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

Objective. 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. Methods. Speed sintered (SS) Katana STMLSS (Kuraray Noritake) (total thermal cycle/sintering time/dwell temperature: 30 min/16 min/1560 degrees C) and CEREC Zirconia (CEREC Zr-SS) (Dentsply Sirona) (15 min/2 min/1578 degrees C) were compared to conventionally sintered (CS) Katana STMLCS (6.8 h/2 h/1550 degrees C) and inCoris TZI(CS) (4 h/2 h/1510 degrees 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-tomonoclinic ZrO2 phase transformation after accelerated hydrothermal aging in steam at 134 degrees C. The indentation fracture toughness, Vickers hardness and biaxial strength of the sintered ceramics were assessed. Results. 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 (approximate to 53 wt%), which resulted in a higher amount of Y2O3 in the remaining tetragonal ZrO2 phases compared to the 3Y-TZP CEREC Zr-SS and inCoris TZI(CS) (8 and 20 wt%, respectively). The sintering program did not affect the hydrothermal aging behavior of Katana STMLSS and CEREC Zr-SS. TP of Katana STMLSS (TP approximate to 32) was not affected by speed sintering, while the translucency of CEREC Zr-SS (TP = 14) was significantly reduced. Hardness, fracture toughness and Weibull characteristic strength of Katana STMLSS and CEREC Zr-SS also reached the optimal level, but speed sintering substantially lowered their mechanical reliability. Significance. 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. (C) 2020 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.