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Biomedical subjects

H Duschner

Publications and source records attributed to H Duschner.

At least 55 records · Page 3Linked to original sources
PubMed1995

The effects of a sodium hypochlorite treatment on demineralized root dentin.

The effects of a 10% NaOCl treatment for 2 min on demineralized human root dentin were investigated by means of: microradiography (MR), scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and secondary ion mass spectroscopy (SIMS). MR measurements revealed that NaOCl caused a tissue contraction not related to water loss but to removal of organic substance(s), resulting in reductions of the lesion depth and mineral loss values by 15% and 42%, respectively. CLSM observations on wet dentin showed that the dentinal tubules underneath the surface are clearly observable and not deformed substantially by the NaOCl, except near the outermost surface. This indicates the importance of wet as well as of dried (high vacuum) observations. SEM micrographs (high vacuum) showed definite changes in the outer dentin surface structure; 85% of the originally open dentinal tubules were closed after NaOCl treatment. No marked changes were observed in the dentin ultrastructure inside lesions, as shown by SEM on fractured surfaces. SIMS data, pertaining to samples in high vacuum, showed a remarkable increase of chlorine (Cl) content in the entire lesion due to the NaOCl, indicating deep penetration of the original OC1 ions. The results suggest that the 2-min treatment of demineralized dentin by NaOCl solutions removes and/or changes part of the dentin matrix in nearly the whole lesion. As a consequence the mineral is somewhat redistributed, the outermost surface of a few mu m is changed, but the main dentin structure and element composition are still intact. These findings indicate that NaOCl treatments are of interest in remineralization and hyper-remineralization studies of dentin.

Adolescent↗
PubMed1991

Effect of a surface-active cation on fluoride/enamel interactions in vitro.

After in vitro treatments of bovine enamel with NaF/Zonyl FSC and NH4F in-depth profiles of the chemical composition of the outermost zone of surface enamel were obtained with electron spectroscopy. The most important finding of the study was that after the treatments with nearly neutral as well as slightly acidic solutions of NH4F the ammonium cation was found on the enamel surfaces. Similarly a Zonyl FSC layer was detected on the enamel surfaces after the NaF/Zonyl FSC treatment, while sodium ion was never detected on the enamel surfaces. The implication is that the sorption of these cations plays a role in fluoride-enamel interactions.

Ammonia↗
PubMed1990

Isolation, characterization, and inhibition kinetics of enolase from Streptococcus rattus FA-1.

One aspect in a broad spectrum of possible mechanisms of cariostatic reactions of fluoride is its interaction with the metabolism of oral bacteria. Information on the mechanisms and kinetics of fluoride inhibition of essential enzymes of the glycolytic pathway of the relevant bacteria is lacking. In this work, the isolation and purification of enolase from Streptococcus rattus and its characterization are described. The enzyme has been isolated in a monomeric (22 kilodaltons) and dimeric (49 kilodaltons) form. The Km for 2-phosphoglycerate is 4.35 mM. Fluoride inhibition kinetics have competitive character, while phosphate in concentrations above 2 mM and in the presence of 0.5 mM fluoride alters the inhibition kinetics from competitive to noncompetitive. Without fluoride, 2 mM phosphate has a slight stimulatory effect on the enzyme. Monofluorophosphate has a noncompetitive inhibiting effect on the enzyme. This finding suggests that the effect of phosphate may be due to an additional binding of fluoride to the enolase, resulting in a conformational change of the enzyme.

Fluorides↗
PubMed1990

Interactions of micromolar concentrations of fluoride with Streptococcus rattus FA-1.

Inhibition of the metabolic activities of bacteria by trace amounts of fluoride is manifested phenomenologically as changes in the pH gradient and/or the electrical potential between the cellular interior and the surrounding medium. These data were obtained from the intracellular/extracellular distribution of radioactivity labelled fluoride (18F), 5,5-dimethyloxazolidine-2,4-dione (14C), and tetraphenylphosphonium chloride (14C). When taken up from acidic media, trace concentrations of fluoride (1-100 microM) reduce the intracellular/extracellular pH gradient and affect the electrical potential across the cell membrane. The chromatographic fractionation of fluoride-charged bacterial homogenates showed that fluoride is attached to many proteins of the cytoplasm, the cell membrane, and to nonproteinaceous components of the cell wall. Lysozyme treatment synergistically affects the vulnerability of the bacteria to micromolar concentrations of fluoride.

Bacterial Proteins↗
PubMed1990

[Mercury release of silver amalgam fillings in vitro].

In vitro mercury release from silver amalgam fillings was analyzed by ICP (Inductively-coupled-plasma-atomic-emission-spectroscopy). Within 14 days 63.2 micrograms Hg and 41.5 micrograms Hg respectively, were released from unfinished and finished amalgam fillings (n = 5). The amounts of mercury found in this study were several times higher compared with the results from other in vitro-studies.

Dental Amalgam↗
PubMed1988

Degradation of surface enamel and formation of precipitates after topical applications of sodium fluoride solutions in vitro.

After topical treatment of enamel pieces cut from bovine incisors, the chemical composition of the solution phases and of the topmost layers of enamel were determined by special techniques of elemental and surface analysis. Fluoride seems to degrade surface enamel when applied in acidic and neutral solutions. Calcium remains immobile on the enamel surfaces, whereas phosphate goes into solution. When treated with acidic solutions (0.05-0.5 mol/l fluoride), a calcium-fluoride-rich phase is precipitated on the enamel surfaces.

Animals↗
PubMed1982

Electron spectroscopic studies of interactions between superficially-applied fluorides and surface enamel.

Despite comparable acidities and fluoride concentrations, distinctly different characteristics of fluoride deposition and enamel degradation were observed. In the sequence of the amine hydrofluorides, this may possibly be due to the increasing cation polarity. Thus, by the concomitant rise in the dissociation constants of the compounds, the increasing effectiveness of fluoride accumulation is due to the presence of more free fluoride in solution. On the other hand, sodium fluoride shows behavior comparable to that of the unsaturated amine hydrofluoride. Presumably, specific interactions between the cations and surface apatite may favor fluoride deposition. Under present conditions of treatment, however, neither sodium nor quaternary ammonium cations are deposited in significant amounts on tooth surfaces. Thus, the behavior of fluoridizing agents cannot be understood only by their properties in bulk solution. Obviously, specific reaction mechanisms between surface-adjacent solutions and enamel apatite must be considered. Similar reactions have been studied extensively in connection with corrosion problems. The investigations clearly demonstrated that, for the interpretation of mechanisms, all relevant parameters must be considered: the ionic composition of solutions, the temperature, the time of treatment, etc. Thus, a series of additional experiments will be necessary for more insight into the reaction mechanisms of fluoride on superficial dental enamel. The consequence of the present studies is that the cariostatic effect of superficially applied fluoridizing agents cannot be discussed in terms of fluoride accumulation only.

Animals↗