Statement of problem

The flexural strength of zirconia restorations is partially dependent on the sintering process. Changes in sintering protocols as well as hydrothermal aging may affect the flexural strength of zirconia materials.

Purpose

The purpose of this in vitro study was to investigate how changes in sintering parameters and hydrothermal aging affect the biaxial flexural strength of monolithic zirconia.

Material and methods

Specimens were produced from 2 translucent monolithic zirconia ceramics (Zircon X ST, Upcera YZ HT). After coloring, specimens of both ceramics were distributed into groups and subjected to 1 of 6 different sintering protocols. Half were subjected to biaxial flexural strength tests directly after sintering, and the remaining specimens were subjected to hydrothermal aging and then to biaxial flexural strength testing. Biaxial flexural strength data were analyzed by using a statistical software program. Normality of distribution was determined by the Shapiro-Wilk test. Biaxial flexural strength data were compared among groups by using 1-way ANOVA and Tukey post hoc tests, and intragroup data were compared by using paired specimens t tests (α=.05).

Results

The highest overall biaxial flexural strength value was obtained in UW-II. The highest biaxial flexural strength for Zircon X was obtained in ZX-VI and ZX-HTA-VI, whereas the highest biaxial flexural strength for Upcera was obtained in UW-II before hydrothermal aging and in UW-HTA-V after aging (P<.05).

Conclusions

The biaxial flexural strength of Zircon X increased with longer sintering times. Upcera specimens were more fracture-resistant than Zircon X both before and after hydrothermal aging. Based on these findings, longer sintering times are recommended to increase the strength of monolithic zirconia.

中文翻译：

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烧结时间和水热老化对整体氧化锆陶瓷体系力学性能的影响

问题陈述

氧化锆修复体的抗弯强度部分取决于烧结过程。烧结方案的变化以及水热老化可能会影响氧化锆材料的弯曲强度。

目的

这项体外研究的目的是研究烧结参数和水热老化的变化如何影响整体氧化锆的双轴弯曲强度。

材料与方法

样品由 2 块半透明的整体氧化锆陶瓷（Zircon X ST，Upcera YZ HT）制成。着色后，将两种陶瓷的样品分成几组并进行 6 种不同烧结方案中的一种。一半在烧结后直接进行双轴弯曲强度测试，其余样品进行水热老化，然后进行双轴弯曲强度测试。双轴抗弯强度数据通过使用统计软件程序进行分析。分布的正态性由夏皮罗-威尔克检验确定。使用单向方差分析和 Tukey post hoc 检验比较组间双轴抗弯强度数据，使用配对样本t检验 (α=.05)比较组内数据。

结果

在 UW-II 中获得了最高的整体双轴弯曲强度值。ZX-VI和ZX-HTA-VI中Zircon X的双轴弯曲强度最高，而UW-II水热老化前和UW-HTA-V老化后UW-HTA-V的双轴弯曲强度最高（P < .05）。

结论

Zircon X 的双轴抗弯强度随着烧结时间的延长而增加。Upcera 试样在水热老化前后都比 Zircon X 更耐断裂。基于这些发现，建议延长烧结时间以提高整体氧化锆的强度。