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.
Highlights
Zirconia and yttria-stabilized zirconia are tough, hard, strong, and wear- and corrosionresistant, and they exhibit low coefficients of friction; they are widely used as coating materials in various industries [1,2]
A comparison of the Weibull characteristic strength values shows that the strength of the C-7 min group (935.9 MPa) is lower than that of the before glazing (Before-G) group, by 13 MPa, but higher than that of the C-0 min and C-4 min groups, by approximately
Within the range of conditions considered in this study, the use of a lower cooling rate than that suggested by the manufacturer during glazing did not affect the flexural strength, optical properties, or crystal structure of 3Y-TZP
Summary
The translucency of natural teeth has been reproduced by fabricating zirconia as the core of the restoration and veneering dental porcelain This method may cause the porcelain to fracture or fall off because of the low tensile strength of porcelain, and the difference in the coefficients of thermal expansion of porcelain and zirconia [7]. A significant difference in the coefficients of thermal expansion of the zirconia core and the veneer porcelain can generate residual stress in the porcelain, which can result in the porcelain being fractured [9,10] Because of these shortcomings of zirconia–porcelain restorations, zirconia with improved translucency has been manufactured and used in the fabrication of monolithic prostheses
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