Lorenzoni Fabio C, Bonfante Estevam A, Valverde Guilherme B, Coelho Paulo G, Bonfante Gerson, Thompson Van P, Silva Nelson R F A
Department of Prosthodontics, Unigran University School of Dentistry, Dourados, MS, Brazil; Lorenzoni Education Institute, Ponta Porã, MS, Brazil.
Department of Prosthodontics and Periodontology, University of São Paulo Bauru School of Dentistry, Bauru, Brazil.
J Mech Behav Biomed Mater. 2020 Aug;108:103831. doi: 10.1016/j.jmbbm.2020.103831. Epub 2020 Apr 28.
Controversy exists about whether the elastic modulus (E) mismatch between the loading indenter and ceramic materials influences fatigue testing results. The research hypotheses were that for porcelain veneered Y-TZP crowns 1) A low modulus Steatite indenter (SB) leads to higher fatigue reliability compared to a high modulus tungsten carbide indenter (WC); 2) Different surface damage patterns are expected between low and high modulus indenters after sliding contact fatigue testing. All ceramic crowns will exhibit similar step-stress accelerated life testing (SSALT) contact fatigue reliability (hypothesis 1) and failure characteristics (hypothesis 2) when using high stiffness tungsten carbide (WC, E = 600 GPa) vs. enamel like steatite (SB, E = 90 GPa) indenters.
Manufacturer (3M Oral Care) prepared Y-TZP-veneered all-ceramic molar crowns were bonded to aged resin composite reproductions of a standard tooth preparation and subjected to mouth-motion SSALT fatigue (n = 18 per indenter type). Failure was defined either as initial inner cone crack (IC), or final fracture (FF) when porcelain fractured (chipping). Selected IC specimens that did not progress to FF were embedded in epoxy resin and sectioned for fractographic analysis.
The distribution of failures across the load and cycle profiles lead to similar calculated Weibull Use Level Probability Plots with overlap of the 2-sided 90% confidence bounds. The calculated reliability for IC and FF was equivalent at a mission of 300 N or 700 N load and 50,000 cycles, although the WC indenter had a trend for lower reliability for IC at 700 N. Both indenters produced similar patterns of wear and cracking on crown surfaces. Fractographic landmarks showed competing failure modes, but sliding contact partial inner cone cracks were the most dominant for both groups.
The more compliant Steatite indenter had similar veneered crown fatigue reliability and failure modes to those found with use of a high stiffness tungsten carbide indenter (hypotheses 1 and 2 rejected).
加载压头与陶瓷材料之间的弹性模量（E）不匹配是否会影响疲劳测试结果，目前仍存在争议。研究假设为，对于烤瓷Y-TZP全冠：1）与高模量碳化钨压头（WC）相比，低模量滑石压头（SB）能带来更高的疲劳可靠性；2）滑动接触疲劳测试后，低模量和高模量压头之间预期会出现不同的表面损伤模式。当使用高刚度碳化钨（WC，E = 600 GPa）与类牙釉质滑石（SB，E = 90 GPa）压头时，所有陶瓷全冠将表现出相似的阶梯应力加速寿命测试（SSALT）接触疲劳可靠性（假设1）和失效特征（假设2）。
由制造商（3M口腔护理）制备的Y-TZP烤瓷全瓷磨牙全冠，粘结到标准牙体预备的老化树脂复合材料复制体上，并进行口腔运动SSALT疲劳测试（每种压头类型n = 18）。失效定义为初始内部锥形裂纹（IC），或烤瓷破裂（崩瓷）时的最终断裂（FF）。将未发展为FF的选定IC标本嵌入环氧树脂中并切片进行断口分析。
在载荷和循环曲线上的失效分布导致计算出的威布尔使用水平概率图相似，双侧90%置信区间重叠。在300 N或700 N载荷及50,000次循环的任务下，IC和FF的计算可靠性相当，尽管WC压头在700 N时IC的可靠性有降低趋势。两种压头在全冠表面产生的磨损和裂纹模式相似。断口特征显示出相互竞争的失效模式，但滑动接触部分内部锥形裂纹在两组中最为常见。
更柔顺的滑石压头与使用高刚度碳化钨压头时的烤瓷全冠疲劳可靠性和失效模式相似（假设1和假设2被否定）。
