Effect of surface treatment of milled cobalt–chromium alloy on shear bond strength to porcelain

Abstract

Background/aim Strong bond between metal and porcelain is essential for success and longevity of porcelain-fused-to-metal restorations. Therefore, the present study aimed to evaluate shear bond strength (SBS) between porcelain and CAD/CAM milled cobalt–chromium (Co–Cr) alloy treated by sandblasting, oxidation, and laser etching in comparison with cast alloy treatment. Materials and methods Co–Cr alloys were used for fabrication of sixty discs (2.5 mm thickness×10 mm diameters), which were split into half (n=30 each): group A, milled discs, and group B, conventional casting discs. Both groups were split into thirds (n=10) according to Co–Cr surface treatment: subgroup S, sandblasting (control); subgroup O, oxidation; and subgroup L, laser etching. Surface morphology of the samples was examined before and after surface treatments by scanning electron microscope. Feldspathic porcelain (3 mm thickness×5 mm diameter) was added to the Co–Cr discs (opaque, dentin, and enamel) and fired. SBS test (MPa) was carried out using material testing machine at crosshead speed of 0.5 mm/min till failure. The modes of failure were evaluated by scanning electron microscope and digital microscope. Statistics were performed by two-way analysis of variance (ANOVA), one-way ANOVA, Tukey post-hoc test, and t-test (P Results Two-way ANOVA results indicated insignificant differences in SBS among Co–Cr fabrication techniques (P=0.259). In contrast, significant differences were demonstrated between the different surface treatments (P Conclusion Bond between surface treated Co–Cr alloys and porcelain is independent of the fabrication technique. Laser etching recorded the least SBS among the tested surface treatments irrespective of the fabrication technique. All SBS values recorded in the present study were clinically acceptable.