Regulation of fluoride ion release from Na₂SiF₆ contained in resin based on hydrophobic siloxane layer coating

Regulation of fluoride release from restorative resin or sealant is beneficial to patients as it will prevent the occurrence of the secondary caries. In this study, we evaluated whether or not the formation of a hydrophobic polysiloxane layer on the surface of the fluoride compound could contribute to the regulation of fluoride release from resin. First, sodium hexafluorosilicate (Na₂SiF₆) powder was treated with γ-methacryloxypropyltrimethoxysilane (γ-MPTS) and analysed with scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR) and electron spectroscopy for chemical analysis (ESCA). Analysis revealed that a hydrophobic polysiloxane layer was formed on the surface of Na₂SiF₆ powder. Heat treatment commonly used during γ-MPTS treatment was not necessary for the polysiloxane layer formation on the surface of Na₂SiF₆ powder. Then Na ₂SiF₆ powder treated with γ-MPTS was loaded in bis-GMA/TEG-DMA resin, immersed in distilled water and fluoride release was measured using a fluoride electrode. We found that the rate of fluoride release was significantly lower from the resin containing Na₂SiF₆ powder treated with γ-MPTS. We concluded, therefore, that γ-MPTS treatment and the resulting hydrophobic polysiloxane layer formation are very effective for the regulation of fluoride release from resin.