Mixed Fluoride-Chloride Containing Bioactive Glasses for Remineralising Toothpaste

Bioactive glasses (BG) with the ability of promoting remineralisation by forming apatite have been increasingly used as an active ingredient of toothpastes in treating dentine hypersensitivity and caries protection. Fluoride has been successfully incorporated into BG to inhibit enamel and dentine demineralisation and facilitate the formation of a more acid resistant fluorapatite. Chloride has recently been introduced to sodium free BG which resulted in reduced hardness and abrasivity of the glass required for antisensitising toothpaste. The objective of this project is to synthesise mixed fluoride-chloride containing BG and investigate their bioactivity.

Method:

The sodium free mixed fluoride-chloride containing BG were synthesised using a melt-quench method. Glasses were characterised by Differential Scanning Calorimetry (DSC). Glass bioactivity was investigated by the immersion of glass powders in physiological buffer (Tris) and the apatite formation was explored by X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Magic Angle Spinning-Nuclear Magnetic Resonance (MAS-NMR). The ion release was quantified by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) and fluoride-ion selective electrode.

Result:

The DSC results demonstrated a distinct decrease in the glass transition temperature (T_g) correlating linearly with an increase in fluoride and chloride content. The decrease of T_g indicates a reduction in glass hardness. These novel glasses are highly degradable within the first hour of immersion in Tris buffer, fluorapatite formation was observed within 3 hours of immersion. This is much faster than any commercially available BG. Glass degradation was accelerated with an increase in chloride content.

Conclusion:

The presence of mixed fluoride-chloride components enables fast glass degradation and fluorapatite formation, which makes these highly bioactive halide (CaF₂ and CaCl₂) containing glasses attractive for remineralising toothpaste.