Coloring Multilayer Zirconia May Affect Its Optical and Mechanical Properties
1Department of Oral Health Sciences, BIOMAT-Biomaterials Research Group & UZ Leuven, Dentistry, KU Leuven, Leuven, Belgium.
Journal of Dental Research
|October 4, 2024
Summary
Pigment additions in multilayer dental zirconia (5Y-PSZ) create agglomerates, reducing optical and mechanical properties and aging resistance. Unpigmented zirconia exhibits superior translucency, strength, and reliability.
Area of Science:
- Biomaterials Science
- Dental Ceramics
- Materials Engineering
Background:
- Monolithic dental zirconia coloring is debated for its effects on material properties.
- Multilayer 5-mol% yttria partially stabilized zirconia (5Y-PSZ) is used for aesthetic dental restorations.
- Pigment incorporation may influence the optical, mechanical, and aging characteristics of 5Y-PSZ.
Purpose of the Study:
- To investigate the influence of pigments on translucency parameter (TP00), fracture toughness, hardness, biaxial strength, and hydrothermal stability of 5Y-PSZ.
- To correlate pigment effects with microstructure, phase composition, and aging behavior.
- To identify the impact of pigment agglomerates on the properties of multilayered zirconia.
Main Methods:
- Analysis of three 5Y-PSZ disks (Zr-AGG_A2, Zr-AGG_BL, Zr-NoAGG) using microscopy (light, fluorescence, nano-SEM), EPMA, XRF, XRD, and micro-Raman spectroscopy.
- Assessment of optical properties (TP00), mechanical properties (fracture toughness, hardness, biaxial strength), and hydrothermal stability.
- Microstructural and phase composition analysis, including grain size and Y2O3 content evaluation.
Main Results:
- Pigmented zirconia (Zr-AGG_A2/BL) contained large, fluorescent agglomerates of Er-, Hf-, and Al-containing grains with lower Y2O3 content compared to unpigmented Zr-NoAGG.
- Zr-AGG_A2 showed the lowest aging resistance, with degradation localized within pigment agglomerates.
- Unpigmented Zr-NoAGG exhibited significantly higher TP00, flexural strength, and lower mechanical reliability than pigmented Zr-AGG_A2/BL, despite similar hardness and toughness.
Conclusions:
- Rare-earth oxide-containing zirconia agglomerates act as pigments, negatively impacting optical and mechanical properties and reducing aging resistance in multilayered 5Y-PSZ.
- The presence of these agglomerates is the primary cause for the inferior performance of pigmented multilayered zirconia.
- Unpigmented zirconia demonstrates superior optical and mechanical characteristics and better aging resistance compared to pigmented variants.
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