Comparison of the metal-to-ceramic bond strengths of four noble alloys with press-on-metal and conventional porcelain layering techniques Mofida R. Khmaj, BDS, MS,a Abdulfatah B. Khmaj, BDS, MS,b William A. Brantley, PhD,c William M. Johnston, PhD,d and Tridib Dasgupta, MSe College of Dentistry, The Ohio State University, Columbus, Ohio; Ivoclar Vivadent, Amherst, NY 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-onmetal 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 (a¼.05). 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. (J Prosthet Dent 2014;-:---)

Scholarship support for first 2 authors was received from the Libyan Ministry of Higher Education. From a thesis submitted by the first author in partial fulfillment of the requirements for Master of Science, The Ohio State University. Two presentations of this work were made at the American Association for Dental Research annual meeting, Tampa, Fla, March 2012. Tridib Dasgupta has a financial interest in the casting alloys and dental porcelains that were investigated in this study. a

Former graduate student, Division of Restorative, Prosthetic and Primary Care Dentistry, College of Dentistry, The Ohio State University. Former graduate student, Division of Restorative, Prosthetic and Primary Care Dentistry, College of Dentistry, The Ohio State University. c Professor, Division of Restorative, Prosthetic and Primary Care Dentistry, and Director, Graduate Program in Dental Materials Science, College of Dentistry, The Ohio State University. d Professor, Division of Restorative, Prosthetic and Primary Care Dentistry, College of Dentistry, The Ohio State University. e Director of Research and Development, Ivoclar Vivadent. b

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Clinical Implications Because acceptable bond strengths are obtained with all 4 noble alloys and both porcelain application techniques, clinical selection of these alloys will depend on other mechanical properties, such as the yield strength and modulus of elasticity, needed for the particular patient as well as the experience of the dental technician. Metal ceramic restorations are central to the practice of fixed prosthodontics, and numerous high-noble (old-platinum-palladium [Au-Pt-Pd]; gold-palladium-silver [Au-Pd-Ag]; and Au-Pd), noble (Pd-Ag; palladium-coppergallium [Pd-Cu-Ga]; and Pd-Ga), and conventional (nickel-chromium [Ni-Cr]; and cobalt-chromium [Co-Cr]) base metal alloys are available for porcelain veneering. These alloy types, mechanisms for metal-to-ceramic bonding, and different modes of metal ceramic failures have been discussed at length.1-4 The major bonding mechanisms involve mechanical retention of the ceramic at the roughened metal surface and chemical bonding by means of a transition oxide layer and interdiffusion between the metal and the ceramic; a close match must be made between thermal expansion coefficients of the metal and ceramic to avoid deleterious residual tensile stresses at the interface.1-4 Diffusion profiles that show the accumulation of secondary elements in the alloy, which form oxides at the interface (such as indium and tin for noble alloys), have been reported, along with images of interfaces for cross-sectioned metal ceramic specimens.5-8 Substantial variation exists in the mechanical properties among the different noble and base metal alloys for porcelain veneering, and rational selection depends on the mechanical properties required for a particular clinical situation and the experience of the dental laboratory, although differences in alloy cost are often a practical consideration.1-3 Although the dental laboratory procedures used for many decades that involve the sintering of several dental porcelain layers on the metal coping

substrate achieve excellent esthetic results,1-3 this procedure is time consuming, and several studies have investigated an alternative approach of more rapidly hot pressing the ceramic onto the coping.9-11 The commercial presson-metal (PoM) technique, developed by Ivoclar Vivadent for dental laboratories, uses special equipment for hot pressing the remainder of the porcelain onto the alloy after the initial oxidation step and sintering of opaque porcelain. A different low-fusing body porcelain composition that has reduced viscosity at the hot-pressing temperature range is needed. The present study compared metalto-ceramic bond strengths obtained with the International Organization for Standardization (ISO) 9693 test12 by using conventional porcelain layers and the PoM technique for 4 recently marketed noble alloys; this information has not been previously available. Results are compared with those from other recent studies that also used the ISO 9693 test to evaluate metal-to-ceramic bonding for other alloys and for conventional porcelain and hot-pressed ceramics.13-15 The origin of the differences in the results obtained with the current ISO bond strength test12 and the porcelain adherence test16 by using the previous American Dental Association specification protocol17,18 also is discussed, along with consideration of mechanics principles19,20 that underlie ISO 9693.12

MATERIAL AND METHODS Four alloys (Aquarius Hard, Evolution Lite, Callisto 75 Pd, and Aries; Ivoclar Vivadent) for metal ceramic restorations were selected. Based on

The Journal of Prosthetic Dentistry

the current American Dental Association classification,21 Aquarius Hard is a high-noble Au-Pt-Pd alloy; Evolution Lite is a high-noble Au-Pd alloy; Callisto 75 Pd is a noble Pd-Ag alloy that contains Au, with higher Pd and lower Ag contents than conventional Pd-Ag alloys; and Aries is a noble conventional Pd-Ag alloy. All 4 alloys are Type 4, according to the current ISO Standard 22674.22 Nominal compositions and properties of the alloys provided by the manufacturer are shown in Tables I and II. Forty metal strips, 2530.5 mm, 10 for each alloy, were cast from wax pattern strips. Dimensions of the metal strips are stipulated in ISO Standard 9693.12 The starting wax sheets were trimmed and sprayed with surfactant (Sure Take Surfactant; Ivoclar Vivadent) to reduce surface tension. The wax pattern strips were invested with a phosphate-bonded investment (Sure Vest Quick; Ivoclar Vivadent). Following the manufacturer’s directions, the phosphate-bonded investment powder (100 g) was mixed with 32% special liquid for the investment and 22% distilled water under vacuum at high speed for 1 minute to remove air bubbles. Each alloy was melted in a dedicated ceramic crucible with a multiorifice torch (70 kPa propane per 35 kPa oxygen) (TorchMate; Ivoclar Vivadent). A standard broken-arm centrifugal casting machine (Kerr; Sybron Dental Specialties) was used, and all casting rings were bench cooled to room temperature. The investment was removed from the cast specimens with airborne 50-mm aluminum oxide (Al2O3) particles (MicroBlaster; Comco), and sprues were removed with a high-speed lathe (Demco) and Rubi Slitters/Dedeco disk (Pearson Dental

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Table I. Alloy Name

3 Compositions (wt. %) provided by manufacturer for 4 noble alloys selected for study

Gold Platinum Palladium Silver Tin Zinc Indium Gallium Ruthenium Iridium Rhenium Other 8.5

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

New noble alloys for metal ceramic restorations introduced by manufacturers are generally lower-cost alternatives to traditional higher-gold alloys. I...
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