ABSTRACT
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.
Subject(s)
Chromium Alloys , Color , Computer-Aided Design , Dental Casting Technique , Dental Porcelain/chemistry , Materials Testing , Metal Ceramic Alloys/chemistry , Porosity , Corrosion , Ions , Surface PropertiesABSTRACT
BACKGROUND/PURPOSE: The mechanical properties of pure gold (Au) are modified by thermal treatments. Thus, the aim of this study was to evaluate the effect of porcelain firing on the elemental composition, microstructure, and mechanical properties of electroformed Au crowns. MATERIALS AND METHODS: Twenty electroformed Au specimens were prepared and divided into two groups. The first group did not receive any treatment (ELEC), and the other group was subjected to porcelain firing (PFIR). After metallographic grinding and polishing, all were investigated by scanning electron microscopy, and elemental composition was determined using energy-dispersive X-ray spectroscopy (EDX). Internal porosity was identified by quantitative image processing. Mechanical properties including Martens hardness (HM), indentation modulus (E IT), elastic index (η ΙΤ), and Vickers hardness (HV) were determined by instrumented indentation testing. The results were statistically analyzed using unpaired t test (α = 0.05). RESULTS: A random distribution of tiny pores was identified in cross section, but no significant difference was found between groups [ELEC (%), 0.24 ± 0.13; PFIR (%), 0.31 ± 0.7]. Backscattered electron images revealed no mean atomic number contrast for both groups, indicating that the material was a single-phase alloy, whereas no differences between groups were identified in the composition of C, N, O, and Au after EDX analysis. By contrast, all mechanical properties tested showed statistically significant differences, with the PFIR group showing significantly lower HM, η ΙΤ, and HV but increased E IT compared with those of the ELEC group. CONCLUSION: Although microstructure and elemental composition of electroformed Au crowns remain unchanged, the mechanical properties are significantly affected by the thermal treatment of porcelain firing.
