International Journal of Computerized Dentistry 2019;22(1):55–67 55 SCIENCE M. Revilla-León, M. J. Meyer, M. Özcan Metal additive manufacturing technologies: literature review of current status and prosthodontic applications Abstract Objectives: To review the current metal-based additive man- ufacturing (AM) technologies, namely powder bed fusion (PBF) technologies, and their current prosthodontic applica- tions. The PBF technologies reviewed are selective laser sin- tering (SLS), selective laser melting (SLM), and electron beam melting (EBM). Materials and methods: The literature on metal AM technol- ogies was considered, and the AM procedures and their cur- rent applications in prosthodontics were collated and described. Published articles about AM metal in dental care were searched (MEDLINE, EMBASE, EBSCO, and Web of Sci- ence). All studies related to the description, analysis, and evaluation of prosthodontic applications using metal AM technologies. Results and conclusions: AM technologies are reliable for many applications in dentistry, including metal frameworks for removable partial dentures (RPDs), overdentures, tooth- and implant-supported fxed dental prostheses (FDPs), and metal frameworks for splinting implant impression abut- ments. However, further studies are needed in future to eval- uate the accuracy, reproducibility, and clinical outcome throughout function of AM technologies. Keywords: 3D printing, additive manufacturing technologies, electron beam melting, metal, selective laser melting, selective laser sintering, prosthodontics Introduction Conventional casting and subtractive computer-aided manu- facturing (CAM) technologies are the most common methods used by dentists to manufacture dental prosthetics. 1 CAM technologies typically refer to a computer numerically con- trolled (CNC) system, which controls power-driven machine tools. Under the direction of computer software, these tools mechanically remove material from a block form to achieve the desired framework. 2-4 Although these technologies are considered the gold standard for the fabrication of fxed den- tal prostheses (FDPs), subtractive technologies present a number of manufacturing limitations. These limitations include a considerable amount of wasted raw material (unused remnants of the milling block), the short running cycle of the milling tool due to the abrasive wear of milling, and the space limitations imposed by the size of the milling burs and the axis of the CNC machine, which in turn limit access to smaller areas of the milling block. 5-7 Additive manufacturing (AM) procedures, in which a pow- der or liquid base material is built into a solid object, provide a promising alternative manufacturing method. 8,9 The Amer- ican Society for Testing and Materials (ASTM International) has defned AM technology as ‘‘a process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing (SM) methodolo- gies.” 10 The industry standard computer-aided design (CAD) data fle format is Standard Triangulation Language (STL), in which boundaries are represented by triangular facets. 11 In 2008, the ASTM International Technical Committee F42 on AM technologies outlined seven AM categories: stereoli- thography (SLA), material jetting, material extrusion, binder jetting, powder bed fusion (PBF), sheet lamination, and direct energy deposition. 10 PBF technologies are most commonly used for 3D metal printing in dentistry. There are three types of PBF technologies: selective laser sintering (SLS), selective laser melting (SLM), and electron beam melting (EBM). 10 Selective laser sintering (SLS) In 1989, Carl Deckard, along with Joe Beaman, developed and patented SLS technology. 12,13 During this procedure, a high-powered laser (Nd:YAG laser) beam is focused onto a bed of powdered metal, which then fuses into a thin solid layer (20 to100 μm). Another layer of powder is then laid down, which becomes the next slice of the framework. The laser then fuses the top layer with the layer beneath. This pro- cess is repeated until the three-dimensional (3D) object is built (Fig 1). 14