Skjold Anneli, Schriwer Christian, Øilo Marit
Department of Clinical Dentistry, Faculty of Medicine, University of Bergen, Bergen, Norway.
Eur J Oral Sci. 2019 Feb;127(1):89-96. doi: 10.1111/eos.12593. Epub 2018 Nov 22.
Zirconia-based restorations are showing an increase as the clinicians' preferred choice at posterior sites because of the strength and esthetic properties of such restorations. However, all-ceramic restorations fracture at higher rates than do metal-based restorations. Margin design is one of several factors that can affect the fracture strength of all-ceramic restorations. The aim of this study was to assess the effect of preparation and crown margin design on fracture resistance. Four groups of bilayer zirconia crowns (with 10 crowns in each group) were produced by hard- or soft-machining technique, with the following four different margin designs: chamfer preparation (control); slice preparation; slice preparation with an additional cervical collar of 0.7 mm thickness; and reduced occlusal thickness (to 0.4 mm) on slice preparation with an additional cervical collar of 0.7 mm thickness. Additionally, 10 hard-machined crowns with slice preparation were veneered and glazed with feldspathic porcelain. In total, 90 crowns were loaded centrally in the occlusal fossa until fracture. The load at fracture was higher than clinically relevant mastication loads for all preparation and margin designs. The crowns on a chamfer preparation fractured at higher loads compared with crowns on a slice preparation. An additional cervical collar increased load at fracture for hard-machined crowns.
由于基于氧化锆的修复体具有强度和美学特性，这类修复体在临床上作为后牙部位的首选正呈增长趋势。然而，全瓷修复体的断裂率高于金属基修复体。边缘设计是影响全瓷修复体断裂强度的几个因素之一。本研究的目的是评估预备体和冠边缘设计对抗折性的影响。通过硬加工或软加工技术制作了四组双层氧化锆冠（每组10个冠），采用以下四种不同的边缘设计：肩台预备（对照）；片切预备；片切预备并带有额外0.7毫米厚的颈部边缘；在片切预备并带有额外0.7毫米厚的颈部边缘的基础上，将咬合面厚度减小至0.4毫米。此外，对10个采用片切预备的硬加工冠进行了长石质瓷贴面和上釉处理。总共90个冠在咬合窝中心加载直至断裂。对于所有的预备体和边缘设计，断裂时的载荷均高于临床相关的咀嚼载荷。与片切预备的冠相比，采用肩台预备的冠在更高的载荷下断裂。额外的颈部边缘增加了硬加工冠的断裂载荷。
