Investigation of the Long-Term Bioactivity and Mechanical Properties of a Novel Glass Ionomer Cement Containing Bioactive Glass

Glass ionomer cements (GICs) release a lot of fluoride, but relatively little calcium/strontium and phosphate, which restricts their ability to remineralise hard carious dentine left after incomplete carious lesions removal. To address this problem, bioactive glass (BAG) and other remineralising agents were incorporated into GIC to promote remineralisation and apatite formation; this adversely affected the mechanical properties of the GIC. The main objective of this study was to investigate the long-term effect of modifying the novel GIC composition with BAG additions on the apatite formation ability and mechanical properties of the material in multiple immersion media. Several ionomer glasses with varying P2O5 proportions and Sr2+/Ca2+ substitution were prepared, milled, and optimised to fine powder. Sodium free BAG was synthesised and milled into coarse powder. BAG in 5%,10% and 20% weight fractions was added to the ionomer glass powder before mixing into cement. The set cements were prepared as cylindrical samples 4x6mm and immersed in Tris, artificial saliva at pH 7 (ASpH7) and pH 4 (ASpH4) for 1, 6, and 12months. The apatite formation was analysed using 31P and 19F solid-state nuclear magnetic resonance. The compressive strength (CS) and modulus (CM) were measured before and after immersion using a universal testing machine. The resulting solution was evaluated using F-ISE, ICP-OES, and pH test to determine elemental concentration and pH values. The results showed significant apatite formation in GICs containing BAG, which increased markedly on adding more BAG and with time. Meanwhile, CS and CM were maintained at acceptable values. The long-term in vitro effectiveness of a novel GIC containing 10%BAG on real-time remineralisation of extracted teeth was determined using X-ray microtomography (XMT). Carious lesions were restored using an atraumatic restorative technique approach using the novel GIC/BAG and the commercial cement Fuji IX (control) and immersed in ASpH7. The evaluation of the XMT slices demonstrated the ability of the novel GIC to increase the mineral concentration of the demineralised dentine in the carious lesion. To conclude, GICs with BAG incorporated in the formulations have potential to form apatite and to remineralise hard carious dentine. It is possible to optimise the composition of these new cements further to ensure that the CS of the GICs with BAG remain high or increases over time