Abstract
Statement of problem
Although several manufacturers market soft metal milling blanks and systems, comprehensive
comparative studies of differences in properties across commercially available soft
metal milling alloys are lacking.
Purpose
The purpose of this in vitro study was to compare the microstructures and mechanical
properties of 3 soft metal milling cobalt-chromium (Co-Cr) alloys (Ceramill Sintron,
Soft Metal, and Sintermetall).
Material and methods
Disk-shaped specimens (for surface characterization and hardness test) and dumbbell-shaped
specimens (for tensile test as per International Organization for Standardization
(ISO) 22674) were prepared by following each soft metal milling manufacturer’s instructions.
The crystal structures and microstructures of the 3 alloys were evaluated with optical
microscopy, X-ray diffractometry (XRD), and scanning electron microscopy with electron
backscattered diffraction (EBSD). The mechanical properties were investigated with
a tensile test and Vickers hardness test (n=6). The results of the mechanical (tensile
and hardness) tests were analyzed with 1-way ANOVA and the post hoc Tukey multiple
comparison test (α=.05).
Results
The Sintermetall specimen showed a finer microstructure and more porosity than the
other 2 alloys. The XRD and EBSD analyses showed that the γ (face-centered cubic, fcc) matrix phase was predominant in the Ceramill Sintron alloy
and the ε (hexagonal close-packed, hcp) matrix phase was predominant in the Soft Metal alloy.
The Sintermetall alloy showed a slightly higher amount of ε phase than γ phase, with more chromium carbide formation than the other 2 alloys. The Ceramill
Sintron alloy showed a significantly higher tensile strength than the other 2 alloys
(P<.05), but a significantly lower 2% offset yield strength than the other 2 alloys
(P<.05). The highest elongation was found in the Ceramill Sintron alloy, followed by
the Sintermetall and Soft Metal alloys. The elastic modulus was the highest in the
Sintermetall alloy, followed by the Soft Metal and Ceramill Sintron alloys. No significant
differences in Vickers hardness values were detected among the 3 alloys (P=.263).
Conclusions
The different commercially available soft metal milling blanks and systems produced
dissimilar alloys in terms of crystal structures and microstructures and, as a result,
different mechanical properties.
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Article info
Publication history
Published online: December 07, 2020
Footnotes
Supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (2017R1A5A2015391).
Identification
Copyright
© 2020 by the Editorial Council for the Journal of Prosthetic Dentistry.
