Identificação da falha inicial de cerâmica simulando as condições do meio oral

Abstract

The objective of this study was to develop a testing method to detect the first acoustic signal related to the initial flaw of a glass-ceramic (IPS Empress CAD), as well as to compare the failure behavior observed with a monotonic compressive test and with fatigue. Fifty seven ceramic slices (1.5 x 8.3 x 8.4 mm) were produced by cutting CAD-CAM blocks and were cemented with resin cement over fiber-reinforced epoxi resin substrates (G10). For the monotonic test (n=27), the specimen were immersed in 37º C water and the load was applied by a G10 piston (3 mm diameter flat end), with cross-head speed of 0.5 mm/min, in a universal testing machine. An acoustic device was used during testing. For the fatigue test, a mechanical cycling machine was used (37º C water, 2Hz) (n=30). Two lifetimes were evaluated (1x 10 6 e 2 x 10 6 cycles) and the applied load was defined by the boundary technique. Fractography was performed with transillumination. Data were analyzed with Weibull analysis. Characteristic strength of 1615 N and Weibull modulus of 5.37 were obtained with the monotonic test. In fatigue, a 90% reduction of the initial fracture load was observed after cycling up to 2 million cycles. In addition, a reduction of 26% of the fracture load was reported when the number of cycles was extended from 1 million to 2 million. The most frequent failure mode was radial crack. It was concluded that the testing method was able to simulate the clinical failure behavior, with the flaw origin located in the inner surface of the ceramic, at the cementation interface. Fatigue testing affects the fracture load and failure mode of ceramic specimens.