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Biomedical subjects

M Thies

Publications and source records attributed to M Thies.

16 recordsLinked to original sources
PubMed2002

A note on the temperature dependence of the flexural strength of a porcelain.

OBJECTIVES: The purpose of this study is to determine the temperature dependence of the flexural strength of a dental porcelain (IPS-Classic Dentin; manufacturer: Ivoclar, Liechtenstein) with temperature between its glass transition (T(g) = 581.7 degrees C) and room temperature. METHODS: The flexural strength was measured in three-point bending tests on an Instron 4204 testing apparatus. The strength values were determined for the temperatures T = 20, 300, 400, 450, 500, 550, and 600 degrees C. RESULTS: In the temperature interval 20 < or = T < or = 400 degrees C the flexural strength decreased slightly from approximately 80 to approximately 73 MPa (mean values), as temperature increased. That is a decay of less than 10%. At higher temperatures the flexural strength increased to a maximum of approximately 98 MPa at 500 degrees C, probably due to the closure of microcracks in the surface on account of the onset of viscous flow. A further increase of the temperature delivered again decreasing strength values. At its glass transition temperature the porcelain's flexural strength was approximately 76 MPa which is only about 5% less than the value at room temperature. SIGNIFICANCE: In order to be able to evaluate the risk of fracture of ceramometallic crowns and bridges due to high temperature gradients and accompanying large transient thermal stresses in the veneer during the fabrication process, flexural strength values at high temperatures must be known. This study was carried out to fill this knowledge gap because to the authors' knowledge there was little published in the literature.

Aluminum Silicates↗
PubMed2000

Field-induced vacancy localization in a driven lattice gas: scaling of steady states

With the help of Monte Carlo simulations and a mean-field theory, we investigate the ordered steady-state structures resulting from the motion of a single vacancy on a periodic lattice which is filled with two species of oppositely "charged" particles. An external field biases particle-vacancy exchanges according to the particle's charge, subject to an excluded volume constraint. The steady state exhibits charge segregation, and the vacancy is localized at one of the two characteristic interfaces. Charge and hole density profiles, an appropriate order parameter, and the interfacial regions themselves exhibit characteristic scaling properties with system size and field strength. The lattice spacing is found to play a significant role within the mean-field theory.

Journal Article↗
PubMed1999

Effects of synthetic delta9-tetrahydrocannabinol on binocular depth inversion of natural and artificial objects in man.

Binocular depth inversion represents an illusion of visual perception that is sensitive to various behavioural and psychiatric conditions. It is affected by cannabinoids, reflecting associated changes in perception. The present study investigated the differences in binocular depth inversion of different classes of natural and artificial objects and the effect of synthetic delta9-tetrahydrocannabinol (Dronabinol) on these illusionary perceptions. Using this model, the effects of orally administered Dronabinol on binocular depth inversion were investigated in 17 healthy male volunteers. Pictures from natural and artificial objects were presented stereoscopically and the depth perception of the volunteers was scored in an operationalized way. The timecourse of the effects of Dronabinol on binocular depth inversion was analyzed with regard to the stimulus classes (natural and synthetic objects). Significant differences in binocular depth inversion of the different groups of stimuli were revealed. Objects with a higher degree of everyday familiarity were generally seen as more illusionary than those with a lower degree of everyday familiarity. A strong impairment of binocular depth inversion due to Dronabinol was found in most classes of objects. Analysis of different stimulus classes provides further information on the underlying perceptual processing of binocular depth inversion. An impairment of top-down processing of visual sensory data by Dronabinol is suggested. The anandamidergic system seems to be involved in areas of visual information processing.

Adult↗
PubMed1990

[3-dimensional ultrasound image of the infant hip].

Clinical and experimental studies proved the usefulness of three-dimensional sonographic diagnosis by means of a newly constructed transducer providing for a coordinated sequence of cuts, and hence initial trials investigated its application in sonographic diagnosis of the infant hip. Differences were found in the three-dimensional anatomic image between normal and dysplastic hips. It is no longer necessary to draw any lines or to perform any calculations of angles as required in "conventional" hip sonography. In contrast to conventional hip sonography, the use of a sector transducer is meaningful with this method, since the drawbacks of the sector transducer stated by Graf, do not apply. Clinical studies will have to confirm the possible use of this new method in diagnosis disturbances in infant hip maturation.

Computer Graphics↗
PubMed1990

Appearance of laminin, heparan sulphate proteoglycan and collagen type IV during initial stages of vascularisation of the neuroepithelium of the mouse embryo.

The appearance of the basement membrane components laminin, heparan sulphate proteoglycan and Type IV collagen was investigated by indirect immunofluorescence during the onset of vascularisation of the neuroepithelium of mouse embryos (Days 10, 11 and 12 of development). All three basement membrane components could initially be seen in the embryonic CNS anlage along with the appearance of capillaries in the neuroepithelial cell layer. From this direct correlation between vascularisation and appearance of basement membrane components in the embryonic anlage one can assume that the basement membrane components laminin, heparan sulphate proteoglycan and collagen Type IV are involved in the initial vascularisation of the CNS anlage of 10 to 12 day old mouse embryos.

Animals↗
PubMed1989

Appearance of lectin-binding sites during vascularization of the primordium of the central nervous system in 10 to 12-day-old mouse embryos.

In the present study lectin-binding sites were investigated for the lectins Ricinus communis agglutinin (RCA I), wheat germ agglutinin (WGA), soya bean agglutinin (SBA), concanavalin A (Con A), Lotus tetragonolobus-(LTA) and Limulus polyphemus agglutinin (LPA) during the initial stages of vasculogenesis of the CNS-anlage in 10 to 12-day-old NMRI mouse embryos. Specific binding sites for the lectins RCA I (sugar specificity: beta-D-galactose, N-acetylgalactosamine), WGA (sugar specificity: N-acetylglucosamine, sialic acid), and SBA (sugar specificity: N-acetylgalactosamine, beta-D-galactose) were detected in the newly formed capillaries within the neuroepithelial cell layer. In contrast, binding sites for Con A, LTA and LPA could not be observed at the start of the vascularization of the CNS-anlage. From these results, the conclusion can be drawn that glycoconjugates containing D-galactose, N-acetylgalactosamine and N-acetyl-glucosamine moieties are involved in the early vasculogenesis of the embryonic CNS-anlage of the mouse.

Animals↗
PubMed1988

Light and electron microscopical postembedding lectin histochemistry for WGA-binding sites in the renal cortex of the mouse embedded in polyhydroxy aromatic resins LR-White and LR-Gold.

This work describes a technique which permits study of the postembedding lectin histochemistry for WGA-binding sites at the light and electron microscopical level on the same resin embedded tissue without removing or etching of the resin. Unfixed kidney pieces or kidney pieces fixed in 4% formaldehyde were embedded in the hydrophilic polyhydroxy aromatic resins LR-Gold and LR-White, following dehydration in up to 70% ethanol, 90% ethanol or 100% ethanol. LR-Gold was cryopolymerised at -25 degrees C using the light sensitive initiator benzil, whereas LR-White was heat-cured at +50 degrees C. The localisation of WGA-binding sites at the light microscopical level was investigated using FITC-labelled WGA. The ultrastructural localisation of WGA-binding sites was performed using 15 nm gold-labelled WGA. The best fluorescence staining results were obtained on fixed or unfixed tissue dehydrated in up to 70% ethanol and embedded in LR-Gold. At the ultrastructural level, the best staining results for WGA-binding sites were seen on tissue sections, dehydrated in up to 90% ethanol prior to embedding in LR-Gold.

Acrylic Resins↗
PubMed1984

Alterations of lectin binding during chondrogenesis of mouse limb buds.

The binding of six different FITC-labelled lectins to mesenchyme, blastemal cells and cartilage was investigated in limb buds of mouse embryos during their development from day 10 to day 13. Concanavalin A, wheat germ agglutinin and phaseolus vulgaris agglutinin labelled mesenchymal cells of earlier stages, day 10 or 11, distinctly more than those of later stages. Chondrogenic blastema, basement membrane and muscle were always strongly stained. The galactosamine-specific ricinus communis agglutinin (RCA) bound preferentially to the blastema, whereas the mesenchyme was only weakly labelled. The galactose-specific peanut agglutinin (PNA), however, stained solely the blastema. In the mesenchyme, no binding was detectable light microscopically with this lectin. In cartilage, RCA- and PNA-staining was found to a lesser extent. With the fucose-specific lectin Lotus A, no staining was detectable. Due to the apparent differences in the binding of PNA in mesenchyme and blastema, peroxidase-labelled PNA was used to study the binding behaviour electron microscopically. It is shown that peroxidase-PNA very strongly labelled the intercellular matrix and the plasma membrane of cells in the late blastemal stages, whereas in young blastema no reaction product was detectable. In contrast to light microscopic findings, some label could be demonstrated also in the mesenchyme. The results show a general reduction of lectin receptors in more developed mesenchyme of later stages and the occurrence of galactose and galactose derivatives during early chondrogenesis in the matrix and at the cell membrane. The significance of these changes for chondrogenesis, however, remains to be elucidated.

Animals↗