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Biomedical subjects

W L Jongebloed

Publications and source records attributed to W L Jongebloed.

At least 91 records · Page 5Linked to original sources
PubMed1978

Crystallites dimensions of enamel.

In this paper the average diameter of enamel crystallites in mature, deciduous and fluorosed human enamel as well as in bovine enamel (in vivo and in vitro remineralized) is discussed. The investigation was carried out on broken surfaces of the various kinds of enamel with a scanning electron microscope. Corrections have been applied for the thickness of the gold-layer deposited. The average crystallite diameters for sound, deciduous and fluorosed human enamel were : 36 nm; 46 nm and 81 nm, respectively. The values for sound, remineralized in vitro and remineralized in vivo bovine enamel were 57 nm; 97 nm and 63 nm, respectively. The results indicate furthermore that if a correction for the sputtered goldlayer is applied, the results for SEM and TEM microscopy are in good agreement with each other. The difference between in vivo and in vitro remineralized bovine enamel is most likely due to differences in speed of remineralization and/or the presence of saliva.

Animals↗
PubMed1977

Mechanism of enamel dissolution and its prevention.

In this paper the mechanism of dental enamel dissolution is discussed. Special attention is given to the anisotropic solubility behaviour (hollow tube formation) of demineralized enamel crystallites. The combined evidence strongly indicates that this peculiar dissolution behaviour is caused by dislocations. The dislocations--linear lattice defects--are present in the crystallite center and are the cause of two active dissolution sites in each crystallite. Initial as well as later stages in the caries process are discussed. Experimental evidence is presented which indicates that the active sites can be inactivated by agents like EHDP and MFP. After inactivation, acid penetration is either prevented or strongly retarded.

Apatites↗
PubMed1977

The enamel substrate-characteristics of the enamel surface.

The outer enamel surface is of considerable interest in dentistry as it is the substrate for the acquired pellicle; the pellicle itself is the plaque carrier. In this paper the interface between outer enamel and pellicle is discussed with special emphasis on the outer enamel from a structural and chemical point of view. The outer enamel layer (less than 1 micron from the anatomical surface) is most likely a non-stoĭchiometric apatite. The chemical composition is obviously strongly different from the composition of bulk enamel. A model for the structure and atomic composition of surface enamel is presented. The available experimental evidence indicates that at an atomic scale, enamel crystallites have mainly phosphate groups (HPO42-groups) on the solid surface; the liquid adhering Stern layer contains most likely large amounts of calcium ions.

Dental Enamel↗
PubMed1976

Investigative studies of the dermatitis caused by the larva of the brown-tail moth (Euproctis chrysorrhoea Linn.) II. Histopathology of skin lesions and scanning electron microscopy of their causative setae.

Two different aspects related to the dermatitis caused by the so-called nettling hairs of the larva of the brown-tail moth, Euproctis chrysorrhoea L., are documented. The first part describes the sequence of histopathologic changes associated with the inflammatory process in the human skin induced by epicutaneous application untreated (UT-N) and heat treated (HT-N) nettling hairs. The penetration of untreated and heat treated nettling hairs into the epidermis is evident from their presence in 12 out of 29 UT-N lesions and 5 out of 10 HT-N lesions respectively. The introduction of nettling hairs into the skin leads to damage and bulla formation of the surface epithelium and early inflammatory signs consisting of edematous changes of the dermis and pervascular infiltration of neutrophils, eosinophils and mononuclear leucocytes. After few hours the intensity of the dermal infiltrate has increased and spongiotic changes appear. After 48--72 h the perivascular infiltrate is mainly composed of mononuclear cells, while along with increased spongiosis the damaged surface epithelium may show repair. The traumatic changes of the surface epithelium in HT-N lesions appear less prominent in comparison with the UT-N lesions. The second part describes the findings obtained by scanning electron microscopy of the nettling hairs. Evidence is brought forward to support the view that the offending setae may be looked upon as tapering, hollow microcapillaries which are open at both ends. The present findings are consistent with the idea that the nettling hairs may serve as microneedles from which irritant substances may be liberated when penetrating into the skin, and that the resulting inflammatory reactions are attributable to combined mechanical and toxic effects.

Dermatitis, Contact↗
PubMed1975

Morphology and size-distribution of sound and acid-treated enamel crystallites.

Citric acid dissolves crystallites of enamel by initially etching out approximately hexagonal holes in the core of the crystallites, parallel to their long axis. Such acid-treatment influences the crystallite diameter only slightly since the distribution of the diameters of crystallites with a hollow core is not essentially different from those found in sound enamel. In both cases, the average diameter is 37 nm. Crystallites having a central defect and an outer diameter of about 40 nm are split into two parts of approximatley 15 nm in diameter following acid treatment. The central defect is caused exclusively by the acid and not by damage from the electron beam, nor by a combination of acid treatment and electron beam damage.

Citrates↗
PubMedDate not supplied

Fungal growth on soft contact lenses: a SEM-study.

Three soft contact lenses of the HEMA type, discarded because of irritation of the cornea, were processed for and subsequently examined with the SEM, A large portion of the convex surface was covered with globular deposits of fungal spores. Cross-fractures of lenses showed penetration of the fungi into the matrix material of the lenses. The concave surface of the contact lenses showed at two points imprints of the epithelial cells of the cornea in the deposited material on that side of the lenses.

Contact Lenses, Hydrophilic↗
PubMedDate not supplied

The keratoconus epithelium studied by SEM.

A keratoconus removed from an 18-year-old male was processed for SEM and examined with special attention for the epithelial surface. A broad degenerative band was found running in the vertical meridian, showing areas devoid of, or with only partially attached, epithelial cells, and also areas with abnormal cells either, with a defective cell membrane and without cell contents or with an intact cell membrane but without a cell nucleus. Stereoscopic images of these defective cells show that cell degeneration is sometimes found several cell layers deep into the epithelium.

Adolescent↗
PubMedDate not supplied

The cisternal anatomy of the vitreous body.

The vitreous body of a fresh human eye removed post-mortem was suspended in water after stripping off the corneo-scleral coat, the choroid and the retina. Coloured ink was injected into the vitreous specimen from different points. Individual spaces (cisterns), transitions between cisterns and specialized structures like the bursa premacularis and the canal of Cloquet became visible when partial filling had taken place. SEM-examination of the individual cisternal walls of the bursa premacularis area showed networks of different density and texture and a considerable variation in the length of the individual fibres, some of which extended from the ciliary body (Retzius bundles) to the rim of the Bursa premacularis.

Humans↗
PubMedDate not supplied

A morphological description of human cataractous lenses by SEM.

Human cataractous lenses from patients of advanced age (101 & 85 year) were investigated by SEM. Various aspects of the cataract morphology could be observed. Even when the overall shape of the lens fibres had remained unchanged (although the typical ball and socket interconnections were barely visible) the homogeneous fibre content had changed into fibrillar and/or granular material, or the lens fibres had been (partly) hollowed out. Where there was shrinkage of the originally hexagonally-shaped lens fibres to a more or less rounded form with a wrinkled surface, the contents had changed into granular material with low density. Both granular and fibrillar material could account for a substantial increase in light scattering, resulting in a considerable decrease in vision through the lens.

Aged↗
PubMedDate not supplied

Descriptive anatomy of the ageing process of the human cornea as visualized by SEM.

Two corneas from elderly patients (87 & 95 years) were studied by SEM and the results compared with in-vitro aged corneas and a keratoconus. The detachment of epithelial cells as part of a cell renewal process leads to loss of epithelium and exposure of Bowman's membrane. The degenerative process in the endothelium leads to porosity and loss of the endothelial cell membrane and finally to (partial) loss of the endothelial cell layer. The start of such a degenerative process is marked by the formation of liquid-filled blebs. The balance of degeneration versus regeneration is clearly biased in favour of the degenerative process, because the cells are not able to produce sufficient collagenous material to cover the denuded areas.

Aged↗