REMINERALISING ABILITY OF EXPERIMENTAL RMGIC UPON IMMERSION IN SBF

Background: Dental caries is one of the most prevalent chronic transmissible diseases causing irreparable damage to the natural tooth structure. Recently, increasing evidence showed that some dental materials have the ability to form apatite at their surface and potentially remineralise carious tissue. Glass ionomer cements have been closely studied and investigated as an apatite forming material. RMGICs which enclose GIC within their structure need to be better understood as a material with remineralising abilities. Objectives: The objective of this research project was to study the remineralising potential of the experimental RMGICs with addition of bioactive glass. Formation of apatite upon immersion in simulated body fluid (SBF) was explored in the experimental cements. The results were compared with the data on the bioactive glass free cements. Materials and methods: The ionomer glass of the nominal composition 4.5 SiO2-0.5 P2O5-3Al2O3-2CaF2-3CaO was synthesised at high temperature. Sodium free bioactive glass containing fluoride and high amount of phosphate (mol%: 35.9SiO2-5.9P2O5-52.2CaO-6CaF2) was made using melt-quench technique. Both glass composition were selected based on the previous research. The experimental RMGIC formulations were prepared using the home-made liquid containing HEMA, PAA and water among other minor components. For the samples with remineralising agent, 10% of the ionomer glass was substituted by the bioactive glass. In order to ensure that bioactive glass reacting in the long term rather than instantly on mixing, the coarse bioactive glass powder was used for making the cements. The cement discs prepared were immersed in SBF solution for 1 day, 1 week, 2 weeks, 3 months and 6 months. At the end of the immersion period the samples were collected and ground in order to be further analysed using FT-IR, NMR and ICP-OES to evaluate their remineralising ability, i,e.apatite formation. Results: The 31P MAS-NMR findings revealed that the addition of bioactive glass to the experimental RMGIC formulation displayed evidence apatite formation on immersion in SBF buffer solution over time. No apatite was seen in the cements without bioactive glass. The FTIR data did not show any apatite formation. The ICP-OES results showed high release of the ionic species of calcium and silicon as well as reduction in phosphate concentration obtained in the solutions after immersion, which was consistent with the former findings of apatite formation potential. Conclusion: The results demonstrated that RMGICs, with incorporation of bioactive glass, are capable of forming apatite upon in immersion in SBF over time. This pointed out that similarly to GIC, RMGIC as well have similar remineralising potential. The remineralising potential can be substantially enhanced via the addition of optimal bioactive glass formulation