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Biomedical subjects

K de Groot

Publications and source records attributed to K de Groot.

At least 181 records · Page 10Linked to original sources
PubMed1985

Effect of the imidazole derivative lombazole on the ultrastructure of Staphylococcus epidermidis and Candida albicans.

Lombazole, an antimicrobial agent of the imidazole class, induced profound ultrastructural changes in Staphylococcus epidermidis and Candida albicans, as observed by freeze fracture electron microscopy. In S. epidermidis cells, the primary effect on ultrastructure was characterized by a distinct change in the morphology of the plasma membrane. Secondary effects of lombazole were cell wall thickening, accumulations of lipidlike material, abnormal cell division, severe change of shape, separation of the plasma membrane from the cell wall, and disruption of cells. The alterations in C. albicans were characterized by the deformation of and a decrease in the number of invaginations in the protoplasmic fracture face and corresponding ridges on the exoplasmic fracture face and by separation of the plasma membrane from the cell wall, leaving a gap which frequently contained small vesicles. Moreover, a considerable thickening of the cell wall occurred at localized regions. These structural alterations are discussed in relation to biochemical changes which may correlate with these phenomena.

Candida albicans↗
PubMed1985

Reconstruction of large bone defects with calcium phosphate ceramics--an experimental study.

The aim of the present study is to evaluate the bone-defect-repairing capacity of dense hydroxyapatite compared with 40% macroporous hydroxyapatite in a weight-bearing model. The experiment consisted of the production of a relatively large mid-diaphysary defect in the left femur of 18 mongrel dogs. Cylindrical and semicylindrical hydroxyapatite implants were placed in these bone defects in order to restore continuity. The biocompatibility of implanted material has been studied physiologically, by radiographs and scintigraphs, by histology and finally by biomechanical tests. The normal weight-bearing of the operated limb restored in three weeks time. There were two mechanical failures in dense cylindric implants and two in porous cylindric implants. Radiographically, no evidence was found of degradation of porous or dense implants. Radionuclide bone imaging to assess osseous changes at the site of implants, showed intense radionuclide accumulation in all recordings of porous implants up to two years after implantation, in contrast to dense implant recordings. Histologically, there was no evidence of bioresorption. The implants were in direct contact with normal bone tissue. The pores were filled by calcified bone. There were no differences between porous and dense implants concerning the biocompatibility of hydroxyapatite.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Reaction of surrounding gingiva to permucosal implants of dense hydroxyapatite in dogs.

Experimental and histological studies on the reaction of surrounding gingiva to permucosal implants of dense calcium hydroxyapatite were carried out in dogs. Epithelial attachment and connection of supra-alveolar collagen fibres to the implant surface seemed to form a biological seal around implants similar to that around natural teeth. However, excellent oral hygiene is very important for the maintenance of this biological seal.

Animals↗
PubMed1984

Relationship between the degradation behaviour of calcium phosphate ceramics and their physical-chemical characteristics and ultrastructural geometry.

The neck geometry of different calcium phosphate materials was studied by scanning electron microscopy. The dissolution rate of these materials, especially of the necks, was determined by chemical analysis. The degradation of calcium phosphate materials in lactate buffer, related to the detachment of sintered particles, was found to be determined by neck dissolution rate and neck geometry. The latter factor depends on the crystallography and stoichiometry of the material and the sintering conditions.

Biocompatible Materials↗
PubMed1984

Induction of immunological tolerance by oral administration of nickel and chromium.

Oral administration of nickel-chromium to guinea pigs by way of a fixed occlusal splint, or the incorporation of metallic powder or salts into the pelleted food, did not induce hypersensitivity to these metals. In addition, a subsequent attempt to immunize the pre-treated guinea pigs failed in most animals, whereas non-pre-treated guinea pigs became clearly hypersensitive. These results show that oral administration of nickel and chromium induced a state of (partial) tolerance to both metals.

Administration, Oral↗
PubMed1983

Biodegradation behavior of various calcium phosphate materials in bone tissue.

In order to study the biodegradation behavior of calcium phosphate materials, cylinders of standard size were implanted in the tibiae of rabbits. Material parameters were stoichiometry (hydroxyapatite with a Ca/P ratio of 1.67 versus tricalcium phosphate with a Ca/P ratio of 1.50), crystallographic structure (apatite versus beta-whitlockite), microporosity, and macroporosity. The extent of biodegradation was evaluated by radiography, light and fluorescence microscopy, microradiography, and porosity measurements. All calcium phosphate materials were biocompatible in bone tissue. Hydroxyapatite ceramics had a higher osteogenic potential than beta-whitlockite materials. Depending on their porosities, sintered tricalciumphosphate (beta-whitlockite) materials were more or less biodegradable, in contrast to sintered hydroxyapatite materials, which showed no detectable resorption over a period of 9 months of implantation.

Animals↗
PubMed1983

Transmucosal implants of dense hydroxylapatite.

Transmucosal application of implants of dense hydroxylapatite has been studied in a long-term animal experiment. Implants were loaded with crowns or removable restorations. It appeared that transmucosal implants adhered to bone similarly as in the submucosal application. The clinical aspect of gingival tissues around the implants was the same as that around the adjacent natural teeth. Histologically, there were indications for a good attachment of gingival tissues to the implants. Implants fractured due to fatigue failure of the ceramic material. Prestressing of the implants may be the solution to this problem. Failing implants can clinically be treated by submerging, removal, or substitution.

Alveolar Process↗
PubMed1983

Activation of complement C3 by different calcium phosphate powders.

The ability of different calcium phosphate to activate the complement system is studied by crossed immunoelectrophoresis demonstrating conversion of C3 to C3b. Complement consumption is determined by a haemolytic assay CH50. Hydroxyapatite powders after sintering induce a significant conversion of C3 and reduction of CH50 value. However the complement system is not activated by sintered tricalciumphosphate (beta-whitlockite). This is not related to the adsorption behaviour; it depends neither on chemical composition nor on crystal lattice. It is argued that C3 conversion is not triggered by the convertase of the classical pathway.

Calcium Phosphates↗
PubMed1982

Implant materials in dentistry.

A review is given of current dental implants, as divided in permucosal and nonpermucosal applications. Each has its own material requirements, and therefore the various biomaterials currently used are discussed separately. The conclusion is that bioactive ceramics made of calcium phosphate, and where necessary reinforced with metals, will be the material of choice for future dental implants.

Acrylic Resins↗
PubMed1981

Comparative histocompatibility testing of seven calcium phosphate ceramics.

Five hydroxyapatite and two tricalcium phosphate ceramics were implanted in rat femora for one to six months. They were compared with each other in regard to biocompatibility and bone induction. After one month bone had grown directly on to the surface of all implants. After six months the on-growth of bone had increased with the exception of two dense HA materials. In these materials some bio-degradation had occurred with subsequent formation of a wide macrophage interlayer. Bio-degradation and biocompatibility of calcium phosphate ceramics seem to depend not only on density but also on other factors. Induction of bone could not be observed in soft tissue environment.

Animals↗