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Biomedical subjects

M Walter

Publications and source records attributed to M Walter.

At least 181 records · Page 10Linked to original sources
PubMed1991

[Is titanium an alternative for base metal alloys?].

Because of the excellent biocompatibility titanium can be considered as an ideal material for prosthetic reconstructions. Especially for base metal alloys titanium is an alternative due to the low cost. Processing still causes problems. In this paper a vacuum pressure casting system and a combination of milling and spark erosion are described and investigated. Both techniques are suitable to manufacture prosthetic restorations with a high accuracy of fit. Problems in dental castings lie in the occurrence of a superficial reaction zone of about 40-100 microns width. No final conclusions concerning the metal-ceramic compound can be drawn at the moment for lack of undisputable results in different mechanical bonding tests. Due to the remaining difficulties the future importance of titanium in prosthetic dentistry cannot be prognosticated.

Dental Alloys↗
PubMed1991

[Castability and accuracy of fit of a titanium casting system].

The titanium casting system Cyclarc (Morita) was examined for its suitability for the fabrication of dense, fitting restorations. The investment material Titavest CB exhibited no setting expansion. Instead, thermal expansion, highly dependent on the liquid/power ratio and the temperature during preheating, was observed. The castability of unalloyed titanium is fully acceptable for the fabrication of prosthetic restorations. Single crowns showed a high accuracy of fit, if an optimal liquid/power ratio was used for investment.

Crowns↗
PubMed1991

[Ceramo-metallic bond of cast titanium].

The ceramo-metallic bond strength of cast titanium was tested according to DIN draft 13927. While the specimens failed in the bending tests, they clearly passed the 3-point bending test after removal of the surface reaction layer prior to firing. Light microscopy and SEM showed a satisfactory wetting of the titanium surface by the ceramic material. The result of X-ray analyses suggest that titanium particles are retained in the ceramic material when this layer is broken off its metallic substructure.

Dental Bonding↗
PubMed1991

[Fixed tooth replacement of milled/spark eroded titanium].

In a clinical study the accuracy of fit of 82 crowns manufactured with the Procera-system (duplication milling/spark erosion) was investigated. The average marginal space width was 71 microns. Roughness of eroded surfaces was found to be similar to that of coarsely ground metal. Below the eroded areas a zone of increased hardness with a width of approximately 20 microns was demonstrated.

Crowns↗
PubMed1990

Prevalence of acute mountain sickness in the Swiss Alps.

OBJECTIVE: To assess the prevalence of symptoms and signs of acute mountain sickness of the Swiss Alps. DESIGN: A study using an interview and clinical examination in a representative population of mountaineers. Positive symptoms and signs were assigned scores to quantify the severity of acute mountain sickness. SETTING: Four huts in the Swiss Alps at 2850 m, 3050 m, 3650 m, and 4559 m. SUBJECTS: 466 Climbers, mostly recreational: 47 at 2850 m, 128 at 3050 m, 82 at 3650, and 209 at 4559 m. RESULTS: In all, 117 of the subjects were entirely free of symptoms and clinical signs of acute mountain sickness; 191 had one or two symptoms and signs; and 158 had more than two. Those with more than two symptoms and signs were defined as suffering from acute mountain sickness. At 4559 m 11 climbers presented with high altitude pulmonary oedema or cerebral oedema, or both. Men and women were equally affected. The prevalence of acute mountain sickness correlated with altitude: it was 9% at 2850 m, 13% at 3050 m, 34% at 3650 m, and 53% at 4559 m. The most frequent symptoms and signs were insomnia, headache, peripheral oedema, and scanty pulmonary rales. Severe headache, vomiting, dizziness, tachypnoea, and pronounced pulmonary rales were associated with other symptoms and signs and therefore characteristic of acute mountain sickness. CONCLUSION: Acute mountain sickness is not an uncommon disease at moderately high altitude--that is, above 2800 m. Severe headache, vomiting, dizziness, tachypnoea, and pronounced pulmonary rales indicate severe acute mountain sickness, and subjects who suffer these should immediately descend to lower altitudes.

Acute Disease↗
PubMed1990

Structural analysis of human apolipoprotein A-I variants. Amino acid substitutions are nonrandomly distributed throughout the apolipoprotein A-I primary structure.

In the course of an electrophoretic mutation screening program of 32,000 dried blood samples from newborns, 17 genetic variants of apolipoprotein A-I (apoA-I) were found and structurally analyzed. The following defects were identified by the combined use of high performance liquid chromatography, time-of-flight secondary ion mass spectrometry, and sequence analysis: Pro3----Arg (1 x), Pro4----Arg (1 x), Asp89----Glu (1 x), Lys107----0 (4 x), Lys107----Met (2 x), Glu139----Gly (2 x), Glu147----Val (1 x), Pro165----Arg (4 x), and Glu198----Lys (1 x). The distribution of point mutations in the apoA-I gene leading to these 9 and 11 other variants of apoA-I reported previously was statistically analyzed. Substitutions are overrepresented in the 10 amino-terminal amino acids (p less than 0.001, chi 2-test) and in residues 103-177 (p less than 0.025, chi 2-test) or residues 103-198 (p less than 0.05, chi 2-test), respectively. We further noted the following. (i) Prolines were substituted by arginine or histidine residues at a frequency much higher than expected on the basis of random nucleotide substitutions (5 out of 18 "electrically non-neutral" amino acid substitutions, p less than 0.001, chi 2-test). These substitutions are the result of transversions of cytosines contained within stretches of at least 5 consecutive cytosines in the apoA-I gene. The observed hypervariability of the apoA-I amino terminus, therefore, might be caused by a hot spot for mutation formed by the 7 subsequent cytosines in codons 3, 4, and 5. (ii) CpG dinucleotides were overrepresentatively affected by C----T transitions (5 out of 18 electrically nonneutral amino acid substitution, p less than 0.001, chi 2-test). The hypervariability of the apoA-I alpha-helical domain might therefore be caused by CpG dinucleotides predominantly occurring in codons 120-208 of apoA-I (82 out of 125). (iii) Comparison of mutation sites in the human apoA-I gene with sites of nonsynonymous substitutions revealed that amino acid substitutions found in human apoA-I were predominantly localized in areas that were little conserved during mammalian evolution. These regions may therefore represent areas of less structural constraint for the function of apoA-I.

Amino Acid Sequence↗
PubMed1990

Survival of bacteria during aerosolization.

One form of commercial application of microorganisms, including genetically engineered microorganisms is as an aerosol. To study the effect of aerosol-induced stress on bacterial survival, nonrecombinant spontaneous antibiotic-resistant mutants of four organisms, Enterobacter cloacae, Erwinia herbicola, Klebsiella planticola, and Pseudomonas syringae, were sprayed in separate experiments in a greenhouse. Samples were collected over a distance of 15 m from the spray site for enumeration. Spores of Bacillus subtilis were used as tracers to estimate the effects of dilution on changes in population over distance. Viable counts of P. syringae, Enterobacter cloacae, and K. planticola decreased significantly over a distance of 15 m. Erwinia herbicola showed no significant decline in counts over the same distance. The degree of survival of P. syringae during aerosolization was dependent on ambient environmental conditions (i.e., temperature, relative humidity), droplet size of the aerosol, and prior preparative conditions. Survival was greatest at high relative humidities (70 to 80%) and low temperatures (12 degrees C). Survival was reduced when small droplet sizes were used. The process of washing the cells prior to aerosolization also caused a reduction in their survival. Results from these experiments will be useful in developing sound methodologies to optimize enumeration and for predicting the downwind dispersal of airborne microorganisms, including genetically engineered microorganisms.

Aerosols↗
PubMed1990

[Metal-porcelain bonding in precious metal dental alloy].

The metal-ceramic bond of a dental alloy free of non-precious components was investigated in bending and three-point-bending test. Light and scanning electron microscopic examination as well as wavelength dispersive x-ray analyses were carried out. They showed no alterations in structure or concentration of the components in the area of the metal-ceramic boundary, due to diffusion and oxidation processes in the extent known from conventional bonding alloys. The results lead to the conclusion that the tested alloy is suitable for ceramic veneering under limited indication.

Dental Bonding↗
PubMed1990

[Computer assisted occlusal diagnosis in complete dentures].

The T-Scan system for computerized occlusal diagnosis was tested in laboratory and clinical experiments. The lowest force level producing a display was approximately 1 N when loading the sensor by a rod with a diameter of 0.5 mm. The sensitivity depended considerably on the position of the testing point on the sensor. In the clinical study contacts in intercuspal position were evaluated as well as the possibility to identify artificial premature contacts. After remounting experiments were carried out in the articulator and in patient's mouth. The results lead to the conclusion that the use of the T-Scan system in complete dentures is limited to the rough evaluation of the occlusal situation.

Dental Articulators↗
PubMed1990

Palladium alloys in prosthodontics: selected aspects.

The high costs of gold and platinum have caused other alloys to be considered in the construction of prosthetic appliances. This paper reports on the grain structure, corrosion resistance and microstructure of palladium alloys. Also discussed are the properties of these alloys and how these affect their technical manipulation.

Chemical Phenomena↗
PubMed1990

[Results of surgical treatment of pulmonary metastases].

During the period from 1. 1. 1980-31. 12. 1989 71 patients underwent lung resection for pulmonary metastases. In 21 cases, the primary tumours were sarcoma, in 19 cases carcinoma of the kidney, and 14 cases of melanoma. There were 9 cases of testicular carcinoma, 5 of colorectal carcinoma, and in 1 case each larynx-, oesophagus-, and oral cavity-carcinoma. In 51 patients we could perform an atypical wedge resection, lobectomy was carried out in 19 patients. 1 patient underwent segmental resection. Hospital lethality counted with 0.7%. For all patients, the cumulative survivals revealed an one-year actuarial about 60%, a 3-year actuarial survival of 40%, and a 5-year actuarial survival rate of 38%.

Follow-Up Studies↗
PubMed1990

[Ergotism--a rare cause of acute ischemia of the extremities].

Clinical ergotism as seen today results almost exclusively from the excessive intake of ergotamine tartrate in the treatment of migraine headache. Vasospasm of peripheral arteries is the leading clinical picture. Beside formation of collaterals and secondary thrombosis, vasospasm is one of the specific findings in angiography. Early diagnosis and withdrawal of the medication makes complete restitution possible. In all other cases intraarterial or intravenous infusion of sodium nitroprusside or nitroglycerin has turned out to be the most effective therapy. Balloon dilatation or operative intervention are an alternative therapy in those cases, where amputation of the limb seems to be necessary.

Acute Disease↗
PubMed1989

[Pathophysiology, diagnosis and therapy of localized frostbite].

Pathophysiology, clinical feature, diagnosis and partially adverse recommendations for therapy are presented. Widening of diagnostic procedures for valuation of the late results by introduction of DSA, fluorescence-video-microscopy and digit phlethysmography are emphasized.

Combined Modality Therapy↗
PubMed1989

[Structural studies of veneered palladium alloys with a focus on the ceramometal interface].

Samples of palladium-silver and palladium-copper alloys with ceramic veneers were examined under incident light and scanning electron microscopes in terms of their metallographic properties. Both materials showed a fine grain structure. The palladium-silver alloy had inhomogeneous crystallites. The palladium-copper alloy showed several heterogeneous phases. Wavelength dispersive x-ray analysis was used to record concentration profiles and element distribution patterns. An accumulation of nonprecious components and oxygen was observed in the immediate ceramometal interface. Adjacent to this a largely homogeneous zone was visible which is probably due to the diffusion of nonprecious elements during the different stages of baking. The results lead to conclusions concerning the final finishing after application of the ceramic veneer.

Copper↗