Comparison of the ceramic adherence to alloys fabricated by different manufacturing techniques using two bond strength tests.

Purpose: The objective of this study was to compare the shear bond strength (SBS) and Schwickerath (ST) tests for the adherence of ceramic to cobalt-chromium (Co-Cr) fabricated by different techniques, zirconia, and nickel chromium alloys.

Material and methods: Five different core/veneer combinations were prepared: Group SLM: selective laser melted Co-Cr; Group SM: soft milled Co-Cr; Group C: cast Co-Cr; Group Zi: soft milled zirconia; and Group Ni: cast nickel chromium, layered with ceramic. Disk-shaped specimens (diameter 15 mm, thickness 2 mm) with a ceramic thickness of 2 mm were prepared for SBS, and bars of 25 × 3 × 0.5 mm with applied ceramic of 8 × 3 mm for ST (N = 100 and n = 20/group). Only half of the specimens from each group were thermocycled (5-55°C/5000 times). SBS test was applied to all the disks, and ST to the bars. Two-parameter Weibull distribution values, including shape (m) and scale (σ0), were calculated.

Results: Thermal cycling had only a significant effect on SBS results for the SLM group (p = 0.017). A significant difference was found between testing techniques and materials (p < 0.001). The lowest value was reported for SLM in the SBS method (p < 0.001). Failure types were mostly mixed in SBS and adhesive in ST. The highest Weibull parameters were obtained for group C.

Conclusion: Both the testing methodology and the specimens manufacturing technique influenced the bond strength of ceramic to different alloys. The aging process influenced the results in the laser-sintered group in large specimens.