Microstructure, hardness, corrosion resistance and porcelain shear bond strength comparison between cast and hot pressed CoCrMo alloy for metal–ceramic dental restorations

By Henriques, B.; Soares, D. & Silva, F.S.
Published in Journal of the Mechanical Behavior of Biomedical Materials NULL 2012

Abstract

Objectives: The purpose of this study was to compare the microstructure, hardness, corrosion resistance and metal–porcelain bond strength of a CoCrMo dental alloy obtained by two routes, cast and hot pressing. Methods: CoCrMo alloy substrates were obtained by casting and hot pressing. Substrates’ microstructure was examined by the means of Optical Microscopy (OM) and by Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). Hardness tests were performed in a microhardness indenter. The electrochemical behavior of substrates was investigated through potentiodynamic tests in a saline solution (8g NaCl/L). Substrates were bonded to dental porcelain and metal–porcelain bond strength was assessed by the means of a shear test performed in a universal test machine (crosshead speed: 0.5 mm/min) until fracture. Fractured surfaces as well as undestroyed interface specimens were examined with Stereomicroscopy and SEM-EDS. Data was analyzed with Shapiro-Wilk test to test the assumption of normality. The t-test ( p < 0.05 ) was used to compare shear bond strength results. Results: Cast specimens exhibited dendritic microstructures whereas hot pressed specimens exhibited a typical globular microstructure with a second phase spread through the matrix. The hardness registered for hot pressed substrates was greater than that of cast specimens, 438±24HV/1 and 324±8HV/1, respectively. Hot pressed substrates showed better corrosion properties than cast ones, i.e. higher OCP; higher corrosion potential (Ecorr) and lower current densities (icorr). No significant difference was found ( p < 0.05 ) in metal–ceramic bond strength between cast (116.5±6.9 MPa) and hot pressed (114.2±11.9 MPa) substrates. The failure type analysis revealed an adhesive failure for all specimens. Significance: Hot pressed products arise as an alternative to cast products in dental prosthetics, as they impart enhanced mechanical and electrochemical properties to prostheses without compromising the metal–ceramic bond strength.

Read Article » Back