Uniaxial/biaxial flexure strengths and elastic properties of resin-composite block materials for CAD/CAM

Abstract

Objective. Comparing strengths under different loading conditions provides useful information on the mechanical behaviour of restorative materials under multiaxial masticatory loading in the oral cavity. The aims of this study was to investigate the flexural strengths and the reliability of resin-composite blocks for CAD/CAM by uniaxial and biaxial flexure tests and to compare the elastic properties measured by different methods including digital image correlation (DIC). Methods. Four resin-composite blocks for CAD/CAM, namely, VE (Vita Enamic), LU (Lava Ultimate), MD (Mazic Duro), and CS (Cerasmart), were investigated. Beam specimens (4.0 x 1.4 x 18.0 mm(3)) and disks (12-14 mm phi x 1.5 mm) were prepared to determine the uniaxial (three-point bending) and biaxial (ball-on-ring, BOR) flexural strengths and flexural moduli. A compression test (8 x 4 x 18 mm(3)) with DIC analysis was utilized to measure the elastic modulus and Poisson's ratio. Data were analysed by a 2-parameter Weibull function and ANOVA with Scheffe's test. Results. The mean uniaxial and biaxial strengths and Weibull moduli of the specimen groups were as follows: uniaxial VE (140.1 f 7.0, 24.1), LU (159.1 1 6.3, 31.5), MD (144.9 1 13.3, 13.6), and CS (165.4 1 16.9, 11.2) and biaxial VE (153.6 1 10.4, 19.0), LU (231.0 1 29.3, 9.7), MD (148.9 1 23.8, 7.4), and CS (249.7 1 22.4, 13.8). Although the ranking of both sets of strength data remained unchanged, the strength reliability was significantly affected by the loading; the Weibull moduli of the specimens decreased when they were subjected to biaxial tests (except for that of CS). The elastic modulus values of the materials varied significantly under the different test loadings, although they were in the same order regardless of the test method: VE approximate to LU MD > CS. The DIC technique yielded elastic moduli that were in good agreement with those measured by the uniaxial flexure test. Significance. The flexural strength, reliability, and elastic modulus of resin-composite block materials differed with the uniaxial and biaxial flexural loading and the test method. The different behaviours under both loadings should be considered in the evaluation of the mechanical performance of those materials. (C) 2018 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.