American Dental Association Foundation, Paffenbarger Research Center, National Institute of Standards and Technology, Gaithersburg, MD, USA.
Dent Mater. 2012 May;28(5):502-11. doi: 10.1016/j.dental.2011.12.005. Epub 2012 Jan 2.
To identify the strength limiting flaws in in vitro test specimens of a fine-grained feldspathic dental porcelain.
Four-point flexural strengths were measured for 26 test specimens. The fracture origin site of every test specimen was studied using stereoptical and scanning electron microscopy. A fractographically labeled Weibull strength distribution graph was prepared.
The complex microstructure of the feldspathic dental porcelain included a variety of feldspars, tridymite, and a feldspathoid as well as pores/bubbles and residual glass. The relatively high flexural strength is due in part to the fine grain size. Fractography revealed five flaw types that controlled strength: baseline microstructural flaws, pores/bubbles, side wall grinding damage, corner machining damage, and inclusions. The baseline microstructural flaws probably were clusters of particular crystalline phases.
Each flaw type probably has a different severity and size distribution, and hence has a different strength distribution. The Weibull strength distribution graph blended the strength distributions of the five flaw types and the apparent good fit of the combined data to a unimodal strength distribution was misleading. Polishing failed to eliminate deeper transverse grinding cracks and corner damage from earlier preparation steps in many of the test pieces. Bend bars should be prepared carefully with longitudinal surface grinding whenever possible and edge chamfers should be carefully applied. If the grinding and preparation flaws were eliminated, the Weibull modulus for this feldspathic porcelain would be greater than 30. Pores/bubbles sometimes controlled strength, but only if they touched each other or an exposed surface. Isolated interior bubble/pores were harmless.
确定细晶粒长石质牙科瓷体外试验标本中的强度限制缺陷。
对 26 个试验标本进行四点弯曲强度测量。使用立体显微镜和扫描电子显微镜研究每个试验标本的断裂起源部位。制备了带有断裂标记的威布尔强度分布图表。
长石质牙科瓷的复杂微观结构包括各种长石、方石英和类沸石以及孔隙/气泡和残余玻璃。相对较高的弯曲强度部分归因于细晶粒尺寸。断裂形貌揭示了控制强度的五种缺陷类型：基线微观结构缺陷、孔隙/气泡、侧壁磨削损伤、角部加工损伤和夹杂物。基线微观结构缺陷可能是特定结晶相的簇。
每种缺陷类型可能具有不同的严重程度和尺寸分布，因此具有不同的强度分布。威布尔强度分布图表融合了五种缺陷类型的强度分布，并且组合数据与单峰强度分布的良好拟合具有误导性。在许多试验件中，抛光未能消除更深的横向磨削裂纹和来自早期制备步骤的角部损伤。只要可能，应仔细进行带有纵向表面磨削的弯曲棒制备，并仔细应用边缘倒角。如果消除了磨削和制备缺陷，这种长石质瓷的威布尔模数将大于 30。孔隙/气泡有时会控制强度，但仅当它们相互接触或与暴露表面接触时才会如此。孤立的内部气泡/孔隙是无害的。
