Abstract
Statement of problem
Dental cobalt-chromium (Co-Cr) alloy manufactured by selective laser melting (SLM)
is not recommended for clinical applications before annealing because of excessive
residual stress. However, limited information is available regarding the relationship
between annealing temperature and the metal-ceramic bond properties of SLM Co-Cr alloys.
Purpose
The purpose of this in vitro study was to investigate the effects of annealing temperature
on the metal-ceramic bond properties of SLM Co-Cr alloys.
Material and methods
Four groups with different annealing temperatures (850 °C; 950 °C; 1050 °C; 1150 °C)
were prepared by using SLM techniques. Bond strengths were measured by using a 3-point
bend test; subsequently, debonded surface morphologies and elements were assessed
by using a scanning electron microscopy (SEM) coupled with energy-dispersive X-ray
spectroscopy (EDS). The area fraction of adherence porcelain (AFAP) value was introduced
to analyze fracture characteristics. Microstructural and interfacial characteristics
were characterized by SEM/EDS and X-ray diffraction analysis. The coefficient of thermal
expansion (CTE) test was used to analyze thermal matching. A 1-way ANOVA and the Tukey
honestly significant difference tests were used to analyze bond strengths and AFAP
values statistically (α=.05).
Results
The mean ±standard deviation values of the metal-ceramic bond strengths were 40.68
±4.34 MPa for the 850 °C group, 37.54 ±5.34 MPa for the 950 °C group, 45.97 ±2.18
MPa for the 1050 °C group, and 50.79 ±1.79 MPa for the 1150 °C group. Significant
differences (P<.05) were observed among all groups. Debonded surfaces and AFAP analysis displayed
a mixed fracture mode of adhesive and cohesive fracture, and 1150 °C-annealing specimens
exhibited better fracture characteristics close to cohesive fractures. As the temperature
increased, native oxide film thicknesses remained unchanged; the 850 °C group had
the thinnest diffusion layer, while the other 3 groups had similar thicknesses. Although
the 1050 °C and 1150 °C groups displayed higher CTE values, their microstructures
were more conducive to atomic diffusion and improved chemical bonding. Microstructure
analysis found that ε phase and second-phase precipitates jointly affected metal-ceramic
bond strength.
Conclusions
Annealing temperatures affected the metal-ceramic bond strengths of SLM Co-Cr porcelain
specimens. 1150 °C annealing SLM Co-Cr specimens displayed higher bond strengths and
improved fracture and interface characteristics among the 4 groups.
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Article info
Publication history
Published online: February 24, 2023
Publication stage
In Press Corrected ProofIdentification
Copyright
© 2023 by the Editorial Council for the Journal of Prosthetic Dentistry.
