Bioactive and antibacterial universal adhesives containing ZnO/Cu and bioactive glass nanoparticles

To evaluate the antibacterial activity, cytocompatibility, mineralizing potential, degree of conversion (DC), enzymatic activity, and resin-dentin microtensile bond strength (μTBS) of a universal adhesive modified with zinc oxide (ZnO), copper (Cu), and bioactive glass (BG) nanoparticles.

Five adhesive formulations were evaluated: control (0 wt %); ZnO/Cu (0.2 wt % Cu + 2.5 wt % ZnO); 5 wt %BG + ZnO/Cu; 10 wt %BG + ZnO/Cu; and 10 wt %BG. Antibacterial activity against Streptococcus mutans was quantified by colony-forming unit counts. Cytocompatibility was assessed using human gingival stem cells (MTS assay, 3 and 7 days). Mineralization was evaluated after immersion in simulated body fluid (7 and 28 days) via FE-SEM and EDX. The DC was measured by Raman spectroscopy. Resin-dentin μTBS was tested under self-etch (SE) and etch-and-rinse (ER) strategies. MMPs activity was assessed by in situ zymography. Data were analyzed with ANOVA and Tukey tests (α = 0.05).

BG nanoparticles significantly enhanced antibacterial and mineralizing responses. The 10 wt %BG and 10 wt %BG + ZnO/Cu groups achieved >80 % bacterial inhibition and marked Ca-P deposition after 28 days. All adhesives exhibited cytocompatibility (>80 % viability) and DC values >60 %. A slight reduction in μTBS was observed for 10 wt %BG groups under the ER strategy. High gelatinolytic activity was detected across all groups, with reduced fluorescence only for the ZnO /Cu group under ER strategy.

Incorporating BG nanoparticles into a ZnO/Cu-modified universal adhesive improved antibacterial and mineralizing properties without impairing cytocompatibility, polymerization, without critically compromising bond strength. MMP activity varied with bonding strategies, with no consistent inhibitory effect observed.

Universal adhesives modified with bioactive glass and ZnO/Cu nanoparticles exhibited enhanced antibacterial and mineralizing properties while maintaining cytocompatibility and degree of conversion, without critically compromising bond strength. Although, no immediate inhibition of MMP activity was observed, this multifunctional approach may contribute to more stable adhesive interfaces and improved long-term performance of composite restorations.