Effects of incorporation of HA/ZrO₂ into glass ionomer cement (GIC)

Glass ionomer cements (GICs) are a class of bioactive cements that bond directly to bone. In this paper, a new bioactive hydroxyapatite (HA)/zirconia (ZrO₂)-filled GIC composite was developed to improve the biocompatibility and bioactivity of the GICs with the surrounding bone and connective tissues. Nano-sized HA/30wt% ZrO₂ powders were heat treated at 700°C and 800°C for 3h to elucidate the influence of the crystallinity of composite powders on the performance of HA/ZrO ₂-GICs. The effects of different volume percentages of HA/ZrO ₂ powders (4, 12, 28 and 40vol%) substituted within GICs were investigated based on their microhardness, compressive strength and diametral tensile strength. The HA/ZrO₂-GICs composite was soaked in distilled water for 1 day and 1 week before subjecting the samples to mechanical testing. Results showed that the glass and HA/ZrO₂ particles were distributed uniformly in the GIC matrix. The substitution of highly crystalline HA/ZrO ₂ improved the mechanical properties of the HA/ZrO₂-GICs due to the slow resorption rate for highly crystalline powders in distilled water. The mechanical properties of HA/ZrO₂-GICs increased with increasing soak time due to the continuous formation of aluminium salt bridges, which improved the final strength of the cements. The compositions 4 and 12vol% HA/ZrO₂-GICs exhibited superior mechanical properties than the original GICs. The mechanical properties of HA/ZrO₂-GICs were found to be much better than those of HA-GICs because ZrO₂ has the attributes of high strength, high modulus, and is significantly harder than glass and HA particles. Furthermore, ZrO₂ does not dissolve with increasing soaking time.