CAST VERSUS LASER-SINTERED CR-CO ALLOYS: STUDY ON MECHANICAL CHARACTERISTICS

Objectives:Additive Layer Manufacture of dental prostheses allows the direct fabrication of parts from CAD data, replacing a human-sensible process with a faster reliable automatic one. Direct Metal Laser Sintering (DMLS) of Cr-Co alloys produces parts to be directly finished with ceramic and employed. Their clinical application requires a solid know-how on mechanical and functional characteristics, with respect to traditional cast parts.Methods:Tensile specimens were built (ASTM E8M) both by DMLS and traditional lost-wax casting, using the same Cr-Co alloy. An experimental plan was designed to evaluate the effect of all process phases. Standard parameters were used on EOSINT-M270 to fabricate the laser-sintered specimens. A group was left as-sintered (DMLS_L) and the others were heat-treated for stress-relief (DMLS). Wax parts were built by drop-on-demand, invested in ceramic and burnt away before casting (CAST). Then, two groups of specimens were subjected to the high temperature treatment used in ceramic covering without deposition (DMLS_H, CAST_H). On all specimens (6 for each of 5 groups) thickness was measured through a measuring microscope. Roughness was determined on Lm=4,8mm. Specimens were tensile tested obtaining UTS and percent elongation.Results:No significant dimensional variations were noticed among different processes. Sintered parts are on average rougher than cast ones (Ra~3.8vs2.6µm). UTS of all sintered specimens (~1400MPa) is almost double than of cast ones, where many porosities were found. Unlike cast parts, heat-treatment increases UTS for DMLS. Laser-sintered specimens are also much more fragile than cast ones (εb~5 vs 20%).Conclusion:DMLS of Cr-Co alloys produces excellent strength and absence of defects with respect to traditional casting. Low εb values are not critical, since deformation of the final prostheses is limited by the ceramic layer fragility. Slightly higher roughness of DMLS parts is likely to improve mechanical bonding with the ceramic layer or might be smoothed.