The effect of firing protocols on the resin-bond strength to alumina-coated zirconia ceramics

Bonding surface pretreatment of zirconia ceramic dental restorations with a nanostructured alumina coating (NAC) provides a substantially stronger and durable bond than clinically established air-particle abrasion. However, the synthesis of NAC should completely comply with everyday dental laboratory practices. In the present study, the effect of various dental laboratory firing procedures, such as glaze, veneer and regeneration firings of zirconia, on the temperature-dependent phase evolution of NAC was studied (XRD) and related to the resin-cement shear-bond strength of as-sintered, high-pressure (4 bar) and low-pressure (1 bar) air-particle-abraded zirconia surfaces with or without a combination of MDP primer. Half of each sample groups (n = 20) were subjected to 12000× thermocycles in water. The results were statistically analysed using t-test and one-way ANOVA. When fired at 900 and 1050°C and topotactically transformed to γ- or a mixture of δ- and θ-aluminas, NAC provided highest and clinically acceptable bond-strengths (>20Mpa) not affected by thermocycling.