Effect of oxidation heat treatment with airborne-particle abrasion on the shear bond strength of ceramic to base metal alloys.

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. PURPOSE: 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 (slashed circle5x8 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 degrees C and rising to 980 degrees C. The airborne-particle abrasion was performed with 100-mum 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 (alpha=.05). RESULTS: 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 (rho=.166; P=.043). The mixed failures were prevalent in Co-Cr alloys (P<.001) and oxidation heat treatment with airborne-particle abrasion (P=.008). CONCLUSIONS: 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.