Purpose: To demonstrate that hydrolytically stable methacrylamide monomers allow one-component self-etching adhesives with comparable adhesive properties and better storage stability than hitherto available methyacrylate-based adhesive formulations. Materials and Methods: The shear bond strength and storage stability of the new one-component self-etching, methacrylamide-based adhesive AdheSE One F (Ivoclar Vivadent) to enamel and dentin was compared to the methacrylate-based Clearfil S3 Bond (Kuraray), G-Bond (GC), Hybrid Bond (Sun Medical), iBond (Heraeus Kulzer), Optibond All In One (Sybron-Kerr), and the methacrylamide-based Xeno V (Dentsply). Hydrolytic stability and adhesive performance of these adhesives was evaluated by accelerated aging at 42°C over 16 weeks and monthly assessment of shear bond strength to dentin. The null hypothesis was that the bond strength of one-bottle self-etching dental adhesives is independent of storage duration and that, disregarding their higher stability against hydrolysis, methacrylamide- based materials offer performance beyond shelf-life time, comparable to methacrylate-based adhesives. Statistical analysis included 1-way-ANOVA and the Tukey-B post-hoc test (p < 0.05). Results: Shear bond strengths on enamel ranged from 32.7 MPa (AdheSE One F) to 16.6 MPa (iBond) and on dentin from 36.1 MPa (Optibond All In One) to 20.5 MPa (G-Bond). During accelerated aging, methacrylate-based adhesives with a pH < 2 exhibited decreasing bond strengths over time with material-dependent losses of up to 68% (Hybrid Bond, 8 weeks, 42°C). Under the same conditions, the methacrylamide-based formulations AdheSE One F and Xeno V were stable for 16 weeks regarding shear bond strength to dentin. Conclusions: The shelf life of one-component self-etching adhesives is determined by their chemical composition. In conventional methacrylate-based adhesives, the inherently acidic environment of such formulations leads to monomer degradation due to hydrolysis. In contrast, methacrylamide-based adhesives are stable to aqueous acid and exhibit much superior storage stability without monomer degradation-related losses in adhesion performance.
Keywords: self-etching adhesive, acrylamide, acidic monomer, degradation, dentin sealing, hydrolytic stability