Department of Prosthetic Dentistry, University Hospital, Ludwig-Maximilians-University, Goethestrasse 70, 80336 Munich, Germany.
Department of Prosthetic Dentistry, University Hospital, Ludwig-Maximilians-University, Goethestrasse 70, 80336 Munich, Germany.
Dent Mater. 2021 Jul;37(7):1073-1082. doi: 10.1016/j.dental.2021.03.013. Epub 2021 Apr 10.
To test the impact of three varying step-stress protocols on the fatigue behavior of two 3Y-TZP, one 4Y-TZP and one 5Y-TZP zirconia materials.
Eight specimens per zirconia material (N = 32) were selected for static testing to determine the start load for dynamic tests (30% of the mean value of static fracture load). 45 specimens per material (N = 180) were used for dynamic load tests using three step-stress protocols: 1. 50 N/5000 cycles; 2. 5% of static load/5000 cycles, and 3. 10 N/1000 cycles. Following materials were tested: 3Y-TZP (O: opaque) 3Y-TZP (T: translucent), 4Y-TZP (ET: extra translucent) and 5Y-TZP (HT: high translucent). The specimens (4 ± 0.02 × 3 ± 0.02 × 45 mm) were placed centrally on the support rolls and the load was applied perpendicularly over the 4 mm specimen side (∼4-point flexural strength according to the DIN 6872:2019). Data was analyzed with Kolmogorov-Smirnov-test, t-test, one-way ANOVA with post-hoc Scheffé-test, Chi-square-test, Kaplan-Meier with Log-Rank-test and two-parametric Weibull analysis (p < 0.05).
The step-stress protocols showed no impact on the fracture load or Weibull modulus within one zirconia material. However, the zirconia materials T, ET and HT showed differences in cycle number to fracture between the step-stress protocols (T: 3 > 2 > 1; ET: 2 > 3 > 1; HT: 2, 3 > 1) with lowest cycle number to fracture for protocol 1. Within one step-stress protocol, the cycle number to fracture varied according to the zirconia material as follows: 1: T, O ≥ O, ET > HT; 2: ET > O, T, HT; 3: O, T, ET > HT. Cracking started at the tensile side of the specimens at all times. All specimens showed typical compression curls (single or double). Fragmentation patterns were similar for all materials with a lot of crack branching and fragmentation due to secondary cracks indicating high energy fractures.
Dynamic fatigue tests seem to provide important information on the long-term stability of zirconia materials. Zirconia materials with higher opacity seem to be more robust towards varying step-stress protocols than translucent zirconia materials. Regarding expenditure of time, a step-stress protocol with a load increase of 50 N every 5000 cycles seems favorable to gain information on the long-term stability of zirconia materials.
测试三种不同阶跃应力方案对两种 3Y-TZP、一种 4Y-TZP 和一种 5Y-TZP 氧化锆材料疲劳性能的影响。
为了确定动态测试的起始载荷（静态断裂载荷平均值的 30%），每一种氧化锆材料选择 8 个试件（N=32）进行静态测试。每种材料使用 45 个试件（N=180）进行动态载荷测试，采用三种阶跃应力方案：1. 50 N/5000 次循环；2. 静态载荷的 5%/5000 次循环；3. 10 N/1000 次循环。测试的材料有：3Y-TZP（O：不透明）、3Y-TZP（T：半透明）、4Y-TZP（ET：超半透明）和 5Y-TZP（HT：高透明）。试件（4±0.02×3±0.02×45mm）放置在支撑辊的中心，垂直于 4mm 试件侧面施加载荷（根据 DIN 6872:2019，约为 4 点弯曲强度）。使用 Kolmogorov-Smirnov 检验、t 检验、单向方差分析和事后 Scheffé 检验、卡方检验、Kaplan-Meier 和对数秩检验以及双参数威布尔分析进行数据分析（p<0.05）。
阶跃应力方案对同一氧化锆材料的断裂载荷或威布尔模数没有影响。然而，T、ET 和 HT 氧化锆材料在阶跃应力方案之间的断裂循环次数上存在差异（T：3>2>1；ET：2>3>1；HT：2，3>1），方案 1 的断裂循环次数最低。在同一阶跃应力方案中，断裂循环次数因氧化锆材料而异，结果如下：1：T、O≥O、ET>HT；2：ET>O、T、HT；3：O、T、ET>HT。在任何时候，裂纹都从试件的拉伸侧开始。所有试件均显示出典型的压缩卷曲（单个或双个）。由于二次裂纹导致大量裂纹分支和碎片，所有材料的断裂模式均相似，表明能量较高的断裂。
动态疲劳试验似乎提供了有关氧化锆材料长期稳定性的重要信息。与半透明氧化锆材料相比，透光率较高的氧化锆材料似乎更能耐受不同的阶跃应力方案。关于时间的花费，每 5000 次循环增加 50N 的阶跃应力方案似乎有利于获得有关氧化锆材料长期稳定性的信息。
