Lecturer, Department of Dental Laboratory Science, College of Health Sciences, Catholic University of Pusan, Busan, Republic of Korea.
Professor and Chairman, Department of Dental Laboratory Science, College of Health Sciences, Catholic University of Pusan, Busan, Republic of Korea.
J Prosthet Dent. 2021 Nov;126(5):692.e1-692.e14. doi: 10.1016/j.prosdent.2021.07.027. Epub 2021 Sep 29.
The traditional sintering of zirconia takes an extended time, and accelerated treatments have been developed to reduce treatment time and manufacturing costs. Studies evaluating the effect of sintering time on the mechanical properties of zirconia are lacking.
The purpose of this in vitro study was to evaluate the effect of the sintering condition and the low-temperature degradation (LTD) of zirconia on the flexural strength of monolithic zirconia.
Zirconia specimens (LUXEN Enamel) were sintered at 1500 °C, 1530 °C, and 1560 °C for 4, 5, 6, 7, and 12 hours and subjected to LTD (n=10). Control specimens were assessed in the nontreated condition. The 3-point flexural strength was measured by using a universal testing machine. The crystal phases of the specimens were compared and quantitatively analyzed through X-ray diffraction (XRD) analysis, and the crystal grain size was measured by using a field emission scanning electron microscope (FE-SEM). Two-way ANOVA and the independent sample t test were used to analyze the experimental results (α=.05).
In the group not subjected to LTD, there was no difference in flexural strength according to the change in sintering temperature and sintering time (P>.05). The group subjected to LTD showed a difference in flexural strength according to sintering time difference (P<.001). The flexural strength of the zirconia with LTD exposure increased compared with that of the zirconia specimen not subjected to LTD (P<.001). With LTD exposure, cubic and monoclinic crystals increased, tetragonal crystals decreased, and the particle size increased. As the sintering temperature increased, the particle size increased, but not according to the sintering time.
At all sintering times, the flexural strength of zirconia was over 800 MPa, which is the minimum flexural strength of a 4-unit or longer prosthesis as specified in the International Organization for Standardization (ISO) 6872. With LTD exposure, the increase in the flexural strength of zirconia was associated with the phase change from tetragonal to monoclinic.
传统的氧化锆烧结需要很长时间，因此已经开发出加速处理方法来缩短处理时间和降低制造成本。目前缺乏研究来评估烧结时间对氧化锆机械性能的影响。
本体外研究的目的是评估烧结条件和氧化锆的低温降解（LTD）对整体氧化锆弯曲强度的影响。
将氧化锆试件（LUXEN Enamel）在 1500°C、1530°C 和 1560°C 下分别烧结 4、5、6、7 和 12 小时，并进行 LTD（n=10）处理。对照组试件在未经处理的条件下进行评估。通过万能试验机测量三点弯曲强度。通过 X 射线衍射（XRD）分析比较和定量分析试件的晶体相，并通过场发射扫描电子显微镜（FE-SEM）测量晶体晶粒尺寸。采用双因素方差分析和独立样本 t 检验对实验结果进行分析（α=.05）。
在未进行 LTD 处理的组中，弯曲强度不因烧结温度和烧结时间的变化而有所不同（P>.05）。进行 LTD 处理的组中，弯曲强度因烧结时间的差异而有所不同（P<.001）。暴露于 LTD 的氧化锆的弯曲强度比未暴露于 LTD 的氧化锆试件的弯曲强度高（P<.001）。暴露于 LTD 后，立方相和单斜相晶体增加，四方相晶体减少，颗粒尺寸增大。随着烧结温度的升高，颗粒尺寸增大，但与烧结时间无关。
在所有烧结时间下，氧化锆的弯曲强度均超过 800 MPa，这是国际标准化组织（ISO）6872 规定的 4 个单位或更长义齿的最小弯曲强度。暴露于 LTD 后，氧化锆弯曲强度的增加与四方相向单斜相的相变有关。
