Solving the problem with stannous fluoride: Formulation, stabilization, and antimicrobial action

Abstract

Background: Stannous fluoride (SnF₂) is a compound present in many commercially available dentifrices; however, oxidative decomposition negatively impacts its efficacy. Stannous oxidation is often mitigated through the addition of complexing agents or sources of sacrificial stannous compounds. The authors have found that the addition of zinc phosphate significantly improved stannous stability more effectively than other stabilization methods. The authors evaluated the chemical speciation of stannous compounds within a variety of formulations using x-ray absorption near edge spectroscopy (XANES), a technique never used before in this manner. These data were compared and correlated with several antimicrobial experiments.

Methods: XANES data of various commercially available compounds and Colgate Total^SF were performed and analyzed against a library of reference compounds to determine the tin chemical speciation. The antibacterial assays used were salivary adenosine triphosphate, short-interval kill test, plaque glycolysis, and anaerobic biofilm models.

Results: XANES spectra showed a diverse distribution of tin species and varying degrees of SnF₂ oxidation. In vitro antimicrobial assessment indicated significant differences in performance, which may be correlated to the differences in tin speciation and oxidation state.

Conclusions: Driven by the excipient ingredients, SnF₂ dentifrices contain a distribution of tin species in either the SnF₂ or Sn(IV) oxidation state. The addition of zinc phosphate provided significant robustness against oxidation, which directly translated to greater efficacy against bacteria.

Practical implications: The choice of inactive ingredients in a dentifrice with active SnF₂ can dramatically impact product stability.

Keywords: Stannous fluoride; antibacterial; chemical speciation; dentifrice; oxidation; x-ray absorption spectroscopy.