Fluoride-containing bioactive glasses: Effect of glass design and structure on degradation, pH and apatite formation in simulated body fluid

Abstract

Effect of fluoride content of bioactive glasses on apatite deposition in simulated body fluid 2/15Summary Bioactive glasses are able to bond to bone through formation of carbonated hydroxyapatite in body fluids, and fluoridereleasing bioactive glasses are of interest for both orthopaedic and in particular dental applications for caries inhibition.Melt-derived glasses in the system SiO 2 -P 2 O 5 -CaO-Na 2 O with increasing amounts of CaF 2 were prepared by keeping network connectivity and the ratio of all other components constant.pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid at 37°C over up to two weeks were investigated. Crystal phases formed in SBF were characterised using infra-red spectroscopy, X-ray diffraction with Rietveld analysis and solid-state nuclear magnetic resonance spectroscopy ( 19 F and 31 P MAS-NMR).Results show that incorporation of fluoride resulted in a reduced pH rise in aqueous solutions compared to fluoride-free glasses and in formation of fluorapatite (FAp), which is more chemically stable than hydroxyapatite or carbonated hydroxyapatite and therefore is of interest for dental applications. However, for increasing fluoride content in the glass, fluorite (CaF 2 ) was formed at the expense of FAp. Apatite formation could be favoured by increasing the phosphate content in the glass, as the release of additional phosphate into the SBF would affect supersaturation in the solution and

High phosphate content significantly increases apatite formation of fluoride-containing bioactive glasses

“…The pH rise was also less pronounced for increasing fluoride contents in the glass (Figures 1c, d), both in the low and high phosphate series: There is a small but significant reduction in pH with increasing fluorine content of the glass which mirrors that found for the low phosphate content glasses in SBF [4]. The resulting pH depends on the particle size/surface area and the concentration of the glass as well as on the buffering capacity of the surrounding solution, and although the pH values shown here are ≤ 7.9 under the experimental conditions in this research, pH values in the oral cavity might potentially be higher depending on the loading of glass in the toothpaste and the amount of saliva present.…”

“…If the glass results in the formation of apatite in the designated time period it is conventionally termed bioactive. However, the saliva in the mouth is diluted after taking in liquids and often no vibration between two adjacent SiO 4 tetrahedra as described previously for SBF-treated glasses [4]. These changes indicate formation of a silica-gel surface layer after leaching of Ca 2+ and Na + ions and formation of Si-OH groups in this ion depleted glass.…”

“…during consumption of fruit juice and carbonated beverages). We have recently showed that fluoride-containing bioactive glasses form FAp in SBF [4]. However, the glass component of the toothpaste needs to perform its function and form FAp before it is diluted away by salivary action.…”

“…It is better to deliver Ca 2+ , PO 4 3-and F -ions together in the appropriate amounts to form FAp from a single glass composition in order to avoid the possible formation of CaF 2 .…”

Structure and Characterization of Some High Chemically Resistance Silicate Glasses

“…The FTIR results refer to the formation of silanol to form a silica rich layer on the surface and there is no evidence on the formation of apatite layer.After soaking the glass samples G 3 G 5 and G 6 in SBF solution for 14 days, additional peaks with different intensities appears in the FTIR spectra around 570 cm -1 , 600 cm -1 and 1080 cm -1 . The appearance of these peaks is characteristic for the formation of apatite layer [43].…”