Influence of sintering programs on microstructure, crystal phase composition, and optical and mechanical properties of multilayer zirconia.

OBJECTIVES

To evaluate the influence of different sintering programs on the density, crystal phase composition, and biaxial flexural strength of composition- and shade-gradient multilayer zirconia (YML/STML). In addition, the microstructure, transmittance, and indentation fracture (IF) resistance were descriptively analyzed.

METHODS

Specimens of KATANA™ Zirconia YML, containing Body 1 and 2 layers, and STML were divided into three groups depending on sintering program, each with specific sintering parameters: high-speed for 20 min (YH20/SH20), speed for 90 min (YS90/SS90), and conventional sintering for 7 h (YC/SC). Density and flexural strength were analyzed using two-way ANOVA with the factors: material and sintering program (α = .05). Microstructure, phase composition, transmittance, and IF resistance were descriptively analyzed.

RESULTS

YML exhibited significantly higher density and flexural strength than STML. The sintering programs showed no statistically significant effect on density or flexural strength. The descriptive analyses showed higher t phase fraction and IF resistance, and lower yttria, t'', and c content, grain size, and transmittance of YML compared to STML. Grain size was similar across YML sintering groups but differed among STML groups (S90 < SC < SH20). For YML, an increase in the t phase fraction was observed for prolonged sintering programs (YH20 < YS90 < YC), with reservation for the limited sample size. Transmittance was lower for YS90 compared to YH20 and YC.

SIGNIFICANCE: The density and flexural strength of composition-gradient and shade-gradient multilayer zirconia are material dependent and are not significantly influenced by the sintering program. For composition-gradient zirconia, speed and particularly high-speed sintering programs may reduce the t phase fraction.