Comparative assessment of the resin-dentin interface using three different universal adhesives: An ex vivo study

Background: Universal self-etch adhesives are increasingly used in restorative dentistry, but comparative evidence about their penetration and interface quality in dentin under simulated clinical conditions is limited. Objectives: To evaluate and compare the resin-dentin interface, depth of penetration, and hybrid layer thickness using three universal self-etch adhesives Single Bond Universal, Tetric N Bond Universal, and Solare Universal Bond under simulated pulpal pressure. Materials and Methods: Forty-five caries-free premolars, extracted for orthodontic reasons, were randomly assigned to three groups. Standardized Class I cavities (1 mm depth into dentin) were restored using each adhesive (15 teeth/group) and corresponding composites. Adhesives were mixed with 0.1% rhodamine B, applied according to manufacturer instructions, and light-cured in two layers. After extraction and storage, specimens were sectioned and examined under confocal laser scanning microscopy for hybrid layer thickness and resin tag penetration. Data were analyzed with ANOVA and post hoc Tukey tests ( P < 0.05). Results: Tetric N Bond Universal showed the highest mean resin tag penetration (697.6 ± 130.0 µm) and hybrid layer thickness (528.7 ± 117.2 µm), statistically different from Single Bond Universal (634.8 ± 71.7 µm tag, 478.3 ± 85.5 µm hybrid layer) and Solare Universal Bond (644.4 ± 92.9 µm tag, 512.7 ± 105.5 µm hybrid layer). No significant difference was found between Single Bond Universal and Solare Universal Bond. All groups demonstrated clinically acceptable interfaces with well-formed hybrid layers and resin tag penetration. Conclusion: Among the tested adhesives, Tetric N Bond Universal exhibited superior hybrid layer thickness and resin tag penetration. This may relate to its specific chemical composition and hydrophilic-hydrophobic monomer balance. Further research with larger samples and additional performance outcomes is warranted.