Tarnishing of a Low-gold Dental Alloy in Different Structural States

Herø, H.; Jørgensen, R.B.

doi:10.1177/00220345830620031401

Cited by 31 publications

(12 citation statements)

References 5 publications

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“…The observed compositions of the eutectic phases are fairly close to the two equilibrium phases formed in this alloy after a long time of annealing [3] at 500~ 50wt% Au-(40 to 42)wt% Ag-(1 to 1.5)wt % Pd and 60wt% Au-28wt % Cu-2.5wt % Pd, respectively However, this heat treatment also produced a third, palladium-rich equilibrium phase, which explains the fairly low palladium content in the other two phases.…”

Section: Resultssupporting

confidence: 71%

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Analytical electron microscopy of cast Au-Ag-Cu alloys

et al. 1986

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The microstructure in an as-cast Au-Ag-Cu-Pd alloy has been examined by electron microscopy (TEM) combined with quantitative X-ray microanalysis (EDS). The primary phase formed during solidification is enriched in silver and palladium, while gold and copper segregate to grain boundaries, where substantial amounts of lamellar eutectic colonies are formed. The compositions of the lamellae were determined by EDS analysis to be 56% Au-13% Ag-26% Cu-6% Pd and 50% Au-42% Ag-5.5% Cu-2.5% Pd (wt%). Ordering and decomposition reactions take place during cooling in the solid state: plate-like precipitates of tetragonal AuCu-I on {001} planes were found within the primary phase and in silver-rich lamellae in eutectic colonies.

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Section: Resultssupporting

confidence: 71%

“…Surveys of the equilibrium phases formed at 500 ~ C and their effect on tarnish formation have been published [2][3][4]. A review of microstructures in Au-Ag-Cu-Pd alloys has been given by Yasuda [5].…”

Section: Introductionmentioning

confidence: 99%

Analytical electron microscopy of cast Au-Ag-Cu alloys

et al. 1986

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“…Because of the large two- phase region in this system, the composition of the alloys should affect their microstructures. Furthermore, previous research has shown that microstructure influences the tarnish response (8)(9)(10)(11)30). Figure 1 shows the ternary phase diagram with the approximate compositional ranges for the five alloys.…”

Section: Experitnental Proceduresmentioning

confidence: 99%

Chemical stability of gold dental alloys

Treacy

German

1984

Gold Bull

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The bzocornpatibzlity and desirable working charactei istics ofgold-based alloys are wzdely recognized in dentisti y. Although there has been considerable activity in understanding such characteizstics as hardenability, there is peihaps more significance to the chemical stability ofa dental alloy sznce degradatzon ofa dental alloy duringservzce can inducea toxic response andpromote gingival tissue irritaion.Because of the recognized role of nobility of a dental alloy in determining chemical stability, various compositional specifications have been issued to help ensure successful service. However, it is recognized that alloys meeting these compositional specifications can prove unacceptable in service (1, 2). Conversely there are several alloys in service which appear to perform satisfactorily in spite of an apparently low nobility. These factors serve to illustrate the complex situation which exists concerning acceptance standards for dental alloys; performance standards are regarded as more reliable than compositional standards.This article describes astudy conducted to obtain quantitative tests and data for the tarnish and corrosion behaviour of gold-based dental alloys. The test data necessarily require clinical corroboration to ensure their validity as an indicatorof alloy suitability fororal use. However, significant progress has been made in determining the nature of a minimum, yet comprehensive, test battery. In addition, the procedures described in this report show quantitatively a capability of separating the performances of dental alloys in laboratory tests. Data obtained from five commercial alloys are given to illustrate the application of the testing approach. BackgroundThe chemical instability of dental alloys has long been recognized as a serious problem. Two distinct occurrences may alter the surface condition of a metal in the mouth; corrosion and tarnish. Corrosion involves the electrochemical dissolution of the metal or the formation of reaction products on the surface. Tarnish is the surface discolouration due to the formation of reaction products and is a specific form of corrosion. There have been several previous investigations of both forms ofattack and these have been reviewed by German (3).Because of the more visible nature of tarnish attack, there has been considerable emphasis on this subject in the previous dental alloy studies. Early research in a sulphurized oil bath by Souder and Paffenbarger (4) indicated that 75 weight per cent noble metal in an alloy was necessary to avoid tarnish. Swartz etal. (5) employed 13 different test solutions, using the as-received alloys in an undefined thermal condition, ranked the results in a subjective manner. The general conclusion was that discolouration occurred preferentially in the low nobility alloys when exposed to sulphide solu tions.The study by Tuccillo and Nielsen (6) demonstrated that on a microscopie scale tarnish attack has a galvanic nature. Silver-rich regions were preferentially attacked by the sulphide-containing solution used in...

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“…Therefore, it was suggested that the tarnish resistance of the quaternary Ag-Au-Pt-Cu alloys designed in the present study would principally depend on the tarnishing behavior of the AgAu-rich matrix phase. As for the deposit formed on the Ag-Au-rich matrix, it was most probably silver sulfide based on the experimental setup of the present study for the tarnishing environment [11][12][13] . After 72-hour exposure to the test solution, the ∆E* values of all the Ag-Au-Pt-Cu alloys were plotted against their Au/(Au+Ag) atomic ratios in Fig.…”

Section: Discussionmentioning

confidence: 81%

Tarnish resistance evaluation of experimental Pd-free Ag-Au-Pt-Cu dental alloys

et al. 2010

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This study evaluated the tarnish resistance of eight experimental Pd-free Ag-Au-Pt-Cu dental alloys in a 0.1% Na2S aqueous solution at 37°C. Color measurements of the plate samples were made using a computerized spectrophotometer before and after immersion in the test solution for up to 72 hours. Tarnish discoloration was evaluated using the color difference vector, ΔE*, in the CIELAB color space. Microstructural observation of each sample through an optical microscope revealed the matrix phase as the major constituent and second-phase small grains in the matrix phase. Selective tarnish discoloration occurred in the matrix, and fractional area of the matrix to the whole surface area was influenced by the sum of Au and Ag concentrations. The ΔE* value significantly decreased with increasing Au/(Au+Ag) atomic ratio. In conclusion, the Au/(Au+Ag) ratio in an alloy and the fractional area of the matrix were found to be primary and auxiliary factors affecting the tarnish resistance of the experimental alloys.

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Tarnishing of a Low-gold Dental Alloy in Different Structural States

Cited by 31 publications

References 5 publications

Analytical electron microscopy of cast Au-Ag-Cu alloys

Analytical electron microscopy of cast Au-Ag-Cu alloys

Chemical stability of gold dental alloys

Tarnish resistance evaluation of experimental Pd-free Ag-Au-Pt-Cu dental alloys

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