Universal Dental Adhesives Containing Zinc Oxide and Copper Nanoparticles Improve Interface on Caries-Affected Dentin After 2 Years: In Vitro Study

Objective: To evaluate the effect of adding zinc oxide and copper nanoparticles (ZnO/CuNp) into universal adhesives (UAs) on resin–dentin microtensile bond strength (μTBS), nanoleakage (NL), and presence of ZnO/Cu within the hybrid layer on caries-affected dentin, both at baseline (T0) and after 2 years of water storage (T2). Materials and Methods: ZnO/CuNp (0% [control]; 5/0.1 and 5/0.2 wt%) were added into Prime&Bond Active (PBA) and Ambar Universal (AMB). Ninety-six extracted human third molars were used. After microbiological induction of caries-affected dentin, UAs were applied in both etch-and-rinse and self-etch modes, followed by composite build-up. Specimens were sectioned to obtain resin–caries-affected dentin bonded sticks for μTBS, NL, and chemical characterization of the hybrid layer for Cu and Zn detection at T0 and T2. Data were statistically analyzed (α = 0.05). Results: ZnO/CuNp had no effect on μTBS at T0 (p > 0.05) but improved μTBS at T2, compared to control (p < 0.05). Both UAs showed a significant decrease in μTBS over time (p < 0.05), except PBA with ZnO/CuNp in etch-and-rinse mode. NL was significantly lower in ZnO/CuNp-containing UAs at both time points (p < 0.05), though all groups showed increased NL over time. ZnO/CuNp remained detectable in the hybrid layer at T2. Conclusions: Adding ZnO/CuNp to UAs decreased adhesive interface degradation on caries-affected dentin, likely due to their presence within the hybrid layer even after 2 years. Clinical Significance: ZnO/Cu nanoparticles into UAs could enhance the stability of adhesive restorations on caries-affected dentin by reducing interface degradation.