Characterization of the interface between prefabricated dental implant component and cast dental alloys

Precise fit between implant parts is important for the long-term success of implant-supported dental restorations. Premanufactured cast-to components, made of either plastic or gold alloy, are commonly used for establishing such a fit between the abutment and the superstructure. Metallurgical compatibility between the cast-to component and the cast dental alloy is essential to prevent clinical failure under in vivo functional loading and the release of problematic ions from in vivo corrosion. The objectives of this study were to characterize and compare the metallurgical compatibility of 6 different representative casting alloys with one selected dental implant component and to evaluate the effect of porcelain firing cycles on the interface of selected casting alloys with the dental implant component.; Two high-gold (gold-platinum-palladium and gold-platinum) ceramic alloys (Aquarius XH and Brite Gold XH), a gold-palladium ceramic alloy (IPS d.SIGN 91), one palladium-silver ceramic alloy (IPS d.SIGN 59), one palladium-silver-gold ceramic alloy (Capricorn 15) and a Type III crown and bridge (non-ceramic) gold alloy (Maxigold KF) were selected, in consultation with the Director of Research (Tridib Dasgupta) at Ivoclar Vivadent (Amherst, NY). These alloys were cast onto the ComOcta Gold Abutments (SS system) provided by OSSTEM located in Korea.; The microstructures and the elemental compositions of the adjacent bulk alloys and the interfacial region were investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) in the as-cast condition and after simulated porcelain firing cycles (heat-treated condition). SEM observations were performed using both secondary (SE) and backscattered electron (BSE) imaging modes at a variety of magnifications. The EDS analyses were performed at a series of spots perpendicular to the interface to determine the variation in elemental composition from the bulk cast alloy to the bulk implant component. The Vickers hardness for the bulk implant components, the bulk cast alloys, and the interfacial regions were determined for both the initial as-cast specimens and after the simulated porcelain-firing heat treatment.; The metallurgical phases in the bulk alloys and the interfacial regions were characterized with micro x-ray diffraction (micro-XRD) for these same two conditions.; Using torch melting, specimens meeting dimensional requirements for ISO Standards 9693 and 8891 for metal-ceramic dental restorative alloys and all-metal restoration alloys, respectively, were prepared. Six specimens for each alloy were loaded in tension to failure at a crosshead speed of 2 mm/min. Values of elastic modulus, 0.1% and 0.2% yield strength (YS), ultimate tensile strength (UTS), and percentage elongation at fracture were obtained. Following observation of the fracture surfaces with the SEM, fractured specimens were embedded in resin, metallographically polished, etched with aqua regia solutions, and coated with graphite for microstructural observations with the SEM. Statistical comparisons of the mechanical properties were made using ANOVA and the REGW multiple range test.; Microstructures of the bulk cast noble alloys were maintained up to a well-defined boundary in most groups for both the as-cast (AC) and heat-treated (HT) conditions. However, an approximately 5-6 micron wide band was observed at the interfacial region, where the microstructure had characteristic features from the casting alloy and/or implant component. The size of the grains at the interface was increased after the simulated porcelain firing cycles, in addition to an increase in the width of the interfacial region. These changes were attributed to the effect of annealing during the high-temperature casting procedure and during the subsequent porcelain firing cycles, which caused substantial diffusion of component elements in the alloy compositions.; This diffusion occurred in both directions across the interface for...