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Biomedical subjects

J Kragstrup

Publications and source records attributed to J Kragstrup.

At least 55 records · Page 3Linked to original sources
PubMed1993

Computer-based simulation model for evaluation of variations in practice patterns of general practitioners: a feasibility study.

Our study aimed at developing a computer-based simulation model for the consultation process in general practice. The model was developed in the computer language COM-CATS and makes use of an IBM-compatible personal computer with an automated diasprojector attached. A feasibility study comprised 122 general practitioners (108 male and 14 female), participating in the 6th Nordic Congress of General Practice (Aarhus, Denmark, 1989). All participants were given a short introduction to the patient and his symptoms, but all further information was optimal and selected by the doctor. There was a large variation in practice patterns of the general practitioners. Their actions were, however, performed selectively, i.e. a few tests were requested by most doctors and none of the doctors performed large numbers of tests. The great advantage of the computer-model in research into clinical decision-making is that it allows for a standardization of the clinical situation, gives the doctor an opportunity to select between optional information, and permits an automatic gathering of huge amounts of information about the decision-making process.

Computer Simulation↗
PubMed1991

[Laser treatment of sinusitis in general practice assessed by a double-blind controlled study].

The effect of Low Level Laser therapy (Galium-Aluminium-Arsenide laser, 30 mW/830 nm, Unilaser 2000 3B) on sinuitis was evaluated in a double-blind randomised clinical study comprising 60 patients from general practice. All patients received three treatments (90 seconds radiation on each sinus) with one to three days interval. No statistically significant differences in pain relief, well-being or duration of illness were observed between patients treated with laser and a placebo.

Adolescent↗
PubMed1991

A reconstruction of the remodelling cycle in normal human cortical iliac bone.

This paper describes the reconstruction of the remodelling cycle in normal iliac crest cortical bone from static and dynamic variables after double labelling with tetracycline in 10 young normal individuals. The average duration of the resorptive period was 27 days during which the average rate of resorption was 4.7 microns/day. The final resorption depth was 76 microns. The diameter of osteoclast containing cutting cones was significantly smaller (P less than 0.05) than cutting cones containing mononuclear cells, indicating an initial osteoclastic resorption phase preceding a mononuclear resorption phase. The average mineralization lag-time was 8 days and the formative period 89 days. Osteoid thickness during this period averaged 5.8 microns. The seam thickness varied with the underlying uncompleted wall thickness, i.e., during the course of the formative period, with matrix deposition initially exceeding, later equalling and finally lower than the rate of mineralization. The mineral appositional rate (MAR) was 1.2 microns/day and the adjusted mineral appositional rate (Aj.AR) 0.9 micron/day. Both MAR and Aj.AR decreased during the formative period. A completed wall thickness of 62 microns left a Haversian canal with a diameter of 29 microns. After a quiescent period of 438 days the osteon (or parts of it) was reactivated. The average activation frequency was 0.93 per year.

Adult↗
PubMed1991

A histomorphometric analysis of the effects of fluoride on experimental ectopic bone formation in the rat.

Ectopic bone formation was induced in 14 rats receiving 100 ppm fluoride in drinking water and in 14 control animals. Sections from ossicles removed after 14 and 20 days were sampled for stereological analysis. Bone volume density and bone volume were reduced in experimental animals on day 14 (p less than 0.05). This difference was no longer present after 20 days. On day 20, surface density and areas of formative surfaces were increased in the fluoride group (p less than 0.05). Osteoid seam thickness was higher in the fluoride group on both days (p less than 0.01). In conclusion, fluoride induced quantitative alterations in ectopic bone formation, and the presented model may prove a useful addendum to previous methods for investigation of fluoride effects on mineralization processes in vivo.

Animals↗
PubMed1991

Morphostereometry of heterotopic ossicles in the rat.

The objective of this study was to describe induced heterotopic bone formation in the rat using stereologic methods and to optimize the sampling for toxicologic studies. Bone formation was induced by implants of demineralized bone powder in 24 male Wistar rats. The ossicles formed were removed after 14, 16, 17, 18, and 20 days. From each ossicle, six sections were sampled equidistantly, and seven microscopic fields were analyzed in each section. Ossicle volume and weight decreased from Day 16 to Day 20. Bone volume density increased during the experimental period because of the reduction in ossicle volume, whereas the total bone volume did not change. Bone thickness increased from Day 14 to Day 20. No changes were observed in the surface density and total area of formative surfaces. The major part of the total variation was due to true variation between animals. The described histomorphometric methods may prove useful in quantitative toxicologic studies, e.g., of fluoride effects on cartilage and bone formation.

Analysis of Variance↗
PubMed1989

Effects of sodium fluoride, vitamin D, and calcium on cortical bone remodeling in osteoporotic patients.

The purpose of this histomorphometric study of iliac bone biopsies from 10 postmenopausal osteoporotic patients was to describe the effects of sodium fluoride (combined with calcium and vitamin D) on remodeling in cortical bone after 6 months and after 5 years of treatment. Biopsies had been fixed in absolute methanol, embedded undecalcified in methylmetacrylate, and cut on a heavyduty microtome. The therapy had no effect on the thickness of cortical bone in the iliac crest but increased the porosity slightly. It had no statistically significant effect on depth of resorption or thickness of new walls formed at remodeling sites but treatment increased the fraction of osteons undergoing remodeling in cortical bone. After 6 months of treatment, the increase was due to an enhanced activation of new remodeling sites, but in biopsies taken after 5 years of treatment, some degree of mineralization defect was observed and the duration of the remodeling cycle appeared to be prolonged. The mechanism underlying this qualitative change in the response to treatment is unknown, and it is unclear whether the mineralization defect may be prevented by, e.g., an altered supplementation of vitamin D or calcium.

Aged↗
PubMed1989

Effects of fluoride on cortical bone remodeling in the growing domestic pig.

The purpose of the experiment was to assess the effects of fluoride (F-) on the remodeling process of cortical bone. Sixteen pigs, eight experimental animals receiving a supplement of 2 mg F-/kg b.w. and eight controls, were studied in individual sites from age 8 to 14 months. At slaughter samples of cortical bone were obtained from the right femur and embedded undecalcified. A new stereologic model based on fluorochrome tissue time markers and isotropic uniform random histologic sections was implied in order to obtain information in three-dimensional terms about dynamic aspects of remodeling. The rate of remodeling was increased in cortical bone from pigs receiving F- due to an increased activation of new remodeling. A doubling of the length density of resorptive and formative osteons was observed, although the change was statistically significant for the formative osteons only. An 11% decrease in depth of resorption and an 8% decrease in thickness of new bone formed led to a small decrease in the radius of Haversian canals in the fluorotic bone. The porosity of cortical bone was slightly but significantly increased. At formative sites the osteoid thickness and the mineralization rate were not significantly changed by F-. It was concluded that the observed changes cannot be explained by F- induced changes in a single cell. Fluoride appears to affect all cells involved in remodeling by direct or indirect mechanisms.

Animals↗
PubMed1989

Stereologic estimators of cortical bone remodeling including a kinetic model.

The purpose of this study was to describe cortical bone remodeling by means of a new stereologic model, which is based on isotropic uniform (IUR) histological sections and two fluorochrome tissue time markers (tetracycline and calcein) given with a 15-day interval. From each of five pigs two samples of cortical bone were sawed out from the middle part of the diaphysis of the left femoral bone and fixed in absolute methanol. Specimens were embedded undecalcified in methylmethacrylate, and the plane of sectioning was sampled by a new procedure, which produce IUR-sections. The extent of remodeling was estimated by length densities, that is, length of Haversian system undergoing resorption or formation per unit volume of bone. These estimates made it possible to express the activation rate and the remodeling rate at tissue level in absolute three-dimensional terms. Such estimates have not previously been published. The shortest diameter of osteon cross-sections was used for obtaining three-dimensional measures of osteons dimensions. The estimated true variance between animals as percentage of the observed variance was above 68% for all morphometric parameters except the length density of resorptive osteons (35%). It was concluded that the proposed stereologic methods enable a detailed description in three-dimensional terms of the remodeling process in cortical bone, and further information may be obtained by combining measurements with observations of cell morphology.

Analysis of Variance↗
PubMed1988

Mercury concentrations in blood from Danish dentists.

Blood samples from a group of 130 dentists and a control group of 40 blood-donors were analyzed by cold vapor atomic absorption spectrophotometry in order to evaluate the extent of mercury exposure. The median blood concentration of mercury was 4.0 (range: 1.2-19.2) micrograms/l for dentists and 2.0 (1.1-4.6) micrograms/l for controls (2P less than 0.01). Practice characteristics obtained in a questionnaire showed no statistically significant relationship to blood mercury, but 49 dentists having one or more fish meals per wk, had a median concentration of mercury, which was 47% higher than dentists seldomly consuming fish (2P less than 0.01). It was concluded that none of the examined dentists had blood concentrations above the level (35 micrograms Hg/l) associated with the hygienic threshold limit.

Adult↗
PubMed1987

Compressive strength, ash weight, and volume of vertebral trabecular bone in experimental fluorosis in pigs.

The aim of the investigation was to measure the effect of fluoride on vertebral trabecular bone compressive strength and to correlate this with fluoride-induced changes in bone density. This correlation would express changes in the quality of bone during fluoride treatment. Pigs were used in the experiment because their trabecular bone structure and remodeling sequences are very similar to the human. Eight animals receiving a supplement of 2 mg F-/kg b.w. per day from age 8-14 months were compared with 8 control animals. Morphologic measurements in the animals receiving fluoride supplement showed a significant increase of 17% in bone density and a smaller, insignificant increase of 3% in ash weight analyses. Meanwhile, the mechanical parameters for the fluorotic animals were unchanged (maximum compressive strength, maximum stiffness, and energy-absorption capacity) or decreased (normalized compressive strength = maximum compressive load corrected for ash density). It is concluded that the increased bone mass during the initial stages of fluoride treatment does not necessarily indicate an improved bone quality. The discrepancy between bone mass and strength could be either a permanent or a temporary phenomenon and requires further investigation.

Animals↗
PubMed1987

Unbiased stereologic estimation of surface density in bone using vertical sections.

The conventional stereologic procedure for estimating bone surface densities in iliac crest biopsies gives biased estimates because bone substructure is anisotropic and the sectioning of the biopsies is intended to be parallel to the cylindrical axis of the iliac crest biopsy. It has recently been shown that random anisotropic sections with an identifiable axis or direction that is arbitrary but fixed can be used for unbiased estimates of surface areas. The arbitrary axis is called "vertical," which does not imply anything about its relation to direction of gravity. To describe the methodology and the practical sampling procedure for vertical sections, surface density of trabecular bone was estimated in 16 bone samples obtained at autopsy from eight persons (mean age 64 years) using an anisotropic cycloid test system designed for vertical sections. In addition, variation in the estimation procedure was quantitated. The average surface density of trabecular bone was 2.8 +/- 0.4 mm-1 (+/- SD). No systematic difference was observed between the two bone specimens from each of the eight persons. Estimation of the variance at each level of sampling showed that the majority of the total observed variance was due to true variance between individuals. Vertical section is, in general, the method of choice when dealing with surfaces not known to have an isotropic orientation distribution. The cycloid test system is easy and fast to use, and the estimate is truely unbiased. The requirements are all sections must be parallel to the vertical axis, the rotation around this axis must be random, the position of the section or of the biopsy must be random, and the vertical axis must be identified in the section.

Aged↗
PubMed1986

Parathyroid glands, calcium, and vitamin D in experimental fluorosis in pigs.

The purpose of this study was to determine whether total serum calcium, parathyroid gland structure, and/or levels of parathyroid hormone, 1,25 and 24,25 DHCC, are altered in pigs with dental and skeletal fluorosis. Eight experimental animals receiving 2 mg F-/kg b.w. per day from age 8-14 months were compared with eight controls. Concentrations of plasma fluoride and total plasma calcium were assessed at intervals throughout the experiment and during a 48 hour period at day 110-111 of the experiment. At the same time, concentrations of immunoreactive parathyroid hormone were measured using a homologous labeled antibody for porcine hormone, and a radioimmunoassay was used to assess concentrations of 1,25 DHCC and 24,25 DHCC. Parathyroid tissue volumes were assessed at the end of the experiment by quantitative histology using volumetry and point counting. Plasma fluoride increased from 0.0007 +/- 0.0001 mmol/liter to 0.0127 +/- 0.002 mmol/liter in pigs receiving fluoride. In spite of this increase, total plasma calcium remained the same throughout the experiment. Volumes of parathyroid tissue, and levels of circulating parathyroid hormone 1,25 DHCC and 24,25 DHCC, were not significantly changed. It was therefore concluded that disturbance of calcium homeostasis is not an obligatory finding in dental and skeletal fluorosis and consequently does not play an essential role in the pathogenesis of these hard tissue lesions.

Animals↗
PubMed1986

Dental fluorosis developed in post-secretory enamel.

The aim of this study was to test whether dental fluorosis can be produced by administration of chronic doses of fluoride during only the post-secretory stage of enamel mineralization. Eight control and eight experimental pigs matched by weight and litter were fed a low-fluoride diet (less than 0.05 mg F-/kg b.w. daily) from weaning to slaughter at 14 months. The test group received an oral dose of 2 mg F-/kg b.w. per day from 8 months of age. Lower fourth pre-molars were at the post-secretory stage at the start of fluoride administration (confirmed by tetracycline marker) and were just erupting at slaughter. All of the fourth pre-molar teeth from the test group developed diffuse enamel hypomineralization indistinguishable from human fluorosis. No such lesions were seen in any of the teeth from the control animals. It was concluded that enamel fluorosis may be caused by fluoride exposure in the maturation phase only. The pathogenic mechanism may be an effect either on the selective loss of protein or on the influx of mineral, both of which occur during the post-secretory or maturation stage of enamel formation.

Amelogenesis↗