Comparative three-point bending flexural test of dental ceramics using standard and self-adjustable specimen support fixtures

Abstract

© 2020 The Japan Institute of Metals and Materials. The flexural strength of dental ceramic specimens was comparatively measured by using the standard fixture and the self-adjustable specimen support fixture which carefully prepared for this work. One hundred and twenty dental ceramic specimen bars fabricated in accordance with the BS EN ISO 6872 standard were ground, polished and classified into 6 groups with opposing surface parallelism differences of 0.00, 0.01, 0.02, 0.03, 0.04 and 0.05 mm. Each group contained 20 specimens which ten specimens were tested by using the standard fixture and the other ten specimens were tested by using the self-adjustable specimen support fixture. The flexural strength and Weibull modulus of both specimen groups were analyzed using two way analysis of variance (ANOVA) and Weibull analysis. The fracture surfaces of both specimen groups were investigated under the scanning electron microscope and analyzed for their fracture behavior. Results from the study found that the self-adjustable specimen support fixture for the three-point flexural test was able to improve the force distribution on the surface of specimens under test. As a result, the actual flexural strength of materials under test with the higher value and reliability was achieved. The flexural strength from this study was found to be comparable to that measured with the bi-axial test. The strength values increased significantly from 79.1 « 5.1 MPa to be 90.1 « 3.4 MPa when tested with the standard fixture and the self-adjustable specimen support fixture respectively. The 10% failure stress and Weibull modulus of specimens tested with the self-adjustable specimen support fixture also improved obviously. The fracture surface characteristics of specimens tested with the standard fixture indicated most crack origin occurred at the specimen edge. In the specimens tested with the self-adjustable specimen support, the crack origin was observed as the appearance of the arrest lines or Wallner lines at the inner area beyond the specimen edge.