Effect of Cooling Rate during Glazing on the Mechanical and Optical Properties of Monolithic Zirconia with 3 mol% Yttria Content

Abstract

Glazing is the final heat treatment process in the manufacturing of a monolithic zirconia prosthesis. Herein, the effect of cooling rate during zirconia glazing was investigated. A 3 mol% yttria-stabilized tetragonal zirconia polycrystal was glazed at the general cooling rate suggested by the manufacturer, as well as at higher and lower cooling rates, and the differences in flexural strength, hardness, optical properties, and crystal structure were evaluated. A higher cooling rate did not affect the flexural strength, hardness, grain size, optical properties, or crystal structure; however, the Weibull modulus decreased by 1.3. A lower cooling rate did not affect the flexural strength, optical properties, or crystal structure; however, the Weibull characteristic strength increased by 26.7 MPa and the Weibull modulus increased by 0.9. The decrease in hardness and the increase in grain size were statistically significant; however, the numerical differences were negligible. This study revealed that a lower cooling rate provides more reliable flexural strength. Therefore, glazing can proceed at a general cooling rate, which takes 3–4 min; however, glazing at a lower cooling rate will provide a more consistent flexural strength if desired, despite being time-consuming.

Effect of Cooling Rate on Mechanical Properties, Translucency, Opalescence, and Light Transmission Properties of Monolithic 4Y-TZP during Glazing

“…The spectral transmittance decreased at ~520 and 650 nm and then increased again. This trend has been reported for other pre-colored zirconia products [16] but not for uncolored zirconia products [33,35]. This decrease in the spectral transmittance of pre-colored zirconia in a specific wavelength range may be attributed to the presence of the pigment [10].…”

“…Therefore, it is considered that the reliability of the flexural strength does not change, regardless of the change in the cooling rate in 4Y-TZP. In the case of 3Y-TZP, as the cooling rate during glazing increased, the Weibull modulus for the flexural strength tended to decrease [33]. In several studies that have focused on the change in flexural strength during the glazing of zirconia, it has been reported that the flexural strength decreases after the glazing process [20,22,23].…”

Effect of High-Speed Sintering on the Optical Properties, Microstructure, and Phase Distribution of Multilayered Zirconia Stabilized with 5 mol% Yttria

“…This increase in Δb* contributed to a significant increase in the OP from the EL to DL. In YSZ, the OP value increases with increasing thickness [ 12 , 39 , 42 ]. In colored zirconia, the increase in the OP value with increasing thickness was greater than that in uncolored zirconia [ 39 , 42 ].…”

“…In YSZ, the OP value increases with increasing thickness [ 12 , 39 , 42 ]. In colored zirconia, the increase in the OP value with increasing thickness was greater than that in uncolored zirconia [ 39 , 42 ].…”

Effect of multiple firings on the color and translucency of monolithic zirconia

“…In addition, different sintering temperatures have been reported to lead to varied colors of nanosized 3Y-TZP, possibly due to enlargement of the grain sizes and increased t → m phase transformations (Dimitriadis et al, 2022). Although multiple firings are usually performed at relatively low temperatures, they may change the grain sizes and increase the t → m phase transformations of Y-TZPs and further affect their color and translucency characteristics (Cho and Seol, 2021;Zhang et al, 2021;Dimitriadis et al, 2022). Fehmi (Fehmi et al, 2018) reported a statistically significant change in the color of monolithic glass ceramics (IPS e. max press, Ivoclar Vivadent AG, Liechtenstein) after 5 rounds of firing.…”