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Biomedical subjects

R Marx

Publications and source records attributed to R Marx.

At least 19 recordsLinked to original sources
PubMed1992

The effect of corrosive environment on the porcelain-to-metal bond--a fracture mechanics investigation.

Microcracks, flaws, and voids inside a metal-porcelain restoration may cause the restoration to fracture in service. Such cracks result in the concentration of stresses. The dynamic nature of the stresses due to mastication promotes crack growth. In addition, corrosive components of the oral environment enhance the growth rate. In the present investigation, fracture mechanics has been used to analyze the in vitro resistance to fracture of the porcelain-fused-to-metal restoration. The risk of a clinical failure of porcelain-fused-to-metal decreases with enlarged crack resistance (increasing work of fracture). The work of fracture represents an average of the energy for initiation and propagation of a crack through the interface separating porcelain and metal. This work also indicates a material's ability to stop a crack once it is moving. This study utilized the three-point bending test for the crack resistance measurement, and investigated one palladium and five base metal alloys. Corrosive components of the oral environment and the details of firing were of crucial importance for long-term bond stability.

Corrosion↗
PubMed1992

Human cell culture studies with dental metallic materials.

The compatibility of cast non-alloyed titanium and eight dental castable alloys (precious, low noble, non-precious) was determined by means of human primary oral fibroblasts derived from the attached gingiva and the periodontium. Furthermore, cast non-alloyed Ti was tested in a human permanent cell culture (MOLT 4). All investigated metallic materials showed cytotoxic properties in primary cultures. The differences in cytotoxicity between the various materials were statistically significant. The best results were found for one noble alloy and for non-alloyed titanium, whereas all non-precious alloys almost completely inhibited cell growth. The cytotoxic potential of the investigated materials might contribute to the irritating effect of dental cast restorations adjacent to the gingiva and the periodontium.

Biocompatible Materials↗
PubMed1992

Combined two-dimensional and Doppler echographic examination of internal mammary artery grafts from the supraclavicular fossa.

The noninvasive examination of internal mammary artery grafts is gaining importance with the increasing use of this vessel in the surgical treatment of coronary atherosclerosis of the left anterior descending artery. We studied 36 patients (37 internal mammary artery grafts) with combined two-dimensional and pulsed Doppler echography from the supraclavicular fossa. Adequate visualization and Doppler signals were obtained in 95% of arterial grafts. Twenty-four grafts leading to an area without evidence of old myocardial infarction or ischemia and 10 grafts leading to an area of old myocardial infarction but without evidence of ischemia on exercise showed a significant decrease of the peak systolic velocity and of the peak systolic velocity/peak diastolic velocity ratio as compared to the controls, which consisted of the contralateral internal mammary arteries in situ. One patient with a distally subtotally occluded mammary artery graft had a flow pattern different from the other bypassed mammary arteries. It seems that combined two-dimensional and pulsed Doppler echography is a useful method to evaluate the functional status of internal mammary artery grafts.

Adult↗
PubMed1991

[Studies on the bond strength of various titanium-ceramic base materials].

The present contribution presents the results of a study comparing the bond strength of Ohara Titan Bond (Tanaka, Bad Homburg), Vita Titankeramik (Vita, Bad Säckingen) and Duceratin Experimental Titankeramik (Ducera, Rosbach) fused to titanium with that of Vita VMK 68 fused to Wiron 88. For the measurement of the bond strength we utilized the three point bending test of fracture mechanics.

Corrosion↗
PubMed1991

[Mechanical strength of ceramic materials for fusing on titanium restorations].

Bending, splitting tensile, and bond strengths of four ceramic systems for veneering titanium frameworks as well as the fatigue strength of the complete metal-ceramic crown were evaluated. The mechanical properties of ceramo-metallic systems are comparable with those of conventional dental ceramics. A slight increase in bending, tensile, and bond strengths when using higher firing temperatures was observed, although this did not result in an increased endurance strength of the complete system.

Crowns↗
PubMed1991

[System for intraoral repair of ceramic blends--an in vitro study of adhesive strength].

We investigated composite repair systems for crown facings which consisted in principle of a silane primer, of an unfilled Bis-GMA bonding agent and of a filled Bis-GMA resin. The in vitro investigations revealed that under oral conditions the longterm durability of the bond strength is still unsufficient, unless care is taken that the debris layer which is caused by mechanical treatment has been removed.

Adhesiveness↗
PubMed1991

[Possibilities for the detection and monitoring of children and adolescents with hypertension].

Blood pressure measurements have been taken for ten years or more on the basis of a standard programme as part of the paediatric mass screening, starting with the second medical examination for school entrance. They have now become an integral component of this checkup routine. The following recommendations are made for a revised prophylactic examination programme: enlargement of case history questionnaire on arterial hypertension, maintenance of present valid norms and recommendations for medical attention in cases of high blood pressure risk, and blood pressure measurements for school entrants in grades 6 and 9.

Adolescent↗
PubMed1991

[Bond strength of etched In-Ceram(R) to tooth enamel].

Laminate veneers of porcelain may be suitable for the correction of enamel anomalies of incisors. They are, however, within the mouth subjected to high mechanical loads, aggressive humidity and abrupt temperature changes. Consequently high strength porcelain and a stable bond between the veneer and the enamel are mandatory. To prepare a retentive surface microscopic investigations reveal that etching of In-Ceram porcelain is less effective than etching of Biodent porcelain, which we investigated as a reference material. This is in accordance with the observed insufficient bond strength between In-Ceram porcelain and enamel. Therefore we conclude that under the environmental condition of the mouth In-Ceram porcelain, even if it is layered with Vitadur porcelain, can not be durably bonded to enamel at present.

Acid Etching, Dental↗
PubMed1976

[Leukocyte and erythrocyte interaction with collagen in vitro: scanning electron microscopy study].

Scanning microscopic investigations show the interaction of Leukocytes and Erythrocytes with fibrillar and aggregating type I and type III collagens in vitro. Leukocytes, in the presence of collagen, form loose aggregates within a minute and these aggregates, after 15 to 30 minutes, coalesce and become compact. The close association of the fibrillar collagens to the leukocyte surfaces is shown. Fibrillar collagen and collagen in solution with erythrocytes form only loose aggregates. Qualitative differences between the various collagen preparations were not found. The pathogenetic implications of these observations are briefly discussed.

Blood Platelets↗
PubMed1976

Platelet-collagen interaction. The influence of native and modified collagen (Type I) on the aggregation of human platelets.

Type I collagen from calf skin, collagen modified by pepsin treatment, methylation, succinylation or deamidation, as well as the alpha-chains and cyanogen bromide peptides of the alpha1-chain were investigated with respect to their capacity to induce aggregation of human platelets. These preparations permitted an evaluation of the efficacy of the amino acid sequence, triple conformation,and various fibrillar structures in platelet aggregation. All collagens in dissolved in dissolved form (collagen dissolved at acid pH, pepsin-treated, methylated, deamidated, and succinylated collagen) induced platelet aggregation only after fibril formation. The arrangement of molecules within fibrils is of secondary importance. Modification of the side chains of amino acid residues affects primarily the formation of fibrils. The effect of these side chains on platelet aggregation is masked by the overwhelming potency of the fibrillar forms.

Amino Acid Sequence↗
PubMed1976

High pull Begg.

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Extraoral Traction Appliances↗
PubMed1976

[Modification of glycylglycine dipeptidase activity in the human ovary using follicle stimulating hormone. I].

The glycyl glycine dipeptidase activity under the in vitro influence of two follicle-stimulating hormone preparations of different concentration was investigated in 36 ovaries. A significant impediment was observed under Folistiman, whereas under Anthrogon the impediment could only be detected with higher concentrations. The FSH/ICSH relation evidently plays an important role in this respect. The results are in support of the statement that the glycyl glycine activity in vivo also depends on the gonadotrophin production. At the same time they affirm the fact that not only endopeptidases play a role in the hormone metabolism of the ovary.

Adnexa Uteri↗