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

Abstract

Objectives: 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 °C) and CEREC Zirconia (CEREC ZrSS) (Dentsply Sirona) (15 min/2 min/1578 °C) were compared to conventionally sintered (CS) Katana STMLCS (6.8 h/2 h/1550 °C) and inCoris TZICS (4 h/2 h/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.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 (≈53 wt%), 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 wt% and 20 wt%, 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.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.

Influence of sintering conditions on translucency, biaxial flexural strength, microstructure, and low-temperature degradation of highly translucent dental zirconia

“…Zpex Smile was not degraded at any sintering temperature in the present study. This was consistent with the observations in previous studies, where Zpex Smile exhibited the highest resistance to LTD 15,18,24,38) . The results of Rietveld refinement revealed that the Y2O3 content in the t-ZrO2 phase of Zpex Smile was more than 3.8 wt%, which lowered the transformability of the t-ZrO 2 phase.…”

“…The increase in the sintering temperature and sintering time increases the susceptibility of the conventional 3Y-TZP to aging 21) . However, the influence of the different sintering temperatures on the characteristics of the second and latest generation of highly translucent zirconia grades remains unexplored [22][23][24] . The present in vitro study demonstrated the influence of the different sintering conditions on the translucency, crystallographic structure, biaxial flexural strength, microstructure, and LTD of three highly translucent zirconia grades i.e., 3Y-TZP, 4Y-PSZ, and 5Y-PSZ.…”

Selected Spectroscopic Techniques for Surface Analysis of Dental Materials: A Narrative Review

“…The XRF is used to test the composition of materials, the coating thickness, and to identify elements in dental materials: implant alloy [ 142 ] and ceramics [ 143 , 144 , 145 , 146 , 147 , 148 , 149 , 150 , 151 , 152 ]. XRD is used to obtain information of crystalline structure of solids such as dental ceramics [ 143 , 144 , 145 , 146 , 147 , 148 , 149 , 150 ].…”

Clinical Feasibility of Fully Sintered (Y, Nb)-TZP for CAD-CAM Single-Unit Restoration: A Pilot Study

“…As an alternative to the conventional sintering protocol, high-speed sintering for dental zirconia with high temperature in the range of 1570–1590 °C was introduced; this may affect the mechanical properties by increasing the grain size [ 4 , 5 ]. Studies have shown contradictory findings regarding the effect of speed sintering on the mechanical properties, either increasing or decreasing the flexural strength of sintered zirconia [ 6 , 7 , 8 , 9 ]. Speed sintering was reported to have a variable influence on the strength, depending on the content of yttria [ 4 , 7 ].…”

“…Speed sintering was reported to have a variable influence on the strength, depending on the content of yttria [ 4 , 7 ]. The optical properties of sintered zirconia may also be affected by speed sintering due to an increase in the grain size [ 4 , 6 , 9 ].…”