Process parameter optimization for removable partial denture frameworks manufactured by selective laser melting

Abstract

Removable partial denture (RPD) frameworks have been traditionally produced with the lost-wax casting technique, although the process is complex because the metal is melted at around 1400 C and the emission of toxic gasses requires a rigorous safety protocol. 1 The accuracy and reliability of RPD framework production can be problematic. 2 In the past 20 years, digital technologies have improved in accuracy, reliability, and repeatability, and currently computer-aided design and computer-aided manufacturing (CAD-CAM), including selective laser melting (SLM), plays an important role in the production of dental prostheses. [3][4][5] SLM 3D printers are used to fabricate metal crowns, copings, and fixed partial denture frameworks, which are typically small components that are not severely deformed by residual heat stress. 6 The deformation of prostheses between the casting and SLM processes has been compared. However, deformation of larger RPD frameworks made by SLM has been described, with physical distortion and bending being observed, a deformation that originates from the residual heat stress caused by thermal expansion of the metal during the laser melting process. 7 Therefore, heat treatment after processing is essential to release the residual heat stress from the 3D-printed metal parts. This process influences the mechanical properties of the metal specimens, and therefore, the method of heat treatment Supported by the Ministry of Trade, Industry and Energy (MOTIE, Korea) (grant number 20001221).

Effects of selective laser melting process parameters on the accuracy of the intaglio surface of maxillary removable partial denture frameworks

“…The study by Gong et al (2014) showed that the porosity of Ti–6Al–4V parts built with a 1,200-mm/s laser speed and 80-W laser power was more than 5%. However, Hwang et al (2021) showed that the porosity of CP Ti parts built with a 1,200-mm/s scan speed and 90-W power was 0.81%. The density and porosity have direct effects on the resiliency and fatigue properties of clasps.…”

“…In this experiment, single prism support structures should be replaced by lightweight ones (Calignano, 2014), for example, tree supports. It is necessary to orientate maxillary RPD frameworks and apply proper support structures to reduce the overhang surface area of clasps' intaglio surface, the residual stress and the deformation of maxillary RPD frameworks (Hwang et al, 2021). The build orientation affects the accuracy of the intaglio surface of RPD frameworks, the fatigue strength of clasps (Xie et al, 2020;Kajima et al, 2018), and the building efficiency of RPD frameworks.…”

“…Of SLM parameters, the build orientation had the most effects, the metallic powder type had the second most effects, and laser process parameters had the least effects. The build orientation not merely has effects on the support generation and postprocessing but affects the stress distribution of maxillary RPD frameworks (Kajima et al , 2018; Hwang et al , 2021). The major connector of maxillary RPD frameworks built at a lower orientation angle had a more accurate intaglio surface than that of maxillary RPD frameworks built at a higher orientation angle.…”

“…Xie et al (2020) pointed out that the mean gap between CP Ti Akers clasp arms built horizontally and the tooth analog was 33.4 m m. The adaption of CP Ti Akers clasps arms built horizontally was better than that of CP Ti Akers clasp arms built vertically or at the orientation angle of 45°. Hwang et al (2021) considered that CP Ti maxillary RPD frameworks built vertically had higher accuracy than those built horizontally. The effects of laser process parameters on the accuracy of RPD frameworks have not been thoroughly investigated.…”

Trueness of 3D printed partial denture frameworks: build orientations and support structure density parameters

“…However, this manufacturing process is still under development, expensive and rarely found in prosthetic laboratories. 5 7 8 Hwang et al 9 have optimized the SLS printing process and found that the transverse build angle and inter-connected support structure had the best accuracy (167 ± 105 µm) and optimum density, surface roughness, and productivity, compared to the other studying groups. SLS was also appraised in the literature on its ability to manufacture RPD with a range of accuracy (166 ± 9 to 123 ± 9 µm).…”