Abstract
Statement of problem
The selective laser melting (SLM) technique has been a promising method of fabricating
Co-Cr metal-ceramic restorations; however, the lower metal-ceramic bond properties
of SLM Co-Cr restorations have become a major issue in clinical use.
Purpose
The purpose of this in vitro study was to propose and verify a method of improving
the metal-ceramic bond properties of SLM Co-Cr alloy with heat treatment after porcelain
firing (PH).
Material and methods
Forty-eight (25×3×0.5 mm) Co-Cr specimens, divided into 6 groups (Control group [CG];
550 °C; 650 °C; 750 °C; 850 °C; 950 °C) according to PH temperatures, were prepared
by using SLM techniques. The 3-point bend tests were performed to evaluate the metal-ceramic
bond strengths; subsequently, the fracture feature was assessed by using a digital
camera and scanning electron microscope (SEM) coupled with an energy-dispersive X-ray
spectroscopy (EDS) detector, to determine the area fraction of adherence porcelain
(AFAP). The interface morphologies and element distribution were determined with SEM/EDS
detectors. Phase identification and quantification were examined with an X-ray diffractometer
(XRD). A 1-way ANOVA and the Tukey honestly significant difference tests were used
to analyze bond strengths and AFAP values (α=.05).
Results
The bond strengths were 35.33 ±1.25 MPa for the CG group, 34.53 ±3.20 MPa for the
550 °C group, 38.20 ±2.60 MPa for the 650 °C group, 42.85 ±2.31 MPa for the 750 °C
group, 33.28 ±3.85 MPa for the 850 °C group, and 29.09 ±2.86 MPa for the 950 °C group.
Significant differences were not observed among the CG, 550 °C, and 850 °C groups
(P>.05) but were found among the other groups (P<.05). Fracture and AFAP results displayed a mixed fracture mode of adhesive and cohesive
fracture. The thicknesses of native oxide films across the 6 groups were relatively
close as the temperature increased, but the thickness of the diffusion layer increased
as well. Excessive oxidation and massive phase transformation caused holes and microcracks
to appear in the 850 °C and 950 °C groups, reducing bond strengths. XRD analysis evidenced
that the phase transformation of γ→ε occurred at the interface during PH treating.
Conclusions
PH treatment significantly affected the metal-ceramic bond properties of SLM Co-Cr
porcelain specimens. The 750 °C-PH-treated specimens displayed higher mean bond strengths
and improved fracture characteristics among the 6 groups.
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Article info
Publication history
Published online: March 02, 2023
Publication stage
In Press Corrected ProofIdentification
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© 2023 by the Editorial Council for the Journal of Prosthetic Dentistry.
