Effect of final endodontic irrigation protocols on the microtensile bond strength of CAD/CAM endocrown materials to pulp chamber dentin: an in vitro study

Background The bond strength of computer-aided design/computer-aided manufacturing (CAD/CAM) endocrowns depends on the condition of pulp chamber dentin after endodontic treatment. Irrigation protocols can alter dentin chemistry and morphology, influencing microtensile bond strength (µTBS). This study evaluated the effect of four irrigation protocols on µTBS and failure modes of two CAD/CAM materials—lithium disilicate (LDS) and polymer-infiltrated ceramic (Vita Enamic, VE). Materials and methods Forty extracted human mandibular first molars were randomly allocated into four irrigation protocol groups ( n = 10/group): Group 1 (Control): distilled water; Group 2: 2.5% sodium hypochlorite (NaOCl) followed by 17% EDTA; Group 3: NaOCl + EDTA + 10% sodium ascorbate (antioxidant); and Group 4: QMix 2-in-1. After standardized endodontic treatment, teeth were restored with LDS or VE ( n = 5 per material/group). Specimens underwent 24-hour storage and thermocycling (10,000 cycles), then were sectioned into ~ 1 mm² sticks (15 sticks per subgroup) for µTBS testing. Failure modes were analyzed using stereomicroscopy and scanning electron microscopy (SEM) . Data were analyzed using two-way ANOVA and Tukey’s HSD (α = 0.05). Results Irrigation protocol exerted a highly significant main effect on µTBS (F = 127.01, df = 3/112, p < 0.001). Mean µTBS was lowest for the control group (8.6–8.9 MPa), intermediate and statistically comparable for NaOCl + EDTA (20.6–23.2 MPa) and NaOCl + EDTA + Antioxidant (23.9–25.1 MPa; p = 0.087), and highest for QMix (27.8–29.6 MPa; p < 0.001 vs. all other groups). CAD/CAM material type did not significantly affect µTBS ( p = 0.056), and no significant protocol × material interaction was observed ( p = 0.759). Failure mode distribution differed significantly across irrigation groups (χ² = 19.43, df = 6, p = 0.003). Conclusions Within the limitations of this in vitro study, QMix was associated with the highest microtensile bond strength values for both CAD/CAM materials. The addition of sodium ascorbate did not significantly improve bond strength compared with NaOCl + EDTA under the tested conditions. CAD/CAM material type was not a statistically significant determinant of bond strength. These findings suggest that the choice of final endodontic irrigation protocol may influence adhesive bonding to pulp chamber dentin, and should be confirmed by future studies using the tooth as the statistical unit of analysis.