Influence of stress-relieving heat treatments on the efficacy of Co-Cr-Mo-W alloy copings fabricated using selective laser melting

Abstract

Cobalt-Cr alloys produced using the traditional lost-wax casting method are commonly used to produce porcelain-fused-to-metal (PFM) crowns because of their good mechanical properties, excellent biocompatibility, and resistance to corrosion and wear [1-3]. However, selective laser melting (SLM) has recently been introduced as a manufacturing technique for the Co-Cr metal substructure of PFM crown restorations and has attracted the attention of dentists. SLM creates three-dimensional (3D) metal components using laser power by melting metal powder layers according to CAD data. This leads to a lower probability of operation errors and causes minimal casting defects, as compared to traditional casting techniques [4,5]. Additionally, SLM techniques allow cost-effective mass production and fabrication of customized restorations with reliable mechanical properties [6]. However, a well-known drawback of SLM parts is the excessive residual stress due to steep temperature gradients, which leads to geometrical distortion and deformation of the indented shape [7,8]. Distortion significantly affects dimensional accuracy [9]; therefore, post-heat treatments are typically required to relieve the residual stress [10][11][12].The adhesion strength between the dental ceramic and the metal substrate in PFM crown restorations is a significant variable that influences the clinical success and survival rate of PFM crowns because poor adhesion strength between the ceramic and the metal frameworks induces fracturing and porcelain exfoliation [4,[13][14][15]. The influence of stress-relieving post-heat treatments on the metalceramic bond strength has been previously investigated. Zhou et al.[16] compared the metal-ceramic bond properties of SLM-processed (SLM-ed) Co-Cr alloys heated to 1150 °C for 1 h with those of conventional casting alloys and found that the metal-ceramic bond properties of heat-treated SLM-ed Co-Cr alloys were lower than those of traditional castings because the diffusion layer of the SLM samples was thinner, thereby contributing to a smaller chemical bonding J Prosthodont Res. 2023; **(**):