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Biomedical subjects

O Fejerskov

Publications and source records attributed to O Fejerskov.

At least 73 records · Page 4Linked to original sources
PubMed1991

Posteruptive changes in human dental fluorosis--a histological and ultrastructural study.

The aim of the present study was to describe the structural features characterizing the severe grades of human fluorotic enamel (TF scores 5-9) with particular emphasis on the posteruptive changes in severely fluorosed teeth. Dental fluorosis is a subsurface hypomineralized lesion deep to a well-mineralized outer enamel surface, which in severe cases breaks apart shortly after eruption. Early signs of posteruptive changes comprise small defects corresponding to the opening of striae of Retzius. The enamel pits which develop after eruption in more severe cases exhibit an increase in mineral content at their base which correspond to the exposed subsurface hypomineralized lesions. Likewise, the extensive removal of surface enamel in the most severe cases of human fluorosis results in a highly varying uptake of mineral into the exposed subsurface hypomineralized lesions. The uptake varies greatly within apparently similar degrees of hypomineralized lesions. In approximal abrasion facets, however, where the subsurface lesions are also exposed, no evidence of mineral uptake was found. At the ultrastructural level, the well-mineralized surface zone consists of large hexagonal enamel crystals separated by rather large intercrystalline spaces in which numerous irregular small crystals are observed. Moreover, the large crystals may exhibit central and peripheral dissolution. In addition, mineral appeared to be deposited into such defects as well as along the side of the crystals, often with the lattices being continuous from the original crystal into the apparently posteruptive formed crystal material. It is concluded that a substantial mineral uptake can take place in exposed porous hypomineralized fluorotic enamel after eruption, but is most likely to be associated with the presence of microbial deposits, the metabolic activity of which may play a keyrole in mineral exchange.

Crystallography↗
PubMed1990

Effects of single doses of 1-hydroxyethylidene-1,1-bisphosphonate on the mineralizing front of rat incisor enamel: a microradiographic and scanning electron microscopic study.

The effects of a single dose of HEBP were examined by injecting rats subcutaneously with various doses (0.5, 1, 2.5, 5 and 10 mg P/kg body wt) and killing them either 2 or 9 days after injection. The maxillary incisors were processed for microradiography and the mandibular incisors for scanning electron microscopy after enzymatic digestion of the enamel organ remains. All doses resulted in a hypomineralized incremental band corresponding to the position of the mineralizing front at the time of injection. At 5 and 10 mg P/kg body wt, a hypomineralized lesion was found throughout the whole thickness of the enamel in an area which corresponded to the stage of late enamel secretion at the time of injection. The surface layer covering this lesion was elevated or disrupted. By scanning electron microscopy, there were three different types of lesions along the enamel surface: a "demarcation groove" corresponding to the initial enamel formation at the time of injection; an "area containing mineral globules" and a "bright band" corresponding to the stages of late secretory and final enamel formation, respectively, at the time of injection. A single injection of HEBP thus interferes with different stages of enamel formation. The findings may be explained as of the physico-chemical effects of HEBP on the mineral phase alone, but a direct effect of the drug on ameloblast function cannot be excluded.

Amelogenesis↗
PubMed1990

Effect of cigarette smoking on the transition dynamics in experimental gingivitis.

This paper reports the findings of an experimental gingivitis study conducted in smokers and non-smokers. 33 volunteers were examined and underwent prophylaxis during a period of 4 weeks. 28 subjects who showed a plaque index less than 0.20 on all prophylaxis occasions were permitted to continue in the study. Subjects then had their gingival status recorded, had their teeth polished and were requested to abstain from all oral hygiene measures for the following 21 days. After 5 days, 10 days and 21 days, plaque and gingival status were recorded using the criteria of the plaque index and gingival index. After the examination on day 21, the teeth were polished and oral hygiene was re-instituted. Following 2 weeks of supervised oral hygiene, recordings of plaque and gingival status were performed. At the initial examination, there was no difference between the clinical assessment of plaque and gingival status in smokers and non-smokers. Similar amounts of plaque accumulated in the 2 groups during the period of no oral hygiene, but smokers exhibited less gingival inflammation assessed clinically than non-smokers. This difference occurred as a result of an apparently lowered incidence rate and a markedly higher recovery rate in smokers compared to non-smokers. These findings may indicate that smokers for reasons yet unknown have a reduced capacity to mount and maintain an effective defense reaction to a given plaque challenge.

Adult↗
PubMed1990

A new approach to investigating associations in periodontal disease data.

This paper presents a method for the analysis of data originating from studies of destructive periodontal disease. The proposed method is an extension of the Mantel-Haenszel technique for the analysis of case-control studies and allows for expression of the site-specificity of destructive periodontal disease while maintaining the individual as the unit of analysis. Using data originating from a cross-sectional study of periodontal breakdown and oral hygiene parameters in a random sample of adult rural Kenyans, the proposed method is illustrated and the results compared with results obtained when two alternative analytical methods are used. The results demonstrate that the choice of analytical strategy may have profound implications for the conclusions to be drawn. Depending on the strategy chosen, one may draw conclusions which are qualitatively different and the present study indicates that the direction of these differences is not predictable.

Adolescent↗
PubMed1990

Depth of occlusal caries assessed clinically, by conventional film radiographs, and by digitized, processed radiographs.

Occlusal caries depth was assessed in 47 extracted premolars and permanent molars by 4 observers on a rank scale by eye inspection, by film radiographs, and by 2 of the observers also by digitized radiographs after filtering and contrast enhancement of the image. Quantitative estimates of caries depth were obtained from the digitized radiographs. Accuracy of scorings was determined with the histologic section as validating criterion. Occlusal caries was present in a spectrum from incipient fissure decalcification to large cavity formation. Clinical as well as radiographic scorings most frequently under-estimated lesion depth. Accuracy of radiographic assessments increased substantially by digital processing of the radiographic image. Quantitative measures of caries depth on digitized radiographs were strongly correlated to the histologic measures (r = 0.91). Interobserver agreement was fair to moderate according to kappa coefficients for the clinical and the radiographic scorings. The agreement was highest for the scorings of the digitally enhanced images. The study suggests that digital processing of radiographic images constitutes a diagnostic aid that may give a more accurate estimate of occlusal caries depth.

Analog-Digital Conversion↗
PubMed1990

An ultrastructural study of bacterial invasion and tissue breakdown in human experimental root-surface caries.

This study describes the structural features of the interface between microbial deposits and root cementum in actively progressing root-surface caries lesions developed experimentally in six elderly individuals. A total of 18 specimens was examined by microradiography, and a further 18 by light and transmission electron microscopy after intra-oral periods of one, two, and three months. All specimens showed various degrees of subsurface dissolution of mineral and bacterial invasion of the cementum. Although the microradiographic pattern of mineral loss was subsurface in nature, transmission electron microscopy showed dissolution of crystals in the outermost layers of the cementum, with a distinct gradient inward. Bacterial invasion occurred along the borders between bundles of relatively well-mineralized extrinsic collagen fibers in which the characteristic cross-banding remained intact. The pattern of bacterial invasion was influenced by the incremental lines and the cemento-dentinal junction. The invading bacteria were almost exclusively Gram-positive, of various shapes, and possessed thick, moderately electron-dense cell walls and electron-lucent "vacuoles" in the cytoplasm. It is concluded that because of pronounced mineral loss of the outermost cementum, accompanied by bacterial invasion, the surface of an active cementum caries lesion, as observed by transmission electron microscopy, is not identical to that seen in microradiograms.

Aged↗
PubMed1990

The nature and mechanisms of dental fluorosis in man.

Any use of fluorides, whether systemic or topical, in caries prevention and treatment in children results in ingestion and absorption of fluoride into the blood circulation. The mineralization of teeth under formation may be affected so that dental fluorosis may occur. Dental fluorosis reflects an increasing porosity of the surface and subsurface enamel, causing the enamel to appear opaque. The clinical features represent a continuum of changes ranging from fine white opaque lines running across the tooth on all parts of the enamel to entirely chalky white teeth. In the latter cases, the enamel may be so porous (or hypomineralized) that the outer enamel breaks apart posteruptively and the exposed porous subsurface enamel becomes discolored. These changes can be classified clinically by the TF index to reflect, in an ordinal scale, the histopathological changes associated with dental fluorosis. Compared with Dean's and the TSIF index, we consider the TF index to be more precise. Recent studies on human enamel representing the entire spectrum of dental fluorosis have demonstrated a clear association between increasing TF score and increasing fluoride content of the enamel. So far, no useful data on dose (expressed in mg fluoride/kg b.w.)-response (dental fluorosis) relationships are available. In this paper, we have, therefore, re-evaluated the original data by Dean et al. (1941, 1942), Richards et al. (1967), and Butler et al. (1985) from the USA, by applying the equation of Galagan and Vermillion (1957) which permits the calculation of water intake as a function of temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental Enamel↗
PubMed1990

Dental caries in developing countries in relation to the appropriate use of fluoride.

Although it is widely believed that caries prevalence in developing countries is increasing rapidly, a review of studies from Africa and China provides equivocal evidence. Data from child and adult populations indicate that the disease is almost ubiquitous but with a slow rate of progression. Theoretically, administration of fluoride in such populations should result in reducing caries progression rates, but too little is known about the magnitude of the effect, and therefore about the cost-effectiveness of different methods of fluoride administration. The lack of a developed infrastructure and of trained personnel in many developing countries limits the applicability of many strategies. Methods of fluoride administration that minimize systemic exposure are to be recommended where affordable or practical. In the light of economic constraints and slow caries lesion progression rates, however, improvements in oral hygiene practices may be the most important method of controlling the disease whether or not fluoride is available or accessible.

DMF Index↗
PubMed1990

The effect of a single dose of 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP) on presecretory ameloblast differentiation in rat incisors.

A single, high dose of HEBP to rats results in a triad of lesions along the mineralizing front of the incisor enamel. One type of lesion is a shallow groove crossing the apical enamel surface. The purpose of this study was to explore the pathogenesis of this "demarcation groove", and to characterize changes in the involved regions of amelogenesis. Rats were given a subcutaneous dose of 10 mg/kg body weight of HEBP and sacrificed by vascular perfusion at intervals ranging from 1 to 36 hours. Mandibular incisors were processed for light and electron microscopy. The region of ameloblasts facing dentin was divided into two subregions: A region of ameloblasts facing unmineralized dentin, comprising a posterior (Aud/p) and an anterior portion (Aud/a), and a region of ameloblasts facing mineralized dentin (Amd). The progressive apical mineralization of the predentin was arrested up to 12 hours after injection of HEBP, while ameloblasts related to already mineralizing dentin continued to differentiate and secrete enamel matrix. At 8 hours the dentin and enamel layers had assumed a common apical border at the start of Amd, marking the position of the future demarcation groove. The length of Aud/p remained constant, Aud/a doubled in length, and Amd was drastically reduced up to 24 hours after injection of HEBP. The normal migration rate of the ameloblasts was unaffected by HEBP. Accumulations of ameloblast secretory products occurred at certain time intervals between the cell apices, but no morphological changes were recorded in the organelles. Most of the changes observed may be indirect in nature resulting from the physico-chemical effect of HEBP on normal mineralization of dentin and enamel. However, further studies are needed to elucidate possible direct cellular effects on ameloblasts.

Ameloblasts↗
PubMed1990

The effect of a single dose of 1-hydroxyethylidene-1, 1-bisphosphonate (HEBP) on secretory ameloblasts and enamel formation in rat incisors.

The present experiment was undertaken in order to study how HEBP affects secretory ameloblasts and the mineralizing front of rat incisor enamel resulting in the formation of a hypomineralized incremental band. Rats were given a single subcutaneous injection of 10 mg/kg body weight of HEBP and sacrificed at intervals ranging from 1 hour to 9 days. The incisors were specially prepared for microradiography, scanning electron microscopy, and light and transmission electron microscopy. The microradiographical examination 9 days after injection revealed a distinct incremental band of hypomineralization from the amelo-dentinal junction to the outer enamel surface. The overall rod pattern and mineral distribution within the enamel was otherwise normal. Under light microscopy the ameloblasts exhibited an increase in vacuoles and dark granules in the supranuclear cytoplasm 2-12 hours after injection. At 12 hours a total disarray of the mineralizing front was evident and confirmed by SEM. However, 24 hours after injection a normal structure of the mineralizing front was regained. Ultrastructurally the organelles of the ameloblasts showed no changes from normal at any time interval. However, 2 hours after injection multivesicular bodies appeared frequently in the Tomes' processes and crystal density had diminished in the interrod enamel. At 8 hours a proteinaceous matrixdevoid of crystals was accumulating corresponding to interrod growth regions, whereas no obvious changes were recorded at the rod growth regions. At 12 hours the newly formed interrod enamel was thin and without crystals in some places. In such areas a granular, less-dense matrix was found and a band of small swellings of the interrod enamel was evident most likely corresponding to the time of injection. After 24 hours the cells and the mineralizing front appeared normal except in the interrod growth regions where the cell processes were still separated by wide intercellular spaces in which crystals were occasionally found in a fine granular matrix. These observations are discussed with particular reference on the known physico-chemical effects of HEBP on mineral formation. A possible direct cellular effect on the ameloblasts should be studied using radioautography and immunocytological techniques.

Ameloblasts↗
PubMed1990

Dental health of children and adults in Guinea-Bissau, West Africa, in 1986.

The aim of the present study was to assess the dental health situation of a relatively urban population in Guinea-Bissau, West Africa. A total of 312 persons aged 12, 30-39 and 50-59 years, respectively, were examined for dental caries, oral hygiene, periodontal pockets, gingival recession and mobility of the teeth present. The state of their oral hygiene was very poor. Although most persons examined had a relatively high number of teeth present a substantial number of these teeth had carious lesions, many of which were rather deep. Teeth with increased mobility were seen in a number of individuals but it appeared that periodontal breakdown was not the major cause of tooth mortality in the majority of the population. The results suggest that future dental health care strategies should focus on the development of a new type of dental health worker. This health worker should be capable of performing simple extractions, simple restorative treatment and intercepting early ongoing carious lesions using modern biologically-founded principles and appropriate technology.

Adult↗
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

Black-pigmented Bacteroides species and Actinobacillus actinomycetemcomitans in subgingival plaque of adult Kenyans.

A microbiological study was performed of the subgingival plaque on 2 sites in each of 20 adults originating from a rural area 40 km outside Nairobi, Kenya. The recovery rate of B. gingivalis was 70%, of B. intermedius 100% and of A. actinomycetemcomitans 40% of the subjects, and 50%, 90% and 28%, respectively, of the sites. The isolated strains exhibited similar biochemical characteristics and antibiotic susceptibility pattern as type strains of these species. The high recovery rate of these 3 bacterial species in adult Kenyans was a rather surprising finding, since pathological pocketing was found only sporadically. Furthermore, the results of 2 methodological approaches tested demonstrated that such microbiological studies can be carried out in countries with limited laboratory facilities.

Actinobacillus↗
PubMed1989

Dental fluorosis among participants in a non-supervised fluoride tablet program.

The aim of the present study was to describe the intraoral pattern of dental fluorosis among fluoride tablet consumers. One hundred and forty-two children, of whom 56 had participated in a fluoride tablet program of 0.5/1.0 mg NaF per day were examined blindly for possible fluoride-induced enamel changes. A low prevalence of dental fluorosis was found among non-participants. The later in life the tooth was formed, the higher was the prevalence. The subjects who had participated in the fluoride tablet program showed a significantly higher prevalence of fluorosis. They could be divided into three groups: Group 1 exhibited a tooth prevalence pattern not statistically different from that of the non-participants, group 2 showed dental fluorosis in almost all teeth except in those formed before the start of the tablet program. In group 3 the early and the late formed teeth showed very little fluorosis while those formed in the few years just after the initiation of the fluoride tablet intake were affected by fluorosis.

Child↗
PubMed1989

Tooth mortality and prosthetic treatment patterns in urban and rural Chinese aged 20-80 years.

The study describes tooth mortality levels and pattern of prosthetic treatments in a sample of 1744 Chinese aged 20-80 yr who are residents of Beijing area. Complete edentulousness was rarely seen before the age of 60 yr. Beyond this age up to 26% were edentulous, depending on age and sex. The mean number of teeth present ranged from 10.0 to 29.7 depending on age, sex, and area of residence. Below the age of 60 yr very few persons had experienced extensive loss of teeth but thereafter the number of teeth missing was substantially increased. Prosthetic treatments in the form of partial dentures, crowns, and bridges were frequently observed even in the younger age groups. In all age groups the number of teeth exhibiting caries lesions involving the pulp was much higher than the number of teeth exhibiting extensive mobility. Although many people retain a high number of teeth even late in life our findings indicate a substantial need for, in particular, relief of pain services. Concurrently, emphasis must be placed on preventive programs aiming at interfering with ongoing disease.

Adult↗
PubMed1989

Chemical and structural challenges in remineralization of dental enamel lesions.

The aim of the present paper was to identify some chemical and structural factors which may prevent a full remineralization of caries lesions and to study whether it is possible to overcome such obstacles. Samples of powdered enamel apatite were equilibrated with solutions metastably supersaturated with respect to enamel hydroxyapatite and fluorapatite. After 10 min and 60 min of equilibration at 20 degrees C the suspensions were centrifuged and the calcium and phosphate concentrations and the pH were determined in the supernatant. In parallel studies, 50 75-microns-thick sections of 27 fluorotic teeth of a severity of 5-7 according to Thylstrup and Fejerskov's classification were examined by microradiography and in polarized light using distilled water, and Thoulett's media or seen dry in air. Five obstacles inhibiting remineralization were identified: 1) Although remineralizing solutions or saliva are supersaturated with respect to enamel apatite the total amount of calcium and phosphate dissolved in it is small, so that after precipitation of the dissolved mineral only 1/20,000-1/30,000 of the volume of the mineralizing solution is occupied by mineral. 2) The concentration gradients from the mineralizing solution into the enamel is small, which indicates a slow diffusion into and out of the lesion. 3) The uptake of calcium and phosphate by the enamel apatite crystals is so rapid that the aqueous phase within the pores can be presumed to be only marginally supersaturated in the deeper parts of the lesion. 4) The surface layer of the enamel lesions was found to be a serious obstacle to remineralization so that a subsurface area remains hypomineralized after exposure to salivary remineralization even for a lifetime. 5) Nucleation of new apatite crystals to substitute lost crystals is an unsolved problem.

Apatites↗
PubMed1989

Langerhans cells in oral epithelium of chronically inflamed human gingivae.

This study describes the histopathological features and the distribution of oral epithelial Langerhans cells in 19 gingival biopsies originating from an adult Tanzanian population characterized by very poor oral hygiene and severe gingival inflammation. Light-microscopically, all biopsies contained often large inflammatory connective tissue infiltrates, 6 of which predominantly contained plasma cells while the rest were dominated by lymphocytes. Seven specimens contained peculiar accumulations of round lymphoid and dendritic cells in the lower cell layers of the oral epithelium. These phenomena have not previously been demonstrated in human gingiva and deserve further attention in studies on the pathogenesis of periodontal diseases. Immuno-histochemical staining with OKT6, OKT4 and OKT8 antibodies showed markedly increased numbers of OKT6-positive cells in 7 specimens and clusters of OKT4- and OKT8-positive cells in the oral epithelium of 4 specimens. High numbers of OKT6-positive cells were not related to the presence of intra-epithelial, non-keratinocyte infiltrates or large connective tissue infiltrates. The variable numbers of oral epithelial Langerhans cells may therefore result from different bacterial antigens elucidating different responses or, alternatively, reflect different responses to similar plaque antigens penetrating the surface of the oral epithelium.

Adult↗