Stannous Fluoride: NMR Characterization and Antibacterial Activity by Microbiome Analysis

This study aimed to characterize the ionization behavior and chemical speciation of stannous fluoride (SnF₂) using NMR spectroscopy and to evaluate its effects on microbial viability and bacterial community composition in saliva-derived polymicrobial biofilms.

SnF₂ speciation was characterized by ¹⁹F NMR spectroscopy. As a physicochemical assessment, biomimetically precipitated apatite samples were analyzed by solid-state ³¹P NMR. Saliva-derived polymicrobial biofilms were formed on hydroxyapatite discs and exposed to SnF₂ or NaF at final F concentrations of 38, 76, and 190 ppm. Deionized water was added instead of the fluoride stock solution, served as the control. ATP-based microbial activity was assessed by luminescence assay, and bacterial community composition was analyzed by 16S rRNA gene sequencing at 190 ppm F.

¹⁹F NMR analysis showed that SnF₂ existed not only as free F⁻ ions but also partly as Sn-F complex species. Solid-state ³¹P NMR suggested that NaF promoted pronounced fluorapatite-like formation, whereas SnF₂ resulted in partial retention of lattice OH groups. SnF₂ produced a greater reduction in ATP-based microbial activity than NaF. The SnF₂ group also showed significantly lower Shannon diversity than NaF and lower abundances of Veillonella and Fusobacterium than the fluoride-free control.

SnF₂ exhibited complex aqueous speciation and affected both apatite formation and saliva-derived polymicrobial biofilms differently from NaF. These findings highlight complementary physicochemical and biological properties of SnF₂, although a direct mechanistic link between them was not established.

Understanding the chemical speciation of SnF₂ may help clarify its anticaries potential, including its effects on apatite mineralization and polymicrobial biofilm control.