The Effects of Hydroxyapatite on Demineralization Resistance and Bonding Strength in Light-Curing Glass Ionomer Dental Cement

The aim of this study was to evaluate the effect of HA on the demineralization resistance and bonding strength of light-curing glass ionomer dental cement. Tests were conducted using (1) pure Fuji II LC GIC, (2) 15% micro HA-Fuji II LC GIC. Physical properties, demineralization resistance and bonding strength to dentin of teeth were determined. The curing depth in all groups were satisfied the requirement of curing depth of ISO 9917-2:2004(minimum curing depth = 1 mm). The depth of cure was reduced with addition of HA, presumably due to the light scattering effect of HA particles. Regarding sensitivity to ambient light, there were no detectable changes of the homogeneity in any groups. Also all groups were satisfied the requirement of the flexural strength of ISO 9917-2:2004(minimum flexural strength = 20MPa). 15% HA-Fuji II LC GIC group was found to present a greater flexural strength than pure Fuji II LC GIC, as the addition of HA promotes a chemical reaction between the HA, the glass powder, and the polyacid. Observing under the CLSM after 4 days of demineralization, there were significant differences in the CLSM and SEM images. Pure Fuji II LC GIC group showed greater enamel demineralization layer than in 15% HA-Fuji II LC GIC group. In SEM analysis, there was greater enamel demineralization in the pure Fuji II LC GIC group, and less demineralized under the influence of HA particles, 15% HA-Fuji II LC GIC group had more even surface particles. 15% HA-Fuji II LC GIC group was found to present a greater bonding strength than pure Fuji II LC GIC group. Observing the fractured surfaces under SEM after the bonding strength test, the cohesive failure rate was found to be in increasing order of pure Fuji II LC GIC, 15% HA-Fuji II LC GIC group. There were bone-like apatite particles observed to be formed in 15% HA-Fuji II LC GIC group.