In-vitro Remineralisation of Bioactive Glass-Containing Glass Ionomer Cements

Method: A series of glasses based on 4.5SiO₂-3Al₂O₃-0.75P₂O₅-3(CaO+SrO)-2(CaF₂+SrF₂) system were designed by substituting (Ca²⁺) with (Sr²⁺). GICs discs were produced by mixing fine glass powder with poly-acrylic acid in powder form and then with water at specific ratio. BAG with specific amounts (0, 5, 10, 15%) were substituted the original ionomer glasses to promote remineralisation of GICs. The cement discs were immersed in artificial saliva (AS) at physiological condition. After a period of time (7-180 days), the samples were collected, dried and ground into a powder and were further characterised using Solid-State Nuclear Magnetic Resonance (NMR) Spectroscopy. The ion concentrations were measured using Inductively Coupled Plasma-Optical Emission (ICP-OES) Spectroscopy.

Result: The formation of apatite in GICs that immersed in AS was investigated with ³¹P NMR spectroscopy. ³¹P NMR spectra showed that specific ionomer glasses contain nano-crystals of fluorapatite (FA) which remain present in cement of those formulations. The fraction of nano-crystaline FA is highly dependent on the composition of the original glasses. The formation of apatite and growth in GICs were noticed when 5 and 10% of BAG added. The setting mechanism of GICs was monitored by changing the coordination number of aluminium from four Al(IV) to six Al(VI) using ²⁷Al NMR. The concentration of strontium ions, released from GICs was markedly high in full Sr-substituted cement and also in the compositions containing SrO rather than SrF₂.

Conclusion: The incorporation of BAG into GICs increases a potential of GICs to remineralise. The synergistic effect of strontium with fluoride could promote the cariostatic activity of GICs.