Long-lasting antimicrobial effect of multipurpose ZnO nanoparticle-loaded dental resins enhanced by blue light photodynamic therapy

Objectives: This study aimed to assess the potential of experimental dental resins containing ZnO nanoparticles (ZnO-NPs) for antimicrobial photodynamic therapy (aPDT) as a functional tool for the modulation of cariogenic biofilm in long-term.

Methods: Minimum inhibitory and bactericidal concentrations (MIC/MBC) of ZnO-NPs against Streptococcus mutans were initially determined under different energy densities of blue LED irradiation (0.00, 1.35, 6.75, or 20.25 J/cm²) to optimize aPDT parameters. Experimental dental resins were then formulated with 0 % (control), 5 %, 10 %, and 20 % ZnO-NPs. Resin disks (1 mm x 6 mm) were prepared to evaluate the antimicrobial and photocatalytic potential of the experimental groups associated with 0 (dark), 1, 2, or 4 light cycles of blue-light irradiation (20.25 J/cm², each cycle). The CFU count and Live/Dead assays were performed on a cariogenic biofilm model (S. mutans) on fresh and 6-month aged resin disks.

Results: Blue light at 20.25 J/cm² decreased MIC (from 250 µg/mL to 125 µg/mL) and MBC (from 1000 µg/mL to 500 µg/mL), establishing the optimal aPDT protocol. Experimental resins with 5 %, 10 %, or 20 % ZnO-NPs, when exposed to 4 cycles of blue light, significantly reduced biofilm viability compared to controls, both initially and after aging. The 20 % ZnO-NP resin sustained > 3.log10 CFU reduction after 6 months, even with 2 cycles of light. Live/Dead assays showed > 50 % dead cells with the 20 % ZnO-NP resin after 2 light cycles.

Significance: ZnO-NP-loaded dental resins associated with blue light aPDT offer promise as a long-lasting antimicrobial alternative, potentially enhancing the control of pathogenic biofilms.