Four-year effects of copper-nanoparticles on durability of resin-dentin interfaces

Objective: To evaluate the effect of the addition of copper nanoparticles (CuNp) at different concentrations in an etch-and-rinse (ER) adhesive on the resin-dentin bond strength (μTBS), nanoleakage (NL) and presence of copper nanoparticles within the hybrid layer, in the immediate time (IM) and after 4 years of water storage (4 y). Material and methods: Seven experimental adhesive systems were formulated according to the concentration of CuNp (0 [control], 0.0075, 0.015, 0.06, 0.1, 0.5 and 1 wt%) added into the ER adhesive Ambar (FGM). The adhesives were applied to flat occlusal dentin surfaces after acid etching, and then a resin restoration was build-up. Specimens were longitudinally sectioned to obtain resin-dentin beam-like, which were used for evaluation of μTBS, NL and identification of presence of CuNp within the hybrid layer, at the IM and 4 y periods. ANOVA and Tukey's test were applied (α = 0.05). Results: Addition of CuNp up to 0.5% in the adhesive system significantly increased the μTBS at IM (p < 0.05). After 4 y, copper-containing adhesives showed higher values of μTBS compare to control (p < 0.05). All adhesives showed a significant decrease in μTBS over time (p < 0.05). Significant decreases in the NL values were observed in the copper-containing adhesives in IM in comparison with control group (p < 0.05). After 4 y, all copper-containing adhesives showed significantly decreased NL values compare to control group. All adhesives showed a significant increase in NL over time (p < 0.05). Presence of copper within the hybrid layer was identified from 0.06% concentration even after 4 y of water storage. Conclusion: The addition of copper nanoparticles from 0.06% to 0.5% concentrations in an adhesive decreased the degradation of the adhesive interface, mainly because it is still present in the hybrid layer even after 4 years of water storage.