The effect of heat treatment on the microstructure and mechanical properties of cobalt-chromium (Co-Cr) removable partial denture (RPD) frameworks fabricated by selective laser melting (SLM) is not well understood. The purpose of this in vitro study was to evaluate the suitability of SLM-fabricated Co-Cr alloys followed by heat treatment as a framework for RPDs by determining the microstructure and mechanical properties. Dumbbell specimens and RPD frameworks were fabricated by using SLM followed by heat treatment. The effects of the heat treatment on the microstructure were studied by using optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD). Tensile and insertion and removal tests were performed to study the mechanical responses of selective laser melting followed by heat treatment specimens, including the ultimate tensile strength (UTS), 0.2% yield strength (0.2% YS), elongation (E), and retentive forces. Specimens fabricated by using the traditional lost-wax process were used as a control (casting) group. X-ray diffraction indicated that the γ-face-centered cubic phase dominated SLM and selective laser melting followed by heat treatment specimens. Results from optical microscopy and SEM showed microstructural changes under different fabrication and postprocessing heat treatments; it was difficult to observe the grain boundary in the SLM group, whereas submicrometer-scale grains had formed in the selective laser melting followed by heat treatment group. The selective laser melting followed by heat treatment group exhibited the highest elongation and retentive forces compared with the casting and SLM groups. SLM increased the mechanical properties of Co-Cr alloys. Postprocessing heat treatment further enhanced the tensile ductility. It is suggested that SLM followed by heat treatment is an efficient strategy for fabricating RPD frameworks.

Oxygen plasma with different treatment powers and durations was utilized to modify the biomedical pure titanium (Ti) surface in the present study. The superficial, microstructural and biological properties of the plasma-oxidized samples were investigated using the electron microscopy, X-ray photoemission spectroscopy, grazing incidence X-ray diffractometer, contact angle goniometer and blood clotting time assay. During different treatment powers and durations, the island-like nanostructural rutile-TiO₂ layer and dimple-like nanostructural rutile-TiO₂ layer were generated on the surfaces of the plasma-oxidized samples, respectively. It was also found that the plasma-oxidized sample with a rough oxide layer resulted in the formation of a higher wettability. Moreover, the blood clotting time assay indicated that the plasma-oxidized samples exhibited the adhesion behaviors of red blood cells. As the Ti surface underwent plasma oxidation at 280 W for 30 min, it not only generates a rough nanostructural rutile-TiO₂ layer, but also presents an excellent hemocompatibility. Therefore, these findings demonstrate that oxygen plasma modification is a potential approach to promote the hemocompatibility of biomedical pure Ti surface.