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Comparison between selective laser melted and cast removable partial denture frameworks
Ahmad Maalhagh-Fard1, Nicholas J Ostrander2, Timothy R Saunders3
1Associate Professor and Director of Faculty Success Program, University of Detroit Mercy School of Dentistry, Detroit, Mich.
Statement Of Problem:
Cast cobalt chromium (Co-Cr) frameworks for removable partial dentures may have undesirable micromechanical properties leading to clinical failures. Co-Cr frameworks made by selective laser melting (SLM) may have improved micromechanical properties, but comparative studies are lacking.
Purpose:
The purpose of this in vitro study was to compare the micromechanical properties of SLM for Co-Cr alloys with those produced by conventional casting.
Material And Methods:
The International Organization for Standardization (ISO) standards were used to determine material constants and failure stress. For flexural testing, 31×11×1.2-mm specimens were cast (n=10) and selective laser melted (n=10) and tested with a 20-mm support span in a 3-point configuration. The cast specimens had been held in a furnace for 5 minutes to encourage dendrite and columnar grain growth to represent the clinical cast RPD framework microstructure at the zone of failure. These failure points were observed with optical and scanning electron microscopy. Three-point bend tests, mimicking the fracture of RPD clasps, were done at room temperature using a universal testing machine (Instron 5569) to characterize the mechanical properties of cast and SLM specimens. The elastic modulus (E), bending yield strength (σy), strain to yield (εy), ultimate flexural stress (σufs), and resilience (Ur) values for the cast and SLM groups were compared using 2-sided t tests (α=.05) and Weibull analysis was completed with the confidence interval of 95%.
Results:
The SLM and cast Co-Cr groups have statistically significant differences. The SLM mean values for toughness, yield strength, strain to yield, resilience, and strain to failure were statistically higher than the cast mean values (P<.001). The Weibull distribution of ultimate flexure strength was also significantly different for both groups (P<.001).
Conclusions:
SLM Co-Cr alloy was found to be tougher than cast Co-Cr alloy. The SLM alloy underwent more flexure before permanent deformation, withstood greater stresses, and had greater failure stress predictability than cast alloy.
