Bioactive glass-containing
toothpastes for treating
dentine hypersensitivity work by precipitating
hydroxycarbonate apatite (HCA) onto the tooth surface, but concerns exist over the long-term durability of HCA in the mouth.
Fluoride-containing bioactive glasses form
fluorapatite (FAp) in physiological solutions, which is more chemically stable against
acid attack. The influence of
phosphate content on
apatite formation was investigated by producing a low-
phosphate (about 1 mol%
P(2)O(5)) and a high-
phosphate (about 6 mol%) series of melt-derived bioactive glasses in the system SiO(2)
P(2)O(5)CaONa(2)O; increasing amounts of CaF(2) were added by keeping the ratio of all other components constant. pH change, ion release and
apatite formation during immersion in
Tris buffer at 37°C over up to 7 days were investigated. Crystal phases formed in
Tris buffer were characterized using infrared spectroscopy, X-ray diffraction and solid-state nuclear magnetic resonance (NMR) spectroscopy. An increase in
phosphate or
fluoride content allowed for
apatite formation at lower pH;
fluoride enhanced
apatite formation due to lower solubility of FAp compared to
hydroxyapatite or HCA. High
phosphate content glasses formed
apatite significantly faster (within 6h) than low
phosphate content glasses (within 3 days). In addition, an increase in
phosphate content favoured
apatite formation rather than fluorite (CaF(2)). (19)F magic angle spinning NMR showed the
apatite formed by
fluoride-containing glasses to be FAp, which makes these glasses of particular interest for dental applications. This study shows that by varying the
phosphate content, the reactivity and
apatite formation of bioactive glasses can be controlled successfully.