Antibacterial and mechanical properties of reduced graphene-silver nanoparticle nanocomposite modified glass ionomer cements

Objectives: Glass ionomer cements (GIC) are widely recognized as important dental restorative materials whilst they often suffer from restoration failures due to the poor mechanical properties and secondary caries. Reduced graphene-silver nanoparticle (R-GNs/Ag) nanocomposite exhibits excellent antibacterial activities. This study aimed to evaluate the antibacterial and mechanical properties of GIC modified by incorporation of different proportion of R-GNs/Ag. Methods: R-GNs/Ag nanoparticles were incorporated into conventional glass ionomer powder at 0-2.00 wt.% concentration and cement specimen were prepared. The antibacterial properties of R-GNs/Ag modified GIC materials were investigated by direct contact test (DCT), scanning electron microscopy (SEM) observation, XTT assay and bacteria live/dead assay. Flexural strength and surface microhardness were measured by a universal testing machine and a microhardness tester, respectively. Results: The DCT demonstrated an obvious decrease of S. mutans quantity with incorporation of 2.00 wt.% nanoparticles (p < 0.05). SEM images showed fewer bacteria and smaller stacks on the surface of modified specimens. No significant difference was found in the metabolic activity of S. mutans according to the XTT assay (p < 0.05). The addition of 1.00 and 2.00 wt.% R-GNs/Ag significantly decreased the percentage of viable bacteria (p < 0.05). There was no significant decrease of flexural strength and surface microhardness with incorporation of up to 2.00 wt.% nanocomposite (p < 0.05). Conclusions: R-GNs/Ag nanocomposite might be a promising agent to improve the antibacterial activity of dental restorative GIC without compromising its mechanical properties.