Antibacterial response of oral microcosm biofilm to nano-zinc oxide in adhesive resin

Abstract

Objective: Various nanoparticles are currently under investigation to impart biointeractivity for dental materials. This study aimed to: (1) formulate an experimental dental adhesive containing ZnO nanoparticles; (2) evaluate its chemical and mechanical properties; and (3) assess the antibacterial response against oral microcosm biofilm.

Methods: Nanosized ZnO was chemically and morphologically evaluated. ZnO was incorporated at 0 (G_CTRL), 2.5 (G_2.5%), 5 (G_5%) and 7.5 (G_5%) wt.% in an experimental dental adhesive. The adhesives were evaluated for the degree of conversion (DC), flexural strength (FS), and elastic modulus (E). The antibacterial activity was evaluated using a 48h-microcosm biofilm model after the formation of acquired pellicle on samples' surfaces. Colony-forming units (CFU), metabolic activity, and live/dead staining were assessed.

Results: Nanosized ZnO presented characteristic peaks of Zn-O bonds, and the particles were arranged in agglomerates. The DC ranged from 62.21 (±1.05) % for G_Ctrl to 46.15 (±1.23) % for G_7.5% (p<0.05). G_7.5% showed lower FS compared to all groups (p<0.05). Despite achieving higher E (p<0.05), G_2.5% did not show differences for G_Ctrl regarding the FS (p>0.05). G_7.5% had lower CFU/mL compared to G_Ctrl for mutans streptococci (p<0.05) and total microorganisms (p<0.05), besides presenting lower metabolic activity (p<0.05) and higher dead bacteria via biofilm staining.

Significance: The dental adhesives' physicochemical properties were similar to commercial adhesives and in compliance with ISO recommendations. G_7.5% restricted the growth of oral microcosm biofilm without impairing the physicochemical performance.

Keywords: Antibacterial agents; Biofilms; Composite resins; Dental caries; Dentin-bonding agents; Polymers.