Abstract
Statement of problem
The metal-ceramic bond strength of dental casting Co-Cr alloys may be improved by
the addition of the rare earth element lanthanum (La), but studies are lacking.
Purpose
The purpose of this in vitro study was to evaluate the effects of the rare earth element
La on the metal-ceramic bond strength of dental casting Co-Cr alloys.
Material and methods
Four groups of specimens with different La content (0; 0.02 wt%; 0.04 wt%; 0.06 wt%)
were prepared using conventional casting methods. The metal-ceramic bond strength
was assessed by using the 3-point bend test. The microstructures were characterized
by metallurgical microscopy, scanning electron microscopy, and X-ray diffraction analyses.
The morphology and element distribution of metal-ceramic interfaces were evaluated
by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy.
The results of bond strengths were statistically analyzed by the Tukey honest significant
difference (HSD) test (α=.05).
Results
The specimens showed typical dendritic microstructures, few defects, and island-shaped
intermetallic compounds rich in Mo and Cr, mainly consisting of α-Co phase of a face-centered
cubic (FCC) structure and ε-Co phase of a close-packed hexagonal (HCP) structure.
As the amount of La increased, the thickness of the native oxide layer and the diffusion
layer at the interface increased, and the wettability between the oxide layer and
the metal matrix improved. The mean ±standard deviation values of the metal-ceramic
bond strengths were 28.11 ±4.53 MPa for group 0%, 33.13 ±5.65 MPa for group 0.02%,
37.48 ±7.86 MPa for group 0.04%, and 40.70 ±5.17 MPa for group 0.06%. The statistical
analysis indicated that significant differences (P<.05) were observed among all groups tested, except for group 0.04% and 0.06% (P>.05). The debonded surfaces of Co-Cr specimens showed a mixed type of adhesive and
cohesive fractures.
Conclusions
The microstructures, morphologies, and compositions of oxide films were influenced
by the La content, and the La addition could significantly improve the metal-ceramic
bond strength of dental casting Co-Cr alloys.
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Article info
Publication history
Published online: January 16, 2019
Footnotes
This study was supported by the National Natural Science Foundation of China (no.: 21575137).
Identification
Copyright
© 2018 by the Editorial Council for The Journal of Prosthetic Dentistry.
