Precious Alloys Research Articles

Effects of metal combinations on cytotoxicity evaluation using a dynamic extraction method.

The effects of metal combinations on cytotoxicity were examined following dynamic extraction by freely gyrating two spherical metals in a glass vessel. The cell viabilities of an Au alloy, a Ag-Pd-Au alloy and Ti were little affected by combinations among three metals. Cell viability ranged between 60 and 80% when precious alloys were in combination with Co-Cr or Ni-Cr alloys. Ti showed a clear difference in cell viability either in combination with Co-Cr or Ni-Cr alloys. The cell viability of the Ti/Co-Cr alloy combination was the same as that of precious alloys/Co-Cr or Ni-Cr alloy combinations. However, in an analogy with Co-Cr alloy/Ni-Cr alloy combination, the Ti/Ni-Cr alloy combination depressed the cell viability below 20%. This suggested that when new metals are to be used in combination with dissimilar metals, the cytotoxicity of the metals could be evaluated in extraction conditions using the mutual dynamic contact of dissimilar metals.

Determination of gold in precious alloys by glow discharge atomic emission spectrometry

The increasing need for harmonization in the determination of trace and matrix elements in precious metals and alloys requires the development of innovative and reliable techniques which might eventually replace the conventional fire assay approach. Three types of alloys of Au, with Ag, Cu and Zn (respectively, 910, 750 and 580‰, i.e., 22, 18 and 14 karats), were taken into account. Samples were shaped as flat disks and analyzed for their Au content by glow discharge atomic emission spectrometry (GD-AES). Wherever possible, use was made of Ag or Cu as the internal standard. The discharge conditions adopted included pulsed current intensity in the range 4–9 mA, voltage between 600 and 700 V and Ar pressure of 200 Pa. The concentration values obtained for Au agree well with the nominal concentrations given by the producer for different lots of alloys, as well as with the data obtained by the fire assay. In particular, in terms of accuracy the GD-AES approach appears to be fully equivalent to the fire assay. Repeatability of measurements was also satisfactory, although it should be improved to comply with current regulations, which require an uncertainty range not exceeding 1‰. Inductively coupled plasma atomic emission spectrometry (ICP-AES), on the other hand, appears to be not so suitable for this application.

Effect of hydrophobicity on in vitro streptococcal adhesion to dental alloys.

Non-specific interactions such as electrostatic interactions, and surface free energy are of importance in bacterial adhesion to dental surfaces as they determine whether or not bacteria are attracted to the surface. The relationship between adherence of Streptococcus mitis, S. mutans, S. oralis and S. sanguinis on precious and non-precious dental alloys, and the bacterial and alloy surface hydrophobicities (a measure of the surface free energy) was studied. The number of adhering bacteria was determined by fluorescence microscopy counts. The hydrophobicity of the bacteria and alloy surfaces were evaluated by adhesion to hexadecane and water contact angles, respectively. Our results showed that (i) the surfaces of the tested alloys were hydrophobic, (ii) S. sanguinis, S. mutans and S. oralis were hydrophobic, and (iii) S. mitis was hydrophilic. S. oralis, the more hydrophobic strain, demonstrated the highest adherence on the tested materials, whereas S. mitis adhered least on the hydrophobic surfaces. For the tested alloys, bacterial adherence was highest for the high gold content alloy, and lowest for the non-precious alloy. Our results showed that for the tested bacterial strains, there was a significant correlation between bacterial adhesion and substratum hydrophobicity: hydrophobic metal surfaces favor adhesion of hydrophobic bacteria.

Polymetallism and osseointegration in oral implantology: pilot study on primate.

In oral implantology, successful results in osseointegration are obtained in the medium term (6-12 months) with commercially pure titanium implants. However, current superstructures can be of a different nature (precious metal or titanium) and of different manufacture (cast or machine-produced). Polymetallism between the implant and the superstructure may lead to conditions of galvanic corrosion, and influence osseointegration. The study described establishes, on the one hand, the procedures of animal experimentation in primates and on the other, the techniques of analysis of histological sections. The first technique of analysis is based on histomorphometry and leads to the definition of an osseointegration index. The second technique of analysis consists of X spectrometry by dispersion of energy which enables a spectral analysis of selected points below the crestal neck of the implant (vulnerable area in the case of corrosive attack) to be obtained. It is noted that after 6months, two of which were of activation, osseointegration did not vary according to the nature of the superstructure (precious alloy or titanium). After 2 months, the presence of a precious alloy superstructure lead to titanium migration towards the area around the cervical region of the implant (10-50 microm). This phenomenon did not occur with a titanium implant. It can therefore be presumed that polymetallism leads to detectable corrosion after 2 months but without apparent modification of osseointegration.

Electrochemical investigations regarding the bioavailability of silver after potentiodynamic corrosion load of precious metal alloys Part 2: Dental alloys

The spectrum of commercial dental alloys has been essentially expanded during the last years. The toxicological effects of dental alloys depend mainly on their element specific corrosion behaviour in the oral cavity. The present study demonstrates the electrochemical boundary conditions regarding the possible formation of AgCl-corrosion products, for which cytotoxic effects has been established, by means of specially adapted electrochemical in-vitro test programs. The prevalence of the developed corrosion mode was proved for two electrolytes and four daily used dental alloys containing different amounts of silver. The results show, that a biological relevant assessment of the released silver ions in both electrolytes, induced by anodic metal dissolution, is only reliable if the measurement takes into account the silver ions within the electrolyte as well as the superficial immobilized amount of silver chloride corrosion products. Thus especially from a biological point of view, interface processes like the formation of immobilized corrosion products seem to be a relevant parameter for the complete testing of biocompatibility of metallic biomaterials. To sum up it can be concluded, that the dental alloys investigated in the course of this study have not shown any adverse susceptibility to corrosion with respect to the clinical practice and can therefore be classified as well biocompatible. Elektrochemische Untersuchungen zur Bioverfugbarkeit von Silber nach der Durchfuhrung von potentiodynamischen Korrosionstests an edelmetallhaltigen Legierungen Teil 2: Dentallegierungen Das Spektrum der kommerziell verfugbaren Dentallegierungen hat sich insbesondere in den letzten Jahren deutlich vergrosert. Dabei bestimmt hauptsachlich das elementspezifische Korrosionsverhalten in der Mundhohle die moglicherweise auftretenden toxikologischen Wirkungen. In der vorliegenden Studie werden durch die Anwendung spezieller elektrochemischer in-vitro Testprogramme die Bedingungen aufgezeigt, unter denen die Bildung von AgCl-Korrosionsprodukten, fur die zytotoxische Wirkungen erwiesen sind, moglich ist. Die Gultigkeit des zugrundeliegenden Korrosionsmodells wurde an vier kommerziellen, silberhaltigen Dentallegierungen in zwei Elektrolytqualitaten gepruft. Die Ergebnisse zeigen, das eine biologisch relevante Einschatzung der durch anodische Oxidation elektrolytspezifisch in Losung gegangenen Silberionen nur dann zuverlassig ist, wenn sowohl die Menge der im Elektrolyten detektierten Silberionen und die auf der Materialoberflache immobilisierte Menge an AgCl-Korrosionsprodukten Beachtung finden. Insbesondere aus biologischer Sicht mus beachtet werden, das Grenzflachenprozesse, wie die Entstehung von immobilisierten Korrosionsprodukten, einen entscheidenden Einflus bei der Bewertung der Biokompatibilitat von metallischen Biomaterialien besitzen. Zusammenfassend kann geschlusfolgert werden, das die hier untersuchten, silberhaltigen Dentallegierungen keine nachteilige Korrosionsanfalligkeit zeigen und dementsprechend als biokompatibel eingestuft werden konnen.

Electrochemical investigations regarding the bioavailability of silver after potentiodynamic corrosion load of precious metal alloys Part 1: Binary model alloys

Electrochemical investigations regarding the bioavailability of silver after potentiodynamic corrosion load of precious metal alloys Part 1: Binary model alloys

生体材料の現状と展望 歯科用貴金属材料の現状と期待

生体材料の現状と展望 歯科用貴金属材料の現状と期待

Role of secondary ion mass spectrometric analysis in the brazing of precious alloys

Secondary ion mass spectrometric characterization of Cd-free and Cd-containing brazing alloys for jewelry are presented, analyzing the surface composition and elemental distribution along the thickness both for master alloys and brazed joints. It was verified that the brazing process induced little modification in In-containing alloys. On the other hand, Cd evaporation from the alloy was verified after heating, confirming its danger to health under these conditions. The presence of intermetallic clusters was detected, indicating interactions between brazing alloys and 18 carat gold. © 1997 John Wiley & Sons, Ltd.

Role of secondary ion mass spectrometric analysis in the brazing of precious alloys

Role of secondary ion mass spectrometric analysis in the brazing of precious alloys

The role of an anaerobic accelerator in dental adhesives

A dental adhesive system was developed to yield a high bond strength to different substrates, enhanced durability, biocompatibility, and absence of interfacial microleakage. Such a system can be cured chemically (self-curing) or by visible light. Based on the assumption of an anaerobic character of the system's polymerization, the effect of the addition of an anaerobic accelerator (saccharin) on the curing mechanism was studied. Subsequently, the composition of the developed adhesive system and its curing conditions were evaluated and optimized. The developed adhesive compositions demonstrate high and durable bonding to dentin, enamel, porcelain, base and precious alloys, and amalgam, and can be used in different adhesive systems.

Thermodynamische Modellierung der Ausscheidungshärtung in Edelmetall-Legierungssystemen

The quaternary system Au-Pt-Pd-Sn is described with the help of the thermodynamic software Chemsage and a specially modelled dataset. Calculations on the stability of precipitated phases show good agreement with experimental results from hardness tests and metallography and thereby provide a better understanding of the observed material properties. The use of such modelling provides an efficient tool for faster and directer development of precious metal alloys.

An advanced multipurpose dental adhesive system

An advanced dental adhesive system, composed of acrylic monomers and coupling agents, characterized by high tensile bond strength, enhanced durability, and biocompatibility was developed. The adhesive composition is curable chemically (self curing) or by visible light. This adhesive composition can be used for bonding to various substrates such as dentin, enamel, precious and nonprecious alloys, 'fresh' and 'set' amalgam, porcelain, and dental composite. Thus, the developed liquid adhesive composition could be considered as a universal dental adhesive.

Analyse de la résistance mécanique d'une interface métal-céramique par l'essai de flexion 4 points : application à des couples metal (Pd-Ag, Pd-Au)-céramique dentaire

Different semi precious alloys (Pd-Ag, Pd-Au) have been studied after thermal oxidation treatments to analyze the mechanical improvement of the interface between the metal and the ceramic. Using the four point bending test, the authors have analyzed the different steps corresponding to the mechanical evolution of the bi-material: cracking energy on the surface, relaxation energy after first cracking, propagation energy of cracks at the interface zone. It has been shown that some alloys only have a high resistance to the interface cracking and the role played by the interface reactions to improve this property

Bonding fixed prosthodontic composite resin and precious metal alloys with the use of a vinyl-thiol primer and an adhesive opaque resin

Adhesive bonding of a light-cured fixed prosthodontic composite resin joined to silver- and gold-based alloys was investigated with the use of a metal primer and an adhesive opaque resin. The primer contained an adhesive bonding promoter for precious alloys, 6- (4-vinylbenzyl- n-propyl) amino-1, 3, 5-triazine-2, 4-dithiol (VBATDT). The cast metal specimens were alumina-blasted and primed with VBATDT acetone solution. A self-curable 4-META/MMA-TBB opaque resin was used to bond the primed metals and a light-cured composite resin. Prepared specimens were thermocycled in water and bond strengths were determined. The shear bond strengths after 100,000 thermocycles (4 °C to 60 °C for 1 minute) were 28.4 MPa for Ag-Pd-Cu-Au alloy and 20.8 MPa for type III gold alloy. This simple method may be used to bond silver or gold alloy and light-activated fixed prosthodontic composite resin.

Dental Materials and Magnetic Resonance Imaging

Radiologists may encounter patients with fixed dental prostheses that may produce image distortion on MRI scans of the face and jaw. In this work, we assessed the MRI appearances of dental prosthetic materials in vitro, including precious alloys, nonprecious alloys, ceramic prostheses, dental amalgam, and composite materials. For in vivo studies, these materials were placed in the patient's mouth. Nonprecious alloys produce large image deformations, whereas precious alloys had no effect on MRI images. The in vivo study showed the anatomical zones that were most affected on MRI scans. The size of these zones produced by the presence of nonprecious alloys is influenced by the volume of the prosthesis and is related to the scanning sequence used.

Pre-treatment of Dental Alloys using Adhesive Primer for Precious Alloys

Pre-treatment of Dental Alloys using Adhesive Primer for Precious Alloys

An in vitro evaluation of a prototype CFRC prefabricated post developed for the restoration of pulpless teeth

Carbon fibre reinforced carbon (CFRC) in the form of a prefabricated post has recently been developed and is theoretically acceptable for consideration in an endodontic post-retained crown system. This study compared four different types of postcore system cemented into 40 extracted anterior human teeth. The test groups consisted of CFRC posts cemented with a composite resin luting agent, and used with either a cast gold alloy core (Group B) or a composite resin core (Group C). Two existing post-core techniques were used as controls for comparison with the CFRC groups. One control was a prefabricated wrought precious alloy post having a cast gold alloy core, and cemented with zinc phosphate cement (Group A). The other was a prefabricated stainless steel post with a composite resin core, and cemented with a composite resin luting agent (Group D). All specimens were restored with a gold alloy crown and tested to failure with an obliquely applied compressive load at 130 degrees in an Instron using a cross-head speed of 5 cm min-1. The results showed that post-retained crowns using a prefabricated CFRC post exhibited properties comparable with, and in some cases better than, those of existing prefabricated posts. The mode of failure of specimens restored with a CFRC post was more favourable to the remaining tooth tissue than was that of specimens restored with a metallic post.

Metal-porcelain bonding to a magnetizable alloy

The bond strength of porcelain to a magnetizable Pd-Co alloy was compared with that of a precious and nonprecious ceramic alloy by using the four-point flexure test and a direct shear test. The test procedure consisted of continuous loading until a bond failure occurred. The fractured surfaces were then examined with a scanning electron microscope. A good strength of the magnetizable Pd-Co alloy comparable to that of two specific ceramic alloys and intermediate between precious and nonprecious alloys was observed. Most of the failures of the precious alloy occurred at the oxide-porcelain interface. The preferential fracture paths were observed for the nonprecious alloy between the metal fracture and the oxide layer. The fractures of the magnetizable alloy occurred at the oxide-porcelain interface and in the bulk of the porcelain, clearly pointing out the possibility of using magnetizable Pd-Co alloy for metal ceramic abutment crowns.

A New Inexpensive Customized Plaque for Choroidal Melanoma Iodine-125 Plaque Therapy

The authors have developed a new inexpensive precious metal alloy plaque for use in customized iodine-125 plaque therapy. Each plaque is formed from two flat circular gold/palladium foils which are used in dental crown work. Using a simple manual mechanism, the two forms are stamped over a customized acrylic die shaped to the dimensions of the tumor base plus a 2-mm margin. Completed plaques consist of a back wall, a 2-mm side wall, and a 1.5-mm wide lip with holes for suture placement. Advantages include: simple construction from inexpensive components, customized shape, and iodine seeds that are readily visible on plane radiographs.

A comparison of diamond and tungsten carbide burs for preparing endodontic access cavities through crowns

Diamond and tungsten carbide burs designed for cutting metal were tested with precious and nonprecious bonding alloys. Standard cavities were prepared and timed. Tungsten carbide burs were most effective in preparing cavities in precious alloy but only a coarse dome-shaped cylindrical diamond bur effectively prepared a succession of five cavities in nonprecious alloy without untoward vibration. Diamond and tungsten carbide burs designed for cutting metal were tested with precious and nonprecious bonding alloys. Standard cavities were prepared and timed. Tungsten carbide burs were most effective in preparing cavities in precious alloy but only a coarse dome-shaped cylindrical diamond bur effectively prepared a succession of five cavities in nonprecious alloy without untoward vibration.