Bending fracture of Co-Cr dental bridges, produced by additive technologies: experimental investigation

Abstract

The aim of this paper is to investigate the fracture during bending test of Co-Cr dental bridges, produced by additive technologies. Three groups of samples (four-part dental bridges from 1-st premolar to 2-nd molar) were produced by conventional casting with handmade wax patterns, casting with 3D printed patterns and selective laser melting (SLM). The bending test was done using Tira Test 2300 SE/50 kN machine and especially designed appliance, ensuring loading closest to the actual during masticatory process. The loadings until cracking and fracture were evaluated. The fractured surfaces were investigated by optical microscopy. It was established that the SLM dental bridges of Co212-f alloy are being destroyed in 9.255 kN loading, which is commensurable with that for cracking of the samples, cast from Biosil-F alloy – 9.820 kN in conventional casting and 10.171 kN in casting with 3D printed patterns. The destruction of the cast Co-Cr bridges consists of three stages – crack initiation in the most loaded area, its growth and final fracture, while the destruction of the SLM samples suddenly occurs because of a network of cracks in the entire volume. The destruction type of the Co-Cr bridges, produced by SLM and casting, is identical - ductile, but the way that fracture occurs is different due to their structure. The specific layered macrostructure, the fine microstructure with dendritic morphology, the phase composition – the presence of ε-phase and the typical defects of the SLM Co-Cr alloy define the fracture mechanism during bending.