Effect of Ceramic Veneering on the Metallurgical Properties of Cobalt-Chromium Alloys Fabricated Using Different Techniques.

This study was designed to assess the interface between ceramic and cobalt-chromium (Co-Cr) and to detect changes in the alloys microstructure after ceramic layering. Thirty disks (n = 36) were fabricated from cobalt-chromium (Co-Cr) alloys, cast, milled, and selective laser melting (SLM) (n = 12 in each group). Half of each group (n = 5) were observed as initially fabricated. The remaining disks were ceramic veneered. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were used to observe the morphology and chemical-analysis of the materials. Non-veneered disks were submitted to ceramic firing protocol without ceramic. X-ray diffraction (XRD) and atomic force microscope (AFM) were used to study the crystalline structure and surface roughness of the specimens. The alloys' microstructure was observed before and after ceramic veneering in each group. The General Linear Model was used to assess the means differences among groups, mainly grain size and surface roughness. The mean difference is significant at the 0.05 level. Intimate bonding interface between Co-Cr and ceramic was observed on SEM images. In milled Co-Cr, the ceramic veneering led to a significant reduction in grain sizes (P = 0.017), but to an increase in the cast and SLM groups (P = 0.012). A significant increase in the surface roughness of cast Co-Cr (P = 0.031) and SLM (P = 0.005) resulted from ceramic veneering. XRD analysis showed differences in the crystalline structure after porcelain veneering in cast and SLM Co-Cr. Co-Cr showed an intimate interface with ceramic. Unlike Co-Cr cast and SLM, milled Co-Cr attained a stable and final crystal arrangement upon sintering. Presintered materials showed fine homogenous surface.