## 1 Introduction  
Selective laser melting (SLM), a powder-bed fusion technique, is used in the dental field for fabricating dental prostheses such as crowns, bridges, and frameworks of removable dentures [1, 2] because it enables the rapid, low-cost, semi-automatic, and highly accurate fabrication of intricate products [3]. Co-Cr alloys are extensively used in fabricating dental prostheses [1] owing to their excellent mechanical properties and biocompatibility [4]. Compared to conventional casting methods, SLM-fabricated samples exhibit superior mechanical properties and corrosion resistance because of their unique fine cellular or columnar dendritic microstructures, which are formed through repeated rapid heating and cooling during fabrication [5, 6, 7]. Additionally, SLM builds exhibit smaller grain sizes compared to conventional casting, which contribute to improved mechanical properties. These microstructure patterns are created by the coupled effects of solid/liquid interface instability and melt hydrodynamic instability [8]. In such patterns, the Cr and Mo contents at the cellular or columnar dendritic boundary are higher than those at the center of the dendrite, contributing to improved corrosion resistance [5, 7]. However, rapid heating and cooling during fabrication induce thermal gradients, resulting in high levels of residual stress [9]. Consequently, SLM-fabricated parts generally require post-heat treatment to relieve the residual stress [10]. The heat-treatment conditions affect the mechanical properties of Co-Cr alloys produced by SLM. [PERSON] et al. reported that heat treatment at 1100 \({}^{\circ}\)C, rather than 880 \({}^{\circ}\)C,resulted in higher elongation in a Co-Cr alloy fabricated by the EOS M100 [11]. Therefore, 1100 \({}^{\circ}\)C is more suitable for fabricating dental prostheses requiring toughness, such as frameworks for removable partial dentures (RPDs) [12]. A study reported that Co-Cr alloy heated at 750 and 900 \({}^{\circ}\)C induced transformation of the \(\gamma\) phase to \(\epsilon\) phase, resulting in high-proof strength and hardness; however, the elongation decreased [3; 11]. Heat treatment at 1150 \({}^{\circ}\)C for \(\geq\)45 min was reported to change the grain structure from columnar to equiaxed, resulting in a recrystallized microstructure with excellent strength and ductility [13]. Two types of EOSINT CoCr powder are commercially available for use in dental prostheses: one comprises a Co-Cr-Mo-based alloy (MP1) suitable for metal frameworks, while the other contains a Co-Cr-Mo-W-based alloy (SP2), which meets the chemical and thermal requirements of the ISO 9693 standard for CoCr porcelain fused to metal in dental materials. The manufacturer of this powder has recommended different heat treatments for each type. SP2 has been recommended to be heated at 750 \({}^{\circ}\)C for 60 min to relieve the residual stress, while MP1 has been recommended to be heated at 1150 \({}^{\circ}\)C for six hours to relieve the residual stress and undergo recrystallization. However, continued heat treatment after recrystallization leads to coarsening of the grains and subsequent deterioration in the mechanical properties [2; 13]. In our previous studies on MP1, we reported that for dental prostheses that are not typically large, heat treatment at 1150 \({}^{\circ}\)C for -60 min was sufficient for recrystallization and achieving excellent mechanical properties [2; 13]. Fitness, defined as the gap between RPD frameworks and cast, is comparable for RPDs fabricated by SLM using the EOS M270 and those that are conventionally cast [14]. The trueness of RPD frameworks fabricated by SLM using the M270 is superior to that of cast RPD frameworks [15]. Additionally, clasps fabricated by SLM using the M270 exhibit less initial retention force degradation than those fabricated by casting and have shown superior survival rates in fatigue tests [15]. Therefore, SLM is considered a promising alternative method for fabricating partial dentures compared to casting.