Pittayachawan Piyapanna, McDonald Ailbhe, Young Anne, Knowles Jonathan C
Division of Biomaterials and Tissue Engineering, UCL Eastman Dental Institute, London, United Kingdom.
J Biomed Mater Res B Appl Biomater. 2009 Feb;88(2):366-77. doi: 10.1002/jbm.b.31064.
Yttria partially-stabilized zirconia polycrystalline (Y-TZP) has been the subject of extensive research because of its high strength and toughness. The aim of this study was to evaluate the biaxial flexural strength, fatigue life, and to investigate in more detail on single cycle specimens, the pressure-induced phase transformation of a Y-TZP dental ceramic using Raman microspectroscopy.
Thirty standardized discs (15 x 1.2 mm(2)) were used to examine the biaxial flexural strength (ISO 6872 standard) using a Dartec HC10 Servohydraulic testing machine (Zwick Ltd., UK). The specimens were also submitted to Vickers hardness (on polished and as-received surfaces within the same specimen) and dynamic fatigue test. The initial bulk phases were examined via X-ray diffraction and the local phase transformations that occurred in the zirconia induced by the various Vickers indentation loads (20-50 kg) were examined via Raman microspectroscopy on single cycle specimens. The fracture surface after biaxial flexural testing was also examined via Raman spectroscopy.
The Cercon specimens tested had flexural strength and Weibull modulus (m) of approximately 823.3 (+/-114.7) MPa and 8.3, respectively. As-received surfaces (1378.7 +/- 51.8 Hv) had slightly higher hardness value compared with polished surfaces (1354.33 +/- 50.9 Hv); however, two-way analysis of variance showed no significant difference in hardness values between polished and as-received surfaces (P > 0.05). Additionally, the specimens survived to 5 x 10(5) cycles when using a load of 70% of the mean biaxial flexural strength or lower. Raman microspectroscopy showed transformation of tetragonal to cubic and monoclinic phases within the indentation area. The fraction of monoclinic phase showed only limited variation with load or distance from the center to indentation edge. The level of cubic phase, however, was greatest at the indentation center. Transformation to cubic phase was observed on the lower surfaces (tension side) of fractured specimens. It was also observed near the specimen center exposed upon fracture. In the latter region an increase in monoclinic phase was additionally observed. Further work will be carried out using Raman microspectroscopy to assess the effect of fatigue on phase transformations.
The zirconia based ceramic has mechanical properties that may allow it to withstand the loading found in posterior areas. Transformation toughening was found when high loads impacted on the surface of zirconia. However it should be born in mind that this work was not carried out on veneered specimens, which exhibit different failure modes.
钇部分稳定氧化锆多晶体（Y-TZP）因其高强度和韧性而成为广泛研究的对象。本研究的目的是评估其双轴弯曲强度、疲劳寿命，并使用拉曼光谱更详细地研究Y-TZP牙科陶瓷单循环试样的压力诱导相变。
使用30个标准圆盘（15×1.2mm²），通过Dartec HC10伺服液压试验机（英国Zwick有限公司）按照ISO 6872标准检测双轴弯曲强度。对试样还进行了维氏硬度测试（在同一试样的抛光表面和原始表面上）以及动态疲劳试验。通过X射线衍射检测初始体相，并通过拉曼光谱对单循环试样上由不同维氏压痕载荷（20 - 50kg）引起的氧化锆中的局部相变进行检测。双轴弯曲试验后的断口表面也通过拉曼光谱进行检测。
测试的Cercon试样的弯曲强度和韦布尔模量（m）分别约为823.3（±114.7）MPa和8.3。原始表面（1378.7±51.8 Hv）的硬度值略高于抛光表面（1354.33±50.9 Hv）；然而，双向方差分析表明抛光表面和原始表面的硬度值无显著差异（P＞0.05）。此外，当使用平均双轴弯曲强度的70%或更低的载荷时，试样可承受5×10⁵次循环。拉曼光谱显示压痕区域内四方相转变为立方相和单斜相。单斜相的比例随载荷或从压痕中心到边缘的距离变化有限。然而，立方相的含量在压痕中心处最大。在断裂试样的下表面（拉伸侧）观察到向立方相的转变。在断裂后暴露的试样中心附近也观察到了这种转变。在后一区域还额外观察到单斜相的增加。将使用拉曼光谱进一步开展工作以评估疲劳对相变的影响。
基于氧化锆的陶瓷具有的机械性能可能使其能够承受后牙区域的载荷。当高载荷冲击氧化锆表面时会发现相变增韧。然而应记住，这项工作并非在具有不同失效模式的贴面试样上进行。
