Development of zirconia-glass ionomer cement composites

Yttria stabilized zirconia (YSZ) powders were used for the replacement of amalgam alloy in Miracle Mix on a volume basis, in order to improve the mechanical properties of the cements. Two types of YSZ powders were used in this study, i.e., nano-sized (5–15 nm) and micro-sized (2–10 μm) YSZ. The effects of YSZ powders substituted within glass ionomer cement (GIC) were investigated based on their microhardness, compressive strength and diametral tensile strength. The effects of the particle size of YSZ powders on the mechanical properties of YSZ-GIC composites were also studied. The YSZ-GIC composites were soaked in distilled water for 1 day and 1 week before the mechanical testing. The mechanical properties of Miracle Mix samples were used for comparison. Results showed that the glass and YSZ particles were distributed uniformly in the matrix of GIC. YSZ-GIC composites had better mechanical properties than Miracle Mix samples. The mechanical properties of YSZ-GIC composites increased with increasing soaking time due to the continuous formation of aluminium salt bridges, which improved the strength of the cements. The micro-sized YSZ/glass powders revealed a bimodal particle size distribution and this ensured a high packing density of glass ionomer cements, giving relatively high mechanical properties of YSZ-GIC composites. YSZ-GIC composites prepared by the nano-sized YSZ powders showed low values of mechanical properties because of the low packing density of the nano-sized powders and hence low powder/liquid ratio of GIC.