Silvestri Tais, Pereira Gabriel Kalil Rocha, Guilardi Luis Felipe, Rippe Marilia Pivetta, Valandro Luiz Felipe
MSciD and PhD Graduate Programs in Oral Science (Prosthodontic Units), School of Dentistry, UFSM - Universidade Federal de Santa Maria, Santa Maria, RS, Brazil.
MSciD Graduate Program, School of Dentistry, IMED - Faculdade Meridional, Passo Fundo, RS, Brazil.
Braz Dent J. 2018 Jan-Feb;29(1):60-67. doi: 10.1590/0103-6440201801735.
This study aimed to investigate the effect of grinding and multi-stimuli aging on the fatigue strength, surface topography and the phase transformation of Y-TZP ceramic. Discs were manufactured according to ISO-6872:2008 for biaxial flexure testing (diameter: 15 mm; thickness: 1.2 mm) and randomly assigned considering two factors "grinding" and "aging": C- control (as-sintered); CA- control + aging; G- ground; GA- ground + aging. Grinding was carried out with coarse diamond burs under water-cooling. Aging protocols consisted of: autoclave (134°C, 2 bars pressure, 20 hours), followed by storage for 365 days (samples were kept untouched at room temperature), and by mechanical cycling (106 cycles by 20 Hz under a load of 50% from the biaxial flexure monotonic tests). Flexural fatigue strengths (20,000 cycles; 6 Hz) were determined under sinusoidal cyclic loading using staircase approach. Additionally, surface topography analysis by FE-SEM and phase transformation analysis by X-ray Diffractometry were performed. Dixon and Mood methodology was used to analyze the fatigue strength data. Grinding promotes alterations of topographical pattern, while aging apparently did not alter it. Grinding triggered t-m phase transformation without impacting the fatigue strength of the Y-TZP ceramic; and aging promoted an intense t-m transformation that resulted in a toughening mechanism leading to higher fatigue strength for as-sintered condition, and a tendency of increase for ground condition (C < CA; G = GA). It concludes that grinding and aging procedures did not affect deleteriously the fatigue strength of the evaluated Y-TZP ceramic, although, it promotes surface topography alterations, except to aging, and t-m phase transformation.
本研究旨在探究研磨和多刺激老化对Y-TZP陶瓷疲劳强度、表面形貌及相变的影响。根据ISO-6872:2008制造圆盘用于双轴弯曲测试（直径：15毫米；厚度：1.2毫米），并考虑“研磨”和“老化”两个因素将其随机分组：C-对照组（烧结态）；CA-对照组+老化；G-研磨组；GA-研磨组+老化。研磨在水冷条件下使用粗金刚石车针进行。老化方案包括：高压釜处理（134°C，2巴压力，20小时），随后储存365天（样品在室温下保持原状），以及机械循环（在双轴弯曲单调测试50%载荷下以20赫兹进行106次循环）。使用阶梯法在正弦循环载荷下测定弯曲疲劳强度（20,000次循环；6赫兹）。此外，通过场发射扫描电子显微镜进行表面形貌分析，通过X射线衍射仪进行相变分析。采用狄克逊和穆德方法分析疲劳强度数据。研磨会促进表面形貌图案的改变，而老化显然不会改变它。研磨引发了t-m相变，但未影响Y-TZP陶瓷的疲劳强度；老化促进了强烈的t-m相变，导致一种增韧机制，使得烧结态的疲劳强度更高，研磨态有增加的趋势（C < CA；G = GA）。研究得出结论，尽管研磨和老化过程会促进表面形貌改变（老化除外）以及t-m相变，但并未对所评估的Y-TZP陶瓷的疲劳强度产生有害影响。
