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

Immunolocalization of FGF-2 and VEGF in rat periodontal ligament during experimental tooth movement

Objective

This article aimed at identifying the expression of fibroblast growth factor-2 (FGF-2) and vascular endothelial growth factor (VEGF) in the tension and pressure areas of rat periodontal ligament, in different periods of experimental orthodontic tooth movement.

Methods

An orthodontic force of 0.5 N was applied to the upper right first molar of 18 male Wistar rats for periods of 3 (group I), 7 (group II) and 14 days (group III). The counter-side first molar was used as a control. The animals were euthanized at the aforementioned time periods, and their maxillary bone was removed and fixed. After demineralization, the specimens were histologically processed and embedded in paraffin. FGF-2 and VEGF expressions were studied through immunohistochemistry and morphological analysis.

Results

The experimental side showed a higher expression of both FGF-2 and VEGF in all groups, when compared with the control side (P < 0.05). Statistically significant differences were also found between the tension and pressure areas in the experimental side.

Conclusion

Both FGF-2 and VEGF are expressed in rat periodontal tissue. Additionally, these growth factors are upregulated when orthodontic forces are applied, thereby suggesting that they play an important role in changes that occur in periodontal tissue during orthodontic movement.

Mechanisms of tooth eruption and orthodontic tooth movement

Teeth move through alveolar bone, whether through the normal process of tooth eruption or by strains generated by orthodontic appliances. Both eruption and orthodontics accomplish this feat through similar fundamental biological processes, osteoclastogenesis and osteogenesis, but there are differences that make their mechanisms unique. A better appreciation of the molecular and cellular events that regulate osteoclastogenesis and osteogenesis in eruption and orthodontics is not only central to our understanding of how these processes occur, but also is needed for ultimate development of the means to control them. Possible future studies in these areas are also discussed, with particular emphasis on translation of fundamental knowledge to improve dental treatments.

The blood vessel system in the periodontal ligament of the equine cheek teeth--part I: The spatial arrangement in layers

Corrosion casts of blood vessels in the periodontium of cheek teeth from eight horses were observed three-dimensionally with a dissection microscope. Selected specimens were examined in a scanning electron microscope. Periodontal blood vessels communicated with those from the gingiva, the alveolar bone, and the apical region. In the upper jaw, there were anastomoses with the blood vessels of the mucosa of the maxillary sinus. The periodontal vascular system was organized in two or three layers. The peripheral layer was mainly composed of large venules, the inner one consisted of capillaries. In the intermediate layer, blood vessels were post-capillary venules. This layer was developed only in horses under 10 years of age. In all layers the vascular orientation was mainly occluso-apical, this was defined as the standard pattern. There were many variations displayed in different courses of certain blood vessels. The vascular organization is discussed with regard to the specialized functions of the periodontal ligament (PDL). The wide vessels of the outer layer are thought to play a mechanical role as part of a shock absorbing system. The capillaries of the inner layer meet nutritional requirements. The disappearance of the intermediate layer in horses older than 10 years is taken as an adaptation to the remodelling of the PDL. Modifications in the standard pattern of vascular arrangements are also interpreted as adaptations to life-long changes in the periodontal space. Anastomoses between the periodontal vasculature and the blood vessels of the maxillary sinus indicate that periodontal disease may be transferred into the sinus.

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.

Blood volume in human bicuspid periodontal ligament determined by electron microscopy

The microvascular volume of periodontal ligament is reported to range from 1.63 to 3.5% in man, whereas that of animals varies from 7.5 to 11.5%. This transmission electron-microscopic investigation was undertaken to determine stereologically the volume in human periodontal ligament. The hypothesis tested was that the ligament blood volume in man is similar to that in animals. Left and right segments of mandible containing first and second premolars came from an adult burns' victim who underwent jaw reconstruction. The segments were immersion-fixed in 2.5% glutaraldehyde, demineralized at 4 degrees C in 0.1 M EDTA and processed for microscopy. Segments of distal periodontal ligament were sectioned at 150-micron intervals from the alveolar crest to the root apex and random tissue quadrats recorded for point counting and data analysis using a generalized linear-regression statistical model. Mean adjusted microvascular luminal volume was 9.52 +/- 2.28% (SEM) and the abluminal volume 12.91 +/- 2.76%; the wall volume was 3.39%. Significant differences existed between the luminal and abluminal volumes of the different vessel type (p < 0.05) and their distribution across the circumferential thirds of the ligament (p < 0.05). Total length density of the blood vessels was 149.84 x 10(3) cm/cm3 and the surface density 330.19 cm2/cm3. Postcapillary-sized venules held 69.1% of the total blood volume and provided 49.3% of the luminal surface area. Venous capillaries were the most common vessel, comprising 48.5%, and they contributed 71.5% of the overall length density. This study confirmed the hypothesis for the blood volume in the periodontal ligament in man. Blood volumes do not reflect the configurations of microvascular beds.

Treatment of an ankylosed central incisor by single-tooth dento-osseous osteotomy

This article presents a case of an ankylosed upper central incisor that did not respond to orthodontic mechanics alone or to surgical luxation followed by orthodontic traction. We performed an osteotomy involving the dento-osseous segment in one surgical stage to allow its inferior displacement. The patient was followed for 18 months and the result was considered satisfactory from both the occlusal and periodontal standpoints.

Vascular changes in the periodontal ligament after removal of orthodontic forces

Vascular changes in the periodontal ligament after release of orthodontic force and their possible contribution to relapse of relocated teeth are poorly understood. This study documented the periodontal vascular changes after 2 weeks of tooth movement and during a 3-week period after release of orthodontic force. This study is the first comprehensive quantitative description of these events. Changes in blood vessel number and density were correlated with the direction of tooth movement (initially mesial in response to force but later distal because of relapse). Application and removal of orthodontic force produced significant changes in blood vessel number and density, which were not related to changes in tissue volume. The vascular changes were dependent on the site of evaluation and the size of the blood vessel. The periodontal vascular distribution and density can be summarized as follows: (1) increased after application of orthodontic force, (2) transient decrease subsequent to removal of force, (3) transient increase during reactivated distal drift, and (4) normalization. Normalization was achieved during an interval equivalent to the duration of orthodontic force, suggesting that the vasculature could modulate interstitial tissue pressures, resulting in relapse of relocated teeth. The role of the periodontal vasculature in alveolar remodeling and in modifying interstitial tissue fluid pressures coincident to human tooth movement requires further study.

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.

Extrusion of root-filled incisors in beagles--a light microscope and scanning electron microscope investigation

The response of the periodontal ligament to orthodontic extrusion of the incisor of a beagle was examined with light microscope and scanning electron microscope techniques. The ligament morphology was slightly altered by the procedure but was essentially normal. Teeth that were extruded and retained for 12 weeks exhibited partial relapse. Where a full thickness mucogingival flap was raised and immediately replaced in lieu of retention, continued extrusion was observed. Root resorption was observed at the interproximal region of the cervical third in three out of five specimens. The resorption had been repaired with cellular cementum.

Ultrastructural morphology of vascular endothelial junctions in periodontal ligament

The TEM was used to categorize vessels and their junctions in normal and tensioned rat maxillary molar periodontal ligament. In tensioned periodontal ligament mean luminal diameters of capillaries were significantly smaller (p < 0.001). Goniometer tilting of sections with apparent tight regions revealed that only 16 per cent were actual tight junctions. The other regions proved to be close junctions (85 per cent) and open junctions (4 per cent). No gap junctions were found. These findings establish that morphologically the periodontal ligament contains a microvascular bed of 'leaky' endothelium with a potentially high permeability factor.

Evidence for endothelial junctions acting as a fluid flux pathway in tensioned periodontal ligament

A continuous tension load of 1.0 N applied to the rat maxillary first molar for 30 min led to a significant increase (p < 0.05) in the mean number of junctions/microns of endothelial perimeter. The mean number of junctions/microns was compared with the mean number of tissue channels/microns 2 as previously reported by fitting linear and quadratic equations. An increase in the mean number of junctions/microns was associated with an increase in mean number of tissue channels/microns 2 (p < 0.01) in control and experimental periodontal ligament. Significant increases in the mean number of junctions/microns occurred in the middle-third zone for venous capillaries (p < 0.01) and in the tooth-third zone for postcapillary-sized venules (p < 0.001). It is concluded that the endothelial junctions of venous capillaries and postcapillary-sized venules provide significant pathways for fluid transport across the tensioned walls of the microvascular bed of the periodontal ligament.

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+_

Effect of experimental traumatic occlusion on periodontal and pulpal blood flow

Fluorescent microspheres (FM) were used to visualize and semi-quantify flood flow in the periodontal ligament (PDL) and dental pulp during experimental traumatic occlusion of the maxillary and mandibular molar teeth in young rats. At different observation points FM were injected systemically, and the number of FM was counted in serial sections from the jaws in the PDL and pulp of the molar teeth in a fluorescent microscope. Blood flow was related to the number of FM in the tissues and in a reference blood sample. In the early stages an increase in blood flow in the PDL and dental pulp was found on the experimental side compared with the contralateral side. Furthermore, there was an increase in blood flow on both sides of the jaws compared with an unoperated control material. The study thus indicates that a local unilateral occlusal trauma initiates blood flow responses in the total molar dentition in rats.

An analysis of the effect of tooth intrusion on the microvascular bed and fenestrae in the apical periodontal ligament of the rat molar

An analysis of the rat apical periodontal ligament (PDL) microvascular bed and fenestrae was conducted to evaluate the effect of a continuous 1.0 N intrusive tooth load for 30 minutes. The microvascular bed consisted of postcapillary-sized venules, venous and arterial capillaries, and terminal arterioles. Intrusion produced significant increases (p less than 0.01) in vascular volume for postcapillary-sized venules and venous capillaries in three of the four animals. Arterial capillaries, overall, showed a statistically significant increase (p less than 0.01). The endothelial surface area (micron2 x 10(6)) per cubic millimeter of PDL responded variably in postcapillary-sized venules and venous capillaries but showed a strong trend to increase in arterial capillaries. After tooth intrusion a significant reduction (p less than 0.01) occurred in the number of fenestrae per square micrometer of endothelium in postcapillary-sized venules and venous capillaries. Fenestrae in the control PDL had a mean diameter of 51.5 nm +/- 0.6 (SE), whereas those on the intrusion side were smaller (p less than 0.05), measuring 49.9 nm +/- 0.4 (SE).