Comparison of the metal-to-ceramic bond strengths of four noble alloys with press-on-metal and conventional porcelain layering techniques.

STATEMENT OF PROBLEM: New noble alloys for metal ceramic restorations introduced by manufacturers are generally lower-cost alternatives to traditional higher-gold alloys. Information about the metal-to-ceramic bond strength for these alloys, which is needed for rational clinical selection, is often lacking. PURPOSE: The purpose of this study was to evaluate the bond strength of 4 recently introduced noble alloys by using 2 techniques for porcelain application. MATERIAL AND METHODS: Aquarius Hard (high-gold: 86.1 gold, 8.5 platinum, 2.6 palladium, 1.4 indium; values in wt. %), Evolution Lite (reduced-gold: 40.3 gold, 39.3 palladium, 9.3 indium, 9.2 silver, 1.8 gallium), Callisto 75 Pd (palladium-silver containing gold: 75.2 palladium, 7.1 silver, 2.5 gold, 9.3 tin, 1.0 indium), and Aries, (conventional palladium-silver: 63.7 palladium, 26.0 silver, 7.0 tin, 1.8 gallium, 1.5 indium) were selected for bonding to leucite-containing veneering porcelains. Ten metal ceramic specimens that met dimensional requirements for International Organization for Standardization (ISO) Standard 9693 were prepared for each alloy by using conventional porcelain layering and press-on-metal methods. The 3-point bending test in ISO Standard 9693 was used to determine bond strength. Values were compared with 2-way ANOVA (maximum likelihood analysis, SAS Mixed Procedure) and the Tukey test (α=.05). RESULTS: Means (standard deviations) for bond strength with conventional porcelain layering were as follows: Aquarius Hard (50.7 ±5.5 MPa), Evolution Lite (40.2 ±3.3 MPa), Callisto 75 Pd (37.2 ±3.9 MPa), and Aries (34.0 ±4.9 MPa). For the press-on-metal technique, bond strength results were as follows: Aquarius Hard (33.7 ±11.5 MPa), Evolution Lite (34.9 ±4.5 MPa), Callisto 75 Pd (37.2 ±11.9 MPa), and Aries (30.7 ±10.8 MPa). From statistical analyses, the following 3 significant differences were found for metal-to-ceramic bond strength: the bond strength for Aquarius Hard was significantly higher for conventional porcelain layers compared with the press-on-metal technique; the bond strength for Aquarius Hard with conventional porcelain layers was significantly higher than the bond strengths for the other 3 alloys with conventional porcelain layers; and the bond strength for Aquarius Hard with conventional porcelain layers was significantly higher than the bond strength for Callisto 75 Pd with conventional porcelain layers and the other 3 alloys with the press-on-metal technique. CONCLUSIONS: For both conventional layering and press-on-metal techniques, all 4 noble alloys had a mean metal-to-ceramic bond strength that substantially exceeded the 25 MPa minimum in the ISO Standard 9693. The results for Aries support the manufacturer's recommendation not to use the press-on-metal technique for alloys that contain more than 10% silver.

Microstructure, elemental composition, hardness and crystal structure study of the interface between a noble implant component and cast noble alloys.

STATEMENT OF PROBLEM: Casting a high-gold alloy to a wrought prefabricated noble implant-component increases the cost of an implant. Selecting a less expensive noble alloy would decrease implant treatment costs. PURPOSE: The purpose of this study was to investigate the interfacial regions of a representative noble implant component and cast noble dental alloys and to evaluate the effects of porcelain firing cycles on the interface. MATERIAL AND METHODS: Six representative alloys (n=3) were cast to gold implant abutments (ComOcta). Scanning electron microscopy (SEM) was used to characterize microstructures. Compositions of interfacial regions and bulk alloys were obtained by energy-dispersive spectroscopy. Vickers hardness was also measured across the interface. By using Micro-X-ray diffraction, the phases were evaluated at 7 points perpendicular to the interface. The effects of porcelain firing cycles on microstructures, diffusion, hardness, and phases were also evaluated. For statistical evaluation of diffusion length and hardness, a 3-way repeated measures ANOVA was used. Pairwise comparisons of interest were conducted with Tukey pairwise comparisons or, when a significant interaction was found, Bonferroni-adjusted t-tests (overall α=.05). RESULTS: Microstructures of bulk alloys were predominantly maintained to a well-defined boundary for both as-cast and heat-treated conditions. An interaction band, 5-6 µm wide, was observed. The alloy grain size at the interface and the interaction band width increased after simulated porcelain firing. The extent of elemental diffusion from the interface was about 30 µm and not affected by simulated porcelain firing. Differences in Vickers hardness for the alloys were consistent with their compositions. Micro-XRD patterns indicated that substantial amounts of new phases had not formed at the interfacial regions. CONCLUSIONS: Less expensive noble alternatives to high-gold alloys provided comparable metallurgical compatibility with the noble implant component.

Mechanical properties, fracture surface characterization, and microstructural analysis of six noble dental casting alloys.

STATEMENT OF PROBLEM: Because noble dental casting alloys for metal ceramic restorations have a wide range of mechanical properties, knowledge of these properties is needed for rational alloy selection in different clinical situations where cast metal restorations are indicated. PURPOSE: The purpose of this study was to compare the mechanical properties and examine both the fracture and polished surfaces of 6 noble casting alloys that span many currently marketed systems. Five alloys were designed for metal ceramic restorations, and a sixth Type GPT has Type IV alloy for fixed prosthodontics (Maxigold KF) was included for comparison. MATERIAL AND METHODS: Specimens (n=6) meeting dimensional requirements for ISO Standards 9693 and 8891 were loaded to failure in tension using a universal testing machine at a crosshead speed of 2 mm/min. Values of 0.1% and 0.2% yield strength, ultimate tensile strength, elastic modulus, and percentage elongation were obtained. Statistical comparisons of the alloy mechanical properties were made using 1-way ANOVA and the REGW multiple-range test (α=.05). Following fracture surface characterization using scanning electron microscopy (SEM), specimens were embedded in epoxy resin, polished, and again, examined with the SEM. RESULTS: When the multiple comparisons were considered, there were generally no significant differences in the elastic modulus, 0.1% and 0.2% offset yield strength, and ultimate tensile strength for the d.SIGN 91 (Au-Pd), d.SIGN 59 (Pd-Ag), Capricorn 15 (Pd-Ag-Au) and Maxigold KF (Au-Ag-Pd) alloys, except that the ultimate tensile strength was significantly lower (P<.05) for Maxigold KF than these other 3 alloys. These 4 mechanical properties were generally significantly lower (P<.05) for Aquarius XH (Au-Pt-Pd) and Brite Gold XH (Au-Pt). The d.SIGN 59 (14.6%) and Capricorn 15 (13.8%) alloys had the highest values of mean percentage elongation, which were not significantly different. Aquarius XH (6.0%) and Maxigold KF (4.2%) had the lower mean values of percentage elongation, which were also not significantly different. The polished and etched surfaces for all alloys revealed equiaxed, fine-grain microstructures, and all fracture surfaces contained casting porosity. Incomplete solidification suggestive of dendritic structures was observed for some alloys. Fracture surfaces were complex, with characteristic features of both brittle and ductile fracture. Precipitate particles on the fracture surfaces indicated the multi-phase character of the alloys. CONCLUSIONS: For the important mechanical property of yield strength, there were generally no significant differences among the Au-Pd, Pd-Ag, Pd-Ag-Au and Au-Ag-Pd alloys. Wide variation was found in percentage elongation, with the Pd-Ag and Pd-Ag-Au alloys having the highest values and the Au-Pd-Pt and Au-Ag-Pd alloys having the lowest values.

The effect of metal recasting on porcelain-metal bonding: a force-to-failure study.

STATEMENT OF PROBLEM: Noble dental alloys are commonly remelted in the dental laboratory, but the effect of repeated casting on porcelain bond strength requires further documentation. PURPOSE: The purpose of this study was to determine if casting up to 3 times affected metal ceramic bond strength for 3 noble alloys using methodology in ANSI/ADA Specification No. 38. MATERIAL AND METHODS: Representative high-gold (Brite Gold XH), gold-palladium (W-5), and palladium-silver (IPS d.SIGN 53) alloys were cast into metal strips (25 x 3 x 0.5 mm), using torch melting. IPS InLine porcelain with overall dimensions of 8 x 3 x 1.1 mm was centrally applied on each strip. Metal ceramic specimens were also prepared after each alloy was melted a second and third time. There were 12 specimens in each of the 9 groups. Force to failure and porcelain bond compatibility index (tau(b)) were determined for each specimen, and statistical comparisons were made using the Ryan-Einot-Gabriel-Welsch multiple range test (experimental alpha=.05). Fractured specimens were examined with a scanning electron microscope. RESULTS: Mean values of tau(b) for specimen groups ranged from 40.6 to 48.2 MPa, and there were no significant differences among the 3 alloys after the first casting. For the high-gold alloy, tau(b) was significantly different for the first and third castings. Increases in size and frequency of interfacial voids were observed with the SEM when all alloys were cast 2 additional times. CONCLUSIONS: All 3 alloys had adequate porcelain bond strength (>25 MPa). The bond strength for the high-gold alloy was significantly greater for the third casting than for the first casting.