Statement of problem
Oxidation heat treatment has been studied to increase the metal-ceramic bond strength.
However, information about its use with cobalt-chromium (Co-Cr) alloys is lacking.
The purpose of this study was to evaluate the effect of oxidation heat treatment and
oxidation heat treatment with alumina airborne-particle abrasion on the metal-ceramic
bond strength of Co-Cr alloys compared with that of nickel-chromium (Ni-Cr) alloys.
Material and methods
In total, 165 metal cylinders (∅5×8 mm) made of 5 base metal alloys were obtained
by casting: 2 Ni-Cr (Fit Cast-SB and Fit Cast-V) and 3 Co-Cr alloys (Keragen, StarLoy
C, and Remanium 2001). The specimens were divided into groups (n=11): no treatment,
oxidation heat treatment, and oxidation heat treatment with airborne-particle abrasion.
Oxidation heat treatment was performed starting at 650 °C and rising to 980 °C. The
airborne-particle abrasion was performed with 100-μm alumina (0.2-MPa pressure, 5
seconds). One specimen had the surface topography and composition evaluated by scanning
electron microscopy and energy dispersive X-ray spectrometry. The feldspathic ceramic
was applied to the base metal alloy specimens (n=10). Shear tests were performed to
obtain the metal-ceramic bond strength (MPa). The failure modes were evaluated. Data
were evaluated by 2-way ANOVA and the Tukey post hoc test, Pearson correlation, and
Fisher exact tests (α=.05).
The group without treatment showed the highest roughness. The treatments increased
oxygen and chromium levels and decreased nickel, molybdenum, and tungsten levels.
Oxidation heat treatment provided an increase in metal-ceramic bond strength (P<.05) for base metal alloys with over 7% molybdenum (Fit Cast-SB, Fit Cast-V, and
Remanium 2001). With oxidation heat treatment with airborne-particle abrasion, there
was improvement only in Fit Cast-SB. No treatment was better for StarLoy C. A weak
correlation was found between metal-ceramic bond strength and failure mode (ρ=.166;
P=.043). The mixed failures were prevalent in Co-Cr alloys (P<.001) and oxidation heat treatment with airborne-particle abrasion (P=.008).
The oxidation heat treatment was only beneficial for base metal alloy with a molybdenum
content of over 7%. Although the oxidation heat treatment with alumina airborne-particle
abrasion was a better treatment for Fit Cast-SB, its use is not justified because
it showed no difference for oxidation heat treatment and requires another step in
the surface treatment.