Acid-Resistant Glass Ionomer Cements: An Assessment of Their Mechanical Properties, Fluoride Ion Release and Protection to Surrounding Tooth Surfaces From Acid Challenges

Abstract

New acid-resistant glass ionomer cements (GIC) claim to be able to withstand acidic conditions while also protecting surrounding tooth structures and preserving function. Currently, there are only a few studies that assessed mechanical properties, ion release, and changes that occur around an acid-resistant GIC–dentine bonded interface under acidic conditions. This study aims to investigate the mechanical properties and fluoride release of GIC and the dentine hardness changes of the tooth that occur near the GIC–dentine bonded interface under in vitro conditions simulating carious and erosive challenges. A total of 96 beam-shaped specimens (2 mm × 2 mm × 25 mm) were prepared from two types of GIC and placed in neutral pH, carious, and erosive conditions for a total of 3 days over 2 time points to determine the flexural strength change and fluoride release. Twenty-four bovine teeth specimens with a 3 mm × 2 mm diameter cavity restored by two GICs (Fuji BULK (acid-resistant GIC)), Fuji IX Extra (conventional GIC) were subjected to carious (pH 4.4) and erosive (pH 2.3) conditions for 8 and 10 days, respectively. Hardness tests of the dentin surrounding the restorative material were conducted on the surface and cross-sectional interface. Data was tested for significant differences (α = 0.05) utilizing three-way analysis of variance with a Bonferroni post hoc test for multiple comparisons. No significant differences were observed in all comparisons of flexural strength between acid-resistant (~32 MPa) and conventional GICs (~26 MPa). Significant differences were observed in the fluoride release (p < 0.05) between different acidic environments for the same material, between different time points for the same material, and between different materials for day 1 in all conditions. The largest difference in fluoride release between conventional and acid-resistant GIC occurred on day 1 in the control groups, where the fluoride release was 63.1 and 28.2 ppm, respectively. This difference dropped substantially by day 3, where the ppm for conventional and acid-resistant GIC measured 11.9 and 3.9 ppm, respectively. Under carious and erosive conditions, both conventional and acid-resistant GIC showed higher fluoride releases, with erosive conditions showing sustained high fluoride releases of 60.1 and 55.2 ppm, respectively. Overall percent mass for the erosive condition from day 1 to day 3 decreased by 55.5% and 47.1% for conventional and acid-resistant GIC, respectively. A significant difference in dentine hardness (p < 0.001) was observed under erosive treatment between conventional and acid-resistant GIC at both the surface (0.27 GPa vs. 0.36 GPa) and cross-sectional (0.24 GPa vs. 0.32 GPa) sites, respectively. A significant difference in hardness (p < 0.001) was observed for acid-resistant and conventional GIC between all conditions, except between carious and erosive for the acid-resistant GIC. In conclusion, acid-resistant GIC was more resistant to demineralization on regions surrounding the restored cavity under erosive conditions compared to conventional GIC. There were no significant differences in flexural strength observed between acid-resistant and conventional GIC for all conditions, while initial fluoride release for conventional GIC was found to be slightly higher compared to the acid-resistant GIC.