Abstract: Abstract：　Objective　To evaluate the color and structural stability of a novel ultra-transparent zirconia ceramic after aging in vitro. Methods　A novel ultra-transparent zirconia ceramic Katana UTML (KU) with different thicknesses (0.5、1.0、1.2 and 1.5mm) were selected (n=5 per group) and then, the CIE L* a* b* parameters of each sample were measured with a dental colorimeter, which was used to calculate the color values with different thicknesses on a white background for the color difference (△E) before and after aging (in an autoclave at 134℃ under 0.2MPa for 20h). Statistical analysis of △E was performed using the SPSS 21.0 statistical software. Furthermore, X-ray diffraction (XRD) and scanning electron microscope (SEM) were applied to evaluate the structural stability of KU after aging. Results　The △E of KU with different thicknesses before and after aging ranged from 0.96 to 1.50, which was acceptable in clinic. The results of XRD and SEM showed that there was no obvious changes in the crystal phase and surface micro-morphology (such as grain size) of KU before and after aging. Conclusions　Katana UTML possesses good color and structural stability regardless of aging.

Key words: zirconia ceramic, lowtemperature degradation, color, microstructure