Biomedical subjects
Publications and source records attributed to R Weill.
Concanavalin A acts in three ways on palatal shelves cultivated in vitro: 1. it has a mitogen effect, particularly on the medio palatal epithelium; 2. this produces thickening of this epithelium; 3. a delayed fusion or no fusion of the palatal shelves. The renewed mitogen activity and loss of adhesion properties seem to be linked.
The distribution pattern of the protein-polysaccharides in the rat incisor enamel was similar whether stained for glycoproteins (phosphotungstic acid) or for proteoglycans (alcian blue, bismith nitrate). Except for the holes at the dentino-enamel junction, where these components seem to exist as amorphous gel, protein-polysaccharides are closely associated to the proteinic fibrous matrix in rods and interrods structures as in prism sheaths where they are particularly abundant.
Planes of longitudinal fractures of human dental enamel observed in scanning electron microscopy showed morphological variations related to age. This late maturation was observed along the enamel sheaths which disappeared in the subsurface and decreased in the rest of the structure. The destructions produced by demineralizing substances (phosphoric acid, citric acid, EDTA) were always more severe in enamel of older teeth when compared to younger samples. A pretreatment of the fragments with a urea solution increased the acid effects only in young enamel. It is suggested that the late maturation of enamel consists in a reduction of matrix components.
An autoradiographic study conducted on the rat incisor showed the presence 4 hours after (3H) proline injection, of 25-30% of the grains on the secreting cells and 70 to 75% on the extracellular matrics. The simultaneous injection of vinblastine sulphate reversed these percentages to 75-80% on the cellular level and 25-25% on the matrics. The vinblastine therefore inhibited the secretory processes of these cell types. On the other hand, due to the alkaloid, the number of grains present increased over the ameloblasts and principally over the intercellular spaces. The effects of these secretion and permeability variations suggested that a flow of precursor rich material reached the epithelial layer whatever the state of ameloblast activity.
Structural observations upon fluorosed enamel were made on human teeth extracted from Nabeul (Tunisia). Longitudinal sections of enamel were made and microradiographed. Topographical observatoons in the S.E.M. showed alterations of the pattern of mineralization. Fissures and clefts filled with plaque material were observed to reach to the surface of the teeth. They penetrated into enamel along the prisms. Acid etching of the surface by 30% H3PO4 revealed enlarged acid-resistant sheaths while the core of the prisms was irregularly etched. Inner portions of the enamel were observed on fractured fragments. The structure was not significantly perturbated except for areas of porosity. After demineralization of the sections by 10% EDTA at pH 7 and critical point drying, the organic matrix was observed in the S.E.M. : It appeared as a fibrous network. Compared with sound teeth the matrix was dense and irregular. Histochemical stainings showed the presence of organic material. Alcian blue and PAS positive contents were very low except near the enamel-dentine junction. Preliminary observations were made using SMI Cameca ion microanalyser and histochemical studies on undecalcified sections were made in order to compare the observations made with light microscopy with S.E.M. findings.
3H Fucose of 14C Galactosamine have been incorporated in vitro into a palatal shelf. This shelf has been associated with the homologous non-labeled palatal shelf on a normal medium. The mesenchyme of the explants which were incubated with the isotope is densely labeled. In the epithelium the cells are scarcely labeled. The isotope is dense in enlarged intercellular spaces. On the free surface, the tracer is located in front of those intercellular spaces and does not form a continuous coat. When the shelves have fused, the isotope migrates through the intercellular spaces of the non-labeled epithelium into the mesenchyme.
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The ultrastructural distribution of the protein-polysaccharides was studied in the predentinal and dentinal matrices of the rat. Used for the indentification of the glycoproteins, the chromic-phosphotungstic acid mixture (Rambourt, 1967) weakly contrasted the predentine, underlined the mineralization front and impregnated the dentinal matrix. Alcian blue (Goldberg et al., 1977) as well as bismuth nitrate (Serafini-Fracassini and Smith, 1966), cationic stains for the proteoglycans, produced a strong contrast in the predentine, whereas in the dentine, which appeared clear, only 100 to 150 A granules associated with the periodic collagen striations were stained. This inverse variation between non collagenous proteoglycans and glycoproteins is discussed in relation to the mineralization process.
Na2 35SO4 was either injected to pregnant mice or added to a "Wolff and Haffen" culture medium. In various experiments, palatine shelves and half-lips remained one hour on this labeled culture medium. They were thereafter associated to another labeled fragment, either to their homologous shelf in a homotypical culture, or to a half-lip in heterotypical culture. In the same way, labeled half-lips were coupled to unlabeled palatine shelves. In all these cases, the mesenchyme was labeled by the tracer while the epithelial cells remained empty. In the medio-palatine epithelium, some dislocations could be noticed between the cells. These gaps were filled by the labeled mesenchyme with which they were in continuity. At this level the tracer appeared on the external surface. In the homotypical associations, it invaded, through these channels, the labeled antagonistic explant; in the heterotypical associations, lips plus palatine shelves, the labial epithelium prevented all the penetrations, except when alterations occurred, due to a long lasting culture. The role of the mesenchyme in the process of fusion and in the possible building of a surface coating is discussed.
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Ultra-thin sections of dental tissues, fixed in glutaraldehyde and osmium tetroxide, embedded without previous demineralization in Epon, were contrasted the grids with an alcian blue solution after previous oxidation periodic acid or hydrogen peroxide. Correlations with histochemical results obtained with the optical microscope, other results obtained with ruthenium red and phosphotungstic acid and controls made after enzymatic digestion with chondroitinase AC suggest that this technique is specific for the detection of acid mucopolysaccharides in those calcified tissues studied.
The innervation of the tooth and the parodont has been studied by autoradiography of 3H proline, unilaterally injected in the Gasser ganglion of adult cats. The presence of neurofibrils has been observed particularly in predentine and dentine, along the collagen fibers of the periodontal ligament, in the superficial layer of bone and cementum, in the papillar layer of the gingiva and as ultraterminal fibrils in the gingival epithelium.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.