Microstructural, mechanical, ionic release and tarnish resistance characterization of porcelain fused to metal Co-Cr alloys manufactured via casting and three different CAD/CAM techniques.

PURPOSE: To perform a comparative analysis of the microstructure, porosity, mechanical properties, corrosion, and tarnish resistance of Co-Cr alloys prepared by casting and three different computer aided designed/computer aided manufacturing (CAD/CAM) techniques.

METHODS: Four groups of metallic specimens were prepared, one each by conventional casting (CST), milling (MIL), selective laser melting (SLM), and milling soft metal (MSM). Ten samples were tested by X-rays, after which their microstructure and elemental composition were tested by scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX) analysis. Martens hardness (HM) and elastic index (ηIT ) were determined by instrumented indentation testing (IIT), while modulus of elasticity (E) was determined by three-point bending. Corrosion measurements were tested according to International Organization for Standardization (ISO) 10271. The electrolytes were analyzed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The results were analyzed by one-way ANOVA and Holm-Sidak's multiple-comparison test (α=0.05).

RESULTS: The CST group illustrated internal flaws while all CAD/CAM group samples were found to be free of them. No statistically significant differences were identified among groups in their elemental composition. SLM showed the highest HM, followed by the MIL, CST, and MSM. Elastic index showed significant differences among all groups, with CST showing the lowest and SLM the highest values. SLM showed the highest elastic modulus values, followed by MSM, MIL, and CST. No significant differences were found in ionic release among groups. No surface deterioration after static and cyclic tarnish testing was determined.

CONCLUSIONS: The manufacturing procedure significantly affects the microstructure, porosity, and mechanical properties of Co-Cr alloys. In contrast, ionic release and tarnish resistance are independent of the manufacturing technique used.