Department of Clinical Dentistry, Faculty of Medicine, University of Bergen, Aarstadveien 19, Bergen N-5009, Norway.
J Dent. 2022 Oct;125:104271. doi: 10.1016/j.jdent.2022.104271. Epub 2022 Aug 27.
The aim of this retrieval study was to analyze the fracture features and identify the fracture origin of zirconia-based single crowns that failed during clinical use.
Thirty-five fractured single crowns were retrieved from dental practices (bi-layered, n = 15; monolithic, n = 20). These were analyzed according to fractographic procedures by optical and scanning electron microscopy to identify fracture patterns and fracture origins. The fracture origins were closely examined. The crown margin thickness and axial wall height were measured.
Three types of failure modes were observed: total fractures, marginal semilunar fractures, and incisal chippings. Most of the crowns (23) had fracture origins at the crown margin and seven of them had defects in the fracture origin area. The exact fracture origin was not possible to identify due to missing parts in four crowns. The crown wall thickness was 20% thinner and wall height 30% shorter in the fracture origin area compared to the opposite side.
The findings in this study show that fractography can reveal fracture origins and fracture modes of both monolithic and bi-layered dental zirconia. The findings indicate that the crown margin on the shortest axial wall is the most common fracture origin site.
Crown design factors such as material thickness at the margin, axial wall height and preparation type affects the risk of fracture. It is important to ensure that the crown margins are even and flawless.
本研究旨在分析临床使用失败的氧化锆基单冠的断裂特征，并确定断裂起源。
从牙科诊所中取出 35 个断裂的单冠（双层，n=15；整体式，n=20）。通过光学和扫描电子显微镜的断口分析程序对其进行分析，以确定断裂模式和断裂起源。仔细检查了断裂起源。测量了冠边缘厚度和轴向壁高度。
观察到三种失效模式：完全断裂、边缘半月形断裂和切缘崩裂。大多数冠（23 个）的断裂起源于冠边缘，其中 7 个在断裂起源区域有缺陷。由于四个冠的部分缺失，无法确定确切的断裂起源。与另一侧相比，断裂起源区域的冠壁厚度薄了 20%，壁高短了 30%。
本研究的结果表明，断口分析可以揭示整体式和双层牙科氧化锆的断裂起源和断裂模式。研究结果表明，最短轴向壁上的冠边缘是最常见的断裂起源部位。
冠设计因素，如边缘处的材料厚度、轴向壁高度和预备类型，都会影响断裂的风险。确保冠边缘均匀无瑕疵非常重要。
