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.