The Effect of Aging on Composition and Surface of Translucent Zirconia Ceramic

Effect of sintering programs and surface treatments on monolithic zirconia

PURPOSE

To investigate the effect of sintering programs and surface treatments on surface properties, phase transformation and flexural strength of monolithic zirconia.

MATERIALS AND METHODS

Zirconia specimens were sintered using three distinct sintering programs [classic (C), speed (S), and superspeed (SS)] (n = 56, each). One sample from each group underwent scanning electron microscopy (SEM) and grain size analysis following sintering. Remaining samples were divided into five subgroups (n = 11) based on the surface treatments: control (CL), polish (P), glaze (G), grind + polish (GP), and grind + glaze (GG). One sample from each subgroup underwent SEM analysis. Remaining samples were thermally aged. Monoclinic phase volume, surface roughness, and three-point flexural strength were measured. Monoclinic phase volume and surface roughness were analyzed by Kruskal-Wallis and Dunn tests. Flexural strength was analyzed by two-way ANOVA and Weibull analysis. The relationships among the groups were analyzed using Spearman's correlation analysis.

RESULTS

Sintering program, surface treatment, and sintering × surface treatment (P ≤ .010) affected the monoclinic phase volume, whereas the type of surface treatment and sintering × surface treatment affected the surface roughness (P < .001). Type of sintering program or surface treatment did not affect the flexural strength. Weibull analysis revealed no significant differences between the m and σo values. Monoclinic phase volume was positively correlated with surface roughness in the SGG and SSP groups.

CONCLUSION

After sintering monolithic zirconia in each of the three sintering programs, each of the surface treatments can be used. However, for surface quality and aging resistance, G or GG can be recommended as a surface finishing method.

Effect of Aging on the Microstructure and Optical Properties of Translucent ZrO 2 Ceramics

Objectives

The development and placement of translucent zirconia ceramics on the dental materials market is in full swing. This research aimed to investigate how aging protocols affect the microstructure, color parameters and translucency of a new-generation monolithic zirconia ceramic.

Material and methods

Translucent zirconia ceramics KATANA-Zirconia STML with different surface treatments (as sintered - control, glazed, polished) was tested using two aging protocols (hydrothermal degradation in autoclave at 134 °C and 2 bars for three hours, chemical degradation in four-percent acetic acid at 80 °C for 16 hours) in order to examine phase composition using X-ray diffraction analysis and ΔE, ΔL and ΔC color parameters through spectrophotometry. The translucency parameter (TP) was calculated using parameters L*, a* and b* on a black and white surface.

Results

Regardless of the surface treatment, aging protocols did not cause a tetragonal-to-monoclinic phase transformation, although hydrothermal degradation in the autoclave transformed the hybrid tetragonal-cubic structure of all specimens to a tetragonal one. All polished and glazed specimens during chemical degradation demonstrated a significant color change ΔE. Lightness ΔL significantly changed in polished specimens aged in the autoclave. In all specimens, ΔC underwent a change manifested through statistically insignificant yellowing. None of the aging protocols altered the translucency of specimens.

Conclusions

Aging, regardless of the final surface treatment, did not manifest a monoclinic phase in the specimens. A tetragonal-cubic microstructure dominates. Unlike polishing, glazing the surface of translucent zirconia ceramics contributed to minor changes in color, lightness and chromaticity. The translucency of translucent zirconia ceramics remains stable regardless of aging and surface treatment.