Nanostructured Zinc Oxide-Loaded Bonding Agent Response against Oral Microcosm Biofilm

Objectives: To formulate an experimental dental bonding agent containing zinc oxide (ZnO) nanoparticles, and evaluate its chemical and mechanical properties and the antibacterial response against mature dental plaque microcosm biofilms.
Methods: Commercial ZnO nanoparticles were evaluated via Fourier-transform infrared (FTIR) and micro-Raman spectroscopies. ZnO was incorporated at 2.5 (G_2.5%), 5 (G_5%) and 7.5 (G_5%) wt.% in the experimental formulation. One group without ZnO was used as control (G_Ctrl). The dental bonding agents were evaluated for degree of conversion (DC), flexural strength (FS) and elastic modulus (E). The antibacterial activity was evaluated using oral microcosm biofilm model with human saliva as inoculum, acquired salivary pellicle formed on the samples’ surfaces and biofilm maturation during 48h. The dental bonding was assessed via colony-forming unit (CFU) counts, metabolic activity, lactic acid production and live/dead staining of biofilms on dental bonding specimens.
Results: FTIR and micro-Raman indicated peaks of Zn-O bonding. The DC ranged from 62.21 (±1.05) % for G_Ctrl to (46.15±1.23)% for G_7.5%, with lower values from G_2.5%, compared to G_Ctrl (p<0.05). Despite achieving higher E (p<0.05), G_2.5% did not show difference for G_Ctrl regarding FS (p>0.05). G_7.5% showed lower FS, compared to all groups (p<0.05). There was no significant difference for total Streptococci counting among groups (p>0.05). G_7.5% had lower CFU/mL compared to G_Ctrl for Streptococcus mutans (p<0.05) and total microorganism (p<0.05), besides presenting lower metabolic activity (p<0.05). G_7.5% had 20% lower lactic acid production without difference for G_Ctrl (p>0.05). Live/dead staining of biofilms showed low differences among groups.
Conclusions: The addition of the highest amount of ZnO (7.5 wt.%) affected the chemical and mechanical properties of the dental bonding agent, and it was the only concentration able to decrease biofilm formation against mature saliva-derived oral microcosm biofilm.