Purpose: Self-etching adhesives partly remove or dissolve the dentin smear layer, causing incomplete resin tag formation or low resin tag density. The quantitative contribution of properly formed resin tags to dentin adhesion was evaluated. Materials and Methods: We assessed how the presence or absence of resin tags affects tubules of human deepcoronal dentin. G-Bond was used to bond Gradia resin composite. To ensure deep tubule penetration, we used a vacuum exsiccator. For eliminating tag formation, dentin tubules were presealed with adhesive and reverse bonded after finishing. Microtensile bond strength (μTBS) was measured on flat specimens and on Class I cavity floors. Thermocyclic loading was used to estimate the influence of resin tags on long-term behavior. Confocal laser scanning microscopy was used to evaluate adhesive interface dimensions. Results: Hybrid layer thickness, tag length, and tag diameter increased under vacuum treatment. Presealing dentin tubules led to a residual tag area of 3.1% with a tag length of 10.8 μm. Under vacuum, 24.7% of the total dentin surface was covered with tags of 87.8 μm. Low C-factor preparations produced superior μTBS (71.8 to 92.7 MPa) compared with high C-factor Class I cavities (47.0 to 67.6 MPa). Thermocyclic fatigue differed from low to high C-factor situations. In Class I cavities, μTBS significantly decreased after thermocycling. On flat specimens, vacuum infiltration led to reduced μTBS after thermocyclic loading. Conclusion: Initially, resin tag formation did not influence the μTBS in either type of C-factor preparation. After thermocyclic loading, μTBS decreased with or without resin tags. Adhesive fracture patterns occurred at the hybrid layer/dentin interface.
Keywords: dentin bonding, adhesion, tag formation, resin composites, hybrid layer, vacuum, C-factor