The bond strength of dental porcelain to cobalt-chromium alloys fabricated by casting, milling and by selective laser melting: A comparative analysis

Abstract

This study was set up to explore the effects of the applied routes for fabricating cobalt-chromium (Co-Cr) dental frameworks on the metal-ceramic bond strength. Three groups (n = 12/group) of Co-Cr specimens (25x3x0.5) mm were fabricated by casting, milling, and by selective laser melting (SLM), and then airborne-particle abraded (110 μm Al2O3 particles). Dental porcelain was applied (8x3x1.1) mm onto the Co-Cr substrates, and the metal-ceramic bond strength was assessed by a three-point bend test according to the ISO 9693-1:2012 standard. Failure modes were determined using stereomicroscopy. Representative specimens from each group were used to assess the element distribution across the metal-ceramic interface, together with an inspection of its microstructure using a scanning electron microscope (SEM) and energy-dispersive spectroscopy (EDS). Average profile roughness (Ra) values were obtained for each group of metal substrates. The metal-ceramic bond strength data and Ra data were statistically analyzed (one-way ANOVA, Tukey's HSD test, α = 0.05). The mean surface roughness was affected by the fabrication technology (p < 0.01), SLM Co-Cr demonstrating a significantly higher Ra value (1.78±0.20 μm), than cast and milled Co-Cr (1.21±0.07 μm and 1.05±0.11 μm respectively). However, the metal processing applied did not affect the metal-ceramic bond (p = 0.104). Differently processed metal-ceramic specimens showed a comparable distribution of elements on the interface, together with good wetting between the alloy and the porcelain. The porcelain bond strengths to cast, milled and SLM Co-Cr alloys are well above the minimum ISO 9693-1:2012 recommended value of 25 MPa for metal-ceramic systems, thus allowing the clinical application of SLM Co-Cr in porcelain-fused-to-metal prostheses.