Wl Jongebloed

INTERACTION OF UREA AND HUMAN-ENAMEL

In this paper the interaction of urea on plaque-free sound human enamel is described. In 1 week urea penetrates in the enamel several hundred micrometers. It weakens or destroys part of the peptide st

Degradation of polypropylene in the human eye: a SEM-study

A polypropylene surgical suture, which had served as fixation suture for an IOL for a period of 6.5 years, was removed from the eye of a Dutch patient because it had broken at one end and thus formed a potential risk for a corneal touch syndrome. After careful rinsing in 50% ethanol, to remove adhering debris, it was prepared for SEM.A virgin piece of polypropylene material from a surgical package underwent the same preparative procedure.The fixation suture showed cracks perpendicular to the longitudinal axis of the suture; part of the surface layer was nearly detached or completely missing; while the diameter of the suture was decreased towards both ends by over 50% in comparison with the original diameter.The exposed subsurface layer showed a fibrillar structure. The degradation phenomena are considered to be caused by the enzymatic action of tissue-fluids.Virgin material did not show any of the phenomena observed on the fixation suture under consideration.

Orientation-Dependent Etchpit Penetration and Dissolution of Fluoroapatite

In this study, fluoroapatite crystals were etched with citric acid (pH 2) at 60 °C parallel and perpendicular to Apatite the c-axis. Quantitative measurements on a number of etchpits, visualized with

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.

THE GONIOSETON, A SURGICAL-TREATMENT FOR CHRONIC GLAUCOMA

A new and simple technique for glaucoma filtering surgery is presented. It is based on the introduction of a stainless steel microspiral or gonioseton into a goniopuncture by way of an ab interno procedure, minimising surgical trauma to the filtration area. Preliminary results are presented.

Action of Urea Solutions on Human Enamel Surfaces

In this study, the influence of urea solutions on both young and mature enamel was investigated. The urea concentrations were 5 and 0.1 M; the interaction period varied between 3 h and 3 months. The hydrogen (H)-bond destruction due to urea produces tiny micro-channels. The scanning electron microscope (SEM) investigations on replicas and by direct observations indicated that: (i) urea solutions destroy H-bonds in specific areas; (ii) these areas are most likely isolated prisms in the perikymata; (iii) interprismatic regions are, in contrast to these prisms, hardly influenced by the urea solutions. It is suggested that the special areas with relatively weak H-bonding are similar to the area attacked initially in artificial caries-like enamel lesions.

Mechanical and biochemical effects of man-made fibres and metals in the human eye, a SEM-study.

Prolene, perlon, supramid and titanium, either used as sutures, ‘Strampelli’ sutures or artificial lens loops, were compared after remaining in the human eye for at least one year. For comparison, non-implanted samples of each of the materials were used as blanks. Prolene and Perlon in particular showed severe biodégradation after a given period; Supramid showed much less degradation of its surface. Titanium showed a rather rough outer surface (even in the non-implanted samples), particularly as bends in the lens loop, which facilitated the adherence of cells, fibres and microorganisms.

Secondary retention of permanent molars: an assessment of ankylosis by scanning electron and light microscopy

Secondary retention refers to the cessation of eruption of a tooth after emergence. This may be the result of pathological changes in the periodontal ligament. The aim of this study was to describe the morphological and histological aspects of the radicular surface of secondarily retained permanent molars. The roots of 12 secondarily retained molars and two control molars, were examined by means of scanning electron microscopy (SEM) and light microscopy (LM) in order to analyse the occurrence and localisation of ankylosis. With SEM it was observed that the root surface of retained molars showed local areas covered with bonelike tissue. LM of these areas showed that this tissue was bone in direct contact with the root surface (ankylosis). In 11 cases, the areas of ankylosis were observed in the bifurcation area and at the interradicular root surface. In the remaining case, ankylosis was located at the outer root surface. The results of this study endorse the assumption that focal ankylosis is an important factor in secondary retention. Treatment recommendations must be based on this fundamental principle, because orthodontic movement of ankylotic molars is not possible.

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.

CRYSTALLITE DIAMETERS OF ENAMEL NEAR THE ANATOMICAL SURFACE - AN INVESTIGATION OF MATURE, DECIDUOUS AND NON-ERUPTED HUMAN-ENAMEL

An investigation of the average crystallite diameters in human enamel has been carried out near the anatomical surface (≈2.5 μm) and far from the surface (≈ 150 μm). Mature human deciduous as well as unerupted human enamel was studied. The results show that in deciduous enamel the average crystallite diameter near the surface and subsurface are 88 and 46 nm, respectively. For mature human enamel the near-surface and far from the surface values were 59 and 38 nm, respectively. In non-erupted enamel, however, no significant differences between near-surface and subsurface enamel were measurable. Furthermore, the fluoride content has been measured at the various positions of interest. No correlation between fluoride content and crystallite diameter was found. The diameter differences measured may be due to the influence of the aggressive oral environment on the teeth surfaces after eruption. After eruption frequent de- and remineralization dissolves small crystallites and by reprecipitation and/or growth larger crystallites are formed near the surface.