RESEARCH AND EDUCATION Influence of build angulation on the mechanical properties of a direct-metal laser-sintered cobalt-chromium used for removable partial denture frameworks John M. Aarts, DipDentTech, PGDipCDTech, Bed, MHealSc, a Joanne Jung Eun Choi, BDentTech (Hon), PGDipCDTech, PhD, b Steven Metcalfe, NZCertEng, c and Vincent Bennani, DDS, Cert Advpros, Cert Advimpl, PhD d Direct-metal laser-sintering (DMLS) and selective laser melting (SLM) additive pro- cessing methods are being used to produce removable partial denture (RPD) frame- works. 1 The DMLS system is based on a layer-by-layer addition and subsequent laser-sintering of a metal powder. 2 The DMLS powder bed method used for dental applications has a material dispensing platform combined with a build platform controlled by a 3D computer- aided design software pro- gram. 1,3 The surface roughness of alloys produced through DMLS is reported to be influ- enced by the sintered surface orientation to the build direc- tion, and the surface parallel to the build direction roughness was reported to be 12.6 mm compared with the parallel (18.2 mm). 4 Kajima et al 5 This study was funded by New Zealand Institute of Dental Technologists. a Senior Lecturer, Faculty of Dentistry, Sir John Walsh Research Institute, University of Otago, Dunedin, New Zealand. b Lecturer, Faculty of Dentistry, Sir John Walsh Research Institute, University of Otago, Dunedin, New Zealand. c Director, Research and Development Division, Additive Manufacture Solutions Ltd, Lower Hutt, New Zealand. d Associate Professor, Faculty of Dentistry, Sir John Walsh Research Institute, University of Otago, Dunedin, New Zealand. ABSTRACT Statement of problem. Direct-metal laser-sintering (DMLS) technologies are being used to manufacture removable partial denture frameworks; however, the build parameters are not well documented. Purpose. The purpose of this in vitro study was to investigate the impact of 3 different build angulations on a dental cobalt-chromium (Sint-Tech ST2724G) alloy by comparing the tensile properties and nanoindentation hardness. The null hypothesis was that no change would be found in the tensile properties of the different build angulation groups. Material and methods. Dumbbell-shaped tensile specimens were produced by using stereolithographic models in accordance with American Society for Testing and Materials testing standard E8/E8M-16ae1. Specimens (n=10) were fabricated by using DMLS additive manufacturing with 3 different angulations (0, 45, and 90 degrees). Tensile testing was carried out to assess yield strength (0.2% permanent offset), elongation (%) at failure, and ultimate tensile strength (GPa). Scanning electron microscope (SEM) images were used to analyze the fracture surfaces. One 10×10×10 mm cube specimen at each orientation was prepared, and nanoindentation was used to determine hardness and elastic modulus. One-way ANOVA was used to evaluate the overall effects with interaction between groups and post hoc testing applied where the interaction was statistically significant (a=.05). Results. The 45-degree build angulation resulted in the lowest mean elastic modulus of 213.3 GPa and the highest tensile strength of 1180.9 MPa. The 90-degree build angulation resulted in the highest mean elongation of 10.6% and the highest elastic modulus of 234.0 MPa. Within comparison of the different angulations indicated that various groups had statistically significant differences (P<.05). The SEM analysis indicated different fracture topography among the different build angles. Conclusions. The cobalt-chromium dental alloy manufactured by DMLS produced favorable mechanical properties. The SEM analysis combined with the tensile test results suggest that the direction of the build angle in relation to the laser melt pattern does impact the mechanical properties of the alloy. (J Prosthet Dent 2020;-:---) THE JOURNAL OF PROSTHETIC DENTISTRY 1