Adjunct Faculty, Division of Operative Dentistry and Biomaterials, Department of Restorative Sciences, University of North Carolina, Chapel Hill, NC; Assistant Professor, Department of Conservative Dentistry, University of Jordan, Amman, Jordan.
Professor, Division of Operative Dentistry and Biomaterials, Department of Restorative Sciences, University of North Carolina, Chapel Hill, NC.
J Prosthet Dent. 2020 Apr;123(4):635-640. doi: 10.1016/j.prosdent.2019.05.012. Epub 2019 Aug 2.
A direct relationship has been reported between yttria concentration and translucency in zirconia restorations. However, increased yttria concentration also increases the cubic phase of the zirconia, which reduces its strength. The effect of increased yttria content on the fracture resistance of zirconia as a function of material thickness after fatigue testing requires evaluation.
The purpose of this in vitro study was to use the biaxial flexural test to evaluate the effect of yttria concentration on the mean fracture load (N) before and after fatiguing and thermocycling as a function of zirconia thickness.
Disk-shaped specimens of 5 mol% yttria partially stabilized zirconia (5Y-PSZ, BruxZir Anterior Solid Zirconia) and 3 mol% yttria partially stabilized zirconia (3Y-PSZ, BruxZir Shaded Zirconia) were prepared to thicknesses of 1.2 and 0.7 mm. For each thickness, the biaxial flexural test was used to measure the fracture load (N) before and after fatigue testing, with 1.2 million cycles at a 110-N load and simultaneous thermocycling at 5 °C to 55 °C (n=20). The data were analyzed by repeated-measures ANOVA (α=.05).
Yttria concentration, thickness, and exposure to fatiguing had a statistically significant effect on the mean biaxial flexural load (yttria concentration: P<.001; thickness: P<.001; fatiguing: P=.004 for the 3Y-PSZ). One of the major findings in this study was that 30% of the 1.2-mm-thick 5Y-PSZ specimens and 80% of the 0.7-mm-thick 5Y-PSZ specimens fractured during fatiguing. All specimens of the 3Y-PSZ groups survived the fatiguing protocol. The 3Y-PSZ groups had statistically significant higher flexural loads than the 5Y-PSZ groups. The 1.2-mm thickness groups had statistically significant higher flexural loads than the 0.7-mm thickness groups.
Yttria concentration had a significant effect on the strength of zirconia. 5Y-PSZ was considerably less resistant to fracture before and after fatigue testing than 3Y-PSZ. Decreasing the thickness of zirconia reduces its fracture resistance, regardless of the zirconia type.
已报道氧化钇浓度与氧化锆修复体透明度之间存在直接关系。然而，氧化钇浓度的增加也会增加氧化锆的立方相，从而降低其强度。需要评估增加氧化钇含量对疲劳试验后氧化锆断裂阻力的影响，以及材料厚度的关系。
本体外研究使用双向弯曲试验，评估氧化钇浓度对疲劳和热循环前后氧化锆厚度为 1.2 和 0.7 毫米的 5 摩尔%氧化钇部分稳定氧化锆（5Y-PSZ，BruxZir Anterior Solid Zirconia）和 3 摩尔%氧化钇部分稳定氧化锆（3Y-PSZ，BruxZir Shaded Zirconia）的平均断裂载荷（N）的影响。
制备厚度为 1.2 和 0.7 毫米的 5 摩尔%氧化钇部分稳定氧化锆（5Y-PSZ，BruxZir Anterior Solid Zirconia）和 3 摩尔%氧化钇部分稳定氧化锆（3Y-PSZ，BruxZir Shaded Zirconia）的圆盘状试件。对于每种厚度，使用双向弯曲试验测量疲劳试验前后的断裂载荷（N），在 110-N 载荷下进行 120 万次循环，同时在 5°C 至 55°C 下进行热循环（n=20）。数据分析采用重复测量方差分析（α=.05）。
氧化钇浓度、厚度和疲劳暴露对平均双向弯曲载荷有统计学显著影响（氧化钇浓度：P<.001；厚度：P<.001；疲劳：P=.004 对于 3Y-PSZ）。本研究的一个主要发现是，30%的 1.2 毫米厚 5Y-PSZ 试件和 80%的 0.7 毫米厚 5Y-PSZ 试件在疲劳过程中发生断裂。所有 3Y-PSZ 组的试件都能耐受疲劳方案。3Y-PSZ 组的弯曲载荷明显高于 5Y-PSZ 组。1.2 毫米厚度组的弯曲载荷明显高于 0.7 毫米厚度组。
氧化钇浓度对氧化锆的强度有显著影响。5Y-PSZ 在疲劳前后的抗断裂能力明显低于 3Y-PSZ。无论氧化锆类型如何，降低氧化锆的厚度都会降低其断裂阻力。
