Mouse Periodontal Ligament Research Articles

Confocal laser scanning-microscopic observations on the three-dimensional distribution of oxytalan fibres in mouse periodontal ligament

The purpose was to improve confocal laser scanning-microscopic (CLSM) techniques to observe the three-dimensional (3-D) distribution of oxytalan fibres in mouse periodontal ligament and to clarify the 3-D relation between those fibres and blood vessels. As aldehyde fuchsin is a contrast agent and the specific wavelength affects the depth of penetration, CLSM reflectance imaging of oxytalan stained with aldehyde fuchsin after oxidization provides strong contrast. Oxytalan fibres, whose precise roles have not yet been clarified, are connective tissue fibres present in human periodontal ligament in addition to collagen fibres. Despite many studies on their arrangement and biomechanical characteristics, their 3-D distribution in relation to other structures has never been reported. Mandibular first molars of mice were sectioned mesiodistally, pre-oxidized by monopersulphate compound (Oxone), stained with aldehyde fuchsin and examined by CLSM. CLSM images clearly revealed the 3-D distribution, and relation of oxytalan fibres to blood vessels and other structures, as well as their branching patterns in the periodontal ligament. The marked anatomical correlations between the direction, distribution and branching patterns of oxytalan fibres and blood vessels suggest that they interact to perform a specialized physiological role in the periodontal ligament.

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 CH 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 ∼ 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.

Morphometry of neural structures in the mouse periodontal ligament mesial to the mandibular first molar

Abstract The periodontal ligament mesial to the mandibular first molars of three mice was analysed stereologically between the alveolar crest and the tooth apex. Ultrathin tissue sections were collected at statistically predetermined intervals, 50 and 200 microns apart, examined in the TEM and quantified using standard point counting procedures (Gundersen et al. 1988). Findings indude evidence that, in the mouse, some unmyelinated axons arise from myelinated axons and that anatomically discrete arrangements of unmyelinated axons occur in the apericytic wall sections of postcapillary-sized venules. Morphometric data indicate that unmyelinated axons constitute approximately 95 percent of all periodontal axons. The greatest relative proportion of myelinated axons is in the bone third of the ligament, at depths between 600 and 800 microns, where the ratio of unmyelinated to myelinated axons is 5:1. Ultrasttucturally, the ligament contains a variety of anatomically discrete neural structures in juxtaposition to periodontal blood vessels. These structures indude nerve endings contiguous with K-cells, partially exposed terminal axons, preterminal and terminal axons protruding into the vessel lumina, and lamellated receptors. Mitochondria-rich terminals and fine nerve endings approximated pericytes in the walls of postcapillary-sized venules and arteriovenous anastomoses. Typically, these neural structures were characterised by the presence of an associated oxytalan fibre meshwork. This study also provides quantitative parameters for axon distribution within the ligament.

Continuous labelling of the periodontal ligament of mice

The growth fraction in the mouse periodontal ligament (PL) was determined by means of continuous labelling for up to 60 days with 3H‐Tdr via the drinking water. The method was tested by comparing the labelling indices (LI) of PL cells obtained in this way with those obtained by repeated injections or via osmotic mini‐pumps. There was no significant difference between the LI obtained by the 3 different routes. Cell density was assayed in the PL of mice who had received no 3H‐Tdr or that were labelled for 60 days with 3H‐Tdr. There were no detectable differences in cell density, and we concluded that 3H‐Tdr cytocide did not significantly change the growth fraction. The growth fraction of PL cells was 30%, and 25 days of continuous labelling were required to obtain this value. No significant change of LI was observed between 25 and 60 days of labelling. This plateau could not be accounted for by loss of PL cells to bone as osteocytes because very few labelled osteocytes were observed, even after 25 days of continuous labelling. The growth fraction of cells within 10 μm of blood vessels was 40% and was significantly higher than the overall growth fraction. These data suggest that cell division in the PL occurs predominantly in a paravascular location and that some of the progeny of dividing cells in the PL die.

Cell density and cell generation in the periodontal ligament of mice.

The number of cell nuclei per mm2 and the volume density of cell nuclei and blood vessels in the periodontal ligament at different levels of the mesial root of the first mandibular molar of the adult mouse and in different areas of the ligament at each level have been examined in the light microscope. Significantly higher numbers of cell nuclei per mm2 were observed adjacent to bone, cementum, and blood vessels than in the avascular body of the ligament at all levels and on all aspects of the root. This distribution of number of cell nuclei per mm2 was constant over 4 1/2 months of aging and a doubling of body weight. The volume density of cell nuclei was significantly higher in cells adjacent to bone and cementum and in gingival connective tissue than in both the vicinity of blood vessels and the body of the ligament. The blood vessels, which were present predominantly in the bone-related half of the ligament, were absent from the zone immediately adjacent to cementum. The labeling indexes of periodontal ligament cells were determined from autoradiographs of the mesial root of the first mandibular molar of the mouse after pulse-labeling with 3H-Tdr. Labeling indexes were highest in zones adjacent to blood vessels, and the labeling index was significantly higher in the middle of the ligament than in zones adjacent to bone and cementum, and consequently was inversely related to cell density.

The microvascular venous pool and its ultrastructural associations in mouse molar periodontal ligament — Periodontal Microvasculature & Nerves

Abstract This transmission electron microscopic investigation revealed that the periodontal ligament of mouse mandibular molars contained a microvascular bed typified by a predominance of vessels corresponding in luminal diameter with postcapillary-venules. Vessels in the cervical region showed large areas of the endothelium and basement membrane directly exposed to the investing collagen fibre bundles. Cervical venous capillaries had a ratio of luminal diameter to wall thickness averaging 20:1, whereas postcapillary-sized venules approximated 30:1. In the apical third of the ligament the venous vessels became significantly larger and morphologically conformed to ‘apericytic' postcapillary venules, since they appeared to be devoid of pericytes, and comprised endothelial-like tubes with only the basement membrane and occasional veil cells intervening between the endothelium and the enveloping collagen fibre bundles. The ratio of luminal diameter to wall thickness exceeded 60:1 in these apical vessels. This venous capillary pool of the ligament consisted of vessels which differed ultrastructurally from the postcapillary venules described as being typical of other microcirculatory systems. Nerve endings, indicated by aggregations of mitochondria, were present adjacent to encapsulated myelinated and unmyelinated nerves located alongside cervical venous capillaries and postcapillary-sized vessels. Encapsulated nerves and nerve groups in the apical region corresponded with descriptions of putative periodontal mechanoreceptors in man, but differed in being related to postcapillary-sized vessels and not collecting veins as reported in human ligament. Unmyelinated axons were frequently located within 0.25 microns of the endothelium of venous capillaries and venules. The oxytalan meshwork fibres were associated with all categories of vessels observed including capillaries having luminal diameters less than six microns. These findings demonstrate that the mouse periodontal ligament has unique, and previously unreported, vascular and neural anatomical features related to its operant role and dynamic behaviour in supporting masticatory loads. Some functional implications of the present findings are discussed.

Electron-microscopic affiliations of oxytalan fibres, nerves and the microvascular bed in the mouse periodontal ligament

Throughout the ligament, oxytalan fibres were contiguous to myelinated nerves, unmyelinated exposed axons and free nerve endings. In the cervical and apical regions, accumulations of vessel-related simple and complex mechanoreceptor units were associated with collagen fibrils and fibres of the oxytalan system. The various receptors and nerve endings penetrated to the abluminal surface of the endothelial wall in the different categories of vessels constituting the microvascular bed. Periodontal receptors with oxytalan fibres were also present in the septal wall of dividing vessels and related to endothelial protrusions into the lumen of microvessels. Similarities existed between periodontal mechanoreceptors and baroreceptors. Anatomically, the oxytalan-fibre meshwork provided coupling between the various mechanoreceptor units in the microvascular bed. This periodontal model has morphological characteristics which support the hypothesis that the oxytalan-fibre meshwork forms part of a proprioceptor system for the regulation of vascular flow.

Junctions between fibroblasts in mouse periodontal ligament.

Quantitative evaluation of the distribution of intercellular junctions between fibroblasts in the incisor and molar periodontal ligament of the mouse indicated that structures resembling gap junctions are more frequent on the tooth side of this tissue than on the bone side. The difference was particularly evident for the ligament of the continuously erupting incisor. Here, the numerical density of gap junction‐like structures was estimated to be approximately 20 per fibroblast in the connective tissue adjacent to the cementum and 4 per fibroblast in the tissue along the alveolar bone. With regard to the distribution of adhaerens‐type junctions less variation was observed between the various zones of the incisor and molar ligament. For the incisor the average number of adhaerens‐type junctions was calculated to be in the order of 30 junctions per cell in the tooth‐related compartment and 20 junctions per cell in the alveolar compartment.Although in the molar intercellular junctions were observed throughout the entire width of the ligament, in the incisor they were confined to the two main connective tissue compartments, i.e. the one of the tooth side which moves with the erupting tooth in the direction of the oral cavity, and the one of the bone side which remains stationary with respect to the alveolar wall. In the transitional area between the two latter compartments junctions were very sparse. It is suggested that the distribution pattern of intercellular junctions between fibroblasts in mouse periodontal ligament reflects functional differences among the cells in the various regions of the tissue, differences that are possibly related to processes involving the movement of cells and the metabolism of collagen.