Objectives

The dental market moves towards high-translucency monolithic zirconia dental crowns, which are usually placed either with – or without – a thin glaze layer. The microstructural features and the mechanical performances of these materials are still controversial, as well as their susceptibility to aging. This paper aims at studying these aspects in the current generation of zirconia dental crowns showing different degrees of translucency.

Methods

Four different commercial zirconia materials were investigated, including one standard ‘full-strength’ 3Y-TZP and three grades with improved translucency. The microstructural features (phase composition and assemblage, grain size) were carefully studied, as well as mechanical properties (biaxial bending strength and indentation toughness), translucency and aging behavior (in autoclave at 134 °C). Aging was conducted on crowns with and without glaze to better represent clinical uses.

Results

Important differences are found in terms of microstructures among the materials in terms of cubic phase content and yttria in the tetragonal phase, leading to different optical, mechanical and aging resistance properties. We show that higher cubic phase content leads to better translucency and stability in water steam, but at the expense of strength and toughness. A compromise is always inevitable between translucency and aging resistance on one side and mechanical properties on the other side.

Significance

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Even so called ‘high translucent’ zirconia ceramics tested in this work should be considered as medium translucency materials.

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Aging occurs in standard state-of-the-art dental zirconia and glazing does not fully avoid this issue. However, aging did not compromise strength even after prolonged duration.

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Aging is null in the ‘highly translucent’ zirconia grades but at the expense of strength, which is then comparable to glass-ceramics.

中文翻译：

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用于整体式牙冠应用的不同氧化钇稳定的氧化锆陶瓷的耐老化性，机械性能和半透明性

目标

牙科市场正朝着高透明度的整体式氧化锆牙冠转移，这些牙冠通常带有（或不带有）薄釉层。这些材料的微观结构特征和机械性能以及它们对老化的敏感性仍然是有争议的。本文旨在研究显示不同程度的半透明性的当前一代氧化锆牙冠中的这些方面。

方法

研究了四种不同的商业氧化锆材料，包括一种标准的“全强度” 3Y-TZP和三种具有改进的半透明性的材料。仔细研究了微观结构特征（相组成和组装，晶粒尺寸），以及机械性能（双轴弯曲强度和压痕韧性），半透明性和时效行为（在134°C的高压釜中）。在有釉和无釉的牙冠上进行时效处理，以更好地代表临床用途。

结果

在材料的微观结构方面，在立方相含量和四方相中的氧化钇方面发现了重要差异，从而导致了不同的光学，机械和耐老化性能。我们表明，较高的立方相含量会导致水蒸汽中的半透明性和稳定性更好，但会以强度和韧性为代价。在一方面的半透明性和耐老化性与另一方面的机械性能之间总是不可避免的折衷。

意义

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即使在这项工作中测试的所谓“高半透明”氧化锆陶瓷也应视为中等半透明材料。

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标准的最新技术牙科氧化锆会发生老化，而上光并不能完全避免此问题。但是，即使长时间使用，老化也不会影响强度。

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在“高半透明”的氧化锆中，老化是无效的，但强度却要与玻璃陶瓷相媲美。