Journal of dentistry · 2026
Effects of fluoride chemical forms of sodium fluoride and monofluorophosphate on microbial viability and diversity in saliva-derived biofilms.
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Gondo Tadamu, Abe Shuntaro, Hiraishi Noriko, Hayashi Fumiaki, Okazaki Yuina, Abe Takashi, Shimabukuro Masaya, Moyes David, Hill Robert G, Shimada Yasushi
Аннотация
OBJECTIVES: Fluorides are widely used for caries prevention; however, knowledge of the differences in their chemical speciation and associated microbiological effects remains incomplete. This study aimed to elucidate the ionization behavior of sodium fluoride (NaF) and sodium monofluorophosphate (MFP) using 19F NMR spectroscopy and to evaluate their effects on biofilm growth, viability, and microbial composition in saliva-derived polymicrobial biofilms.
METHODS: The chemical speciation of NaF and MFP solutions was characterized by 19F NMR spectroscopy. Polymicrobial biofilms were established from human saliva using an in vitro biofilm model on hydroxyapatite discs. Biofilms were then exposed to NaF or MFP at an equivalent fluoride concentration (1450 ppm). Microbial viability was assessed using an ATP-based luminescence assay. Biofilm community composition was analyzed by 16S rRNA gene sequencing, followed by diversity and differential abundance analyses.
RESULTS: 19F NMR analysis demonstrated that NaF fully dissociated into free fluoride ions, whereas MFP existed predominantly as monofluorophosphate ions, with only a small fraction of free fluoride. Both fluoride compounds significantly reduced microbial viability. NaF exerted a strong, non-selective inhibitory effect without significantly altering overall community structure or alpha diversity. In contrast, MFP caused selective suppression of specific taxa and significantly decreased Shannon diversity. Differential abundance analysis confirmed compound-specific shifts in bacterial genera, indicating distinct antimicrobial profiles.
CONCLUSIONS: NaF and MFP exhibited differential antibiofilm effects, with NaF causing a greater reduction in microbial viability than MFP. 16S rRNA analysis revealed that NaF had minimal impact on the overall microbial composition, whereas MFP induced selective changes in bacterial taxa.
CLINICAL SIGNIFICANCE: This study revealed that fluoride compounds exhibit different antibiofilm effects due to their distinct chemical forms. These forms were precisely identified using 19F NMR rather than conventional fluoride ion-selective electrodes. These findings may help improve understanding of fluoride behavior and guide future research in caries prevention.
METHODS: The chemical speciation of NaF and MFP solutions was characterized by 19F NMR spectroscopy. Polymicrobial biofilms were established from human saliva using an in vitro biofilm model on hydroxyapatite discs. Biofilms were then exposed to NaF or MFP at an equivalent fluoride concentration (1450 ppm). Microbial viability was assessed using an ATP-based luminescence assay. Biofilm community composition was analyzed by 16S rRNA gene sequencing, followed by diversity and differential abundance analyses.
RESULTS: 19F NMR analysis demonstrated that NaF fully dissociated into free fluoride ions, whereas MFP existed predominantly as monofluorophosphate ions, with only a small fraction of free fluoride. Both fluoride compounds significantly reduced microbial viability. NaF exerted a strong, non-selective inhibitory effect without significantly altering overall community structure or alpha diversity. In contrast, MFP caused selective suppression of specific taxa and significantly decreased Shannon diversity. Differential abundance analysis confirmed compound-specific shifts in bacterial genera, indicating distinct antimicrobial profiles.
CONCLUSIONS: NaF and MFP exhibited differential antibiofilm effects, with NaF causing a greater reduction in microbial viability than MFP. 16S rRNA analysis revealed that NaF had minimal impact on the overall microbial composition, whereas MFP induced selective changes in bacterial taxa.
CLINICAL SIGNIFICANCE: This study revealed that fluoride compounds exhibit different antibiofilm effects due to their distinct chemical forms. These forms were precisely identified using 19F NMR rather than conventional fluoride ion-selective electrodes. These findings may help improve understanding of fluoride behavior and guide future research in caries prevention.