Effects of ZnO/Cu and bioactive glass-modified universal adhesives on biological properties, bond strength, and interfacial stability under cariogenic challenge.

OBJECTIVES: To evaluate the effect of incorporating zinc oxide (ZnO), copper (Cu), and bioactive glass (BG) nanoparticles into a universal adhesive on the resin–dentin bond stability under a cariogenic challenge. The influence of these nanoparticles on enzymatic activity, mineral deposition, nanoleakage (NL), and microtensile bond strength (µTBS) was assessed. METHODS: Five experimental adhesives were formulated by adding nanoparticles to a commercial universal adhesive: Control (0%), ZnO/Cu (0.2 wt% Cu + 2.5 wt% ZnO), 5 wt% BG + ZnO/Cu, 10 wt% BG + ZnO/Cu, and 10 wt% BG. Human dentin specimens were bonded using etch-and-rinse (ER) or self-etch (SE) strategies and restored with resin composite. After 24 h, specimens were evaluated at baseline and following a 5-day Streptococcus mutans biofilm challenge (pH ≈ 4.0). µTBS and NL were measured before and after challenge. Matrix metalloproteinase (MMP) activity was analyzed via in situ zymography, and mineral deposition was characterized by SEM-EDX after immersion in simulated body fluid. Data were analyzed using ANOVA and Tukey’s post hoc test (α = 0.05). RESULTS: Nanoparticle incorporation enhanced the biofunctional performance of the adhesive. The 10 wt% BG + ZnO/Cu formulation preserved µTBS and significantly reduced NL after the cariogenic challenge (p < 0.05), whereas the control lost than 40% of its initial bond strength. SEM-EDX revealed increased Ca and P deposition at the hybrid layer, approaching hydroxyapatite-like composition. Although MMP activity varied between bonding strategies, no consistent inhibitory effect was detected.