Strength, toughness and aging stability of highly-translucent Y-TZP ceramics for dental restorations

Fei Zhang; Masanao Inokoshi; Maria Batuk; Joke Hadermann; Ignace Naert; Bart Van Meerbeek; Jef Vleugels

doi:10.1016/j.dental.2016.09.025

Strength, toughness and aging stability of highly-translucent Y-TZP ceramics for dental restorations

Dent Mater. 2016 Dec;32(12):e327-e337. doi: 10.1016/j.dental.2016.09.025. Epub 2016 Sep 30.

Authors

Fei Zhang¹, Masanao Inokoshi², Maria Batuk³, Joke Hadermann³, Ignace Naert⁴, Bart Van Meerbeek⁴, Jef Vleugels⁵

Affiliations

¹ KU Leuven, Department of Materials Engineering, Kasteelpark Arenberg 44, Belgium. Electronic address: fei.zhang@kuleuven.be.
² KU Leuven BIOMAT, Department of Oral Health Sciences, KU Leuven & Dentistry, University Hospitals Leuven, Belgium; Gerodontology and Oral Rehabilitation, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo, Tokyo 113-8510, Japan.
³ Electron Microscopy for Materials Science (EMAT), University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
⁴ KU Leuven BIOMAT, Department of Oral Health Sciences, KU Leuven & Dentistry, University Hospitals Leuven, Belgium.
⁵ KU Leuven, Department of Materials Engineering, Kasteelpark Arenberg 44, Belgium.

PMID: 27697332
DOI: 10.1016/j.dental.2016.09.025

Abstract

Objective: The aim was to evaluate the optical properties, mechanical properties and aging stability of yttria-stabilized zirconia with different compositions, highlighting the influence of the alumina addition, Y₂O₃ content and La₂O₃ doping on the translucency.

Methods: Five different Y-TZP zirconia powders (3 commercially available and 2 experimentally modified) were sintered under the same conditions and characterized by X-ray diffraction with Rietveld analysis and scanning electron microscopy (SEM). Translucency (n=6/group) was measured with a color meter, allowing to calculate the translucency parameter (TP) and the contrast ratio (CR). Mechanical properties were appraised with four-point bending strength (n=10), single edge V-notched beam (SEVNB) fracture toughness (n=8) and Vickers hardness (n=10). The aging stability was evaluated by measuring the tetragonal to monoclinic transformation (n=3) after accelerated hydrothermal aging in steam at 134°C, and the transformation curves were fitted by the Mehl-Avrami-Johnson (MAJ) equation. Data were analyzed by one-way ANOVA, followed by Tukey's HSD test (α=0.05).

Results: Lowering the alumina content below 0.25wt.% avoided the formation of alumina particles and therefore increased the translucency of 3Y-TZP ceramics, but the hydrothermal aging stability was reduced. A higher yttria content (5mol%) introduced about 50% cubic zirconia phase and gave rise to the most translucent and aging-resistant Y-TZP ceramics, but the fracture toughness and strength were considerably sacrificed. 0.2mol% La₂O₃ doping of 3Y-TZP tailored the grain boundary chemistry and significantly improved the aging resistance and translucency. Although the translucency improvement by La₂O₃ doping was less effective than for introducing a substantial amount of cubic zirconia, this strategy was able to maintain the mechanical properties of typical 3Y-TZP ceramics.

Significance: Three different approaches were compared to improve the translucency of 3Y-TZP ceramics.

Keywords: Aging; Dental restorations; Mechanical properties; Translucency; Yttria; Zirconia.

MeSH terms

Ceramics
Dental Materials
Dental Stress Analysis
Hardness
Materials Testing
X-Ray Diffraction
Yttrium*
Zirconium*

Substances

Dental Materials
yttria stabilized tetragonal zirconia
Yttrium
Zirconium