Influence of preoxidation cycle on the bond strength of CoCrMoSi–porcelain dental composites

The purpose of this study was to evaluate the effect of preoxidation cycle on the shear bond strength (SBS) of CoCrMoSi alloy–porcelain dental composites. The porcelain was fired onto three types of metal surfaces: non-preoxidized, preoxidized and, preoxidized followed by grinding. The bond strength of metal–porcelain composites was investigated by the means of a shear test. The metal–ceramic interfaces and the fractured surfaces were analyzed using Optical Microscopy, Stereomicroscopy and SEM/EDS. Data was analyzed with Shapiro–Wilk test to test the assumption of normality. The t-test was used to compare shear bond strength results (p < 0.05). The analysis of the three types of surfaces was performed prior to porcelain firing. It was also performed a complementary analysis of an alumina-blasted preoxidized CoCrMoSi surface. The greater metal–porcelain adhesion was obtained for non-preoxidized specimens. eoxidized specimens showed significantly (p < 0.05) higher shear bond strength than preoxidized/ground specimens, 115.5 ± 7.5 MPa and 74.8 ± 8.5 MPa, respectively. Porcelain showed no adhesion to preoxidized specimens. All preoxidized specimens exhibited adhesive failure type while non-preoxidized presented both adhesive and mixed failure types. Preoxidation heat treatment revealed a detrimental effect on the adhesion of CoCrMoSi–porcelain composites for dental restorations. Hence, in order to enhance CoCrMoSi–porcelain adhesion, the preoxidation heat treatment conditions, as performed in this study, should not be performed.