Physicomechanical properties of cobalt-chromium removable partial denture palatal major connectors fabricated by selective laser melting

Abstract

Statement of problem: Additive manufacturing by selective laser melting (SLM) has been claimed to be less challenging than conventional casting of cobalt-chromium (Co-Cr) removable partial dentures (RPDs), providing significant improvements. However, how the physicomechanical properties of Co-Cr RPDs fabricated by SLM compare with those fabricated by conventional casting is unclear.

Purpose: The purpose of this in vitro study was to evaluate the physicomechanical properties of Co-Cr RPD palatal major connectors fabricated by SLM compared with those fabricated by conventional casting.

Material and methods: A master die simulating a maxillary arch of Kennedy class III modification 1 was scanned to create a virtual 3-dimensional (3D) cast. Two groups of 5 Co-Cr RPD major connectors were fabricated. In the 3D printing group, the Co-Cr major connector was virtually designed and exported for direct SLM 3D printing. For the conventional group, Co-Cr major connectors were constructed conventionally. The Co-Cr major connectors were virtually superimposed with the master die for surface adaptation analysis. Additional comparative analyses of surface roughness, relative density, microhardness, and microstructure of the 2 groups were performed. Data were analyzed by using independent t tests (α=.05).

Results: The overall volumetric and linear discrepancies were significantly higher (P<.05) in the 3D printing group. Significant differences in the surface roughness (P<.05) and microhardness (P<.05) were observed, with the 3D printing group having higher surface roughness and microhardness than the conventional group. Unlike conventional connectors, the microstructure of 3D-printed connectors showed fine homogeneous granules.

Conclusions: Compared with the conventional casting technique, SLM 3D printing enabled the fabrication of Co-Cr RPD major connectors with higher microhardness and fine homogenous microstructure. However, the surface adaptation and surface roughness of SLM 3D printing Co-Cr connectors were worse than those produced conventionally. Both techniques showed similar relative densities.