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  • Title: Effects of heat treatment on metal-ceramic combination of selective-laser-melted cobalt-chromium alloy.
    Author: Yan X, Xu YX, Wu Y, Lin H.
    Journal: J Prosthet Dent; 2018 Aug; 120(2):319.e1-319.e6. PubMed ID: 30097265.
    Abstract:
    STATEMENT OF PROBLEM: Components fabricated by selective laser melting (SLM) deform because of residual stress, but heat treatment allows the release of that stress and avoids deformation. Although dental cobalt-chromium (Co-Cr) alloy has been specifically designed for SLM, the effects of heat treatment on the metal-ceramic combination of SLM Co-Cr restorations require investigation. PURPOSE: The purpose of this in vitro study was to evaluate the effects of heat treatment on the metal-ceramic combination of SLM Co-Cr alloy. MATERIAL AND METHODS: Following ISO 9693:2012, Co-Cr metal strips (Solibond C Plus cast alloy and SLM powders; YETI Dental) were fabricated with a dimension of 25×3×0.5 mm by casting and SLM. The SLM specimens were divided into 3 subgroups (n=15 for each subgroup). Two subgroups were subjected to heat treatment at 880°C (SLM-880) and 1100°C (SLM-1100). The third subgroup was not subjected to heat treatment and served as a control (As-SLM). Cast specimens (n=15) also acted as a control. A porcelain layer with a thickness of 1.1 mm was fired to the central area (3×8 mm) of each specimen. The 3-point bend test was used to evaluate the metal-ceramic bond strength (τb). The fractured metal surfaces were examined by the naked eye, using a digital camera, and also using a scanning electron microscope. The area fraction of adherence porcelain (AFAP) was determined by measuring the atomic percentage of silicon using energy-dispersive x-ray spectroscopy (EDS). One-way ANOVA and the Kruskal-Wallis test, followed by the Mann-Whitney test (α=.05), were used for statistical analysis. RESULTS: The 1-way ANOVA found no significant difference in the bond strength among the 4 groups. The EDS analysis indicated that specimens in the groups receiving heat treatment (SLM-880 and SLM-1100) showed higher AFAP values than those in the As-SLM group (P<.05). The SLM-880 also showed significantly higher AFAP values than the SLM-1100. Compared with the cast group, significant differences in AFAP values were also observed, and the specimens in the order of highest to lowest AFAP values were SLM-880>cast>As-SLM; no significant difference was found between the SLM-1100 and cast groups. CONCLUSIONS: Heat treatment at 880°C and 1100°C did not affect the metal-ceramic bond strength of Co-Cr alloy made by SLM but did improve the porcelain adherence. SLM-fabricated and heat-treated Co-Cr alloy shows comparable or more porcelain adherence than cast specimens.
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