Effect of sodium fluoride on the virulence factors and composition of Streptococcus mutans biofilms

Objective: This study aimed to evaluate the influence of NaF (2, 10, 50 and 125 ppm F^-) on the virulence factors and composition of Streptococcus mutans biofilms. Methods: S. mutans UA159 biofilms were formed on saliva-coated hydroxyapatite discs. To assess the influence of NaF on the virulence factors of S. mutans biofilm cells, glycolytic pH drop, proton-permeability and F-ATPase activity assay were performed using 74 h old S. mutans biofilms. Glucosyltransferase (GTF) activity assay in suspension was also performed. To examine the influence of NaF on S. mutans biofilm composition, the biofilms were treated twice daily (5 min exposure/treatment) a total of five times during biofilm formation. After a total of 5 treatments, the biomass, colony forming unit (CFU) and polysaccharide composition of the treated 74 h old S. mutans biofilms were analysed by microbiological and biochemical methods, and scanning electron microscopy. Results: NaF showed inhibitory effects on the acid production and acid tolerance of S. mutans biofilm cells at 10, 50 and 125 ppm F^-, compared to the vehicle control (P < 0.05) and the treatments at these concentrations also affected the biomass, water-insoluble extracellular polysaccharides and intracellular iodophilic polysaccharides of the biofilms, compared to the vehicle control (P < 0.05). Conclusions: These results indicate that NaF (10, 50 and 125 ppm F^-) has inhibitory effects on the virulence factors and composition of S. mutans biofilms, suggesting the potential use of these concentrations as an effective measure for controlling dental biofilms.