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Biomedical subjects

J Payan

Publications and source records attributed to J Payan.

At least 37 records · Page 2Linked to original sources
PubMed1987

Experimental observation of silver and gold penetration into dental ceramic by means of a radiotracer technique.

A radiotracer technique was used to study silver and gold diffusion into dental porcelain under experimental conditions close to the real conditions in prosthetic laboratories for porcelain bakes. It was clearly shown that these non-oxidizable elements were able to diffuse into the ceramic as well as oxidizable ones. The penetration depth varied widely according to the element. The ratio DAg/DAu was about 10(3) around 850 degrees C. In contrast to gold, the silver diffusion rate was high enough to allow silver, from the metallic alloy, to be present at the external ceramic surface after diffusion into the ceramic. Hence, the greening of dental porcelains baked on silver-rich alloys could be explained mainly by a solid-state diffusion mechanism.

Chemical Phenomena↗
PubMed1986

Changes in physical and chemical properties of a dental palladium-silver alloy during metal-porcelain bonding.

The hardening ability of a dental palladium-silver (Pd-Ag-Sn-In) bonding alloy has been investigated, and the distribution of the elements along the metal-ceramic interface have been studied by microprobe analysis. The alloy was found to be highly heterogeneous in its 'as-cast' condition, but homogenized alloy was obtained after heating the alloy at 1000 degrees C for 2 h. Hardening occurred after annealing at 650 degrees C for 1 h. A longer thermal treatment caused the hardness to decrease (over-ageing). The change in hardness could be attributed to an internal oxidation phenomenon. The additional elements tin and indium segregated towards the ceramic-metal interface, with a diffusion of indium only into the porcelain. Diffusion of silver in the ceramics, supposed to be the cause of the 'greening' of dental porcelains baked on silver-rich alloys, has not been detected by the microprobe across the interface.

Chemical Phenomena↗
PubMed1983

The natural history of acute painful neuropathy in diabetes mellitus.

Observations have been made on nine cases of painful diabetic neuropathy of acute onset. All cases were male and all were associated with and preceded by precipitous and severe weight loss. The pain was of a continuous burning quality and experienced mainly in the legs, especially distally. Contact discomfort of the skin was often a troublesome feature, but sensory loss was mild or absent, and reflex loss or depression not invariable. There were no accompanying motor signs. Depression and impotence were constant features. The weight loss responded to adequate control of the diabetes with insulin and was followed by improvement in the neuropathy. The severe manifestations subsided in all cases within 10 months, and in most cases within 6 months, and later resolved completely in all except one. No recurrences were observed after follow-up periods of up to 6 years. Abnormalities of nerve conduction were mild or even lacking. Sural nerve biopsies from three cases taken in the acute stage showed evidence of active degeneration of myelinated nerve fibres of all diameters and also degeneration of unmyelinated axons. There was a mild degree of demyelination. It is concluded that acute painful diabetic neuropathy is a distinct syndrome, occurring in insulin or noninsulin dependent patients of any duration, and unrelated to other diabetic complications. It is separable from other types of painful diabetic sensory polyneuropathy that have been described.

Acute Disease↗
PubMed1980

Neuralgic amyotrophy.

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Brachial Plexus Neuritis↗
PubMed1980

[Effect of the treatments preceding porcelain baking on the strength of the ceramic-metal bond].

The influence of various prefiring treatments of the metallic structure on the metal-ceramic bond strength has been shown for a gold-platinum ceramic alloys. Using analytical techniques with a high sensitivity, it has been possible to show that indium accumulates considerably on and below the metallic surface and that a subsequent sand blasting or acid pickling (hot diluted sulfuric acid) brings the indium level down to the initial value of the alloy. Changes in the resulting mean coefficient of thermal expansion have been computed and verified experimentally. They have then been correlated with the mechanical behavior of the tested metal-porcelain bonds. It has thus been shown that a preliminary oxidation in the air, followed by a hot acid pickling, is the best prefiring procedure. The superficial indium concentration is more homogeneous and closer to the initial content and the bond strength thus obtained is among the highest, with the lowest dispersion. This procedure enables to enhance the fiability on the porcelain-baked-to-metal technique and to increase the safety margin of the bond itself.

Dental Alloys↗
PubMed1979

Evaluation of alternative alloys to precious ceramic alloys. 1. Mechanical properties.

In the first part of this study, the microstructures and the mechanical properties of precious, semi-precious, and nonprecious dental casting alloys for the porcelain-baked-to-metal technique have been determined. The semi-precious alloys contained only 50% gold, and palladium, silver, and some base metals. The nonprecious alloys were of the nickel-chromium type. Discs and miniaturized tensile bars have been cast and tested either in the as cast condition, or after a simulation of the various porcelain bakes. Proof stress, ultimate tensile strength, elongation, and plastic stiffness have been measured and results compared by use of analyses of variance. The microstructure examination shows that the simulation of the porcelain bakes improves the homogeneity of the precious and semi-precious alloys. Simultaneously, the mechanical properties of the same alloys are also improved. One semi-precious alloy, still under development at the time of these tests, has its mechanical characteristics markedly downgraded by the thermal treatments. The nickel-chromium alloys exhibit the best range of mechanical properties for the porcelain-baked-to-metal technique, when considering the three most relevant properties: proof stress, plastic stiffness, and modulus of elasticity.

Chemical Phenomena↗
PubMed1977

[Comparative testing of various resins for model dies].

The value of resins for model dies is controversial. This objective study indicates that epoxy- and epimine resins may be successfully used as die materials, if certain measures are taken as a precaution. The resin should be centrifuged and a slight contraction of the material must be calculated into the chain of manufacture. The material should not be poured into hydrocolloid impressions, as the humidity of this impression material may interfere with the proper polymerization of the resin. A major inconvenience are the frequent formation of air bubbles on the angles of the preparation, and this in spite of the use of the vibrator.

Acrylic Resins↗
PubMed1975

[Attempt at a statistical analysis of the values of the free-way space measured on a sample of 54 patients].

The measurements of the free-way space (= distance between physiologic rest position and centric occlusion) vary according to the method used. In order to get a more distinct reference point, the authors suggest tattooing the Menton (lowest chin point) rather than the Pogonion (most anterior chin point). The free-way space measured in this study ranged from 0.5 to 8 mm. 75% of all cases examined revealed a free-way space between 1 and 2 mm and only 5% showed extreme values such as 0.5 and 8 mm. In contrast to Thompson, who believes that the vertical dimension of occlusion equals the vertical dimension in rest position minus 2 mm the results of this study are in agreement with the findings of those authors, who observed an individually great variation of the free-way space.

Cephalometry↗