Bonding effectiveness of experimental one-step self-etch adhesives to sound and caries-affected dentin

Experimental one-step, self-etch adhesives containing different contents of an acidic methacrylate monomer (GDMA-P) were formulated and their effectiveness in bonding to sound dentin (SoD) or caries-affected dentin (CAD) was investigated. The CAD was obtained using a microcosm biofilm model. HEMA-based adhesives were formulated with 5, 20, or 35 wt% of GDMA-P (AD5, AD20, AD35), with pH ranging between 1.05 ± 0.05 and 1.93 ± 0.15. Shear bond strength to dentin was assessed after storage for 24 h or 6 months. Morphology of the bonded interfaces was observed using SEM. The exposed collagen area at bonded interfaces was measured using a histological staining technique. Degree of C=C conversion within the hybrid layer, measured by micro-Raman spectroscopy, indicated that AD35 had lower in situ C=C conversion than the other adhesives. A more evident exposed collagen zone along the base of the hybrid layer was observed in CAD samples. The hybrid layer was generally thicker in CAD. AD20 had the highest in situ C=C conversion and yielded stable bond strengths that were generally independent of the dentin condition. Additionally, the bonding effectiveness was dependent on adhesive acidity, type of dentin bonding substrate, and water storage time.