University Hospital Tübingen, Section "Medical Materials Science & Technology", Osianderstr. 2-8, 72076 Tuebingen, Germany.
University Hospital Tübingen, Section "Medical Materials Science & Technology", Osianderstr. 2-8, 72076 Tuebingen, Germany.
Dent Mater. 2021 Feb;37(2):284-295. doi: 10.1016/j.dental.2020.11.016. Epub 2020 Dec 22.
The aim of this interlaboratory round robin test was to prove the robustness of the DIN EN ISO 6872:2019 and to identify the influence of processing and testing variations.
Each of the 12 laboratories participated (A-L) received 60 (n = 720) assigned zirconia specimens. All participants seperated the specimens from the blanks, sintered them, polished half of all specimens and performed the biaxial flexural test (DIN EN ISO 6872:2019). The surface roughness was determined by using tactile measuring device. Fractographic examination was performed under scanning-electron-microscopy (SEM). Data was analysed using Kolmogorov-Smirnov-, Kruskal-Wallis-, Mann-Whitney-U-test and two-parametric Weibull statistic (p < 0.05).
The results for both preparation methods (as-fired and polished) showed significant differences for some participants. The values for as-fired groups ranged between 513 (I) and 659 (E) MPa. H showed higher Weibull modulus than C, E and I. Within polished groups flexural strengths values from 465 (L) to 1212 (E) MPa were observed, with a tendency to clustered groups A, I, J, L (465-689 MPa) and remaining groups (877-1212 MPa). E presented the highest and H the lowest Weibull modulus. Within A and J, no impact of the preparation method on flexural strength values was observed. Within L, as-fired specimens showed higher flexural strength than polished ones. The flexural strength increase did only associate to a certain extent with measured surface roughness. Fractography showed defect populations depending on polishing techniques, associated to the strength level, especially for polished groups. Reduced strength is related to machining defects, regardless of the surface state.
DIN EN ISO 6872:2019 can be seen as guidance to biaxial flexural strength testing but additional effort is necessary to ensure interlaboratory comparability. Calibrated furnaces and reliable sintering conditions are mandatory requirements together with detailed specifications on finishing or polishing procedures. Biaxial flexural testing is really a matter of understanding specimen preparation, alignment and mechanical testing by itself. DIN EN ISO 6872:2019 should further recommend reporting of mean surface roughness along with any biaxial flexural strength data. Fractography is a mandatory tool in interpretation and understanding of strength data.
本实验室间对比研究旨在验证 DIN EN ISO 6872:2019 的稳健性，并确定加工和测试变化的影响。
每个参与的 12 个实验室（A-L）都收到了 60 个（n=720）分配的氧化锆样本。所有参与者都将样本从空白样本中分离出来，烧结，对所有样本的一半进行抛光，并按照 DIN EN ISO 6872:2019 进行双轴弯曲试验。表面粗糙度使用触觉测量设备进行测定。在扫描电子显微镜（SEM）下进行断口形貌分析。使用柯尔莫哥洛夫-斯米尔诺夫（Kolmogorov-Smirnov）、克鲁斯卡尔-沃利斯（Kruskal-Wallis）、曼-惠特尼 U 检验和双参数威布尔统计（p<0.05）对数据进行分析。
两种制备方法（煅烧和抛光）的结果对一些参与者来说都存在显著差异。煅烧组的数值范围在 513（I）至 659（E）MPa 之间。H 的威布尔模数高于 C、E 和 I。在抛光组中，观察到的弯曲强度值范围为 465（L）至 1212（E）MPa，A、I、J、L 组（465-689 MPa）和其余组（877-1212 MPa）有聚集的趋势。E 呈现出最高的威布尔模数，H 呈现出最低的威布尔模数。在 A 和 J 内，制备方法对弯曲强度值没有影响。在 L 内，煅烧样本的弯曲强度高于抛光样本。弯曲强度的增加仅在一定程度上与测量的表面粗糙度相关。断口形貌显示出与抛光技术相关的缺陷种群，与强度水平相关，特别是对于抛光组。强度降低与加工缺陷有关，与表面状态无关。
DIN EN ISO 6872:2019 可作为双轴弯曲强度测试的指南，但需要额外的努力来确保实验室间的可比性。校准炉和可靠的烧结条件是强制性要求，同时还需要详细说明精加工或抛光程序。双轴弯曲试验本身确实是一个理解样本制备、对准和机械测试的问题。DIN EN ISO 6872:2019 应进一步建议报告平均表面粗糙度以及任何双轴弯曲强度数据。断口形貌是解释和理解强度数据的强制性工具。
