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Biomedical subjects

J Geis-Gerstorfer

Publications and source records attributed to J Geis-Gerstorfer.

At least 19 recordsLinked to original sources
PubMed1991

[The effect of inorganic fillers on the properties of light-curing composites].

Light curing composite resins became the preferred material in treating carious or traumatic lesions of anterior teeth. Attempts to improve the properties of these materials lead to the development of hybrid composites with an amount of anorganic fillers of more than 80 weight %. It was the purpose of this study to investigate whether composites with higher amounts of anorganic filler show better properties than those with lower amounts of filler. Eight commercial and two experimental composites have been tested for their resistance to abrasion by simulated toothbrushing, polymerization shrinkage, water sorption, porosity, and surface quality. The results showed no correlation between the amount of anorganic filler on the one hand and tested properties on the other. The amount of anorganic filler is no quality criterium per se, the properties of a composite are rather influenced by composition and quality of the organic matrix, even if the amount of anorganic fillers increases to more than 80 weight %.

Composite Resins↗
PubMed1990

[Ultimate tensile strength of plasma- and laser-welded cast titanium (Titaniumer, Ohara)].

The ultimate tensile strength (UTS) of titanium castings (Titaniumer, Ohara) as cast and after plasma-welding, laser-welding and soldering was investigated according to DIN 13912. The UTS of titanium as cast was 567 (+/- 36) MPa. After plasmawelding UTS decreased by 69% on the average, after laser-welding by 20%, after soldering with Ag65Cu20Pd15 (1060 degrees C) by 46% and after soldering with Ag72Cu20Ti8 (980 degrees C) by 63%. The highest tensile strength was observed in laser-welded titanium under the conditions described.

Dental Casting Technique↗
PubMed1990

[Properties of a measuring system for digital occlusion diagnosis].

The properties of a new digital technique of demonstrating and quantifying occlusal contacts (T-scan) were tested in vitro the sensor foil used was 95 microns in thickness and had approx. 1350 measuring points. When a given force was applied at the same point on one foil several times in sequence, the readings were highly reproducible. Applying the same force at different points on the same foil and at points on different foils, however, failed to bring about reproducible results. The reasons for this lack of reproducibility and possible modifications are discussed.

Bite Force↗
PubMed1990

[In-vivo corrosion tests of dental alloys in relationship to saliva pH].

The corrosion of four dental alloys and titanium was studied in relationship to saliva pH and plaque accumulation in vivo. Test specimens were scanned for porosities with an image analysis system before and after exposure to the oral milieu. The saliva pH was monitored during the study period. After four days of exposure in the mouth the plaque accumulation and the vitality of the plaque on the alloy surfaces was evaluated. Plaque accumulation and mean saliva-pH were not correlated with the observed surface corrosion. The least surface effects were observed on titanium, which showed the highest plaque accumulation. Different alloys showed different bacteriostatic effects. The least amount of living bacteria was found on titanium. Plaque accumulation and bacteria vitality depended on material and test person.

Corrosion↗
PubMed1989

In vitro substance loss due to galvanic corrosion in Ti implant/Ni-Cr supraconstruction systems.

To characterize the galvanic corrosion of supraconstructions consisting of Ni-Cr alloys that come in contact with titanium implants, the resultant substance loss was determined. The measurement of the released substance masses was conducted by analysis of the electrolyte solutions with the aid of atomic absorption spectrometry and by approximate calculation using current density time curves, according to Faraday's law. The results of this study show that both methods allow a clear differentiation of the corrosion behavior of various Ni-Cr alloys that come in contact with titanium.

Chromium Alloys↗
PubMed1989

[Wetting of various restorative materials].

The mechanisms of varying degrees of plaque accumulation on restorative materials have not been fully clarified yet. Apart from surface morphology, interface phenomena between restorative material, saliva and microorganisms have been discussed. In this study a digital tensiometer was used to determine the degree of wetting of various restorative materials with natural saliva. The veneering material Dentacolor exhibited the highest degree of wetting, followed by dental porcelain and electrolytic gold. The non-precious metals displayed the lowest degrees of wetting. These in vitro results have been compared with the clinical behavior of the materials studied. A critical discussion is given.

Composite Resins↗
PubMed1989

[Effects of caries-preventive fluoride gels on dental ceramics].

The effects of several fluoride gels on ceramic surfaces (Dicor, Optec, Biodent ceramic and Vita VMK) were tested by SEM and by means of an electrical stylus instrument. After 10 min exposure time an acidulated gel (Oral-B Fluoride-Gel) showed a significant effect, whereas the effect of two non-acidulated gels (Elmex-Gelee, Blend-a-med Fluoride Gel) was not significant. After 24 h exposure time, Elmex and Blend-a-med gel showed an effect, too.

Dental Porcelain↗
PubMed1989

[Effect of Mo content and pH value on the corrosion behavior of Ni-20Cr-Mo dental alloys].

The results showed that the resistance against pitting corrosion in an acid milieu was dramatically improved by increasing the Mo content, while in a neutral milieu the pitting potential Ep remained unchanged. Remarkably, a Mo-content of more than 6 wt. % resulted in a further reduction in the pitting corrosion potential Ep, when pH 2 has been exceeded. A similar behaviour has been observed with the critical pitting potential Ec: Ec is also reduced at pH values between 3 and 7. To avoid pitting corrosion in the clinically relevant pH range of 4 to 7, a pitting resistance equivalent (PRE) of at least 43 is required.

Chromium Alloys↗
PubMed1989

[Profilometric studies on the surface reproduction of dental impression materials].

The reproduction of elastic impression materials is described with a laser-technique. This technique allows a quantitative evaluation without touching and deforming the surfaces. Although it is possible to measure differences, clinically relevant differences between several elastomere and one hydrocolloid material are not found.

Dental Impression Materials↗
PubMed1989

[Finishing of cast titanium for crowns and bridges].

The surface roughness of cast Titanium compared with a precious alloy (Au-Ag-Cu), two Pd-base alloys (Pd-Ag-Sn-In, Pd-Sn-Ga-Cu) and two base metal alloys (Ni-Cr-Mo, Co-Cr-Mo) was determined by surface profile measurements after polishing with six different polishing pastes. The results revealed the best surface quality for Au-Ag-Cu followed by Ni-Cr-Mo, Co-Cr-MO, Pd-Sn-Ga-Cu and Pd-Ag-Sn-In. The highest but still acceptable surface roughness was found with Ti.

Dental Alloys↗