Effect of internal design changes on the mechanical properties of laser-sintered cobalt-chromium specimens

Statement of problem: Changing the internal design of a metal framework may decrease the manufacturing time, the weight of the restoration, and the amount of alloy powder used, as well as simplify the fabrication process. Purpose: The purpose of this in vitro study was to evaluate the effect of framework internal design changes on the mechanical properties of cobalt-chromium (Co-Cr) specimens manufactured by using direct metal laser sintering (DMLS). Material and methods: Dumbbell-shaped test specimens were designed as per the International Organization for Standardization (ISO) 22674(E) standard by using a 3-dimensional software program. A total of 70 dumbbell-shaped specimens were prepared by using Co-Cr alloy powder and DMLS (n=10). The control group specimens were solid with the internal completely filled. For the test groups, the internal design of the dumbbell-shaped specimens was modified. Leaving the outer shell thickness of the specimens at 0.5 mm for all test groups, 6 different internal designs were created, and the specimens were weighed. The tensile strength test was used to evaluate the mean peak strength, elastic modulus, and percentage elongation of the specimens. One-way ANOVA followed by the Dunnett T3 test was used for statistical analysis (α=.05). Results: A statistically significant difference was found among the groups in terms of bar weight and peak strength (P.05). Conclusions: Decreasing the weight of the frameworks by changing the internal design of the specimens also decreased the peak strength. However, it did not affect the elastic modulus or the percentage of elongation.