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

Publication date: Available online 21 December 2018

Source: The Journal of Prosthetic Dentistry

Author(s): Hee-Kyung Kim, Sung-Hun Kim

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 (17.0×17.0×1.5 mm, n=50) and lithium disilicate glass-ceramic specimens (16.0×16.0×1.5 mm, n=50) were artificially aged in an autoclave at 134°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 (ΔE₀₀) 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 (α=.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 [η_p²]=0.689; L* η_p²=0.186; a* η_p²=0.176; and TP η_p²=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 ΔE₀₀ 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.

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