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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↗
PubMed1990

Regulation of 1,25-dihydroxyvitamin D3 receptor gene expression by 1,25-dihydroxyvitamin D3 in the parathyroid in vivo.

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3 dramatically decreases parathyroid hormone (PTH) gene transcription. We have now studied the effect of 1,25(OH)2D3 on the 1,25(OH)2D receptor (VDR) in the parathyroid in vivo. Rats were injected with 1,25(OH)2D3 and the parathyroid-thyroid tissue analyzed for PTHmRNA and VDRmRNA. 1,25(OH)2D3 (50 and 100 pmol ip) decreased PTHmRNA at 6 h with a maximum at 48 h (less than 4% of basal), whereas VDRmRNA was increased only after 6 h with a 1.7-fold increase at 24 h. VDRmRNA levels peaked at 25 pmol 1,25(OH)2D3 with a twofold increase. Serum calcium did not affect VDRmRNA. Parathyroid VDRmRNA ran at 2.2 and 4.4 kb, whereas duodenum VDRmRNA had a single band, all of which increased after 1,25(OH)2D3. Weanling rats on a vitamin D-deficient diet for 3 wk had a more intense 2.2-kb transcript, whereas vitamin D-replete rats had a more intense 4.4-kb band. Dispersed parathyroid-thyroid cells were separated by a flow cytometry (FACS) into a parathyroid cell peak containing PTHmRNA and a second peak with cells positive for thyro-globulin mRNA and calcitonin mRNA. VDRmRNA was concentrated in the parathyroid cell peak. In situ hybridization of parathyroid-thyroid and duodenum for VDRmRNA showed its localization to the parathyroid cells and the duodenal mucosa. Therefore, the VDRmRNA in the parathyroid-thyroid tissue represents predominantly parathyroid cell and not C-cell VDRmRNA which is also a 1,25(OH)2D3 target organ. The increased VDR gene expression in the parathyroid cell would amplify the effect of 1,25(OH)2D3 to decrease PTH gene transcription.

Animals↗
PubMed1990

[Use of titanium in conservative dentistry].

Non alloyed titanium is characterized by an excellent resistance to corrosion, a relatively low thermal conductivity, a good ductibility and biocompatibility. Furthermore the costs for this material are very low. First clinical experiences with respect to inlays, onlays, partial and full crowns fabricated out of this metal can be classified as positive. Problems in processing cast titanium (e.g. reduction of the material, polishing) should be solved by the development of special instrument sets.

Crowns↗
PubMed1990

[The refining of liquid swine manure as a substrate for biotechnologic transformation processes].

Pure and mixed cultures of Clostridium Spec. were tested in sterile and nonsterile batch fermentations in order to increase the content of short chain fatty acid in different liquid swine manure substrates. Fatty acid concentrations of 15 g/l were reached by a thermochemical pretreatment of the substrates and the application of a mixed culture of Cl. acetobutylicum, Cl. butyricum and Cl. paraputrificum. The distributions of C2-C5 fatty acids were determined. The results represent the basis to intensify the process of the biotechnological conversion of liquid swine manure.

Animals↗
PubMed1989

Oxidized fibrin(ogen) derivatives enhance the activity of tissue type plasminogen activator.

Oxidation of fibrinogen degradation products (FDP) with chloramines, results in a five- fold increase of their property to stimulate plasminogen activation by tissue type plasminogen activator (t-PA). Binding studies with immobilized stimulators demonstrated greater affinity of t-PA to oxidized than to unmodified FDP. The fibrin (ogen) domain responsible for this oxidant mediated increase in t-PA stimulation is localized in the D- subunit of fibrin(ogen). Thus, experimental data with (oxidized) I-labelled fibrin(ogen) should be interpreted with caution: the oxidized product might behave in a distinct manner than the unoxidized, native, one. As activated leukocytes release large amounts of oxidants of the chloramine type (Weiss et al., Science 222, 625-628, 1983), oxidation of fibrin might contribute significantly to fibrinolysis and proteolysis in areas of inflammation. The data give further evidence for an involvement of physiological components of haemostasis in non haemostasis but inflammation related processes.

Chloramines↗
PubMed1989

Sensitivity distribution in the central and midperipheral visual field determined by pattern electroretinography and harmonic analysis.

To investigate the value of the extrafoveal pattern electroretinogram for evaluation of local retinal defects, electroretinographic responses to contrast reversal stimulation were recorded at various locations in the central and midperipheral retina. Normal values were established in 20 eyes, and spatial selectivity at different retinal eccentricities was determined in four eyes. The response amplitude was found to decrease steeply from the fovea until about 12 degrees eccentricity and to decline only slowly thereafter. For central stimulation a clear attenuation for coarser patterns was observed. At 20 degrees and at 30 degrees eccentricity the spatial tuning function exhibited a bandpass characteristic, with the maximum amplitude shifting to lower spatial frequencies. Despite the relatively low peripheral amplitudes a satisfactory signal to noise ratio of the second harmonic responses can be obtained by Fourier analysis, which improves clinical applicability. The comparison of sensitivity in the upper and lower retina revealed a considerable asymmetry, with responses in the upper retina approximately 20% higher. No significant difference, however, was found when the temporal or nasal retina was stimulated. The reproducibility of these results is high enough to encourage clinical studies. A case of retinal venous branch occlusion exemplifies the applicability of this technique in eccentric fundus lesions.

Adult↗
PubMed1989

Social factors and trachoma: a review of the literature.

Although great advances have been made in the clinical understanding of trachoma, the disease remains endemic in many parts of the world. Economic, environmental, cultural and behavioral factors continue to play an important role in trachoma transmission and progression. The trachoma literature however, contains relatively few studies which rigorously assess the importance of social factors. A critical review of the trachoma literature implicates individual and community hygiene as important risk factors for disease. Specific risk behaviors remain to be identified and validated as independent predictors of infection in different settings. Collaboration between biomedical and social science professionals is needed to design and carry out further research.

Attitude to Health↗
PubMed1989

Limbal disease in trachoma and other ocular chlamydial infections: risk factors for corneal vascularisation.

Ocular infection with Chlamydia trachomatis, whether of genital or endemic trachoma origin, usually produces diffuse infiltration and swelling of the scleral limbus, grey infiltrates of the corneal limbus, and superficial extension of vessels onto the corneal limbus. In genitally transmitted C. trachomatis infections, subepithelial infiltrates have been reported as well. In classic endemic trachoma, limbal changes also include limbal follicles which resolve, leaving Herbert's peripheral pits, and an extensive vascular pannus. To evaluate the limbal changes in trachoma, follow-up studies were done in 1986-1987 in a group of 213 children originally seen between 1969-1972. Pannus formation occurred at a much earlier age than conjunctival scar formation and was an excellent predictor of later severe conjunctival scarring. The evidence from this study suggests that the mechanisms for corneal pannus formation from the limbus are quite different from those for scarring of the conjunctiva.

Adolescent↗