Fujishima A, Ferracane J L
Department of Oral Biomaterials and Technology, Showa University, Tokyo, Japan.
Dent Mater. 1996 Jan;12(1):38-43. doi: 10.1016/S0109-5641(96)80062-5.
Investigators have reported on the measurement of fracture toughness (K(lc)) of dental composites using a variety of testing methods. However, fracture toughness has been shown to be dependent upon several variables, including crack-tip sharpness and specimen geometry. This study was designed to compare the fracture toughness values obtained for two experimental and three commercial posterior composites, using four popular testing methods.
The four methods for testing fracture toughness included single-edge notched, compact tension, short rod with chevron notch and double torsion. The results were compared by ANOVA and Tukey's multiple comparison test (p < or = 0.05).
The values obtained from the short rod test were significantly higher than those from the three other tests. Evaluation of the load-deflection curves and fracture surfaces suggested that the data for this test may not have been valid because a stable crack growth region could not be identified. In general, the fracture toughness results obtained from the double torsion test were lower than values obtained from the single-edge notched and compact tension methods. The double torsion test was the most difficult to conduct, resulting in only a 50% success rate.
The double torsion test, though possibly the most technique-sensitive of the four fracture toughness methods evaluated provides the most information about crack initiation and propagation and may be most indicative of the true fracture toughness of dental composites.
研究人员已报道了使用多种测试方法测量牙科复合材料的断裂韧性（K(lc)）。然而，已表明断裂韧性取决于几个变量，包括裂纹尖端的尖锐度和试样几何形状。本研究旨在使用四种常用测试方法比较两种实验性和三种市售后牙复合材料获得的断裂韧性值。
测试断裂韧性的四种方法包括单边切口、紧凑拉伸、带人字形切口的短棒和双扭转。通过方差分析和Tukey多重比较检验（p≤0.05）对结果进行比较。
短棒测试获得的值明显高于其他三种测试的值。对载荷-挠度曲线和断裂表面的评估表明，该测试的数据可能无效，因为无法确定稳定的裂纹扩展区域。一般来说，双扭转测试获得的断裂韧性结果低于单边切口和紧凑拉伸方法获得的值。双扭转测试最难进行，成功率仅为50%。
双扭转测试虽然可能是所评估的四种断裂韧性方法中对技术最敏感的，但它提供了关于裂纹萌生和扩展的最多信息，可能最能表明牙科复合材料的真实断裂韧性。
