Chaux-de-Fonds, Switzerland) and gutta-percha using the single-cone technique. For RT, the fillings were removed with the ProTaper Universal Retreatment (Dentsply Maillefer) system and an additional preparation with size X4 was performed. The specimens were then randomly divided into five groups (n=16) according to the final irrigation activation method: SNI, EDDY, PUI, PIPS, and SWEEPS. In all groups, 1 mL of irrigant was activated for three 30-second cycles. After activation, canals were refilled using the same materials and technique and stored at 37 °C for 14 days to allow complete sealer setting. The roots were sectioned into 1.5 ± 0.1 mm slices representing coronal, middle, and apical thirds. Push-out bond strength was measured using a universal testing machine (AGS-X, Shimadzu Corp., Kyoto, Japan) at a crosshead speed of 1 mm/min, and values in Newtons were converted to MPa. Data normality was assessed using the Shapiro–Wilk test, and since normality was not satisfied, the Kruskal–Wallis and Mann–Whitney U tests were applied. Results: In the coronal third, bond strength was significantly higher with SWEEPS compared with EDDY, SNI, and PUI (P<0.05). No significant differences were observed among groups in the middle and apical thirds. Within-group analysis showed that in the SWEEPS group, coronal bond strength was significantly higher than in middle and apical thirds (P<0.05). No significant intra-group differences were observed for SNI, EDDY, PUI, or PIPS. Conclusion: SWEEPS provided significantly higher bond strength in the coronal third compared to other methods, while no differences were found at middle and apical levels. Cohesive failures were the most frequent, with coronal predominance in SWEEPS. These findings suggest that irrigation activation methods particularly affect coronal bond strength, and SWEEPS may offer a clinical advantage in this regard. Keywords: Non-surgical retreatment; irrigation activation techniques; push-out bond strength; photoacoustic streaming; sonic activation; calcium silicate-based sealer.