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 (∅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). 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 (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). 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.

Effect of casting atmosphere on the marginal deficiency and misfit of Ni-Cr alloys with and without beryllium.

STATEMENT OF PROBLEM: The marginal adaptation of prosthetic crowns is still a significant clinical problem. PURPOSE: The purpose of this in vitro study was to evaluate the marginal deficiency and misfit of Ni-Cr alloys with and without beryllium under different casting conditions. MATERIAL AND METHODS: Four casting conditions were selected: flame-torch, induction/argon, induction/vacuum, and induction/air; and 2 alloys were used, Ni-Cr-Be and Ni-Cr. For each group, 10 metal specimens were prepared. Silicone indirect impressions and analysis of the degree of rounding were used to evaluate the marginal deficiencies of metal copings, and a standardized device for the setting pressure associated with optical microscopy was used to analyze the marginal misfit. Results were evaluated with 2-way ANOVA (α=.05), followed by the Tukey honest significant difference post hoc test, and the Pearson correlation test (α=.05). RESULTS: Alloy (P<.001) and casting technique (P<.001) were shown to affect marginal deficiencies. The Ni-Cr cast using the torch technique showed the highest marginal deficiency, and the Ni-Cr-Be cast in a controlled argon atmosphere showed the lowest (P<.001). Alloy (P=.472) and casting techniques (P=.206) did not affect the marginal misfit, but significant differences were found in the interaction (P=.001); the lowest misfit was achieved using the Ni-Cr-Be, and the highest misfit occurred with the molten Ni-Cr, using the cast torch technique. No correlation was found between deficiency and marginal misfit (r=.04, P=.69). CONCLUSIONS: The interactions demonstrated that the alloy containing beryllium that was cast in an argon atmosphere led to reduced marginal deficiency. Improved marginal adaptation can be achieved for the same alloy by using the torch technique.