The aim of this study will be to characterize the microstructure of four dental ceramics obtained by CAD/CAM and evaluate their surcpetibility to stress corrosion under dynamics fatigue, with pre-cracked specimens. For the microstructural characterization, surface treatments will be made on the ceramics so that the diferent phases can be seen under SEM and chemical analysis can be performed with EDS. To evaluate the crystal patterns we will use XRD. 240 ceramic discs (12 mm de diâmetro e 1,2 mm de espessura) will be made of four ceramics: feldspathic ceramic (Vita Mark II, Vita Zahnfabrik, Bad Sackingen, Alemanha), hybrid ceramic (Vita Enamic, Vita Zahnfabrik, Bad Sackingen, Alemanha), lithium dissilicate ceramic (IPS e.max CAD, Ivoclar Vivadent, Barueri, São Paulo, Basil) and lithium silicate ceramic (Vita Suprinity, Vita Zahnfabrik, Bad Sackingen, Germany). Ten specimens will be indented on a Vickers hardness for evaluation of fracture toughness, crack meaurements e inert strenght calculation. The remaining specimens will be indented and submitted to five stressing rates (0,001; 0,01; 0,1; 1 e 10 MPa/s). The remaining specimens to determine the subcritical crack growth (SCG) parameters (n = susceptibility to SCG e J0 = inical crack velocity propagation). The log-log correlation of flexural strength and stress rate will be used to determine such parameters. SEM of the fractured specimens will be made to evaluate the crack interaction with the microstructure and the fracture characteristics of the materials.
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