Kwon Woo-Chang, Park Mi-Gyoung
Interdisciplinary, Department for Advanced Innovative Manufacturing Engineering, Pusan National University, 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. 2023 Dec;130(6):909-916. doi: 10.1016/j.prosdent.2021.12.006. Epub 2022 Feb 1.
The dry processing of zirconia has the disadvantage of dust dispersal during milling; thus, wet milling may be preferable. However, research on the mechanical properties of dental zirconia milled under different conditions and sintered at different temperatures is lacking.
The purpose of this in vitro study was to evaluate changes in the mechanical properties of zirconia specimens after milling under dry and wet conditions at different sintering temperatures.
Four hundred Ø20.0×1.5-mm presintered zirconia specimens were prepared by using a computer-aided design and computer-aided manufacturing (CAD-CAM) system and divided into 8 groups (n=50) based on the sintering (1230, 1330, 1430, and 1530 °C) and milling conditions (dry or wet). The mechanical properties (Vickers hardness, biaxial flexural strength, and fracture toughness) and physical properties (linear shrinkage and density) were examined. The microstructures of the specimens were observed with a scanning electron microscope. The crystal phases of the sintered green bodies were analyzed by using an X-ray diffractometer. The data were analyzed with descriptive statistics and 1-way and 2-way analyses of variance with Tukey HSD tests (α=.05).
The mechanical properties of all specimens increased with increasing sintering temperature, except for 1530 °C and the dry milling condition. The mechanical properties of the groups fabricated under wet milling conditions were better than those of the groups fabricated under dry milling conditions. Microscopic examination of the structure showed that the porosity decreased with increasing sintering temperature regardless of the milling conditions.
Higher sintering temperatures increased the mechanical properties (biaxial flexural strength, Vickers hardness, fracture toughness). However, phase transformation from tetragonal to cubic was observed for dry milled specimens sintered at 1530 °C, with decreased mechanical properties. Specimens fabricated by wet milling exhibited better mechanical properties than those fabricated by dry milling.
氧化锆的干法加工存在研磨过程中粉尘扩散的缺点；因此，湿法研磨可能更可取。然而，目前缺乏关于在不同条件下研磨并在不同温度下烧结的牙科氧化锆力学性能的研究。
本体外研究的目的是评估在不同烧结温度下，氧化锆试件在干法和湿法研磨后的力学性能变化。
使用计算机辅助设计和计算机辅助制造（CAD-CAM）系统制备400个直径为20.0×1.5mm的预烧结氧化锆试件，并根据烧结温度（1230、1330、1430和1530℃）和研磨条件（干法或湿法）分为8组（n = 50）。检测力学性能（维氏硬度、双轴弯曲强度和断裂韧性）和物理性能（线性收缩率和密度）。用扫描电子显微镜观察试件的微观结构。用X射线衍射仪分析烧结坯体的晶相。采用描述性统计以及单因素和双因素方差分析和Tukey HSD检验（α = 0.05）对数据进行分析。
除1530℃干法研磨条件外，所有试件的力学性能均随烧结温度的升高而提高。湿法研磨条件下制备的组的力学性能优于干法研磨条件下制备的组。结构的显微镜检查表明，无论研磨条件如何，孔隙率均随烧结温度的升高而降低。
较高的烧结温度提高了力学性能（双轴弯曲强度、维氏硬度、断裂韧性）。然而，在1530℃烧结的干法研磨试件中观察到从四方相到立方相的相变，力学性能下降。湿法研磨制备的试件比干法研磨制备的试件表现出更好的力学性能。
