Effect of layered manufacturing techniques, alloy powders, and layer thickness on metal-ceramic bond strength

Statement of problem. Direct metal laser sintering (DMLS) and direct metal laser melting (DMLM) have become popular for fabricating the metal frameworks of metal-ceramic restorations. How the type of layered manufacturing device, layer thickness, and alloy powder may affect the bond strength of ceramic to metal substructure is unclear. Purpose. The purpose of this in vitro study was to evaluate the bond strength of dental porcelain to metal frameworks fabricated using different layered manufacturing techniques (DMLS and DMLM), Co-Cr alloy powders, and layer thicknesses and to evaluate whether a correlation exists between the bond strength and the number of ceramic remnants on the metal surface. Material and methods. A total of 75 bar-shaped metal specimens (n=15) were fabricated using either DMLS or DMLM. The powder alloys used were Keramit NP-S and EOS-Cobalt-Chrome SP-2 with layer thicknesses of 20 mu m and 30 mu m. After ceramic application, the metal-ceramic bond strength was evaluated with a 3-point-bend test. Three-way ANOVA followed by the Tukey honest significance difference test were used for statistical analysis (alpha=.05). De-bonding surface microstructure was observed with scanning electron microscopy. Energy dispersive spectroscopy analysis was conducted to evaluate the correlation between ceramic remnants on the metal surface and bond strength values. Results. The mean bond strength value of DMLS was significantly higher than that of DMLM. While no statistically significant difference was found between layer thicknesses, alloy powders closely affected bond strength. Statistical comparisons revealed that the highest bond strength could be achieved with DMLS-Cobalt-Chrome SP2-20 mu m, and the lowest bond strength was observed in DMLS-Keramit NP-S-20 mu m (P <=.05). No correlation was found between porcelain remnants on the metal surface and bond strength values. Conclusions. The layered manufacturing device and the alloy powders evaluated in the current study closely affected the bond strength of dental porcelain to a metal framework. However, layer thickness did not affect the bond strength.