Sir John Walsh Research Institute, Faculty of Dentistry, University of Otago, Dunedin, New Zealand.
Dent Mater. 2011 Nov;27(11):1111-8. doi: 10.1016/j.dental.2011.08.003. Epub 2011 Sep 9.
The aim of this study was to evaluate the fracture toughness and surface residual stresses present in various pressable ceramics to zirconia resulting from cooling induced temperature gradients.
Indentation fracture toughness was used to evaluate the residual stress present in various pressable ceramics (Noritake CZR Press, Vita PM9, Wieland PressXzr and IPS e.max ZirPress) to zirconia when subjected to different cooling regimen. The cooling responses of two ceramics were evaluated by thermocouples embedded in the surface of the porcelains and at the porcelain-zirconia interface.
The effective K(c) results obtained by indentation tests confirmed the presence of surface residual compressive stress for all-ceramic systems subjected to different cooling procedures. The residual stresses were quantified from the change in the radial crack size and the values compared for each ceramic before pressing, pressed ceramic only and pressed ceramic veneered on zirconia, from fast to slow cooling rates. A significant level of residual stress was found in the materials before pressing. Slow cooling significantly reduced the formation of residual stress for all pressed ceramics. From data produced by the thermocouples it was found that 'slow cooling' generated the least temperature difference between inner and outer surfaces of porcelain. A direct relationship was found for the cooling induced temperature difference between the surfaces, and interface thermocouples, and magnitude of the surface residual stresses.
Leucite containing porcelains have higher intrinsic fracture toughness, and for all porcelains fast cooling generated significant residual stress within the veneering porcelain. To reduce development of residual stress, slow cool is recommended on the last heating cycle (e.g. glazing cycle).
本研究旨在评估不同可压陶瓷向氧化锆冷却诱导温度梯度产生的表面残余应力和断裂韧性。
采用压痕断裂韧性法评估不同可压陶瓷（Noritake CZR Press、Vita PM9、Wieland PressXzr 和 IPS e.max ZirPress）向氧化锆冷却时的残余应力。通过嵌入陶瓷表面和陶瓷-氧化锆界面的热电偶评估两种陶瓷的冷却响应。
压痕试验获得的有效 K(c)结果证实，所有陶瓷系统在不同冷却程序下均存在表面残余压应力。通过比较各陶瓷在压制前、仅压制陶瓷和压制陶瓷上覆氧化锆的径向裂纹尺寸变化来量化残余应力，从快速冷却到缓慢冷却速率。在压制前的材料中发现了相当大的残余应力水平。缓慢冷却显著降低了所有压制陶瓷残余应力的形成。从热电偶产生的数据中发现，“缓慢冷却”在瓷体内部和外部表面之间产生的温差最小。表面残余应力的大小与冷却引起的温差之间存在直接关系，与界面热电偶也存在直接关系。
含白榴石的陶瓷具有更高的固有断裂韧性，对于所有陶瓷，快速冷却会在贴面瓷中产生显著的残余应力。为了减少残余应力的发展，建议在最后一个加热周期（如上釉周期）中缓慢冷却。
