Doctoral student, Department of Dental Materials and Prosthodontics, Araraquara Dental School, São Paulo State University, Araraquara, São Paulo, Brazil.
Postdoctoral researcher, Department of Dental Materials and Prosthodontics, Araraquara Dental School, São Paulo State University, Araraquara, São Paulo, Brazil.
J Prosthet Dent. 2017 Jul;118(1):61-68. doi: 10.1016/j.prosdent.2016.09.026. Epub 2016 Dec 23.
Despite improvements in computer-aided design and computer-aided manufacturing (CAD-CAM) systems, grinding during either laboratory procedures or clinical adjustments is often needed to modify the shape of 3 mol(%) yttria-tetragonal zirconia polycrystal (3Y-TZP) restorations. However, the best way to achieve adjustment is unclear.
The purpose of this in vitro study was to evaluate the microstructural and crystallographic phase changes, flexural strength, and Weibull modulus of a 3Y-TZP zirconia after grinding with or without water cooling and regeneration firing.
Ninety-six bar-shaped specimens were obtained and divided as follows: as-sintered, control; as-sintered with regeneration firing; grinding without water cooling; grinding and regeneration firing with water cooling; and grinding and regeneration firing. Grinding (0.3 mm) was performed with a 150-μm diamond rotary instrument in a high-speed handpiece. For regeneration firing, the specimens were annealed at 1000°C for 30 minutes. The crystalline phases were evaluated by using x-ray powder diffraction. A 4-point bending test was conducted (10 kN; 0.5 mm/min). The Weibull modulus was used to analyze strength reliability. The microstructure was analyzed by scanning electron microscopy. Data from the flexural strength test were evaluated using the Kruskal-Wallis and Dunn tests (α=.05).
Tetragonal-to-monoclinic phase transformation was identified in the ground specimens; R regeneration firing groups showed only the tetragonal phase. The median flexural strength of as-sintered specimens was 642.0; 699.3 MPa for as-sintered specimens with regeneration firing; 770.1 MPa for grinding and water-cooled specimens; 727.3 MPa for specimens produced using water-cooled grinding and regeneration firing; 859.9 MPa for those produced by grinding; and 764.6 for those produced by grinding and regeneration firing; with statistically higher values for the ground groups. The regenerative firing did not affect the flexural strength. Weibull modulus values ranged from 5.3 to 12.4. The SEM images showed semicircular cracks after grinding.
Adjustments by grinding in 3Y-TZP frameworks should be performed with water cooling, and regeneration firing should be undertaken to obtain a more reliable material.
尽管计算机辅助设计和计算机辅助制造（CAD-CAM）系统有所改进，但在实验室程序或临床调整过程中，经常需要研磨来修改 3 摩尔（%）氧化钇四方氧化锆多晶（3Y-TZP）修复体的形状。然而，实现调整的最佳方法尚不清楚。
本体外研究的目的是评估研磨后（有或没有水冷和再生烧制）3Y-TZP 氧化锆的微观结构和结晶相变化、弯曲强度和威布尔模数。
获得 96 个条形样本并进行如下分组：烧结后，对照组；烧结后再生烧制；无水冷研磨；水冷研磨和再生烧制；以及研磨和再生烧制。研磨（0.3mm）使用高速手持设备中的 150μm 金刚石旋转仪器进行。对于再生烧制，将样品在 1000°C 下退火 30 分钟。通过 X 射线粉末衍射评估晶体相。进行四点弯曲试验（10kN；0.5mm/min）。使用威布尔模数分析强度可靠性。通过扫描电子显微镜分析微观结构。使用 Kruskal-Wallis 和 Dunn 检验（α=.05）评估弯曲强度试验的数据。
在研磨后的样品中鉴定出四方相向单斜相的转变；R 再生烧制组仅显示四方相。烧结后样品的中值弯曲强度为 642.0；烧结后再生烧制的样品为 699.3MPa；水冷研磨的样品为 770.1MPa；水冷研磨和再生烧制的样品为 727.3MPa；研磨的样品为 859.9MPa；研磨和再生烧制的样品为 764.6MPa；研磨组的数值更高。再生烧制不会影响弯曲强度。威布尔模数值范围为 5.3 至 12.4。SEM 图像显示研磨后出现半圆形裂纹。
在 3Y-TZP 框架中进行调整时应进行水冷研磨，并且应进行再生烧制以获得更可靠的材料。
