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Biomedical subjects

W Beertsen

Publications and source records attributed to W Beertsen.

At least 109 records · Page 6Linked to original sources
PubMed1979

Resorption of connective tissue in the gingiva of the mouse incisor.

During eruption of the mouse incisor part of the periodontal ligament moves along with the tooth in occlusal direction and is degraded in the gingiva, just apically of the junctional epithelium. When studied with the electron microscope some connective tissue cells (fibroblasts) showed disorganization of both nucleus and cytoplasm. In other cells vacuoles were observed containing partly degraded cellular constituents. Sometimes within these vacuoles electron dense material with the appearance of clumped chromatin was observed. On the basis of this observation it is concluded that heterophagocytosis contributes to the process of fibroblast breakdown. The ultrastructure of these heterophagic cells resembled that of fibroblasts. Collagenous fibrils were observed within cytoplasmic vacuoles of fibroblasts indicating that collagen is phagocytosed and probably digested in the lysosomal apparatus. Part of the intercellular space was filled with a homogeneous material of moderate electron density, intermingled with some collagenous fibrils. Within some cells of the junctional epithelium partly degraded material was observed which may indicate that the epithelium contributes to the removal of residual products of connective tissue degradation.

Animals↗
PubMed1979

Unipolarity of fibroblasts in rodent periodontal ligament.

In order to investigate whether fibroblasts in rodent periodontal ligament have a structural polarity, the position of the Golgi apparatus or the centriolar region in the cells was studied using light and electron microscopy. It appeared that, in the periodontal ligament of continuously erupting mouse and rat incisors, centrioles in fibroblasts on the tooth side of the ligament are preferably located in the anterior (occlusally directed) part of the cytoplasm. Polarity of fibroblasts in a single direction was less pronounced or absent on the bone side of the tissue. In the mouse, fibroblasts in the connective tissue adjacent to the incisor also contained an extensive system of cytoplasmic microtubules, whereas in the fibroblasts on the bone side of the ligament microtubules were less frequent. Unipolarity of fibroblasts was also observed in the periodontal ligament of the rat maxillary first molar, which is characterized by a limited eruption. Here, the Golgi region was usually situated in that pole of the cells that was directed towards the alveolar wall and the occlusal plane. It is suggested that structural polarity of fibroblasts in the periodontal ligament of rodent teeth is associated with orientation of functional activities of the cells, such as unidirectional movement or unidirectional deposition or phagocytosis of collagen.

Animals↗
PubMed1979

Remodelling of collagen fibers in the periodontal ligament and the supra-alveolar region.

Although the rate of turnover of collagen in the periodontal ligament may be somewhat higher than in the gingiva, it is doubtful whether this is the only factor that may explain why rearrangement of collagen fibers in the ligament occurs much more rapidly than in the supra-alveolar region under certain experimental conditions. It may well be that there are other factors that determine the ability of the periodontal tissues to rearrange themselves. On the basis of the distribution pattern of collagen phagocytosis by fibroblasts and the pattern of incorporation of 3H-proline it seems that turnover of collagen, at least in the periodontal ligament is evenly distributed across the width of the tissue. However, local variations in the presence of cells containing intracellular collagen fibrils may occur, as indicated by the observation that a relatively high concentration of ingested collagen fibrils is seen in fibroblasts in the direct vicinity of osteoclasts. It is suggested that coordinated action of fibroblasts and osteoclasts near the alveolar bone surface may represent part of a local mechanism through which rapid remodelling of certain areas in the periodontal ligament may be accomplished.

Alveolar Process↗
PubMed1978

The site of collagen resorption in the periodontal ligament of the rodent molar.

In an attempt to determine the pattern of collagen phagocytosis by fibroblasts in the periodontal ligament, a stereologic investigation of the mesial root of the maxillary first molar of the rat was undertaken. The distribution of fibroblasts containing intracellular collagen fibrils was studied at the electron microscope level in the periodontal ligament along resorbing and non-resorbing surfaces of the alveolar wall. It appeared that fibroblasts with collagen-containing vacuoles were more or less randomly distributed across the width of the periodontal ligament. No major differences were observed among the alveolar, cemental and intermediate zones of the ligament. However, local variations in the occurrence of cells containing intracellular collagen fibrils may occur. A relatively high concentration of ingested collagen fibrils was seen in fibroblasts located in the direct vicinity of osteoclasts, but not in the vicinity of osteoblasts. These observations suggest that remodelling of collagen is evenly distributed throughout the ligament, but may be influenced by local circumstances, such as the occurrence of bone resorption.

Animals↗
PubMed1978

Identity of a population of progenitor cells in gingival connective tissue of the mouse incisor.

In the gingiva of the mouse incisor, connective tissue cells were observed which were undergoing mitosis and contained collagen fibrils enclosed in vacuoles in their cytoplasm. The presence of intracellular collagen was noted in the majority of the dividing cells. On the basis of this observation it is suggested that renewal of the fibroblast population in the gingiva occurs preferentially by division of differentiated fibroblasts rather than by division of cells with a lower degree of differentiation.

Animals↗
PubMed1977

Fine structure of an end organ in the periodontal ligament of the mouse incisor.

Nerve endings were observed between collagen fiber bundles in the alveolar compartment of the periodontal ligament. In close relation to these endings, cells were observed with a rounded cell body from which cytoplasmic extensions protruded, each forming part of a sheath around the terminal region of a small nerve fiber. The nuclei of these cells occupied an eccentric position in the cytoplasm and were characterized by a typical kidney shape. In the cell's center a prominent Golgi complex was present. In the peripheral cytoplasm ladder-like structures with a periodicity of 160 nm were occasionally observed. The cell bodies were surrounded by a basal lamina, while the cytoplasmic extensions investing the nerve endings were surrounded by an envelope consisting of alternating electron dense and electron translucent layers containing material that stained with PAS and Alcian Blue. Where these envelopes bordered on the connective tissue, areas of filamentous material with a periodicity of 100-150 nm were occasionally found. The end organs may be considered to form part of a receptor system.

Animals↗
PubMed1977

The site of remodeling of collagen in the periodontal ligament of the mouse incisor.

In an attempt to localize the site of remodelling of collagen in the periodontal ligament of the continuously erupting mouse incisor a radioautographic and stereologic investigation was undertaken. Grain distributions in radioautographs for light microscopy were studied at various time intervals after administration of [3H]-proline. The distribution of rough endoplasmic reticulum cisternae in fibroblasts and the incidence of collagen phagocytosis across the ligament were studied by means of stereologic methods at the electron microscopic level. No significant differences were found in half lives of [3H]-labelled substances among the various regions across the ligament. Rough endoplasmic reticulum cisternae within fibroblasts were distributed more or less uniformly throughout the entire width of the ligament. Analysis of the distribution of collagen phagocytosis, however, revealed that in the midregion of the ligament the amount of phagocytosed collagen was approximately four times as high as in the area adjacent to the tooth and about nine times as high as in the alveolar compartment. It is concluded that synthesis and turnover of total protein occurs throughout the periodontal ligament but that remodelling of collagen predominantly takes place in an intermediate area of the ligament.

Animals↗
PubMed1975

Frequency of occurrence and position of cilia in fibroblasts of the periodontal ligament of the mouse incisor.

Solitary cilia occur in motile as well as in non-motile fibroblasts of the peridontal ligament. The cells which moved with the erupting incisor are bipolar and oriented with their long axes parallel to the tooth surface. In cross section these cells have a flattened appearance. Cilia are localized in close vicinity to the nuclear area and show a definite orientation with respect to the transverse cell axis. The frequency of occurrence of this organelle was estimated from the percentage of diplosomes containing a basal body. Analysis of the composition of the paired structures indicated that at least 70 per cent of the fibroblasts are ciliated. The frequency of cilia in motile fibroblasts does not differ from that in non-motile cells suggesting that the presence of this organelle is not directly associated with cell locomotion.

Animals↗