La Chaux-de-Fonds, Switzerland
La Chaux-de-Fonds, Switzerland

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Sohn S.,Yale University | Liu Y.,Yale University | Liu J.,Yale University | Gong P.,Huazhong University of Science and Technology | And 7 more authors.
Scripta Materialia | Year: 2017

A series of noble metal high entropy alloys with up to six constituent elements has been produced by casting. PtPdRhIrCuNi forms single-phase face-centered cubic solid solution, and its stability is confirmed by annealing experiments. This alloy deforms homogeneously to ~ 30% to a high ultimate compression strength of 1839 MPa. We discuss rules for the formation of single-phase solid solution. © 2016


Ardelean L.,Victor Babes University of Medicine and Pharmacy Timisoara | Reclaru L.,PX Holding SA | Susz C.,PX Dental Qualident | Rusu L.C.,Victor Babes University of Medicine and Pharmacy Timisoara
Revista de Chimie | Year: 2012

The aim of this study is to determine the causes which lead to a significant colour change and loss of the metallic shine of a 4-element bridge made of a low-gold-content conventional alloy, only a few months after cementation. The authors used scanning electron microscopy (SEM) with retrodiffused electrons and energydispersive X-ray spectroscopy (EDX), applied to the restoration surface and in transversal section. The failure occurred due to the incorrect melting conditions of the alloy which leads to internal porosities and areas with very different superficial composition. On the other hand, the improper polishing of the surface led to diminished corrosion resistance and the degradation of the prosthetic piece only a few months after cementation in the mouth.


Reclaru L.,PX Holding SA | Ardelean L.,Victor Babes University of Medicine and Pharmacy Timisoara | Govor I.,University of Oradea | Tigmeanu C.V.,Privat Praxis Armila | Rusu L.-C.,Victor Babes University of Medicine and Pharmacy Timisoara
Revista de Chimie | Year: 2014

The subject of this work limits itself to the aspects of the toxicity from the point of view of the mutagenic potential of the palladium in the PdCl3form. The essays of gene mutation were realized on cell cultures of mouse lymphoma L5178Y according to the protocol: Test No. 476 OECD: In vitro Mammalian Cell Gene Mutation. The test allows to detect gene mutations induced by chemical substances. In the cell lines the most commonly-used genetic endpoints measure mutation at thymidine kinase (TK) and hypoxanthineguanine phosphoribosyl transferase (HPRT), and a transgene of xanthineguanine phosphoribosyl transferase (XPRT). Cell L5178Y is treated with PdCl3 until the limit of the toxicity. After several subcultures, trifluorothymidine (TFT) is added to the cultures and the cloning of mutants cells is carriedouton a multiwall cell-culture. At the same time there is a cloning of a sample of cells in absence of TFT to determine how the cellular survives the treatment. The number of mutant cells compared with the number of surviving cells allows to calculate the frequency of transfer and is compared with untreated control cells. The results show that in absence of metabolic activation no significant mutagenic effect is observed.


Reclaru L.,PX Holding S.A. | Unger R.E.,Johannes Gutenberg University Mainz | Kirkpatrick C.J.,Johannes Gutenberg University Mainz | Susz C.,PX Holding S.A. | And 4 more authors.
Materials Science and Engineering C | Year: 2012

In the last years the dental alloy market has undergone dramatic changes for reasons of economy and biocompatibility. Nickel based alloys have become widely used substitute for the much more expensive precious metal alloys. In Europe the prevalence of nickel allergy is 10-15% for female adults and 1-3% for male adults. Despite the restrictions imposed by the EU for the protection of the general population in contact dermatitis, the use of Ni-Cr dental alloys is on the increase. Some questions have to be faced regarding the safety risk of nickel contained in dental alloys. We have collected based on many EU markets, 8 Ni-Cr dental alloys. Microstructure characterization, corrosion resistance (generalized, crevice and pitting) in saliva and the quantities of cations released in particular nickel and CrVI have been evaluated. We have applied non parametric classification tests (Kendall rank correlation) for all chemical results. Also cytotoxicity tests and an evaluation specific to TNF-alpha have been conducted. According to the obtained results, it was found that their behavior to corrosion was weak but that nickel release was high. The quantities of nickel released are higher than the limits imposed in the EU concerning contact with the skin or piercing. Surprisingly the biological tests did not show any cytotoxic effect on Hela and L929 cells or any change in TNF-alpha expression in monocytic cells. The alloys did not show any proinflammatory response in endothelial cells as demonstrated by the absence of ICAM-1 induction. We note therefore that there is really no direct relationship between the in vitro biological evaluation tests and the physico-chemical characterization of these dental alloys. Clinical and epidemiological studies are required to clarify these aspects. © 2012 Elsevier B.V.


Kumar G.,Yale University | Prades-Rodel S.,PX Holding SA | Blatter A.,PX Holding SA | Schroers J.,Yale University
Scripta Materialia | Year: 2011

The bending plasticity of Pd-based and Pt-based bulk metallic glasses (BMGs) is compared. Low cooling rates obtained during bulk casting render Pd-BMG (Pd 43Cu 27Ni 10P 20) brittle, whereas Pt-BMG (Pt 57.5Cu 14.7Ni 5.3P 22.5) retains high plasticity at all cooling rates. The ratio of the shear modulus (G) to the bulk modulus (B) in the two alloys is similar (∼0.2). A previously proposed critical G/B value of 0.41 for tough to brittle transition is not supported by our findings, which rather suggest an alloy specific critical G/B. © 2011 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.


Dirras G.,University of Paris 13 | Gubicza J.,Eötvös Loránd University | Tingaud D.,University of Paris 13 | Billard S.,University of Paris 13 | Billard S.,PX Holding S.A.
Materials Chemistry and Physics | Year: 2011

Aluminum/alumina nanocomposites were processed by hot isostatic pressing at 450 °C and 550 °C. In the bulk material sintered at 550 °C, the composite microstructure was formed by in situ phase transformation of the native amorphous layer on the Al particle surfaces into nanocrystalline alumina dispersoids. The microstructure consisted of an aluminum matrix containing both ultrafine and coarse grains as well as embedded γ-Al2O 3 nanocrystals. The large grains in the matrix stopped the crack propagation during deformation thereby increasing the toughness of the composite. When fracture occurred during deformation at 200 °C in air, the heat released due to oxidation smelts aluminum resulting in filament formation between the fracture surfaces. The samples sintered at 450 °C and 550 °C had similar crystallite size and dislocation density in the matrix while in the former specimen crystallization of the amorphous phase did not occur. Additional annealing of this sample in a calorimeter resulted in the formation of nanocrystalline Al2O3 accompanied by an endothermic peak at about 527 °C and mass-reduction of about 3%, probably as result of gaseous products release. The stresses induced by the volume change during crystallization of alumina yielded an increase of the dislocation density in the Al matrix. © 2011 Elsevier B.V. All rights reserved.


Reclaru L.,PX Holding SA | Ardelean L.,Victor Babes University of Medicine and Pharmacy Timisoara | Rusu L.-C.,Victor Babes University of Medicine and Pharmacy Timisoara
Revista de Chimie | Year: 2013

The aim of this study is to determine the causes which lead to corrosion of a 4-element bridge, shortly after cementation. We used scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), applied to the restoration surface and in section. The tests showed failure due to localized corrosion, effect of internal oxidation of the less noble alloy elements, under the effect of secondary bonding in the furnace. The same bridge rebuilt with the same materials, but with a correct finishing phase, including a deoxidation in an etching salt and cemented to the same patient has not shown signs of corrosion.


Ardelean L.,Victor Babes University of Medicine and Pharmacy Timisoara | Reclarip L.,PX Holding SA | Rusu L.-C.,Victor Babes University of Medicine and Pharmacy Timisoara
Revista de Chimie | Year: 2015

Low gold-content dental alloys nowadays represent viable alternatives to high nobility alloys. The casting techniques and equipment used for low-gold content alloys are similar to those used for conventional gold alloys. This, coupled with their acceptable properties, good clinical performance and lower cost, has lead to their widespread use. The alloy performance in the dental laboratory is an important factor affecting alloy selection. One of the main properties of alloys is their capacity to very accurately reproduce the wax pattern, therefore resulting in a fine structure, with minimum internal porosity and no surface defects. These performances represent what we call castability. The aim of our study is to determine castability for a low gold-content dental alloy.


Ardelean L.,Victor Babes University of Medicine and Pharmacy Timisoara | Reclaru L.,PX Holding SA | Bortun C.,Victor Babes University of Medicine and Pharmacy Timisoara | Rusu L.-C.,Victor Babes University of Medicine and Pharmacy Timisoara
Solid State Phenomena | Year: 2014

The aim of this study is to assess the quality of laser welded joints, by different methods such as: scanning electronic microscopy, metallography, microhardness testing, spectrographic and radiographic analyses. The alloys assessed are a titanium-based alloy used in manufacturing prefabricated pieces for implantology, a standard Au-Pd alloy for the metallo-ceramic technique and a Cr-Co-Mo alloy used for manufacturing the metallic components of partial dentures. The conclusion of the testing is that laser welded joints are generally mechanically satisfactory. Laser is best suitable to weld titanium and its alloys because they have higher rates of laser beam absorption and lower thermal conductivity than other dental casting alloys. © (2014) Trans Tech Publications, Switzerland.


PubMed | Johannes Gutenberg University Mainz, PX Holding S.A., Polytechnic University of Bucharest and University of Basel
Type: Journal Article | Journal: Materials science & engineering. C, Materials for biological applications | Year: 2013

In the last years the dental alloy market has undergone dramatic changes for reasons of economy and biocompatibility. Nickel based alloys have become widely used substitute for the much more expensive precious metal alloys. In Europe the prevalence of nickel allergy is 10-15% for female adults and 1-3% for male adults. Despite the restrictions imposed by the EU for the protection of the general population in contact dermatitis, the use of Ni-Cr dental alloys is on the increase. Some questions have to be faced regarding the safety risk of nickel contained in dental alloys. We have collected based on many EU markets, 8 Ni-Cr dental alloys. Microstructure characterization, corrosion resistance (generalized, crevice and pitting) in saliva and the quantities of cations released in particular nickel and CrVI have been evaluated. We have applied non parametric classification tests (Kendall rank correlation) for all chemical results. Also cytotoxicity tests and an evaluation specific to TNF-alpha have been conducted. According to the obtained results, it was found that their behavior to corrosion was weak but that nickel release was high. The quantities of nickel released are higher than the limits imposed in the EU concerning contact with the skin or piercing. Surprisingly the biological tests did not show any cytotoxic effect on Hela and L929 cells or any change in TNF-alpha expression in monocytic cells. The alloys did not show any proinflammatory response in endothelial cells as demonstrated by the absence of ICAM-1 induction. We note therefore that there is really no direct relationship between the in vitro biological evaluation tests and the physico-chemical characterization of these dental alloys. Clinical and epidemiological studies are required to clarify these aspects.

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