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Biomedical subjects

M M Vrijhoef

Publications and source records attributed to M M Vrijhoef.

At least 37 records · Page 2Linked to original sources
PubMed1988

Oxidation of a gold-palladium PFM alloy.

In this study, the influence of oxygen pressure, as well as oxidation time and temperature, on the oxide formation of a gold-palladium-indium-gallium alloy was investigated. After oxidation (vacuum/air, 1-10 min, 940-1020 degrees C) the oxides were removed selectively by means of leaching in 37% hydrochloric acid. Concentrations of the metallic parts of the oxide layers were determined by means of an emission spectrometer. The composition of the oxide layer was computed on the basis of these measurements. Palladium oxide was not found. The formation of In2O3 and Ga2O3 was detected. The oxidation time did not influence the composition of the oxide layer. A higher oxidation temperature gave a slightly greater In2O3 concentration. Oxidation in vacuum resulted in a much higher Ga2O3 content. Under all conditions gallium oxidized preferentially.

Gallium↗
PubMed1988

The corrosion resistance of a new cobalt-chromium-molybdenum-ceramic alloy.

Cobalt-chromium alloys are extensively used for removable partial dentures and implants. Recently, this type of alloy has been introduced for porcelain-fused-to-metal crown and bridgework. The objective of this in vitro study was to evaluate the corrosion behaviour of such a ceramic alloy (Vicomp) and compare it to a cobalt-chromium alloy for removable partial dentures (Vitallium). A 0.9% saline solution and an artificial saliva were used as electrolytes. Results indicate a similar, adequate, corrosion resistance.

Ceramics↗
PubMed1988

Carbon absorption of palladium-enriched ceramic alloys.

Palladium-enriched alloys are sensitive to carbon absorption. High carbon levels in ceramic alloys negatively influence some mechanical properties and cause porosities in the porcelain during the firing process. The influence of the palladium content on carbon absorption of alloys with a range of palladium content from 5 to 80% approximately was investigated. Carbon content was measured for alloys in the 'as received' condition as well as after melting once and three times. Carbon contents up to 200 ppm were measured in the case of a high-palladium system.

Absorption↗
PubMed1988

Metallurgical aspects of high-palladium alloys.

Nine commercial high-Pd alloys were investigated. Microstructure and phase composition were screened by x-ray diffraction, light microscopy, and an electron microprobe. After being etched, some high-Pd alloys revealed dendritic structures. The others showed a more homogeneous structure with distinct grain boundaries. Etching was necessary to reveal distinct structures, though the overall etching effect turned out to be limited. On unetched specimens, only a slight chemical heterogeneity could be determined. Except for one alloy, the systems turned out to have complex multi-phase structures. The main face-centered-cubic (fcc) phase was Pd-based. As secondary phases, body-centered-cubic (bcc) and/or simple cubic ones were detected. The latter phases were similar to a Cu3Ga and PdGa intermetallic compound, respectively. Face-centered-tetragonal (fct) structures reported by other investigators were not found.

Chemical Phenomena↗
PubMed1987

The influence of the condensation instrument on the clinical behaviour of amalgam restorations.

The influence of the condensation instrument on the behaviour of amalgam restorations was investigated in a clinical study for which in a group of forty-nine patients, 125 Class I or II amalgam restorations were made by each of two operators. The restorations were made in series of five per patient. For each restoration within a series, the amalgam was condensed with a different instrument (hand condensation, Amalgam Condensaire, Speedomatic, Bergendal Vibrator and Electro-mallet). For a period of 2.5 years the restorations were checked at half-year intervals for failures. The marginal integrity of the restorations was assessed half-yearly with a six-point photo rating scale. The discolouration, roughness formation and the marginal integrity of the restorations were assessed clinically with four-point rating scales. The number of failures and the assessments were analysed for the effect of the condensation instrument, the patient and the operator. After 2.5 years, 12% of the restorations had failed, which is too few for the tracing of a condensation instrument and a patient effect. The operator, however, had an influence on the failure percentage. The condensation instrument had no influence on the clinical behaviour of the restorations, however the patient had. The operator only had an influence on the marginal integrity. This suggests that clinically the condensation results depend more on the operator rather than the instrument.

Dental Amalgam↗
PubMed1987

Corrosion of ferromagnetic alloys used for magnetic retention of overdentures.

Three ferromagnetic casting alloys intended for use with magnetically retained overdentures (compositions in wt%: #1, Pd 50, Co 47, Ga 2, Pt 1; #2, Pd 60, Co 37, Ga 2, Pt 2; #3, Pd 49, Co 46, Ga 2, Pt 2) were investigated. A 0.9% saline solution and an artificial saliva (Meyer) were used for evaluation of the electrochemical corrosion behavior of these alloys, utilizing standard potentiodynamic techniques. All alloys investigated possessed a good corrosion resistance in the potential range of the oral environment (from -100 to 300 mV versus SCE). In addition, alloys #1 and 3 appeared to be susceptible to pitting above +300 mV (SCE), while #2 was resistant to pitting and was found to passivate in 0.9% saline solution.

Chromium Alloys↗
PubMed1986

A clinical comparison of three types of resin-retained cast metal prostheses.

A preliminary clinical trial comparing three types of resin-retained cast metal FPDs was conducted. Micromechanical retainers were found to be more retentive than macromechanical retainers. The retention values in this investigation were in agreement with similar studies, but longitudinal studies are still desirable.

Acid Etching, Dental↗