Nano-chitosan modified restorative materials suppress Streptococcus mutans biofilm and virulence gene expression.

Secondary caries and biofilm production remain a persistent concern, prompting the development of antibacterial restorative materials. However, worries about synthetic additives’ safety and long-term effects urge the use of natural, biocompatible alternatives. This study explored the antibacterial efficacy of chitosan (CH) and nano-chitosan (NCH) incorporated into different restorative materials: amalgam (Am), glass ionomer cement (G), and resin composite (R). This study employs a direct comparative analysis of both modified and unmodified restorative materials against Am to evaluate their efficacy against Streptococcus mutans ATCC 25,175 using agar diffusion, broth inhibition, biofilm formation assays, and qPCR investigation of virulence genes (ldh and gtfB). Incorporating CH and NCH, especially at 15%, decreased biofilm biomass, downregulated virulence gene expression, and significantly increased the effectiveness of bacterial growth suppression. When compared to controls, the G modified with 15% NCH (GN15) showed the strongest inhibition of bacterial growth by 43.1%. The most significant finding was the ability of GN15 to downregulate the expression of ldh and gtfB by 50% and 28%, respectively, indicating a disruption in acid production and biofilm matrix synthesis. While Am showed the highest overall inhibition (86%, 65%). These results demonstrate that nano-chitosan is a biocompatible and promising addition to restorative materials, providing improved defense against cariogenic biofilms and facilitating the creation of dental biomaterials of the future.