## 1 Introduction  
Selective laser sintering (SLS), a rapid prototyping and manufacturing technology, was developed in the late 1980s and has been widely employed to produce products from almost any type of material [1]. However, a different power binding mechanism from that of the SLS is necessary to fabricate objects with high density [1, 2]. Selective laser melting (SLM) can be used to produce products with near full density, preferably with minimal or no post-processing requirements [1]. The SLM technique is currently widely applied for the fabrication of various high-quality metallic devices for medical and dental applications.  
During the SLM process, the alloy powders are completely melted by a laser, and subsequently undergo rapid solidification. Therefore, this process can be used to produce objects of high geometrical complexity [3]. During fabrication, a high power laser beam is directed on an alloy bed and programmed to fuse particles according to a computer-assisted design (CAD) file [4]. This consequently generates a thin metal layer [4]. The apposition of subsequent layers results in the production of the desired three-dimensional (3D) form [4]. Therefore, using this technique, it is possible to fabricate medical and dental metallic devices of different shapes and sizes, directly from a CAD model [4].  
However, the surface quality and mechanical properties of such SLM-fabricated metallic products may vary depending on the laser process parameters used [5, 6, 7]. Laser power, scan rate, and scan-linespacing, which directly affect the melting behavior of the metallic powders, are the common process parameters adjusted to optimize the process [5; 6; 8]. The laser beam melts the material along a specific line of powder particles, thereby forming a molten pool, which acquires the shape of a circular or segmental cylinder under the effect of surface tension [9]. The fragmentation of the remelted line is known as the balling effect, and is a well-known drawback of SLM [5; 9]. The balling phenomenon renders it difficult to stack the subsequent layers, and occasionally causes failure during 3D printing. Therefore, the laser process parameters should be carefully controlled to successfully fabricate high-quality medical and dental metallic devices with appropriate surface roughness to eliminate post-processing procedures such as extensive finishing or polishing [10; 11]. However, the relatively high surface roughness of SLM products is a significant drawback [10].  
Recently, [PERSON] et al. [12] studied the influence of various process parameters on the surface quality of a Co-Cr alloy produced by SLM. However, the results of the study were derived using a two-dimensional (2D) single-line formation test. Therefore, such evaluations should be extended to include multi-layer formation tests to determine how various processing parameters affect the surface roughness of 3D-printed Co-Cr alloy products produced by SLM.  
Therefore, the purpose of this laboratory study was to investigate the effect of three laser process parameters, namely laser power, scan rate, and scan-line spacing, on the surface roughness of an SLM-fabricated Co-Cr alloy used for dental applications, using both single-line formation (2D) and multi-layer formation (3D) tests.