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Biomedical subjects

H Weber

Publications and source records attributed to H Weber.

At least 271 records · Page 15Linked to original sources
PubMed1989

[Use of the thermal laser effect of laser irradiation for cardiovascular applications exemplified by the Nd:YAG laser].

Techniques of percutaneous transluminal application of laser energy for vessel recanalization have been used clinically since 1983. The commonly used Nd:YAG and argon lasers achieve ablation of atherosclerotic plaques by thermal action (vaporization). In order to reduce undesirable thermal damage in the neighborhood of the target tissue and to avoid vessel perforation, optimal irradiation parameters, modified (atraumatic) fiber tips (hot tips, sapphires), and steerable catheter systems needed to be implemented. Favorable results from peripheral application have encouraged use in the coronary circulation. More recently, coagulative tissue effects of circumferential irradiation of the vessel wall during balloon dilatation have been used for stabilization of acute and late results after mechanical balloon angioplasty. Enhancement of the differential light absorption of atherosclerotic plaque by use of biological dyes may further improve selective intravascular laser application. Intraoperative ECG-guided laser coagulation of arrhythmogenic areas of myocardium is a method for treatment of malignant arrhythmias. Transluminal non-operative application of myocardial laser photocoagulation has now been tested experimentally and shown to be safe and effective. There was no arrhythmogenicity or thermal damage of coronary arteries associated with this method. Innovative techniques such as nanosecond pulsed excimer lasers (athermal action) and development of "intelligent" lasers--which are equipped with spectroscopy-guided feedback systems for plaque recognition--have opened new perspectives and will further improve safety and efficacy of clinical laser application. However, according to current experience, the thermally acting Nd:YAG laser is an effective and versatile mode of laser therapy for selected cardiovascular indications.

Angioplasty, Balloon↗
PubMed1989

Complete dentures fixed on dental implants: chewing patterns and implant stress.

Electrognathographic measurements on 18 patients with implant-attached mandibular complete dentures showed larger and more stable chewing patterns compared to their former dentures without implants. Strain gauge measurements revealed mechanical stress acting on the implants even during the fixation of the bar. In addition to simulating the periodontal ligament, the intramobile element (IME) of the IMZ system compensated minor, clinically undetectable mismatches inherent with technical procedures (casting, soldering). Although the implants are loaded with tensile and compressive stress, tensile stress dominated during the chewing process. The implants were also loaded during swallowing. This load reached half of the value of the chewing loads.

Dental Implantation, Endosseous↗
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

Macro square wave jerks in a rhesus monkey: physiological and anatomical findings in a case of selective impairment of attentive fixation.

An otherwise normal female rhesus monkey executed large saccadic eye movements (macro square wave jerks) when required to attentively fixate a small visual target (fixation point). The jerks were observed exclusively in this specific testing situation. They occurred periodically at a frequency of 2.04 + - 0.18 Hz to the right side with an amplitude of 23.5 deg. Direction of the jerks was about 3-4 degrees downward from horizontal. These parameters remained constant throughout the several months of daily recording. No jerks were executed during periods when the behaviourally important target was absent or substituted by another, behaviourally non-relevant visual stimulus. The monkey could perform normal visually guided saccades as well as smooth pursuit eye movements, but with the jerks always superimposed, when the monkey paid attention to the visual target. Histologic inspection of the brain revealed the presence of an incapsulated nematode in the cortex of lobulus simplex of the right cerebellar hemisphere, i.e., in a region involved in oculomotor control.

Animals↗
PubMed1989

Pharmacokinetics of acarbose. Part I: Absorption, concentration in plasma, metabolism and excretion after single administration of [14C]acarbose to rats, dogs and man.

The absorption, disposition, metabolism, and excretion of acarbose (O-4,6-dideoxy-4-[[(1S, 4R, 5S, 6S)-4,5,6-trihydroxy-3- (hydroxymethyl)-2- cyclohexen-1-yl]amino]-a-D-glucopyranosyl- (1----4)-O-a-D-glucopyranosyl- (1----4) -D-glucopyranose, Bay g 5421) have been studied following a single administration of the 14C-labelled compound to rats and dogs via different routes (intravenous, oral, intraduodenal) in the dose range of 2-200 mg.kg-1 as well as to man in a single oral dose of 200 mg. After intravenous administration [14C]acarbose was eliminated rapidly and completely via the renal route. There was no indication for a systemic metabolization of [14C]acarbose. The (renal) clearance for [14C]acarbose was in the range of the glomerular filtration rate. After oral administration [14C]acarbose was very poorly absorbed (1-2% of dose in rats and man and 4% in dogs). Additionally, up to 35% of the radioactivity of [14C]acarbose were absorbed after degradation by digestive enzymes and/or intestinal microorganisms. The delayed and biphasic absorption of the radioactivity strongly influenced the plasma concentration vs time profiles of total radioactivity. Maximum concentrations dependent on the degree of microbial degradation (dog less than rat, man) and on the intestinal transit time were reached at 1.2 h (dogs), 8 h (rats) and 14-24 h (man). The excretion of the radioactivity absorbed occurred rapidly and completely mostly via the renal route.(ABSTRACT TRUNCATED AT 250 WORDS)

Acarbose↗
PubMed1989

Pharmacokinetics of acarbose. Part II: Distribution to and elimination from tissues and organs following single or repeated administration of [14C]acarbose to rats and dogs.

Acarbose (O-4,6-dideoxy-4-[[1S,4R,5S,6S)-4,5,6-trihydroxy-3- (hydroxymethyl)-2-cyclohexen-1-yl]amino]-alpha-D-glucopyranosyl- (1----4)-O-alpha-D-glucopyranosyl-(1----4)-D-glucopyranose, Bay g 5421) labelled with 14C was administered to male rats, pregnant and lactating rats as well as to female dogs with single intravenous or oral doses (2 or 4 mg.kg-1) and with repeated oral doses of 2 mg.kg-1 to male rats for 3 weeks. The distribution of radioactivity to organs and tissues, the placental transfer and the secretion into milk was studied using whole-body autoradiographic methods and/or quantitative determination of total radioactivity after autopsy. Unchanged [14C]acarbose was distributed predominantly in the extracellular space, as observed after intravenous dosing to rats. According to the main excretion route, high concentrations were found in kidneys and urine and additionally in blood, lung, and connective tissue or interstitial space. The permeability of the blood/brain barrier for [14C]acarbose and/or its metabolites was very low. No indication was found for distinct differences in the distribution patterns in rats and dogs after intravenous and also in dogs after oral administration. In contrast, in rats after oral dosing the distribution pattern of radioactivity was different with relatively high concentrations in liver, kidney, adrenal gland, spleen, and intestinal mucosa. Due to the slow absorption of the microbial degradation products of [14C]acarbose from the intestine maximum concentrations in the different tissues were reached 8-24 h after dosing.(ABSTRACT TRUNCATED AT 250 WORDS)

Acarbose↗
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

[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↗
PubMed1989

[Technology and progress in dental prosthodontics and dental materials].

This publication describes and scrutinizes new technologies in the field of prosthodontics including functional analysis and therapy, fixed and combined fixed/removable prosthetics, and implant supported/relained dentures. In spite of all new developments with regard to digitized imaging (CT;NMR) of the TMJ as well as in spite of all electronic devices for recording the mandibular movement, new therapies have not been established. The clinical examination is still of primary importance. In fixed prosthetics the different ceramic and glass/ceramic systems represent aesthetic and hygienic alternatives to single, porcelain-fused-to-metal restorations. Titanium exhibiting good biocompatibility, sufficient strength, and a low price gradually becomes of greater importance. In combined fixed/removable prosthetics the various metal-resinbonding-systems as well as the spark erosion technique--the latter being used for precision attachment work utilizing base metal alloys--can be described as major achievements in our profession. In dental implantology, a great variety of different implant systems have been introduced to the market. Based on the clinical experience of the last decade, the following can be stated: The implantological prosthetic treatment of the lower jaw using two implants and a clip-to-bar retained denture shows the best cost-risque-benefit ratio among all possible indications. In the future, more research should be directed to the prosthetic suprastructures and their influence on the long lasting success of implant supported retained constructions.

Dental Implantation↗