Comparative Evaluation of Bond Strength Between Flowable and Condensable Composites to Dentin Treated by Sandblasting and Different Adhesive Systems: An In Vitro Experimental Study

PURPOSE: To evaluate the bond strength of flowable and packable composites to sandblasted dentin using different adhesive systems. MATERIALS AND METHODS: A total of 160 extracted premolars were sectioned at the upper-middle third and allocated into 16 groups (n = 10) based on composite type, surface treatment, and adhesive system. In sandblasted groups, dentin was air-abraded with 50-μm aluminum oxide for 10 seconds. Composite cylinders (3 × 3 mm; 7.065 mm2) were bonded using Single Bond 2, Palfique Bond, or Single Bond Universal. Shear bond strength (SBS, MPa) and failure modes were recorded, and bonding interfaces were examined by scanning electron microscopy (SEM). Data were analyzed using three-way ANOVA with Tukey HSD, Kruskal-Wallis with Bonferroni correction, and Weibull analysis. RESULTS: Flowable composites, sandblasting, and the two-step application of Single Bond Universal each significantly improved bond strength. A three-way interaction was observed (F = 5.12, P = .01). Groups 1, 8, and 13 showed the highest bond strengths (11.47 ± 6.44, 15.88 ± 5.39, and 12.90 ± 4.98 MPa; P < .05), with Groups 8 and 13 demonstrating superior Weibull modulus (m) and characteristic strength (σο). SEM analysis revealed that these groups exhibited the most intimate adhesive-dentin contact with minimal interfacial defects. Failure mode assessment showed predominantly cohesive and mixed failures in Groups 1, 8, and 13. CONCLUSIONS: Sandblasting, flowable composites, and two-step Single Bond Universal enhance dentin bond strength. The most effective combinations were sandblasted dentin with flowable composite and Single Bond Universal (one-step), and non-sandblasted dentin with packable composite and Single Bond Universal (two-step).