Epithelial rests of Malassez in vitro. Phagocytosis of collagen and the possible role of their lysosomal enzymes in collagen degradation

Cells from porcine epithelial rests of Malassez were cultured in vitro with collagen prepared from rat tail tendons. Serial sections of the cultures were prepared for examination in the electron microscope. Some of the material was processed to demonstrate activity of acid phosphatase. Electron microscopy showed that the epithelial cells had phagocytosed collagen in vitro, and study of the serial sections indicated that much of the phagocytosed collagen was contained wholly within the cells. Reaction product indicating sites of acid phosphatase activity was found to be associated with intracellular collagen, and some of the intracellular fibrils exhibited nonsymmetrical loss of material and also localized loss of banding, suggesting intracellular digestion of collagen. A lysosomal fraction was prepared from epithelial cells cultured from the rests of Malassez, and this was shown using biochemical assays to contain activities of thiol-dependent cathepain, cathepsin D, beta-D-glucuronidase, aryl sulfatase, and acid phosphatase. The lysosomal fraction had the capacity in vitro to depolymerize and digest collagen obtained from rat tail tendon. It was concluded from these observations and results that epithelial cells cultured from the rests of Malassez can digest collagen in vitro. The findings suggests a possible mechanism whereby the epithelial cells can destroy the extracellular substance of connective tissue during their well known participation in cyst formation in vivo.

Electron dense staining affinities of mouse oxytalan and elastic fibers

The staining affinity of electron dense stains to mouse palatal elastic fibers and periodontal oxytalan fibers was assessed and compared. Tissues were stained routinely with uranyl acetate and lead citrate or with elastic tissue stains including: (1) silver tetraphenylporphine sulfonate, (2) tannic acid technique, and (3) a high iron diamine sequence. Staining results were assessed with an electron microscope. Palatal elastic fibers demonstrated staining affinity to all elastic stain techniques. Oxytalan fibers did not demonstrate affinity to elastic fiber stains used. Based on electron dense stains, elastic and oxytalan fibers were dissimilar, in contrast to results reported utilizing light microscopic stains.

An electron microscopic study of attachments between periodontal fibers and bone during alveolar remodeling

Three types of periodontal membrane-to-bone attachments are described for remodeling surfaces of the bony alveolar wall. An adhesive type, which is the most widespread means for tooth anchorage on resorptive bone surfaces during active tooth movements, involves the following histogenic steps: A layer of ground substance is first deposited by fibroblast-like cells on the naked surface of recently resorbed bone. As this continues, new precollagen and the dissociated ends of collagenous fibrils become embedded in the accumulating ground substance, and these fibrils in turn become joined to intact collagenous fibrils, blending with the remainder of the periodontal stroma. Such adhesive attachments continuously form and re-form as the resorption front proceeds. A continuous type of attachment also occurs on resorptive bone surfaces in which some (not all) bone matrix fibrils survive the resorptive process. These former bone fibrils become incorporated into the periodontal membrane and are continuous between the bone matrix and the stroma of the contiguous periodontal membrane. An intermediate type of attachment also occurs and is primarily an adhesive attachment that also contains a scattering of fibrils which are continuous from the bone matrix across the resorptive bone surface into the fibrous matrix of the periodontal membrane.

A histochemical and electron microscopic study of an adhesive type of collagen attachment on resorptive surfaces of alveolar bone

This study describes (1) the composition of the "adhesive" type of periodontal membrane attachment onto resorptive surfaces of actively remodeling alveolar bone; (2) the structure of reversal lines in alveolar bone; and (3) the role of certain fibroblast-like "osteoclast companion cells" in the attachment process of periodontal fibers onto resorptive bone surfaces. Adesive attachments involve a layering of specific zones at the interface between the periodontal membrane and the resorptive bone surface, and one or more types of osteoclast companion cells appear to function in the secretion of components of proteoglycans (probably glycosaminoglycans) and precollagenous fibrils. The proteoglycans appear to serve as a principal component of the adhesive substance secreted on a bone surface and also as a binding agent for the linking and progressive relinking of new and old collagenous fibers to each other and to the resorbed bone surface. If a reversal in the direction of remodeling occurs, and new bone deposition occurs on a surface that was formerly resorptive, the zones of the adhesive interface become calcified and then constitute a "reversal line."

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.

Light and ultrastructural relationship between oxytalan fibers in the periodontal ligament of the guinea pig

The interfaces and the relationships between collagen and oxytalan fibers were observed under light and electron microscopy. Guinea pig periodontal ligament was prepared for light and electron microscopy with perfusion using Peter's buffered formalin for light microscopy and GTA-S-collidine and OSO4 for electron microscopic studies. The tissue for light microscopy was stained with a modified Gomori's aldehyde fuchsin technique, in which pre-oxidization with potassium monopersulfate was carried out before staining so as to demonstrate the oxytalan fibers. EM tissues were routinely stained with lead citrate and uranyl acetate. Two different structural relationships were observed. First, the subcomponents of the collagen and oxytalan fiber types interweave with each other; and, second, some of these two-fiber subcomponents appear attached to each other. These relationships and the known orientation of oxytalan fibers as seen in the periodontal ligament provide insight as to the function of oxytalan fibers. The oxytalan fibers may provide increased structural integrity and increased distribution of forces over a wider area of the periodontal ligament. Because of their close relationship to blood and lymph vessels in the periodontal ligament, they may also help to stabilize these elements by the same structural relationships to collagen fibers.

Collagen fibre architecture in the periodontal ligament

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In vitro phagocytosis of exogenous collagen by fibroblasts from the periodontal ligament: an electron microscopic study

There have been numerous electron microscopic reports of apparent phagocytosis of collagen by fibroblasts and other cells in vivo. We have developed an in vitro system which, to the best of our knowledge, will permit for the first time the study of regulatory mechanisms governing phagocytosis and digestion of collagen fibres. Cells were cultured from explants of monkey periodontal ligament, subcultured, and grown to confluence in alpha-MEM plus 15% fetal calf serum plus antibiotics. The confluent cells were then cultured together with minced rat tail tendon collagen in alpha-MEM lacking proline, lysine, glycine and fetal calf serum for up to 7 days, after which they were processed for electron microscopy. Intracellular collagen profiles could be seen in cultured cells that were associated with exogenous collagen fibrils as early as 24 hours after addition of the collagen. Through electron microscopic examination of serial sections of the culture, we have demonstrated: (1) that fibroblasts can phagocytose collagen; (2) that the observed intracellular collagen is not the result of aggregation of endogenous synthesized collagen; (3) that it is not possible to base a decision as to whether a collagen fibril has been phagocytosed in whole or in part by the type of vesicle with which it is associated; (4) that cleavage of collagen into small pieces may not be a necessary prelude to its phagocytosis.

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.

Periodontosis: a case report with scanning electron microscopic observations

A tooth and associated periodontal tissues from a patient with the diagnosis of periodontosis was subjected to scanning electron microscopic evaluation after reflection of the soft tissue portion of the lingual defect. The cemental surface of the apical portion of the lesion was found to be populated by markedly similar rod-shaped organisms. The microorganisms were observed to be continuously present in a coronal-apical direction as the transition from cementum to the attached soft tissues at the base of the defect were examined. These findings provide additional evidence that the lesion of periodontosis is characterized by a rather distinct microbial population of rod-shaped organisms located predominately at the base of the defect.

Ultrastructural analysis of glycosaminoglycan hydrolysis in the rat periodontal ligament. I. Evidence for macrophage involvement in bone remodelling

We identified the cellular sites of glycosaminoglycan hydrolysis by localizing a key enzyme, N-acetyl-beta-glucosaminidase, in the rat periodonatal ligament. Reaction product was seen in osteoclasts, osteoblasts, fibroblasts, and in macrophages situated perivascularly in areas of bone remodelling. The preferential location of macrophages in areas of both bone formation and bone resorption, and their intense NAGase activity identified the macrophage as a significant participant in the total process of bone remodelling. We considered the presence of reaction product in the Golgi zone and the rough endoplasmic reticulum of osteoblasts and fibroblasts as possible localization of a NAG-transferase.

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.

Oxytalan fibre organization in marsupial mandibular periodontal tissues

The arrangement and distribution of oxytalan fibres in Australian marsupials has not previously been reported. Periodontal tissues of wombat, wallaby, possum, and marsupial mouse were examined to ascertain oxytalan fibre organization. Despite adaptation of the marsupial masticatory apparatus to different diets the oxytalan fibre organization in the periodontal ligament shows a basic pattern which corresponds with that reported in other animals. The oxytalan system forms a continuous meshwork of fine, branching fibres which completely invests each tooth root and connects adjacent teeth. Thick ribbon-like apico-occlusally orientated oxytalan fibres, thought to form by the coalescence of thinner fibres, are restricted to the periodontal ligament. The oxytalan fibres are embedded in cementum and attached to blood vessels in the pariodontal ligament. Oxytalan fibres do not insert into alveolar bone. Histological evidence indicates functional remodelling of the oxytalan fibre system in continuously erupting teeth.