Development of intraosseous fibers of the mouse periodontium: a high-voltage electron microscopic study

Age-dependent changes of the periodontal ligament in rats

Even after the end of the natural tooth eruption, there is a continuous renewal of the periodontal collagenous fiber system, depending on functional demands. The aim of this study was to analyse the age-dependent changes and regional differences of the collagen renewal rate of the periodontal ligament in healthy rats. The study was performed by autoradiography of the molars of rats aged 1, 8, and 18 months, where collagen was labelled by intravenously applied 3H-proline. After an 8-hour incorporation period, the animals were killed. For comparative examinations, molar roots were subdivided into cervical, middle, and apical thirds. Structural and quantitative analyses were performed by light microscopy and autoradiography, using an image-analysing computer-assisted operating unit that determined the 3H-proline-labelled collagen by photometry based on extinction measurement. With increasing age of the animals, the number of silver grains (3H-proline-blackened collagen) was reduced and the quantitative evaluation indicated a reduction of 3H-proline in the periodontal ligament. The lowest level of 3H-proline activities was observed in the middle, and the highest level in the apical root third, independent of age. All preparations revealed condensations of silver grains, which were located in the region of the periodontal ligament adjacent to the alveolar bone, but did not reveal any preferred position with regard to the dental topography. With progressive age, the uptake of 3H-proline in the periodontal ligament was reduced by about 20 to 30%, a result that corresponds to a decrease in collagenous fiber production. Collagen was mainly formed in the apical and cervical root third, starting from the alveolar bone side, presumably in response to functional strain.

Distribution of type I and type III collagen in the developing periodontal ligament of mice

In order to localize type I and type III collagen in developing periodontal ligament, immunofluorescent and immunoelectron microscopic examinations were undertaken. The materials used were the maxillary molars of CF1 mice, 13 days to 6 months old. The antibodies used were monospecific polyclonal antibodies against type I or type III collagen raised in rabbits or guinea pigs, respectively. Single- and double-staining methods were employed in immunofluorescent as well as immunoelectron microscopic examinations. In immunofluorescent examinations, during the development of the periodontal ligament, periodontal fibers showed intense and homogenous staining for both type I and type III collagen; while Sharpey's fibers in the alveolar bone showed a heterogenous staining in cross and longitudinal sections for both types of collagen. In immunoelectron microscopic examinations, fibrils of periodontal fibers showed positive staining for type I and type III collagen simultaneously and had characteristic cross-banding and had a large diameter (ranging 40 approximately 80 nm) which remained constant during development. Sharpey's fibers in the alveolar bone or in the cementum showed the same staining pattern as the periodontal fibers, except for an afibrillar area which showed negative staining for both type I and type III collagen. The results obtained suggest that periodontal fibers and Sharpey's fibers consist of cofibrils of at least type I and type III collagen.

Effects of tooth function on adjacent alveolar bone and Sharpey's fibers of the rat periodontium

There is little information about the effects of short-term non-hypo-, and hyperfunction of teeth on the 1) mineralization patterns of intrinsic and extrinsic (Sharpey's) fibers and 2) mean number and diameter of Sharpey's fibers of adjacent alveolar bone. The mineral density of intrinsic and Sharpey's fibers and the size and number of Sharpey's fibers could indicate the relative strength of the attachment of a tooth to bone in various functional situations. In the present study, non- and hypofunctional situations were created by selective extraction of right molar teeth of the rat; the contralateral teeth were placed in hyperfunction by the surgery. In non- and hypofunctionals, intrinsic and Sharpey's fibers of the crestal third of the alveolus were less densely mineralized than in hyperfunctionals or untreated controls. Mean Sharpey's fiber diameters were significantly greater and their mean number/unit area significantly less in non- than in hypo- or hyperfunctionals or untreated controls (P less than 0.001). Mean Sharpey's fiber diameters in hyperfunctionals were significantly less than in untreated controls (P less than 0.05). Hypofunction ameliorated the effects of nonfunction on mean diameter and number of Sharpey's fibers, but had little effect on the density of mineralization of either the intrinsic or Sharpey's fibers of the alveolus, suggesting that their mineralization may be controlled by factors other than occlusal forces from the adjacent teeth. Thus changes in the stress/strain environment within the periodontium, coincident to altered occlusal function of the adjacent teeth, rapidly affects the morphology of intrinsic and Sharpey's fibers of alveolar bone and ensures that adequate tooth support is maintained in the new functional situation.

Preparation of bone for high-voltage electron microscopic radioautography

This paper presents a reliable technique for the preparation of radioautographic specimens for study by high-voltage electron microscopy. Tissues are fixed by ventricular perfusion of aldehydes, sectioned, collected on slides, and coated with nuclear track emulsion using a coating machine. Sections are developed after 17 weeks' exposure in either undiluted Microdol-X or diluted D-19 developer, fixed in 25% sodium thiosulfate, and stained through the emulsion with uranyl acetate in absolute methanol and aqueous lead citrate. The technique produces sections of even thickness and staining density with negligible numbers of background grains and non-specific labeling. In this report, the efficacy of this technique for the study of the periosteal surface of demineralized alveolar bone specimens is demonstrated.

Effects of orthodontic forces on the morphology and diameter of Sharpey fibers of the alveolar bone of the rat

There is little information available concerning the effects of functional and therapeutic forces on Sharpey fibers and adjacent bone matrix. In the present study, springs were placed between the left first and second maxillary molar teeth of rats and retained for 1, 2, 3, 4, or 5 days. The right side served as a control. Tissues from sham-operated, untreated animals were also studied. Maxillae were removed, fractured, rendered anorganic with sodium hypochlorite, and then examined by scanning electron microscopy (SEM). Some tissues were demineralized and examined by high-voltage electron microscopy (HVEM). Sharpey fibers were studied at the alveolar wall and at the midline of the interdental septum (intra-septal Sharpey fibers). In 5-day experimental tissues, SEM showed intra-septal Sharpey fibers had either a reduced number of, or lacked, unmineralized cores. Unit collagen fibrils in 5-day tissues viewed by HVEM were densely packed into Sharpey fibers which had no afibrillar areas. Sharpey fibers at the alveolar wall demonstrated no observable changes in morphology or in pattern of mineralization. After 5 days of spring placement, the mean diameters of intra-septal fibers were significantly less than those at the alveolar wall (p less than 0.001). The disparity in Sharpey fiber diameters of treated and untreated control animals suggests that untreated controls are essential to the design of studies of rodent tooth movement. This study suggests that orthodontic tooth movement produces changes in the morphology and mineralization patterns of Sharpey fibers which might affect the mechanical strength of the periodontium.

A classification of Sharpey's fibers within the alveolar bone of the mouse: a high-voltage electron microscope study

In the remodeling interdental septum of the mouse, four types of Sharpey's fibers were observed. Classification of these fiber types was based on characteristics of their termination within the septum in relation to the resorption-related reversal line separating old and new bone. "Severed fibers" were located only within old bone and terminated at the reversal line. "Arborized fibers" were located only within new bone and terminated therein. "Adhesive fibers" were located within new bone and terminated within a heavy band of granular material at the reversal line. "Continuous fibers" had components within old and new bone. These components were connected across the reversal line by nonstriated fibrils. Adhesive fibers were the least numerous type; severed and arborized fibers were observed at nearly equal frequency. Continuous fibers were the most numerous type, their numbers being significantly greater than any of the other types (P less than .001). Mean numbers of continuous fibers were greater than the mean total of the three other fiber types (P less than .001). Mean numbers of severed, adhesive, and arborized fibers were not statistically different. The study suggested that continuous fibers could be transalveolar--that is, ones which pass through the septum without interruption joining fibers of the adjacent periodontal ligament. Maintenance of their spatial continuity appeared to require a connecting protein to orient new unit collagen fibrils to old ones in areas of reversal. Thus, transalveolar fiber bundles could be characterized as being composed of old and new segments joined by a connecting protein. As their unit collagen fibrils did not cross resorption-related reversal lines these fibers were spatially continuous but temporally discontinuous.

A new look at the mineralized and unmineralized components of intraosseous fibers of the interdental bone of the mouse

The degree of mineralization of deeply embedded intraosseous fibers has been the subject of speculation. However, there were few available descriptive morphological studies addressing this question. The present study demonstrated that morphological differences were evident between intraosseous fibers of different levels of the interdental septum. It also revealed that the degree of mineralization of intraosseous fibers was often different at the wall of the tooth socket in comparison to that at deeper levels of interdental bone. Except in the superior crestal third, intraosseous fibers became less mineralized as they passed from the wall of the tooth socket to the midline of the interdental septum. They were surrounded by sheaths throughout their distribution. It was concluded that there might be significant differences in the morphology of intraosseous fibers of the mouse in comparison to the morphology of intraosseous fibers of the dog, which have previously been described in detail.