Annual Scientific AODES Meeting location:Haasrode, Belgium date:11 May 2012
There are several ways to characterise the hydrothermally degraded layer in metastable tetragonal zirconia ceramics: X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The aim of this study is to compare different surface characterization methods to get a more profound understanding of the degradation process taking place in dental zirconia ceramics after exposure to a humid environment. Fully-sintered IPS e.max ZirCAD (Ivoclar-Vivadent) blocks were sliced into rectangular bars with an approximate volume of 15x5x3 mm3. Both the top and bottom surface of the specimen were mirror polished and analyzed by a θ-2θ XRD (Seifert3003TT, Seifert) in order to confirm that no monoclinic phase (m-phase) was present in the as-sintered ceramic. The low-temperature degradation test was performed at 134°C for 4 hours under 2 bar within a custom-made autoclave. θ-2θ XRD was applied to both the top and bottom surface of the degraded sample. The diffraction patterns were compared with those recorded using a grazing incident XRD. Fracture surfaces of the degraded samples were analysed by micro-Raman spectroscopy (XploRA, Horiba). Finally, a micro-structural analysis was performed using SEM. Before hydrothermal treatment, no m-phase could be detected. After degradation, θ-2θ XRD revealed the presence of approximately 22% m-phase within 8 μm of the sample. Grazing incident XRD showed that over 60% m-phase was present down to a depth of 2 μm below the sample surface, while the proportion m-phase significantly decreased from 3 μm below the surface. Micro-Raman analysis indicated that the m-phase content decreased quite rapidly below the degraded sample surface, and even 2 µm below the surface was nearly absent. SEM disclosed that the thickness of the degraded layer varied significantly over the sample surfaces. It can be concluded that the three methodologies tested allow to quantify and characterise the hydrothermally degraded zones in dental zirconia ceramics.