Method: A series of glasses based on 4.5SiO2-3Al2O3-1.5P2O5-(5-x)CaO-xCaF2 system, where x=0,1,2,3,3.5,4 were synthesised with varying CaF2/CaO proportions. The powders were then mixed with poly-acrylic acid, water and HAp in different ratios at specific powder to liquid ratios. The cement paste was transferred into Teflon mould, clamped, stored at 37oC for 1hr. The cement discs were immersed in 10ml of phosphate buffer saline at physiological pH for different durations, 7,14,28,56 days. The samples were collected at certain time, dried, ground into a powder and further characterised using Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR).
Result: The 31P MAS-NMR results used to monitor changes in apatitic phosphorus showed that added HAp as remineralising agent was partially consumed during the setting reaction. No apatite formation was detected in the cements without HAp. The 27Al MAS-NMR was used to follow the setting reaction on conversion of the four-coordinated aluminium Al(IV) from the glass to the six-coordinated aluminium Al(VI) crosslinking the polymer. The results indicated that proportion of Al(VI) after setting, in the cements with HAp added was slightly higher compared to the same compositions with no HAp. However, the abundance of Al(VI) was identical in the cements with 0% and 2% HAp after 28 days.
Conclusion: Addition of HAp to GICs as remineralising agent causes partial dissolution of apatite and consumption of the calcium ions in crosslinking the polymeric acid during the setting reaction.