Studies on the testing methods for interfacial fracture toughness for evaluating the interfacial property of dental prostheses.

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Testing method for interfacial fracture toughness (modes I and II) between two different materials in a dental prosthesis, such as opaque porcelain/metal and adhesive resin/metal interfaces, was investigated by changing thickness, width, length and intial crack length of test specimen. Test specimen is of sandwich construction with an intial crack. In mode I testing, the test speciman was loaded by using two square cross-sectional block with a hole for loading bonded on test specimen end. And the crack length was measured by using a traveling microscope in conjunction with the measurement of the marginal load and crack opening displacement. Mode II testing was done by 3-point bending test. From their results of measurement, both values of interfacial fracture toughness was obtained. Results obtained are as follows. In case of the opaque porcelain/metal test specimen, its thickness of 0.3-0.5mm and its width of 3-5mm were appliciated, and its length was enough in region of 30-40mm. Initial crack length in region of 8-10mm was reasonable. Testing speed of 0.05mm/min was appreciated. As reference data, interfacial fracture toughness of this test specimen was about 15j/m^2. Next, in adhesive resin/metal test specimen, its thickness in region of 1.5-2.0mm was reasonable because the values of fracture toughness were shown for 400-500j/m^2. Width of 5mm was good than that of 10mm considering the procedure of adhesion. Length was 50mm only. By the way, thickness of adhesive resin layr was about 70mum. Initial crack length of 15-20mm was good because th crack length propagated was comparatively easy to measure. Therefore, in order to evaluate the interfacial property, it was recognized that such the testing methods for fracture toughness were more effective.