Biological, mechanical and adhesive properties of universal adhesives containing zinc/copper-nanoparticles.

Objectives: To evaluate the effect of addition of zinc-oxide and copper-nanoparticles (ZnO/CuNp) at different concentrations into two universal adhesives, on antimicrobial activity(AMA), cytotoxicity(CTx), ultimate tensile strength(UTS), microhardness(MH), water-sorption(WS) and solubility(SO), in-vitro degree of conversion(DC-v), as well as, microtensile bond strength(μTBS), nanoleakage(NL) and in-situ degree of conversion(DC-s) on sound and caries-affected dentin.
Methods: Six universal adhesives were formulated according to the addition of ZnO/CuNp (0% [control]; 5/0.1 and 5/0.2wt%) in Ambar Universal(AMU) and Prime&Bond Active(PBA). The AMA was evaluated against Streptococcus mutans using agar diffusion assay. For CTx analysis, osteoblast-like cell line SaOS-2 was used. For UTS and MH, specimens were tested after 24h and 28-days. For WS and SO specimens were tested for 28-days. For DC-v, specimens were tested after 24h for micro-Raman spectroscopy. The occlusal enamel of 144 caries-free third molars was removed. After enamel removal, a microbiological caries induction model was applied in 72 of them. Then, the experimental adhesives were applied to sound and caries-affected dentin in etch-and-rinse or self-etch mode. After composite resin build-ups, specimens were longitudinally sectioned to obtain resin–dentine bonded sticks. For μTBS, NL and DC-s, bonded sticks from each tooth were prepared and analyzed after 24h of water storage. Statistical significance was defined in α = 0.05.
Results: For AMA and CTx, difference between ZnO/CuNp groups and control were detected. For UTS, MH and DC-v, ZnO/CuNp addition not negatively influenced these properties. For the 28-day WS and SO, significant differences of ZnO/CuNp groups when compared with control were observed. After 24h, ZnO/CuNp did not influence negatively the μTBS and DC-s and decrease the NL, in both adhesives and adhesive strategies, in sound and caries-affected dentin.
Conclusions: The addition of ZnO/Cu Np in the tested concentrations in universal adhesive systems may be an alternative to provide antimicrobial activity and improves the integrity of the hybrid layer, without jeopardizing mechanical properties.