Mechanical and surface properties of Co–Cr alloy produced by additive manufacturing for removable partial denture frameworks

Statement of problem Conventional analog methods have been replaced with digital methods for removable partial denture (RPD) frameworks. However, limited information is available regarding the build direction of RPD frameworks and its effect on properties. Purpose The purpose of this in vitro study was to evaluate the mechanical and surface properties of the cobalt chromium (Co–Cr) alloy produced at different build angles by the laser powder bed fusion additive manufacturing (AM) technology used for RPD framework fabrication. Material and methods Plate-shaped Co–Cr specimens (n=6) were produced by the AM technology and divided into 3 groups depending on the build angle (0, 45, or 90 degrees). The elastic modulus and fracture properties were evaluated by flexural testing. Additionally, 15 disks were printed by using the same parameters of the plates (n=5) to analyze the surface hardness with microhardness testing, and surface properties were determined by surface free energy by using the contact angle and surface roughness measured by using a profilometer. Twelve Co–Cr cylindrical specimens were produced by using the same parameters (n=4), and their microstructure was examined by using an optical microscope. One-way ANOVA was used to evaluate the overall effects of the interaction between groups, and the Tukey test was applied when the interaction was statistically significant (α=.05). Results The flexural strength showed a statistically significant difference (P<.05), with the peak value exhibited by the 0-degree group. A statistical difference was also observed between the angulation and modulus of elasticity; however, the highest value was exhibited by the 45-degree group. For the fracture topography, all groups observed a dimple-like fracture, although the 45-degree group showed wider cleavage planes of fractures than other angulations. For microhardness, the 0- and 45-degree groups exhibited a statistical difference in relation to the 90-degree group (P<.05). For surface properties, no statistically significant difference (P>.05) was found in any of the evaluated parameters. Dependence on the build angles was evidenced by the molten pool boundaries during observation of the microstructure. Conclusions The build angle influenced the flexural strength and microhardness of the Co–Cr alloy produced by AM; however, it does not affect surface free energy and surface roughness.