Effect of hydrothermal aging on the optical properties of precolored dental monolithic zirconia ceramics

Abstract

STATEMENT OF PROBLEM: The long-term color stability of precolored monolithic zirconia has not been thoroughly investigated. PURPOSE: The purpose of this in vitro study was to evaluate the effect of hydrothermal aging on the optical properties, phase transformation, and surface topography of precolored monolithic zirconia ceramics. MATERIAL AND METHODS: Precolored monolithic zirconia specimens (17.0x17.0x1.5 mm, n=50) and lithium disilicate glass-ceramic specimens (16.0x16.0x1.5 mm, n=50) were artificially aged in an autoclave at 134 degrees C under 0.2 MPa for 0, 1, 3, 5, or 10 hours (n=10). CIELab color parameters were obtained from spectral measurements. The translucency parameter (TP) and CIEDE2000 color differences (DeltaE00) were calculated. The microstructural and surface properties were analyzed by X-ray diffraction (XRD), atomic force microscope (AFM), and scanning electron microscope (SEM). Data were analyzed with 2-way ANOVA and pairwise comparison (alpha=.05). RESULTS: Significant interactions were found between aging time and ceramic material on L*, a*, b*, and TP (P<.001) as follows: b* partial eta squared [etap(2)]=0.689; L* etap(2)=0.186; a* etap(2)=0.176; and TP etap(2)=0.137. The b* values significantly decreased after aging for zirconia (P<.001), whereas TP increased after aging for zirconia (P<.014) except at 10 hours (P=.389) and for lithium disilicate (P<.001). The DeltaE00 values relative to baseline ranged from 2.03 to 2.52 for aged zirconia and from 0.07 to 0.23 for aged lithium disilicate. XRD analysis revealed that hydrothermal aging promoted an increase in m-phase contents. AFM and SEM demonstrated surface alterations after aging. CONCLUSIONS: Optical properties and microstructures of precolored monolithic zirconia ceramics were affected by hydrothermal aging, and translucency increased slightly with aging time.