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Biomedical subjects

J Vahl

Publications and source records attributed to J Vahl.

At least 37 records · Page 2Linked to original sources
PubMed1979

[A comparison of light-hardened and UV-polymerizable sealants and composites].

Ultraviolet irradiation has been used for the photopolymerization of composites and sealers. As new initiators were developed, the effectivity of this system was extended into the visible spectral region. Photo-sensitivity probably only limits the processing period slightly, at least under these conditions relevant for the dental practice. One important advantage is the extension of the maximal tempering depth (2 to 3 times, compared to ultraviolet polymerization). The improved penetrability of the dental substance with increasing wave lengths also reduces the risk of portions of the undercuts not being polymerized.

Composite Resins↗
PubMed1979

[A scanning electromicroscopic determination of the depth of penetration of dental enamel adhesives in the etched enamel].

The surface tension of the liquid preservative was held responsible for the loss of plastic tags in the penetration zone between sealer and enamel due to the preparation. This loss is demonstrable with fluorescence, interference, and polarization microscopy. With the help of freeze-drying procedures, tags of approximately 200 mum could be exposed and photographed with the scanning electron microscope.

Acid Etching, Dental↗
PubMed1978

[Tear resistance of laser-welded dental alloys].

The investigation was undertaken to establish the place of lasers as tools in the dental technical laboratory. Tests were undertaken to study resistance to tears in laser welded dental metal alloys. (Degudent U, Degulor M of Fa. Degussa.) Availabel as laser apparatus were a cw Nd:YAG-laser (400 Watt capacity) and a pulse Nd:YAG-laser (max. 45 pulse energy, 9.2 pulse length). Welding tests on models with both lasers resulted in higher resistance to tears than was achievable by conventional soldering processes. Furthermore it could be shown that in certain alloy compositions, used in our experiments, welding by the cw process resulted in greater resistance to fissuring than by the pulse process. By adopting the alloy as well as the preparation of appliances to the laser process we feel that markedly superior results can be achieved as we describe in this first communication.

Dental Alloys↗
PubMed1978

[Relationship between hardness, abrasion and bending strength of UV-polymerizable adhesives].

These experiments were undertaken to explore the influence of hardening on bending and bending strength of photopolymerisable adhesives. It was shown that light sources at present in use only influence the bending strength to a small degree but enable 40% variation in bending. The use of more intensive light sources not yet in commercial use led to further improvements.

Biomechanical Phenomena↗
PubMed1978

[Effect of oxygen and humidity on UV-polymerizable sealing materials].

The influence of humidity, oxygen and protecting gases on the wetting capacity of UV polymerisable adhesives is examined by means of border-angle measurements. The thickness of the upper layer not polymerisable through the presence of oxygen is determined and its effect on the surface structure of compounds is clarified by scanning electron microsc-investigations. For solution the use of a protecting gas is discussed.

Bicuspid↗
PubMed1978

[Thermic behavior of dental enamel, dentin and selected dental materials].

The linear coefficient of expansion of enamel, dentin as well as selected dental working materials is estimated by means of holographic-interferometric measurements. A good correlation was found between hard dental texture and a phosphate glass envisaged for use with lasers. The possible effects of the greatly increased coefficient of expansion of tested composites is discussed.

Biophysical Phenomena↗
PubMed1978

[Physical properties of highly polishable filling materials compared to composites].

Physical characteristics of three highly polishable filling materials (Estic R Microfill, Isopast and Superlux) were compared with those of current composites (Concise, Adaptic). It was shown that the materials with improved polishing qualities exhibit lower bending strength. Critical comments of practical importance are based on special temperature measurements of the material as well as of the pulp cavity. Aspects of testing and preparing the material are mentioned. Tests were further performed on the abrasion behaviour of the dental materials mentioned and the reciprocal changeable influence of the granularity of the abrasive and the quality of the working material is debated.

Dental Materials↗
PubMed1977

[Hardening of photopolymerizable sealing materials in variously deep enamel zones (in vitro)].

The effect of irradiation times of various lengths on the resulting Vickers-hardness and polymerisation of adhesives (Estilux glaze, Nuva Seal) was estimated for varying UV light sources. Secondary effects depending on position were found in the polymerisation, the progress of which could be estimated. The results of the polymerisation experiments, irradiating caries-containing and healthy enamel sections, using appropriate UV light sources, show polymerisation of adhesives with definable Vickers-hardness in enamel zones of various depths.

Dental Cements↗
PubMed1977

[Studies on silicate-containing and silicate-free adhesives compared to composite materials II].

The photo-polymerisable adhesive Estilux glaze and its successor product Estiglaze microfill as well as a compound from the same firm were subjected to comparative investigations. Maximal polymerisable thickness of the named materials were ascertained by means of variable intensive light sources. Electron-microscopic investigations were carried out on the matrices in order to estimate the wetting behaviour. No generally valid connection between hardness and abrasion of comparative materials could be observed, but Estiglaze microfill, containing filling-substance shows reduced abrasiveness to the factor 2.5 in comparison to products free from filling substance.

Composite Resins↗
PubMed1976

[Ultrastructure of conditioned enamel surfaces and their adhesive matrices in dental enamel sealing].

The enamel sealant Nuva Seal was tested in model tests on caries-free human molars and premolars. Under the scanning electron microscope the acid-etched enamel areas (natural and ground surfaces) and the corresponding Nuva Seal matrices were studied. In the evaluation, the surface reliefs of the objects were compared. Thus, information on flow capacity, wetting and polymerization behavior of the adhesive was obtained. Evaluation of pairs of stereo pictures of the inverse surface reliefs in the enamel/adhesive contact zone suggests that the sealant has an average measurable depth of penetration of 7 mum. Peg-shaped elevations 10-20 mum in size that can sometimes be observed in the Nuva Seal impressions are interpreted as representing enamel defects.

Bicuspid↗