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Biomedical subjects

H Uchtmann

Publications and source records attributed to H Uchtmann.

12 recordsLinked to original sources
PubMed2000

Anisotropic crystal structure distortion of the monoclinic polymorph of acetaminophen at high hydrostatic pressures.

The anisotropy of structural distortion of the monoclinic polymorph of acetaminophen induced by hydrostatic pressure up to 4.0 GPa was studied by single-crystal X-ray diffraction in a Merrill-Bassett diamond anvil cell (DAC). The space group (P2(1)/n) and the general structural pattern remained unchanged with pressure. Despite the overall decrease in the molar volume with pressure, the structure expanded in particular crystallographic directions. One of the linear cell parameters (c) passed through a minimum as the pressure increased. The intramolecular bond lengths changed only slightly with pressure, but the changes in the dihedral and torsion angles were very large. The compressibility of the intermolecular hydrogen bonds NH...O and OH...O was measured. NH...O bonds were shown to be slightly more compressible than OH...O bonds. The anisotropy of structural distortion was analysed in detail in relation to the pressure-induced changes in the molecular conformations, to the compression of the hydrogen-bond network, and to the changes in the orientation of molecules with respect to each other in the pleated sheets in the structure. Dirichlet domains were calculated in order to analyse the relative shifts of the centroids of the hydrogen-bonded cycles and of the centroids of the benzene rings with pressure.

Acetaminophen↗
PubMed1997

High-pressure replica technique for in vitro imaging of pore morphologies in teeth.

The presence of a natural pore morphology is an essential factor in chemical and mechanical stability of teeth. Common histological methods give only an insufficient picture of the three-dimensional pore distribution in sound or carious teeth. This paper describes a new technique to obtain complete images of the pore structure in teeth or other biological hard tissues. Whole extracted human teeth from orthodontic therapy are mechanically cleaned and organic remnants removed chemically. After being (partly) dried, the teeth are penetrated by a freshly prepared and colored (rhodamine B dye) two-component epoxy resin. The resin is pressed into the pores and cavities of the teeth with pressures of up to 2000 bar in a high-pressure vessel by means of a manually driven piston screw pump for pressure generation. The resin fills all hollow spaces of the tooth down to sizes below 0.1 micron. The pulp and the root canals are cast in massive forms of the hardened epoxy resin, giving an exact replica of the natural structure. The penetrated samples in the form of whole, intact teeth are investigated microscopically so that the pore morphology of the tooth surface, including carious defects, can be examined. The structure of the pores extending into the interior of the tooth can be made visible by dissolution of the hard tissue--for example, in acid solutions. Micro-cavities filled with the resin are observed in thin, ground, and polished cross- and longitudinal sections cut from the teeth. The colored resin induces a high contrast to the dental apatite material. In fluorescence microscopy, only the resin structures are visible.

Animals↗
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↗