Mechanical properties, aging stability and translucency of speed-sintered zirconia for chairside restorations

• Published in: Dental materials 2020-07, Vol.36 (7), p.959-972
• Main Authors: Cokic, Stevan M., Vleugels, Jef, Van Meerbeek, Bart, Camargo, Bernardo, Willems, Evita, Li, Maoyin, Zhang, Fei
• Format: Article
• Language: English
• Subjects: Aging; Ceramics; Chemical composition; Dentistry; Diamond pyramid hardness; Electric induction furnaces; Fracture toughness; Hardness; Indentation; Mechanical properties; Microstructure; Monolithic zirconia; Multilayer zirconia; Optical properties; Partially stabilized zirconia; Performance evaluation; Phase composition; Phase transitions; Reliability; Sintering; Speed sintering; Stability analysis; Steam; Tetragonal zirconia polycrystals; Yttria-stabilized zirconia; Yttrium oxide; Zirconia; Zirconium dioxide
• ISSN: 0109-5641; 1879-0097
• DOI: 10.1016/j.dental.2020.04.026

•Similar primary zirconia properties by speed-sintering as conventional sintering.•Speed-sintering 3Y-TZP decreased its translucency but not that of 5Y-PSZ.•Speed-sintering lowered the mechanical reliability of 3Y-TZP and 5Y-PSZ zirconia. To evaluate the performance of zirconia ceramics sintered in a speed sintering induction furnace by comprehensive understanding of their optical and mechanical properties, microstructure, phase composition and aging stability, in comparison to ceramics sintered in a conventional furnace. Speed sintered (SS) Katana STMLSS (Kuraray Noritake) (total thermal cycle/sintering time/dwell temperature: 30min/16min/1560°C) and CEREC Zirconia (CEREC ZrSS) (Dentsply Sirona) (15min/2min/1578°C) were compared to conventionally sintered (CS) Katana STMLCS (6.8h/2h/1550°C) and inCoris TZICS (4h/2h/1510°C). The translucency parameter (TP) and contrast ratio (CR) were measured with a spectrophotometer. The chemical composition of the materials was determined by XRF and phase composition was characterized using XRD. Hydrothermal aging behavior was evaluated by measuring the tetragonal-to-monoclinic ZrO2 phase transformation after accelerated hydrothermal aging in steam at 134°C. The indentation fracture toughness, Vickers hardness and biaxial strength of the sintered ceramics were assessed. Speed and conventionally sintered zirconia revealed similar density, microstructure, average strength and hydrothermal aging stability. Both Katana STMLSS/CS 5Y-PSZ ceramics were characterized with a higher content of cubic phase (≈53wt%), which resulted in a higher amount of Y2O3 in the remaining tetragonal ZrO2 phases compared to the 3Y-TZP CEREC ZrSS and inCoris TZICS (8 and 20wt%, respectively). The sintering program did not affect the hydrothermal aging behavior of Katana STMLSS and CEREC ZrSS. TP of Katana STMLSS (TP≈32) was not affected by speed sintering, while the translucency of CEREC ZrSS (TP=14) was significantly reduced. Hardness, fracture toughness and Weibull characteristic strength of Katana STMLSS and CEREC ZrSS also reached the optimal level, but speed sintering substantially lowered their mechanical reliability. Speed sintering of 3Y-TZP and 5Y-PSZ in a speed sintering induction oven appeared suitable for clinical applications. However, further studies should focus on improving of translucency and mechanical reliability of the speed-sintered zirconia ceramics.