Effect of A Rapid-Cooling Protocol on the Optical and Mechanical Properties of Dental Monolithic Zirconia Containing 3–5 mol% Y2O3

• Published in: Materials Vol. 13; no. 8; p. 1923
• Main Author: Kim, Hee-Kyung
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 19.04.2020; MDPI
• Subjects: Aging; Annealing; Bend strength; Cooling; Cooling effects; Dentistry; Diamond pyramid hardness; Flexural strength; Fracture toughness; Glass ceramics; Grain boundaries; Heat; Heat treatment; High temperature; Indentation; Lithium; mechanical phenomena; Mechanical properties; Modulus of rupture in bending; optical phenomena; Optical properties; Partial stabilization; Partially stabilized zirconia; phase transition; Phase transitions; Scanning electron microscopy; Yttrium oxide; Zirconium dioxide; zirconium oxide; Grand Rapids Michigan; United States > US; Japan; Liechtenstein
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma13081923

Many attempts have been made to improve the translucency of zirconia in dentistry. The purpose of this study was to evaluate the effect of a rapid-cooling heat treatment on the optical and mechanical properties of dental monolithic zirconia. Zirconia containing 3, 4, and 5 mol% Y2O3 were sintered, sectioned, and polished. The specimens were rapidly cooled from high temperature inducing a diffusionless cubic-to-metastable tetragonal (t’) phase transformation. The changes in L*a*b* color coordinates, translucency parameter (TP), and total transmittance (T%) were measured. Three-point bending strength, Vickers hardness, and indentation fracture toughness tests were performed. Quantitative phase analyses were carried out by X-ray diffraction with Rietveld refinement. Scanning electron microscopy (SEM) images were obtained. With increasing Y2O3 contents, TP and T% values increased while strength and toughness decreased. The Rietveld analysis showed that the amount of t’-phase increased after rapid-cooling and annealed 5Y-partially stabilized zirconia (PSZ) contained the highest amount of t’-phase (64.4 wt%). Rapid-cooling improved translucency but the translucency of annealed 5Y-PSZ did not approach that of lithium disilicate glass-ceramic. Rapid-cooling decreased flexural strength significantly, being 306.1 ± 61.8 MPa for annealed 5Y-PSZ. SEM revealed that grains tended to get larger after rapid-cooling. A rapid-cooling treatment can produce t’-phase which can contribute to an increase in translucency but has a negative effect on the mechanical properties of zirconia.