Department of Conservative and Preventive Dentistry, Academic Centre for Dentistry Amsterdam, Amsterdam, The Netherlands.
Dent Mater. 2013 Oct;29(10):1020-5. doi: 10.1016/j.dental.2013.07.008. Epub 2013 Jul 31.
A high-viscosity consistency of the glass-ionomer cement (GIC) may lead to poor adaptation into the cavity. The use of a flowable GIC layer seemed to improve its adaptation in approximal restorations in vitro. In this study we assessed the flexural strength of a two-layered GIC, using a flowable GIC as a liner (two-layer technique). Additionally, finite element analysis on standardized bar-shaped models and on a representative tooth model was performed to rationalize the obtained results.
The flexural strength and Young's modulus were calculated from the results of a three-point-bending test. Bar-shaped specimens were prepared either with a conventional GIC, with a flowable GIC (powder/liquid ratio 1:2), or with two-layers (either with the flowable layer down or on the top of the specimen). Three dimensional FEA models of the bar-shaped specimens and a model of tooth 46 provided information on the stress distribution of each component of the specimen and on the restoration.
The apparent flexural strength and Young's modulus of both two-layered groups were significantly lower than that of the conventional group. FEA showed that the layers of the two-layer specimens with the flowable GIC down separated from each other under load. The tooth model showed better stress distribution for the two-layer restorations.
The two-layer GIC showed inferior flexural strength, which might be explained by the detachment of the layers under load. Nevertheless the tooth model showed that the two-layer GIC provides a lower stress concentration on the occlusal surface of the material.
玻璃离子水门汀（GIC）的高粘度一致性可能导致其在窝洞内适应性差。使用可流动性 GIC 层似乎可以改善其在体外近中修复体中的适应性。本研究通过使用可流动性 GIC 作为衬层（双层技术）来评估双层 GIC 的弯曲强度。此外，还对标准化棒状模型和代表性牙齿模型进行了有限元分析，以合理化所得结果。
通过三点弯曲试验的结果计算弯曲强度和杨氏模量。棒状试件采用常规 GIC、可流动性 GIC（粉液比 1:2）或双层（可流动性层位于试件底部或顶部）制备。棒状试件和 46 号牙模型的三维有限元分析模型提供了关于试件和修复体每个组成部分的应力分布的信息。
两个双层组的表观弯曲强度和杨氏模量明显低于常规组。有限元分析表明，在载荷下，具有可流动性 GIC 层的双层试件的层彼此分离。牙齿模型显示双层修复体具有更好的应力分布。
双层 GIC 的弯曲强度较低，这可能是由于在载荷下各层分离所致。然而，牙齿模型显示双层 GIC 可降低材料咬合面的应力集中。
