Adhesive properties of universal adhesives systems containing zinc oxide and copper nanoparticles on sound dentine: A 2-year evaluation

Objectives: This study evaluated the effect of adding zinc oxide and copper nanoparticles (ZnO/CuNp) to universal adhesives (UA) on resin-dentine microtensile bond strength (μTBS), nanoleakage (NL), and the presence of ZnO/CuNp within the hybrid layer at immediate time (IM) and after 2 years of water storage (2y). Methods: ZnO/CuNp (commercial adhesive [control]; 5/0.1 and 5/0.2 wt%) were added to Prime&Bond Active (PBA) and Ambar Universal (AMB). The UAs were applied to flat dentine surfaces, followed by composite resin build-ups. These were then sectioned into resin–dentine bonded sticks. μTBS, NL and presence of ZnO/CuNp in the hybrid layer were evaluated at IM and after 2y. Data were analyzed with three-way ANOVA and Tukey's post hoc test (α = 0.05). Results: The addition of ZnO/CuNp to UAs did not affect μTBS at IM (p > 0.05). After 2y, μTBS values were higher in the 5/0.1 and 5/0.2 wt% groups for AMB (p < 0.05), with values maintained for the PB (p > 0.05). All groups showed a decrease in μTBS over time (p < 0.05), except for the AMB-5/0.1 wt% group in etch-and-rinse mode. NL was lower in the ZnO/CuNp groups at both IM and 2y compared to control (p < 0.05). NL increased over time for all groups (p < 0.05). ZnO/CuNp remained in the hybrid layer after 2y. Conclusions: ZnO/CuNp improves adhesive interface stability and remains effective in the hybrid layer after 2 years of water storage.