The role of copper nanoparticles in an etch-and-rinse adhesive on antimicrobial activity, mechanical properties and the durability of resin-dentine interfaces

Objectives To evaluate the effect of addition of copper nanoparticles at different concentrations into an etch-and-rinse adhesive (ER) on antimicrobial activity, Knoop microhardness (KHN), in vitro and in situ degree of conversion (DC), as well as the immediate (IM) and 2-year (2Y) resin-dentine bond strength (μTBS) and nanoleakage (NL). Methods Seven experimental ER adhesives were formulated according to the amount of copper nanoparticles incorporated into the adhesives (0 [control], 0.0075 to 1 wt.%). We tested the antimicrobial activity of adhesives against Streptococcus mutans using agar diffusion assay after IM and 2Y. The Knoop microhardness and in vitro DC were tested after IM and 2Y. The adhesives were applied to flat occlusal dentine surfaces after acid etching. After resin build-ups, specimens were longitudinally sectioned to obtain beam-like resin-dentine specimens (0.8 mm²), which were used for evaluation of μTBS and nanoleakage at the IM and 2Y periods. In situ DC was evaluated at the IM period in these beam-like specimens. Data were submitted to appropriate statistical analyses (α = 0.05). Results The addition of copper nanoparticles provided antimicrobial activity to the adhesives only in the IM evaluation and slightly reduced the KHN, the in vitro and in situ DC (copper concentrations of 1 wt.%). However, KHN increase for all concentrations after 2Y. After 2Y, no significant reductions of μTBS (0.06 to 1% wt.%) and increases of nanoleakage were observed for copper containing adhesives compared to the control group. Conclusion Copper nanoparticles addition up to 0.5 wt.% may provide antimicrobial properties to ER adhesives and prevent the degradation of the adhesive interface, without reducing the mechanical properties of the formulations.