A scanning electron-microscopic, stereo-pair study of methacrylate corrosion casts of the mouse palatal and molar periodontal microvasculature

Angioarchitecture of the anterior and medium parts of the palatine mucosa of the gerbil, Meriones unguiculatus

The aim of this study was to examine the microvasculature of the anterior and medium portions of the hard palatine mucosa in the adult gerbil (Meriones unguiculatus) using scanning electron microscopy. The vascular corrosion casts were obtained by injection of Mercox CL-2B synthetic resin and tissue corrosion was performed using sodium hydroxide solution. These casts revealed the presence of capillary loops in the palatine plicae and a smoother/flatter vascular network in the interplicae areas. The capillary loops consisted mainly of anteriorly oriented hair-pins and we also verified a differentiation in the shape of endothelial cell nuclei, which were elongated in arterial and circular in venous vessels.

Distinct fibro-vascular arrangements in the periodontal ligament of the horse

OBJECTIVE

The periodontal ligament (PDL) of the hypsodont cheek teeth of the horse meets specific requirements of tooth support: (1) to fix the tooth; (2) to withstand pressure and tension during the laterolateral mastication movement; (3) to restore the original tooth position. These requirements are assumed to be met by the periodontal collagen fiber apparatus and by the vascular system. Distinct fibro-vascular arrangements are described here in order to reveal the structural prerequisites for these distinct functions.

DESIGN

Specimens from nine horses were processed for (1) collagen labeling with fluorescein, (2) oxytalan fiber staining, (3) immunostaining of smooth muscle actin, and (4) TEM examinations.

RESULTS

Blood vessels were found to be integrated in the PDL in three distinct ways:

CONCLUSIONS

The sheaths formed by veil cells (type-I arrangement) isolate distinct groups of blood vessels from deformations of the surrounding tissue. In contrast, the distinct fibro-vascular arrangements of anchored blood vessels (type-II arrangement) and ballooned venules (type-III arrangement) are assumed to accept the forces generated by masticatory tooth movements. The anchored blood vessels sustain tractive forces by means of what is called a lateral compression mechanism, whereas the ballooned venules act as a hemodynamic cushion.

Histomorphometric study of the periodontal vasculature during and after experimental tipping of the rat incisor

The periodontal vasculature encircling the entire length of the rat lower incisor was studied at the time of tipping movement and 3 months later. In 12 rats (212+/-4 g b.w.), loads (0.19+/-0.016 N) were applied to the lower left incisor in a linguointrusive direction. After 2 weeks of loading, six experimental animals were killed with the loading springs in place. The springs were removed in the six remaining rats, which were killed 12 weeks later. Six additional rats with intact teeth served as control. All incisors were fixed, demineralized, embedded in glycol methacrylate and cross-sectioned perpendicular to the long axis of the tooth. The distance of each section (2 microm) from the apex was calculated. A computerized image-analysis program was used to measure the width and area of the labial and lingual periodontal ligament to establish whether the measured segments corresponded to the compressed or expanded zones. In each cross-section, the various types of blood vessels were counted and the cross-sectional area of all venous vessels was measured. The results showed that after 2 weeks of loading (1) the general trend of vascular changes was similar under pressure and tension; (2) the large-diameter vessels were unaffected by loading; (3) the mean number of terminal arterioles had decreased significantly, while the number of capillaries and postcapillary venules had increased significantly in the apical tooth part; (4) the venous blood vessel area had decreased significantly in the apical tooth part; (5) the intensity of the vascular reaction was dependent on the degree of tissue distortion; and (6) after 12 weeks' recovery the vascular changes were still present, demonstrating a rebound effect. The findings suggest that microvascular alterations following tooth loading are not directly related to the spatial effect of loading itself and are of a much longer duration than expected.

Microvascular luminal volume changes in aged mouse periodontal ligament

Data for the microvascular bed in the aged periodontal ligament have not been established. This investigation tested the hypothesis that the luminal microvascular volume decreased in the aged ligament. Mice 35 days old and one year old were vascular-perfused and the mandibular first molar periodontal ligament processed for electron microscopy. Tissue quadrats from each circumferential third ligament region were recorded at 150-microns intervals from the alveolar crest to the apex for randomized sampling of blood vessel lumina. The data were analyzed with a generalized linear model at the p < 0.01 level for the interaction of the aging effect with differences across regions. Stereological parameters were established for vessel lumen volume, and for surface and length densities. Mean ligament width decreased from 119.9 +/- 16.94 (micron +/- SE) in young mice to 60.0 +/- 10.58 (micron +/- SE) in aged mice. The luminal volume of 8.63 +/- 1.37 (% +/- SE) in young ligament increased to 9.83 +/- 2.14 (% +/- SE) in aged ligament. Collecting venules and the combined group of arterio-venous anastomoses with terminal arterioles showed a two-fold increase in luminal volume density (p < 0.01). In aged ligament, regional shifts affected the microvascular bed distribution, but these changes were not consistent across regions, or with depth. The average cross-sectional tissue area served per capillary decreased from 2117 microns 2 to 1451 microns 2 for young and old. Average ligament thickness served per capillary dropped from 52.5 microns to 27.5 microns. These reductions in average diffusion distances indicated a change in the quality of the diffusion barrier with age.

Histomorphometric study of the periodontal vasculature of the rat incisor

This study assessed quantitatively the vascular system in the cementum-related periodontal ligament (PDL) along the rat incisor. The lower left incisors of six rats (+/- 200 g) were subjected to routine histological procedures and cross-sectioned serially (2 microns), and the distance between each section and the apex was computed. The PDL of five sections at different levels along the tooth was divided into mesial, lingual, and lateral parts. The number and area of small and terminal arterioles, capillaries (C), sinusoids (S), post-capillary venules (PCV), and connecting venules, as well as the area of the PDL, were established. Blood vessels (BV) occupied 47 +/- 2% of the PDL area in the apical half and 4 +/- 2% at the incisal end. Of the total BV area, 41%, 32%, and 27% were located on the lingual, mesial, and lateral tooth sides, respectively. The majority of BV belonged to the venous system (98.5 +/- 0.6% and 82.5 +/- 3.0% in the apical and incisal parts, respectively). The apical venous system comprised 95.4 +/- 1.6% S and 3.2 +/- 1.0% PCV, reversing to 27.2 +/- 14.2% S and 55.2 +/- 11.3% PCV in the incisal half. The number of arterial profiles increased gradually from 6.8 +/- 1.5 at the apex to 25.3 +/- 2.4 in the incisal part and that of C from 9.0 +/- 1.18 to 25.0 +/- 4.3. The extensive vascularization in the apical half of the PDL is consistent with the high metabolic demands and with the need for protective cushioning of the constantly growing dental and periodontal tissues.2+_

A scanning electron microscope study of microcorrosion casts of the microvasculature of the marmoset palate, gingiva and periodontal ligament

In the hard palate, sagittally oriented capillary loops, 8-10 microns in diameter and 70-250 microns high, extended perpendicularly from a subcapillary plexus to the connective tissue papillae. These loops formed a well-delineated vascular spine beneath the rugal crests. Capillary loop density was estimated to be 200-270/mm2 on the rugal crest, 75-160/mm2 on the rugal slopes and 70-140/mm2 in the trough. In the gingiva, the crevicular loop system was separated by a gap from the vestibular, palatal and col loop systems. Anastomoses occurred between these systems at a deeper level. The crevicular circular plexus varied from 1 to 4 vessels. Apical to the gingival margin the buccal vasculature was composed of occluso-apically orientated loops draining towards the vestibular sulcus. The capillary loops were 60-120 microns high near the gingival margin, compared with 40-60 microns near the mucogingival junction. The mucogingival margin was demarcated by a change in capillary orientation. The periodontal ligament contained mainly postcapillary-sized venules, 10-25 microns in diameter, orientated occluso-apically. Capillary loops, 50-100 microns long and directed at right angles to the root surface, occurred in the cervical third. These microvascular patterns of the marmoset are different from those of the mouse and rat.

Tooth extrusion effects on microvessel volumes, endothelial areas, and fenestrae in molar apical periodontal ligament

Extrusive tooth loads, simulating short-term orthodontic movements, have not previously been used for transmission electron microscopic quantification of their effects on the periodontal ligament vessels. In this study, a continuous extrusive load of 1.0 N, applied to the rat maxillary first molar for 30 minutes, produced statistically significant changes in the microvascular bed of the tensioned apical periodontal ligament. The mean vascular volume, as a percentage of apical periodontal ligament volume, increased (p less than 0.01) in postcapillary-sized venules, venous capillaries, arterial capillaries, and terminal arterioles from 16.6% to 22.3%, 2.0% to 2.7%, 0.4% to 1.0%, and 1.0% to 2.5%, respectively. Mean endothelial surface area per cubic millimeter of apical periodontal ligament tissue increased (p less than 0.01) in postcapillary-sized venules from 16.8 to 25.7 x 10(6) microns 2/mm3, in venous capillaries from 3.0 to 4.8 x 10(6) microns 2/mm3, and in arterial capillaries from 0.7 to 1.5 x 10(6) microns 2/mm3. The number of fenestrae per square micron of endothelium in postcapillary-sized venules, venous capillaries, and arterial capillaries showed a mean increase from 0.02 to 0.07, 0.11 to 0.31, and 0.02 to 0.21 fenestrae/microns 2, respectively (p less than 0.01). Fenestrae per cubic millimeter of periodontal ligament tissue also demonstrated a statistically significant increase with extrusion (p less than 0.01) in postcapillary-sized venules from 0.37 to 1.55 x 10(6) fenestrae/mm3, in venous capillaries from 0.27 to 1.34 x 10(6) fenestrae/mm3, and in arterial capillaries from 0.02 to 0.22 x 10(6) fenestrae/mm3. Fenestrae in control vessels had a mean diameter of 54.2 +/- 0.56 nm (SE) compared with 61.1 +/- 0.7 nm in tensioned vessels (p less than 0.01). This investigation demonstrates multiple ultrastructural changes in the periodontal ligament microvascular bed after tooth extrusion.