Alhotan Abdulaziz, Yilmaz Burak, Weber Anna, Babaier Rua, Bourauel Christoph, Fouda Ahmed Mahmoud
Department of Dental Health, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia.
Department of Reconstructive Dentistry and Gerodontology, School of Dental Medicine, University of Bern, Bern, Switzerland.
J Prosthodont. 2024 Sep 3. doi: 10.1111/jopr.13943.
This study aimed to evaluate the impact of artificial aging on the fracture toughness and hardness of three-dimensional (3D)-printed and computer-aided design and computer-aided manufacturing (CAD-CAM) milled 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP).
Forty bar-shaped specimens (45 × 4 × 3 mm) were prepared using two manufacturing technologies: 3D printing (LithaCon 3Y 210, Lithoz GmbH, Vienna, Austria; n = 20) and milling (Initial Zirconia ST, GC, Japan; n = 20) of 3Y-TZP. The chevron-notch beam method was used to assess the fracture toughness according to ISO 24370. Specimens from each 3Y-TZP group were divided into two subgroups (n = 10) based on the artificial aging process (autoclaving): nonaged and aged. Nonaged specimens were stored at room temperature, while aged specimens underwent autoclave aging at 134°C under 2 bar-pressure for 5 h. Subsequently, the specimens were immersed in absolute 99% ethanol using an ultrasonic cleaner for 5 min. Each specimen was preloaded by subjecting it to a 4-point loading test, with a force of up to 200 N applied for three cycles. Further 4-point loading was conducted at a rate of 0.5 mm/min under controlled temperature and humidity conditions until fracture occurred. The maximum force (F) was recorded and the chevron notch was examined at 30 × magnification under an optical microscope for measurements before the fracture toughness (K) was calculated. Microhardness testing was also performed to measure the Vickers hardness number (VHN). A scanning electron microscope (SEM) coupled with an energy dispersive X-ray unit (EDX) was used to examine surface topography and chemical composition. X-ray diffraction (XRD) was conducted to identify crystalline structure. Data were statistically analyzed using two-way ANOVA and Student's t-test with a significance level of 0.05.
The nonaged 3D-printed 3Y-TZP group exhibited a significantly higher fracture toughness value (6.07 MPa m) than the milled 3Y-TZP groups (p < 0.001). After autoclave aging, the 3D-printed 3Y-TZP group maintained significantly higher fracture toughness (p < 0.001) compared to the milled 3Y-TZP group. However, no significant differences in hardness values (p = 0.096) were observed between the aged and nonaged groups within each manufacturing process (3D-printed and milled) independently.
The findings revealed that the new 3D-printed 3Y-TZP produced by the lithography-based ceramic manufacturing (LCM) technology exhibited superior fracture toughness after autoclave aging compared to the milled 3Y-TZP. While no significant differences in hardness were observed between the aged groups, the 3D-printed material demonstrated greater resistance to fracture, indicating enhanced mechanical stability.
本研究旨在评估人工老化对三维（3D）打印及计算机辅助设计与计算机辅助制造（CAD-CAM）铣削的3摩尔％氧化钇稳定四方氧化锆多晶体（3Y-TZP）的断裂韧性和硬度的影响。
使用两种制造技术制备了40个棒状试样（45×4×3mm）：3Y-TZP的3D打印（LithaCon 3Y 210，Lithoz GmbH，维也纳，奥地利；n = 20）和铣削（Initial Zirconia ST，GC，日本；n = 20）。根据ISO 24370，采用人字形切口梁法评估断裂韧性。每个3Y-TZP组的试样根据人工老化过程（高压灭菌）分为两个亚组（n = 10）：未老化和老化。未老化的试样保存在室温下，而老化的试样在134°C、2巴压力下进行高压灭菌老化5小时。随后，使用超声波清洗器将试样浸入无水99％乙醇中5分钟。每个试样通过四点加载试验进行预加载，施加高达200N的力，循环三次。在控制温度和湿度条件下，以0.5mm/min的速率进行进一步的四点加载，直至发生断裂。记录最大力（F），并在光学显微镜下以30倍放大倍数检查人字形切口以进行测量，然后计算断裂韧性（K）。还进行了显微硬度测试以测量维氏硬度值（VHN）。使用配备能量色散X射线单元（EDX）的扫描电子显微镜（SEM）检查表面形貌和化学成分。进行X射线衍射（XRD）以确定晶体结构。使用双向方差分析和Student's t检验对数据进行统计分析，显著性水平为0.05。
未老化的3D打印3Y-TZP组的断裂韧性值（6.07MPa·m）明显高于铣削的3Y-TZP组（p < 0.001）。高压灭菌老化后，3D打印的3Y-TZP组与铣削的3Y-TZP组相比，断裂韧性仍显著更高（p < 0.001）。然而，在每个制造工艺（3D打印和铣削）中，老化组和未老化组之间的硬度值没有显著差异（p = 0.096）。
研究结果表明，基于光刻的陶瓷制造（LCM）技术生产的新型3D打印3Y-TZP在高压灭菌老化后比铣削的3Y-TZP具有更高的断裂韧性。虽然老化组之间的硬度没有显著差异，但3D打印材料表现出更强的抗断裂能力，表明其机械稳定性增强。
