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.

[Ultrastructure of the alveolodental ligament of the rat]

The ultrastructural study of periodontal ligaments of adult rat molars showed that the predominant cellular element consisted of fibroblasts and fibrocytes. These cells were responsible for the elaboration of the collagen precursors and for their destruction as was demonstrated by the presence of ellipsoidal intracytoplasmic vacuoles containing collagen. The abundance of microfilaments and microtubules as well as the presence of intermediary and tight junctions and nexus between the cell processes seemed to indicate that these cells are contractile and motile. Other cell types were intrequent. The ligament presented a high density of collagen fibrils grouped in bundles. Oxytalan fibrils were also observed. The blood capillaries showed mainly a continuous endothelium. Numerous myelinated and non-myelinated nerve fibrils, as well as nerve endings and mechano-receptors were identified.

Ultrastructural changes in tension zones of rat molar periodontium incident to orthodontic tooth movement

The purpose of this study was, by introducing transmission electron microscopy, to clarify fine details of tissue reactions in the periodontal ligament on the tension side. A preliminary investigation was undertaken on nine rats in which experimental tooth movement lasted 2 days, 14 days, and 28 days. It was hoped that these new observations might help in the planning and directing of further studies. A marked increase of interstitial spaces between the formed ligament structures of the periodontal ligament was characteristic of the initial phases of tension. The cells and the endoplasmic reticulum within the cells were spindle shaped and oriented in the direction of strain. Occasionally, collagen fibrils were observed within the cytoplasm of fibroblasts. During experimental tension a higher prevalence of elastic fibers was observed and new details of the reaction of collagen fibrils were obtained. The new cementum and bone deposited during the experiment were studied. The preliminary study indicated that electron microscopy may become a valuable tool for the study of the tension side.

Collagen resorption by fibroblasts. A theory of fibroblastic maintenance of the periodontal ligament

Periodontal ligament fibroblasts contain numerous intracellular or cytosegragated collagen fibrils. These fibrils appear to be broken down within the lysosomal apparatus of the cells. There is an increase in this activity in fibroblasts associated with osteoclastic bone resorption. Cytoplasmic microfilaments and attachments to substrata indicate that the fibroblasts of the ligament have the potential of migration and cytoplasmic contraction. A theory of collagen fiber maintenance within the periodontal ligament is proposed which takes into account: (1) the motility and contractility of fibroblasts, (2) the phagocytic and degradative potential of fibroblasts, (3) the presence of intracellular collagen and (4) the reported high turnover rate of acid-insoluble collagen within the periodontium.

The role of fibroblasts in the remodeling of periodontal ligament during physiologic tooth movement

Our findings indicate a cellular basis for the connective tissue remodeling which takes place during physiologic tooth movement. This cell is the fibroblast which is capable of synthesizing and degrading collagen simultaneously and, utilizing this ability, the orderly control of collagen remodeling within the periodontal ligament is possible. It is suggested that this cellular basis of connective remodeling will have a direct significance for orthodontic tooth movement once control mechanisms have been established.

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.

[Ultrastructural odontological study of a case of Papillon-Lefèvre disease]

An ultrastructural study of the teeth and alveolar bone was carried out in a case of Papillon-Lefevre disease, using sweep electron microscopy. There were structural abnormalities of the enamel, numerous zones of cement resorption, the absence of mineralisation of the parodontal fibres inserted in the cement. Osteogenesis was disturbed and the lamina dura showed a granular pattern without any defined orientation.

Cultivation of periodontal ligament fibroblasts on dental implant materials and enzymatically debrided teeth

Rhesus monkey periodontal ligament-derived fibroblasts were cultured on glass, Vitallium, poly(methyl methacrylate) and enzymatically debrided teeth. Scanning electron micrographs of these preparations and of the periodontal ligament surrounding normal and replanted teeth were compared. The fibroblasts cultured in vitro could organize on implant material and enzymatically debrided teeth to produce a network with fibers resembling those that are seen in the normal periodontal ligament.

Oxytalan connective tissue fibers: a review

Oxytalan connective tissue fibers are a separate and distinct fiber type. Although current histochemical methods cannot distinguish pre-elastic from oxytalan fibers, the two fiber types are readily distinguished by electron microscopy. Oxytalan fibers are found in periodontal membranes of all teeth of man, monkeys, rats, guinea pigs and mice. Increased numbers and size of oxytalan fibers are observed in periodontal membranes of teeth subjected to increased stress, such as those used for bridge abutments. Edwards (1968) observed increased size and number of oxytalan fibers in periodontal membranes of dog incisors subjected to orthodontic forces. Some oxytalan fibers serve to support the blood and lymphatic vessels leading to the teeth. Oxytalan fibers appear to have a protein component and a stainable component digestible with beta-glucuronidase after peracetic acid digestion. Oxytalan fibers develop in repair tissues of the periodontal membrane. Although oxytalan fibers probably develop in relation to tumors developed from dental tissues, electron microscopy must be employed to distinguish oxytalan from developing elastic tissues inasmuch as histochemical methods are inadequate.