Synergistic effects of arginine and fluoride on human dental biofilm control

•In situ biofilm model used to examine effects of arginine and fluoride on bacteria.•Arginine + fluoride do not reduce the number of viable bacteria.•Arginine + fluoride suppress bacteria associated with dental diseases.•Arginine and fluoride have synergistic effect on bacterial flora of dental biofilms. The aim of this study was to quantitatively and comprehensively investigate the combined effects of arginine and fluoride on the suppression of pathogenicity using an in situ biofilm model and next-generation sequencing (NGS). Using the in situ model, dental biofilms were formed and the viable bacterial counts and arginine activity in the arginine- and fluoride-containing dentifrice and control groups were measured. We also compared their effects on the bacterial microbiota and predictive functional factors in the control, arginine (arg), and arginine + fluoride (argF) groups using NGS analysis. Compared to the control treatment, the use of 8 % arginine and 1450 ppm fluoride toothpaste resulted in significantly high oral NH4+ concentrations without affecting the number of viable bacteria (P < 0.05). NGS analysis revealed that the oral microbiota of the control, arg, and argF groups were significantly different. Heat map analysis of the predicted functional factors revealed that the arg group had different properties from the other groups and activated specific substrate metabolic pathways; contrastingly, argF treatment inhibited the activity of these pathways and prevented an increase in the abundance of bacterial genera that utilize substrates such as sucrose, suggesting the synergistic effect of arginine and fluoride. This study indicates that the combination of arginine and fluoride has a synergistic effect on the bacterial microbiota and pathogenicity of dental biofilms compared with arginine alone. Our findings suggest that the combination of arginine and fluoride could be used as an effective prebiotic and may inhibit the growth of bacteria associated with dental diseases.