Taskonak Burak, Griggs Jason A, Mecholsky John J, Yan Jia-Hau
Department of Biomaterials Science, Baylor College of Dentistry, Texas A&M University System Health Science Center, United States.
Dent Mater. 2008 May;24(5):700-7. doi: 10.1016/j.dental.2007.08.001. Epub 2007 Sep 12.
The aim of this study was to test the hypothesis that the flexural strengths and critical flaw sizes of dental ceramic specimens will be affected by the testing environment and stressing rate even though their fracture toughness values will remain the same.
Ceramic specimens were prepared from an aluminous porcelain (Vitadur Alpha; VITA Zahnfabrik, Bad Säckingen, Germany) and an alumina-zirconia-glass composite (In-Ceram Zirconia; VITA Zahnfabrik). Three hundred uniaxial flexure specimens (150 of each material) were fabricated to dimensions of 25 mmx4 mmx1.2 mm according to the ISO 6872 standard. Each group of 30 specimens was fractured in water using one of four different target stressing rates ranging on a logarithmic scale from 0.1 to 100 MPa/s for Vitadur Alpha and from 0.01 to 10 MPa/s for In-Ceram Zirconia. The fifth group was tested in inert environment (oil) with a target stressing rate of 100 MPa/s for Vitadur Alpha and 1000 MPa/s for In-Ceram Zirconia. The effects of stressing rate and environment on flexural strength, critical flaw size, and fracture toughness were analyzed statistically by Kruskal-Wallis one-way ANOVA on ranks followed by post hoc comparisons using Dunn's test (alpha=0.05). In addition, 20 Vitadur Alpha specimens were fabricated with controlled flaws to simplify fractography. Half of these specimens were fracture tested in water and half in oil at a target stressing rate of 100 MPa/s, and the results were compared using Mann-Whitney rank sum tests (alpha=0.05). A logarithmic regression model was used to determine the fatigue parameters for each material.
For each ceramic composition, specimens tested in oil had significantly higher strength (P<or=0.05) and smaller critical flaw size (significant for Vitadur Alpha, P<or=0.05) than those tested in water but did not have significantly different fracture toughness (P>0.05). Specimens tested at faster stressing rates had significantly higher strength (P<or=0.05) but did not have significantly different fracture toughness (P>0.05). Regarding critical flaw size, stressing rate had a significant effect for In-Ceram Zirconia specimens (P<or=0.05) but not for Vitadur Alpha specimens (P>0.05). Fatigue parameters, n and lnB, were 38.4 and -12.7 for Vitadur Alpha and were 13.1 and 10.4 for In-Ceram Zirconia.
Moisture assisted subcritical crack growth had a more deleterious effect on In-Ceram Zirconia core ceramic than on Vitadur Alpha porcelain. Fracture surface analysis identified fracture surface features that can potentially mislead investigators into misidentifying the critical flaw.
本研究的目的是检验以下假设：即使牙科陶瓷试件的断裂韧性值保持不变，其弯曲强度和临界裂纹尺寸也会受到测试环境和加载速率的影响。
陶瓷试件由一种铝质瓷（维他灵阿尔法；维他牙科工厂，德国巴特萨克京根）和一种氧化铝 - 氧化锆 - 玻璃复合材料（全瓷氧化锆；维他牙科工厂）制备而成。根据ISO 6872标准，制作了300个单轴弯曲试件（每种材料150个），尺寸为25mm×4mm×1.2mm。每组30个试件在水中断裂，使用四种不同的目标加载速率之一，加载速率在对数尺度上范围为维他灵阿尔法从0.1至100MPa/s，全瓷氧化锆从0.01至10MPa/s。第五组在惰性环境（油）中测试，维他灵阿尔法的目标加载速率为100MPa/s，全瓷氧化锆为1000MPa/s。通过Kruskal - Wallis秩和单向方差分析对加载速率和环境对弯曲强度、临界裂纹尺寸和断裂韧性的影响进行统计分析，随后使用邓恩检验进行事后比较（α = 0.05）。此外，制作了20个带有可控裂纹的维他灵阿尔法试件以简化断口分析。这些试件中的一半在水中以100MPa/s的目标加载速率进行断裂测试，另一半在油中测试，结果使用曼 - 惠特尼秩和检验进行比较（α = 0.05）。使用对数回归模型确定每种材料的疲劳参数。
对于每种陶瓷成分，在油中测试的试件比在水中测试的试件具有显著更高的强度（P≤0.05）和更小的临界裂纹尺寸（维他灵阿尔法显著，P≤0.05），但断裂韧性没有显著差异（P>0.05）。在更快加载速率下测试的试件具有显著更高的强度（P≤0.05），但断裂韧性没有显著差异（P>0.05）。关于临界裂纹尺寸方面，加载速率对全瓷氧化锆试件有显著影响（P≤0.05），但对维他灵阿尔法试件没有显著影响（P>（此处原文有误，应为P＞0.05））。维他灵阿尔法的疲劳参数n和lnB分别为38.4和 - 12.7，全瓷氧化锆的为13.1和10.4。
水分辅助的亚临界裂纹扩展对全瓷氧化锆核陶瓷比对维他灵阿尔法瓷具有更有害的影响。断口表面分析确定了可能会误导研究人员错误识别临界裂纹的断口表面特征。
