An unusual disordered alveolar bone material in the upper furcation region of minipig mandibles: A 3D hierarchical structural study

Teeth are subjected to compressive loads during mastication. Under small loads the soft tissue periodontal ligament (PDL) deforms most. However when the loads increase and the PDL is highly compressed, the tooth and the alveolar bone supporting the tooth, begin to deform. Here we report on the structure of this alveolar bone in the upper furcation region of the first molars of mature minipigs. Using light microscopy and scanning electron microscopy (SEM) of bone cross-sections, we show that this bone is hypermineralized, containing abundant small pores around 1-5 μm in diameter, lacunae around 10-20 μm as well as larger spaces. This bone does not possess the typical lamellar motif or other repeating structures normally found in cortical or trabecular mammalian bone. We also use high resolution focused ion beam scanning electron microscopy (FIB-SEM) in the serial surface mode to image the 3D organization of the demineralized bone matrix. We show that the upper furcation bone matrix has a disordered isotropic structure composed mainly of individual collagen fibrils with no preferred orientation, as well as highly staining material that is probably proteoglycans. Much larger aligned arrays of collagen fibers - presumably Sharpey's fibers - are embedded in this material. This unusual furcation bone material is similar to the disordered material found in human lamellar bone. In the upper furcation region this disordered bone comprises almost all the volume excluding Sharpey's fibers. We surmise that this most unusual bone type functions to resist the repeating compressive loads incurred by molars during mastication.

Effect of preameloblast-conditioned medium and CPNE7 on root surfaces in dogs: a histologic and histomorphometric evaluation

Preameloblast-conditioned medium (PACM) has been reported as a potent dentin regenerative material, but its effects as a mixture on periodontal regeneration and the role of CPNE7 in PACM are not known. The purpose of this study is to evaluate the histologic and histomorphometric effects of preameloblast-conditioned medium (PACM) and CPNE7 on periodontal tissue healing in dogs. Seventy-two mandibular premolar roots from ten dogs were extracted and randomly divided into six groups (n = 12 each): (1) positive control group; (2) negative control group; (3) cementum-removed and PACM-treated group; (4) cementum-preserved and PACM-treated group; (5) CPNE7-inactivated PACM-treated group; and (6) recombinant CPNE7-treated group. The extracted roots were replanted into extraction sockets for 4 and 8 weeks and analyzed histologically. Most of the root surfaces in the negative control group showed ankylosis; and those in the experimental groups showed newly formed PDL-like and cementum-like tissues. Histomorphometric analysis of horizontal sections showed that the mean length of the PDL on the roots of the positive controls was similar to those in cementum-removed or -preserved and PACM-treated group at 8 weeks (p = 1.08). Sagittal sections showed that the mean length of the new cementum on the roots in cementum-removed and PACM-treated group was significantly greater than that in CPNE7-inactivated PACM-treated group (p = 0.037). The mean length of the newly formed PDL on the roots in CPNE7- inactivated PACM-treated and rCPNE7-treated groups was significantly greater than that in the negative controls at 8 weeks (p = 0.037, p = 0.036). The use of PACM and CPNE7 in tooth replantation resulted in increased PDL and cementum formation, suggesting the beneficial role of PACM and CPNE7 in periodontal tissue healing.

Mechanobiology of the tooth movement during the orthodontic treatment: a literature review

Orthodontic tooth movement differs significantly from the physiological tooth movement, as it determines a biological response of the surrounding tissues of the teeth, resulting in a remodelling of the periodontal ligament and the alveolar bone. The result is a biochemical adaptive response to the application of the orthodontic force with the reorganization of the intracellular and the extracellular matrix, in addition to a change of the local vascularization. This in turn leads to the synthesis and the release of arachidonic acid, growth factors, metabolites, cytokines and various enzymes. Biologically, not only the intensity of the force, but also its duration and the tissue response to the application of the same are important for tooth movement. Having these insights it will possible to examine the concept of optimal orthodontic force, a determining factor for the success of orthodontic treatment. The purpose of this revision was to describe the biological processes and future perspective of the application of orthodontic force, by providing relevant information to understand the changes at the molecular and cellular level occurring when the tissues are subjected to such forces. Knowledge on the subject of mechanics and biology in orthodontics is constantly growing, producing an increasingly strong basis for clinical success.

The plastic nature of the human bone-periodontal ligament-tooth fibrous joint

This study investigates bony protrusions within a narrowed periodontal ligament space (PDL-space) of a human bone-PDL-tooth fibrous joint by mapping structural, biochemical, and mechanical heterogeneity. Higher resolution structural characterization was achieved via complementary atomic force microscopy (AFM), nano-transmission X-ray microscopy (nano-TXM), and microtomography (MicroXCT™). Structural heterogeneity was correlated to biochemical and elemental composition, illustrated via histochemistry and microprobe X-ray fluorescence analysis (μ-XRF), and mechanical heterogeneity evaluated by AFM-based nanoindentation. Results demonstrated that the narrowed PDL-space was due to invasion of bundle bone (BB) into PDL-space. Protruded BB had a wider range with higher elastic modulus values (2-8GPa) compared to lamellar bone (0.8-6GPa), and increased quantities of Ca, P and Zn as revealed by μ-XRF. Interestingly, the hygroscopic 10-30μm interface between protruded BB and lamellar bone exhibited higher X-ray attenuation similar to cement lines and lamellae within bone. Localization of the small leucine rich proteoglycan biglycan (BGN) responsible for mineralization was observed at the PDL-bone interface and around the osteocyte lacunae. Based on these results, it can be argued that the LB-BB interface was the original site of PDL attachment, and that the genesis of protruded BB identified as protrusions occurred as a result of shift in strain. We emphasize the importance of bony protrusions within the context of organ function and that additional study is warranted.

An experimental study on periodontal regeneration after subcutaneous transplantation of rat molar with and without cryopreservation: an in vivo study

This study analysed the effects of cryopreservation on periodontal regeneration of autotransplanted rat molars. First and second maxillary molars (n=92) of 24 four-week-old Wistar rats were gently extracted and autotransplanted into the abdominal tissue immediately (control group n=44) or after cryopreservation in liquid nitrogen for 7 days (experimental group n=48). At 1, 2, 4 and 10 weeks after transplantation, the transplanted molars were excised and regeneration of the periodontal tissues was analysed on histological sections stained with routine H&E and Goldner method. Different tissue responses were scored on a tooth basis: inflammation, regeneration of the periodontal ligament, resorption/apposition of cementum, and alveolar bone formation. Sixty-two teeth were available for histological evaluation, including 30 experimental and 32 control samples. One week after transplantation, both control and test teeth were surrounded by granulation tissue and some areas of root resorption could be seen. After 2 weeks, signs of regeneration of the periodontal ligament, cementum apposition, and new bone formation roughly coincided in both groups, however markedly retarded in the experimental group. After 4 weeks, regeneration progressed equally in both groups, presenting fewer areas of cementum apposition in experimental samples. Finally, 10 weeks after baseline transplantation, no significant differences between both groups could be observed. Cryopreservation followed by autotransplantation of extracted teeth in rats appears to have minimal detrimental effects on regeneration of periodontal tissues after integration periods of 1-10 weeks. However, the present findings indicated that the regeneration process in general is retarded for cryopreserved teeth, as compared to their immediately transplanted homologues.

A comparison between two fourth generation apex locators

AIM

The aim of this study was to evaluate ex vivo the accuracy of two fourth generation apex locators and compare the measurements obtained.

METHODS

Forty single and multiroots of permanent teeth (i.e., sixty-two canals) without caries or restorations were selected. After determining the real canal length using a stereomicroscope and a digital calliper, we evaluated the accuracy of two fourth generation electronic apex locators (the Bingo 1020 and the Propex) by means of an experimental study model and an endodontic simulator. The experimental model uses a digital comparator to determine the root canal length to a precision of 0.001 mm, while the endodontic simulator replicates the normal clinical condition. The difference between the real length of each canal and that obtained with the two study models was calculated.

RESULTS

In both experiments, the Bingo 1020 expressed a 94.35% and the Propex expressed a mean accuracy of 90.31% in positioning the file at ± 0.5 mm.

CONCLUSION

The Bingo 1020 and the Propex apex locators are equally accurate and provide reliable measurements in calculating root canal length.

[Effects of emdogain on human periodontal ligament cells in vitro]

OBJECTIVE

To investigate the effects of emdogain, enamel matrix derivative (EMD), on the proliferation, cell cycle, mineralization and ultrastructure of human periodontal ligament (PDL) cells in vitro.

METHODS

The influence of cell growth on PDL cells was evaluated by Cell Counting Kit-8 (CCK-8) in the presence and absence of emdogain, after 1, 3, and 5 d of culture. DNA synthesis and ultrastructure of PDL cells were observed by flow cytometry(FCM) and transmission electron microscopy (TEM) in the presence and absence of emdogain after 3 d of culture. The increasing of osteogenic capacity was verified by the expression changes of osteogenic differentiation markers of bone sialoprotein (BSP) and osteopontin (OPN) in emdogain-treated PDL cells by immunohistochemicl staining.

RESULTS

Incubation of PDL cells with emdogain after 3 d significantly stimulated cell growth and DNA synthesis. Emdogain enhanced the osteogenic potential of PDL cells by high expression of osteogenic differentiation markers of BSP and OPN.

CONCLUSION

The data indicate that Emdogain enhances cell proliferation and promotes differentiation of PDL cells, which contributes to periodontal tissue regeneration .

The biomechanical characteristics of the bone-periodontal ligament-cementum complex

The relative motion between the tooth and alveolar bone is facilitated by the soft-hard tissue interfaces which include periodontal ligament-bone (PDL-bone) and periodontal ligament-cementum (PDL-cementum). The soft-hard tissue interfaces are responsible for attachment and are critical to the overall biomechanical efficiency of the bone-tooth complex. In this study, the PDL-bone and PDL-cementum attachment sites in human molars were investigated to identify the structural orientation and integration of the PDL with bone and cementum. These attachment sites were characterized from a combined materials and mechanics perspective and were related to macro-scale function. High resolution complimentary imaging techniques including atomic force microscopy, scanning electron microscopy and micro-scale X-ray computed tomography (Micro XCT) illustrated two distinct orientations of PDL; circumferential-PDL (cir-PDL) and radial-PDL (rad-PDL). Within the PDL-space, the primary orientation of the ligament was radial (rad-PDL) as is well known. Interestingly, circumferential orientation of PDL continuous with rad-PDL was observed adjacent to alveolar bone and cementum. The integration of the cir-PDL was identified by 1-2 microm diameter PDL-inserts or Sharpey's fibers in alveolar bone and cementum. Chemically and biochemically the cir-PDL adjacent to bone and cementum was identified by relatively higher carbon and lower calcium including the localization of small leucine rich proteins responsible for maintaining soft-hard tissue cohesion, stiffness and hygroscopic nature of PDL-bone and PDL-cementum attachment sites. The combined structural and chemical properties provided graded stiffness characteristics of PDL-bone (E(r) range for PDL: 10-50 MPa; bone: 0.2-9.6 GPa) and PDL-cementum (E(r) range for cementum: 1.1-8.3 GPa), which was related to the macro-scale function of the bone-tooth complex.

[Relationship between tissular structure and strength of fresh bull periodontal ligament]

OBJECTIVE

To study the relationship between the width and the content of fiber in peridontal ligament (PDL) and the strength of peridontal membrane.

METHODS

Fresh mandible of bull was obtained to prepare for a 5 mm x 2 mm x 10 mm cuboid including teeth, peridontal membrane, and alveolar bone. The width of the PDL was measured under a stereomicroseope. Pull stress was loaded on the test piece until it broke. The stress-strain curve was recorded. The broken ends of the PDL was dyed with siriue to adalyze the content of fiber.

RESULTS

The relationship between the width of the PDL and the maximum stress was expressed as Y = 9.786e(-3.6693x). The relationship between the width of the PDL and the physiological ultimate stress was expressed as Y = e((2.188(-3.953)x). The relationship between the percentage of fiber and maximum stress was expressed as Y = 20.788-0.755x + 0.007x(2). The relationship between the percentage of fiber and the physiological ultimate stress was expressed as Y = 1.39e(-14) x x(7.666). The initial physiological stress was 0.28 N/mm2.

CONCLUSION

The strength of PDL increases with the decrease of PDL width and increase of fiber content.

An immunohistochemical, histological, and electron-microscopic study of the human periodontal ligament during orthodontic treatment

The periodontal ligament lies between the hard tissues of alveolar bone and cementum of teeth and serves to anchor the tooth to the alveolus and functions as a cushion between these hard tissues to migrate occlusal force during mastication. This tissue is always exposed to mechanical stress during mastication. When occlusal forces exceed the adaptive capacity of the periodontal ligament, the periodontal ligament tissue will be injured and then occlusal trauma will occur. The different modifications of periodontal ligament during load deformation can be monitored by analysis of the expression of different collagen types and fibronectin, with immunohistochemical techniques, and by morphological study of ligament, with light- and transmission electron-microscopic techniques. The use of continued and light orthodontic force generates a pressure of ligament with ejection of parodontal fluid externally and partial closing of vessels. On these basis we performed a study in order to evaluate periodontal ligament collagen types I and IV and the fibronectin modifications induced by application of a precalibrated orthodontic strength. We integrated these results, with light and transmission electron-microscopic observations, in order to evaluate the morphological modifications of periodontal tissue. Our observations showed that the type I collagen immunofluorescence staining is increased in the pressure side; in the tension side, it shows prior to treatment an increase, and after 72 h of treatment, a diminution of the staining pattern. Type IV collagen staining is reduced in both sides, but increased gradually after 7 days from treatment; finally, fibronectin staining pattern is gradually increased in the pressure side and reduced in the tension side. In light and transmission electron-microscopic observations it is possible to show a reduction of vessels at 72 h from treatment, and an increase of vessels after 7 days from treatment. The Malassez's epithelial residues are decreased at 72 h, while they are increased after 7 days from treatment. The modifications of immunofluorescence staining patterns of tested proteins revealed angiogenesis and reparative processes, and a thickening of fibrillar matrix as a defensive reply to mechanical stress. The modification of normal staining patterns of tested protein in our observations, could be determined by variation of scaffold geometry of periodontal ligament. The reduced movements of contraction and relaxation of periodontal ligament, due to orthodontic treatment, provoke a loss of mechanical stresses transmitted over ligament surface. Mechanical signals, therefore, could be integrated with other environmental signals and transduced into biochemical signals through force-dependent changes in scaffold geometry. Physical forces of gravity, hemodynamic stresses, and movement play a critical role in tissues, since the cells use tensegrity architecture for their structural organization.

Functional interleukin-7/interleukin-7Ralpha, and SDF-1alpha/CXCR4 are expressed by human periodontal ligament derived mesenchymal stem cells

Hematopoiesis in the bone marrow (BM) is maintained by specific interactions between both hematopoietic and non-hematopoietic stromal cells, which are mesenchymal stem cells (MSCs) capable of giving rise to several cell types. The human periodontal ligament (PDL), a tissue of ectomesenchymal origin, has been shown to also be a source of MSCs. We have investigated whether MSCs expanded from the PDL of healthy volunteers express characteristics similar to BM-derived stem cells using structural, immunocytochemical and molecular approaches. Their ability to support the growth of hematopoietic progenitors was also analyzed. The PDL-MSCs exhibited a fibroblast-like morphology and their chromatin was dispersed, indicating active gene transcription. The mesenchymal-related antigens CD90, CD29, CD166, CD105, and CD44 were homogeneously detected by cytofluorimetric analysis, whereas membrane CXCR4 was expressed only by a minority of cells. The PDL-MSCs differentiated in vitro into osteogenic and adipogenic cells. Immunolocalization of IL-7, IL-7Ralpha, SDF-1alpha, and CXCR4 resulted in a diffuse but specific labeling. RT-PCR analysis confirmed the expression of the above-mentioned transcripts. The cells spontaneously produced high levels of IL-7 and SDF-1alpha and were able to support the development and long-term maintenance of BM precursor cells more efficiently than murine stromal cells and similarly to normal BM human stromal cells. We examined IL-7 and SDF-1alpha secretion pathway during adipogenic and osteogenic differentiation. IL-7 increased during osteogenic and adipogenic differentiation, while the SDF-1alpha secretion was downregulated during osteogenic differentiation but increased during adipogenic induction. Our study provides evidence that in human PDL there is an accessible niche of MSCs showing the features of BM-derived MSCs.

Neutrophil elastase is involved in the initial destruction of human periodontal ligament

BACKGROUND AND OBJECTIVE

It has been reported that noncollagenous proteins may provide mechanical strength to the periodontal ligament. Several proteolytic activities, including that of neutrophil elastase, are reported to increase significantly in periodontal disease. The aim of this study was to investigate the function of neutrophil elastase in the initial destruction of periodontal ligament at early stages of periodontal disease.

MATERIAL AND METHODS

The detection and identification of proteinases in chronic periodontitis and healthy periodontal ligament were examined by zymographic and zymo-Western analysis. The morphological changes of periodontal ligament, digested with or without authentic proteinases, were observed using scanning electron microscopy.

RESULTS

Increases in neutrophil elastase, plasminogen, and matrix metalloproteinase-9 were detected in periodontal ligament from chronic periodontitis, compared with healthy periodontal ligament. Among these proteinases, only neutrophil elastase digested the intact noncollagenous proteins of periodontium. When human healthy periodontal ligament was directly digested by neutrophil elastase in an in vitro system, the morphological features were quite similar to that of the periodontal ligament in chronic periodontitis . In healthy periodontal ligament, the collagen fibrils are covered with noncollagenous proteins containing 110 kDa acidic glycoprotein, which was degraded initially by the neutrophil elastase.

CONCLUSION

It was concluded that neutrophil elastase is involved in the degradation of noncollagenous protein-covered collagen fibrils in the early destructive stages of periodontal disease.

Microscopic qualitative evaluation of fixation time and decalcification media in rat maxillary periodontium

The rat model is widely used in periodontal research and the quality of histological sections is essential. The purpose of this study was to evaluate the histological characteristics of periodontal tissues in Wistar rat maxillae, with different times of fixation and decalcified by nitric acid or formic acid (Anna Morse Solution). Fifteen rats were used. Fixation was performed for 24, 48 and 72 hours. The maxillae were hemi-sectioned and each part was decalcified either in nitric acid for 7 days or in Anna Morse solution for 35 days. Two trained and blinded examiners performed the evaluation. Fourty eight hours of fixation and decalcification with Anna Morse solution showed more clear characteristics of the epithelium-connective tissue interface and of the periodontal structures. Mean measurements between the cementum-enamel junction and the bone crest varied in the different experimental times from 176.5 (± 60.45) to 210.94 (± 39.33) pixels on the buccal aspect, and from 199.69 (± 38.33) to 298.55 (± 70.81) pixels on the palatal aspect, with no statistically significant differences (ANOVA, p > 0.05). In the same fixation period, decalcification with nitric acid or Anna Morse solution did not display any statistically significant differences. It may be concluded that for a qualitative histological analysis, fixation should preferably be for 48 hours and the demineralization should be made by Anna Morse solution. For a histomorphometric analysis, the decalcification solution does not interfere in the results.

Application of fluorescence microscopy on hematoxylin and eosin-stained sections of healthy and diseased teeth and supporting structures

Destruction of dental tissue and supporting structures is usually microscopically assessed by routine hematoxylin and eosin (HE)-stained sections. This short communication is concerned with the potential role of fluorescence microscopy of HE-stained sections to study morphological aspects of intact and pathological teeth in dental research. This methodology improves the visualization of the anatomical structures of the intact teeth, especially anatomical features and periodontal ligament spatial distribution. This technique also improves the visualization of the root and bone resorption and the delineation of the periapical lesion extension. The fluorescence microscopy technique of HE-stained sections is an easy, reliable and inexpensive method that seems to be a useful tool for evaluating morphological aspects of intact and pathological teeth in dental research.

Demonstration of mitochondrial oestrogen receptor beta and oestrogen-induced attenuation of cytochrome c oxidase subunit I expression in human periodontal ligament cells

OBJECTIVE

Periodontal ligament (PDL) cells express oestrogen receptor beta (ERbeta) protein, but cellular functions regulated by ERbeta in these cells have not been identified. In this study we determine if ERbeta is localised to mitochondria and if oestrogen regulates mitochondrial function in human PDL cells obtained from teeth extracted for orthodontic reasons.

DESIGN

Subcellular distribution of ERbeta was determined by confocal microscopy of cells co-stained with ERbeta antibody and the mitochondrion-selective probe MitoTracker and by immunogold electron microscopy. Expression of the mitochondrial enzyme cytochrome c oxidase subunit I, involved in oxidative phosphorylation, was determined by Western blotting in cells treated with or without physiological concentrations of the endogenous oestrogen 17beta-oestradiol.

RESULTS

ERbeta immunoreactivity was observed both in the nuclei and the cytoplasm. MitoTracker-labelling was observed in the cytoplasm, especially in the perinuclear region, but not in the nuclei. Co-localisation of ERbeta and MitoTracker was observed in cells derived from both male and female subjects. Mitochondrial localisation of ERbeta was confirmed by immunogold electron microscopy. Cells treated with or without 17beta-oestradiol (100 nM) displayed an identical pattern of staining for mitochondria. Treatment with 100 nM 17beta-oestradiol attenuated cytochrome c oxidase subunit I expression by about 30%, while combined treatment with 17beta-oestradiol and the ER blocker ICI 182780 (10 microM) had no effect.

CONCLUSION

This study demonstrates mitochondrial localisation of ERbeta and oestrogen-induced decrease in the expression of cytochrome c oxidase subunit I in human PDL cells, suggesting that oestrogen probably via ERbeta influences mitochondrial function and PDL cell energy metabolism.

Diverse effects of c-src deficiency on molar tooth development and eruption in mice

C-src deficiency is characterized by osteopetrosis due to impaired bone resorption by hypofunctional osteoclasts and the resultant failure of tooth eruption. In preliminary observations, we frequently encountered erupted molars in c-src deficient mice unlike in other osteopetrotic animals. Here we examine the effects of c-src deficiency on the development of molar teeth with an emphasis on the spatial relation of growing teeth with the surrounding bones. In c-src deficient mice, the magnitude of tooth impaction differed considerably among the types of molars; all maxillary 1st molars were totally impacted deep in the alveolar sockets, whereas most mandibular 1st molars fully erupted into oral cavity. Distribution of osteoclasts in the alveolar bone was identical among all types of molars, and electron microscopy revealed signs of bone resorbing activity in these osteoclasts despite the absence of a ruffled border. From early development, the alveolar space was much narrower in the upper molar tooth germs than in the lower ones in both wild type and homozygous animals, and particularly so in the upper 1st molars. Current observations thus indicate a significant contribution of "hypofunctional osteoclasts" in c-src deficient mice in molar tooth development except for the upper 1st molars, which appear to require highly functional osteoclasts to gain sufficient space for them to grow normally. Taken together, these findings on the seemingly tooth-type specific effects of c-src deficiency on the development and eruption of molar teeth in c-src deficient mice can be attributed to the given differential spatial relation of the respective tooth germs with the surrounding bones in the presence of hypofunctional osteoclasts.

Collagen fiber architecture of the periodontal ligament in equine cheek teeth

The objective of this study was to examine the spatial arrangement of the fiber apparatus of the equine periodontium which is supposed to meet two contrary requirements: (1) to attach the tooth firmly and elastically to the alveolar bone; and, to be appropriately remodeled and reconstructed in order to facilitate the prolonged eruption of the tooth. Specimens of periodontal ligament were obtained from the buccal and lingual/palatal aspects of the first molars from the maxilla and mandible of 12 horses. The animals were assigned to three age groups. Histological sections were prepared from three specific horizontal levels of the periodontal ligament and examined with conventional and polarized-light microscopy. At the gingival level, collagen fascicles (diameter > 200 microm) were densely packed. Their spatial alignment was the same in all age groups. The architecture of the collagen fiber apparatus differed at the middle and apical levels in the three age groups. There was a clear distinction between fibers, bundles, and fascicles. Bundling of collagen fibers, density of the fiber arrangement, and collagen fascicles with an alveolo-cemental orientation increased with age. The collagen fiber apparatus of the equine periodontal ligament is highly adaptive, responding continuously to the dynamic changes in the periodontal environment. Site-specific arrangements and age-dependent structural variations are assumed to maintain tooth support as the reserve crown gradually decreases in length with progressive dental attrition. Most of the age-dependent changes to the periodontal ligament in teeth examined in this study occurred at the apical level. The apical region of young teeth had no periodontal attachment, while the roots of older teeth were firmly attached to the alveolus. When evaluating periodontal ligament development, the individual tooth's 'dental age' should be considered rather than the animal's age to account for individual tooth eruption times.

Immunohistochemical characterization of elastic system fibers in rat molar periodontal ligament

Among elastic system fibers, oxytalan fibers are known as a ubiquitous component of the periodontal ligament, but the localization and role of elastin-containing fibers, i.e., elastic and elaunin fibers, has yet to be clarified. In this study, we immunohistochemically investigated the localization of elastin and fibrillin, major proteins of elastin-containing fibers in the periodontal ligament of rat lower first molars. At the light microscope level, distribution of elastin-positive fibers was not uniform but often concentrated in the vicinity of blood vessels in the apical region of the ligament. In contrast, fibrillin-positive fibers were more widely distributed throughout the ligament, and the pattern of their distribution was comparable to the reported distribution of oxytalan fibers. At the ultrastructural level, assemblies or bundles of abundant fibrillin-containing microfibrils were intermingled with a small amount of elastin. This observation indicated that elastin-positive fibers observed under the light microscope were elaunin fibers. No mature elastic fibers, however, were found in the ligament. These results show that the major components of elastic system fibers in the periodontal ligament of the rat mandibular first molar were oxytalan and elaunin fibers, suggesting that the elastic system fibers play a role in the mechanical protection of the vascular system.

Characteristics of periodontal ligament subpopulations obtained by sequential enzymatic digestion of rat molar periodontal ligament

Periodontal ligament (PDL) consists of different cell populations in various differentiation stages. In the present study, we isolated cell populations from rat molar PDL by sequential enzymatic digestion and characterized growth potential and mineralization activity of the PDL subpopulations (PDL-SP) to throw light on the mechanism of PDL remodeling and, in its turn, periodontal tissue regeneration. PDL attached to extracted rat molars was digested 2 mg/ml collagenase and 0.25% trypsin at 37 degrees C for 30 min. Then four consecutive digestions were performed for 20 min each in a fresh digestive solution. The solutions were centrifuged to collect released cells and 5 PDL subpopulations (30M-, 50M-, 70M-, 90M-and 110M-PDL-SP) were obtained. Light microscopic observation showed that about a half of PDL in width attached on the root surface of extracted teeth and 30M-PDL-SP was considered to contain cells mainly from middle portion of PDL. Scanning electron microscopic examination indicated that 110M-PDL-SP was enriched by root lining cementoblastic cells. 30M-PDL-SP showed a high level of proliferative activity. Although the growth potential of a subpopulation decreased in PDL-SP toward the root surface, 110M-PDL-SP had a high proliferative activity equivalent to that of 30M-PDL-SP. Analyses of alkaline phosphatase (ALP) and mineralization activities showed that higher activities in PDL-SP toward the surface of roots and that 110M-PDL-SP had the highest activity of ALP and the largest number of mineralization nodules. The present study shows as supposed by previous studies on cell kinetics in PDL that subpopulations with larger growth potential were generally located in the middle portion of PDL and those with higher mineralization activities toward the surface of the roots. It is suggested, however, that a possible pathway of PDL cell turnover may exist within the PDL-SP on the root surface in addition to the generally recognized pathway from the middle area of PDL to root surface.

Periostin is an extracellular matrix protein required for eruption of incisors in mice

A characteristic tooth of rodents, the incisor continuously grows throughout life by the constant formation of dentin and enamel. Continuous eruption of the incisor is accompanied with formation of shear zone, in which the periodontal ligament is remodeled. Although the shear zone plays a role in the remodeling, its molecular biological aspect is barely understood. Here, we show that periostin is essential for formation of the shear zone. Periostin-/- mice showed an eruption disturbance of incisors. Histological observation revealed that deletion of periostin led to disappearance of the shear zone. Electron microscopy revealed that the disappearance of the shear zone resulted from a failure in digestion of collagen fibers in the periostin-/- mice. Furthermore, immunohistochemical analysis using anti-periostin antibodies demonstrated the restricted localization of periostin protein in the shear zone. Periostin is an extracellular matrix protein, and immunoelectron microscopy showed a close association of periostin with collagen fibrils in vivo. These results suggest that periostin functions in the remodeling of collagen matrix in the shear zone.

Morphological and cytofluorimetric analysis of adult mesenchymal stem cells expanded ex vivo from periodontal ligament

Many adult tissues contain a population of stem cells that have the ability of regeneration after trauma, disease or aging. Recently, there has been great interest in mesenchymal stem cells and their roles in maintaining the physiological structure of tissues, and their studies have been considered very important and intriguing, after having shown that this cell population can be expanded ex vivo to regenerate tissues not only of the mesenchymal lineage, such as intervertebral disc cartilage, bone, tooth-associated tissue, cardiomyocytes, but also to differentiate into cells derived from other embryonic layers, including neurons. Currently, different efforts have been focused on the identification of odontogenic progenitors from oral tissues. In this study we isolated and characterized a population of homogeneous human mesenchymal stem cells proliferating in culture with an attached well-spread morphology derived from periodontal ligament, a tissue of ectomesenchymal origin, with the ability to form a specialized joint between alveolar bone and tooth. The adherent cells were harvested and expanded ex vivo under specific conditions and analysed by FACScan flow cytometer and morphological analysis was carried out by light, scanning and transmission electron microscopy. Our results displayed highly evident cells with a fibroblast-like morphology and a secretory apparatus, probably indicating that the enhanced function of the secretory apparatus of the mesenchymal stem cells may be associated with the secretion of molecules that are required to survive and proliferate. Moreover, the presence in periodontal ligament of CD90, CD29, CD44,CD166, CD 105, CD13 positive cells, antigens that are also identified as stromal precursors of the bone marrow, indicate that the periodontal ligament may turn out to be a new efficient source of the cells with intrinsic capacity to self-renewal, high ability to proliferate and differentiate, that can be utilized for a new approach to regenerative medicine and tissue engineering.

Expression of mRNAs encoding for growth factors, ECM molecules, and MMP13 in mono-cultures and co-cultures of human periodontal ligament fibroblasts and alveolar bone cells

Although the function and effects of many growth factors and extracellular matrix (ECM) molecules have been described for several periodontal tissues in vivo and in vitro, the molecular interactions involved in the communication between cells of the periodontal ligament and the alveolar bone are poorly understood. To contribute to the identification of such interactions, we have generated co-cultures (CCs) of periodontal ligament fibroblasts (PDLs) and alveolar bone cells (ABCs) and compared mRNA expression for various growth factors, ECM molecules, and matrix metalloproteinase13 (MMP13) after 1 and 2 weeks with matched mono-cultures (MCs) by reverse transcription/polymerase chain reaction. Compared with CCs of 1 week, PDLs and ABCs after 2 weeks revealed relatively high levels of all analyzed mRNAs, viz., for EGF, HGF, VEGF, TGFbeta1, collagen-I (COL1), osteonectin (ON), fibronectin (FN1), and MMP13. At week 2, when compared with MCs, CCs showed an elevation of all tested mRNAs in PDLs and ABCs, except for TGFbeta1 and FN1, which only increased in PDLs. After 1 week, when CCs were compared with MCs, mRNAs for HGF and TGFbeta1 were less abundant in PDLs and ABCs, whereas the other genes exhibited lower expression levels in only one of the cell types. Analysis of our data indicated that the expression of mRNAs for growth factors and for COL1, ON, FN1, and MMP13 was modulated in the distinct cell types with respect to culture time and culture type. The differences in the mRNA expression patterns between CCs and MCs suggest that the respective genes are involved in the molecular interactions of PDLs and ABCs.

PLATELET-RICH PLASMA PROVIDES NUCLEUS FOR MINERALIZATION IN CULTURES OF PARTIALLY DIFFERENTIATED PERIODONTAL LIGAMENT CELLS

Platelet-rich plasma (PRP) has been used to promote periodontal regeneration following the premise that constituent transforming growth factor-beta1 (TGF-beta1) and platelet-derived growth factor-AB will stimulate cell proliferation at the site of application. In previous studies, we demonstrated that PRP mimics TGF-beta1 to modulate proliferation in a cell type- specific manner, that fibrin clot formation by PRP upregulates type I collagen, and that an unidentified factor(s) in PRP increases alkaline phosphatase (ALP) activity in human periodontal ligament (PDL) cell cultures. We have now examined the effects of PRP on in vitro mineralization. Platelet-rich plasma and PDL cells were prepared from human adult volunteers or rats. After 20 d of continuous treatment with PRP in dexamethazone (Dex)-containing osteogenic medium, PRP time dependently promoted mineralization by rat PDL cells but failed to fully induce the osteoblastic phenotype. Furthermore, when human PDL cells were induced to increase ALP activity in osteogenic medium that lacked Dex, a condition that should delay (or suppress) osteoblastic differentiation, transmission electron microscopy revealed that mineralized spicules were initially deposited onto PRP-derived platelet aggregates. Taken together with our previous data, these findings suggest that PRP provides platelet aggregates as nuclei to initiate mineralization while stimulating PDL cell proliferation, differentiation, and collagen production. The combination of these effects may effectively mediate PRP's ability to promote regeneration of periodontal tissue, including skeletal tissue, at the site of injury.

Effects of Shuanghuangbu on the total protein content and ultrastructure in cultured human periodontal ligament cells

BACKGROUND

Successful periodontal regeneration depends on the migration, proliferation and differentiation of periodontal ligament cells in periodontal defects. The total protein content and the ultrastructure demonstrate the metabolizability and activity of periodontal ligament cells. This study was conducted to observe the effects of Shuanghuangbu, a mixture of medicinal herbs, on the total protein content and the ultrastructure of human periodontal ligament cells.

METHODS

Periodontal ligament cells were grown to confluence and then cultured in Dulbecco's modified eagle medium (DMEM) supplemented with Shuanghuangbu over the concentration range of 0 to 1000 microg/ml. The total protein content in cultured cells was determined by using Coommasie brilliant blue technique. Periodontal ligament cells were incubated in 0 and 100 microg/ml Shuanghuangbu decoction for 5 days, then observed through transmission electron microscope.

RESULTS

The total protein content of human periodontal ligament cells increased in each experiment group added 10 - 1000 microg/ml Shuanghuangbu respectively, and the effect of 100 microg/ml was excellent. Under the transmission electron microscope, there were more rough endoplasmic reticulums and mitochodrias in the experiment group than those in the control group.

CONCLUSION

Shuanghuangbu stimulates the protein synthesis of human periodontal ligament cells and improves human periodontal ligament cells' metabolizability and activity.

Tensile and compressive behaviour of the bovine periodontal ligament

The mechanical response of the bovine periodontal ligament (PDL) subjected to uniaxial tension and compression is reported. Several sections normal to the longitudinal axis of bovine incisors and molars were extracted from different depths. Specimens with dimensions 10 x 5 x 2 mm including dentine, PDL and alveolar bone were obtained from these sections. Scanning electron microscopy suggested a strong similarity between the bovine PDL and the human PDL microstructure described in the literature. The prepared specimens were tested in a custom made uniaxial testing machine. They were clamped on their bone and dentine extremities and immersed in a saline solution at 37 degrees C. Stress-strain curves indicated that the PDL is characterized by a non-linear and time-dependent mechanical behaviour with the typical features of collagenous soft tissues. The curves exhibited hysteresis and preconditioning effects. The mechanical parameters evaluated in tension were maximum tangent modulus, strength, maximizer strain and strain energy density. For the molars, all these parameters increased with depth except for the apical region. For the incisors, all parameters increased with depth except ultimate strain which decreased. It was assumed that collagen fibre density and orientation were responsible for these findings.

Early root alterations after orthodontic force application studied by light and scanning electron microscopy

The purpose of the study was to characterize root surface alterations in orthodontically moved teeth. Thirty-six 40-50-day-old male Wistar rats were used. The maxillary right first molar was mesialized by means of a fixed appliance, exerting 50 g of force upon insertion. One, 2 and 4 days after force application the animals were sacrificed (nine animals per observation period) and block sections processed for analysis. Nine animals served as untreated controls. In total, 20 specimens were prepared for examination of the mesial aspect of the mesiobuccal root by scanning electron microscopy (SEM). The remaining specimens were processed for light microscopy. Three morphologically distinct types of resorption defect were observed: isolated small lacunae, wide shallow resorption bays, and deep resorption lacunae. The area occupied by each resorption type varied significantly (P < 0.05) with time. Isolated small lacunae were the earliest to be observed, sometimes found in continuity with wide shallow resorption bays. Mononucleated macrophage-like cells were associated with both resorption types. Deeper lacunae extending into the dentine were found at the 4 day observation period. These always occurred within shallow resorption bays and appeared to be created by multinucleated cells. From the sequence of the different root surface defects and associated cell types observed during the development of orthodontically induced root resorption, it may be concluded that different cell types, with different resorptive potential but functionally interrelated, are involved in the successive phases of the process, and that each cell type leaves a characteristic resorption pattern on the root surface.

Phosphatidylinositol-dependent bond between alkaline phosphatase and collagen fibers in the periodontal ligament of rat molars

Alkaline phosphatase (ALP) is anchored to the outer leaflet of the lipid bilayer via phosphatidylinositol (PI) and ALP activity has been localized in the plasma membrane of numerous tissues. In the periodontal ligament ALP activity is found in the collagen fibers in addition to the plasma membrane of the osteoblasts and fibroblasts. In this study, we examined the distribution of ALP activity in the periodontal ligament of rat molars and also examined whether the bond between ALP and collagen fibers is dependent on PI by using phosphatidylinositol-specific phospholipase C (PI-PLC). ALP activity was distributed in the periodontal ligament. The activity mirrored the distribution of collagen fibers in the periodontal ligament. Cytochemical analysis also demonstrated that ALP activity was located not only in the plasma membrane of fibroblasts, but also in the collagen fiber bundles and fibrils in the periodontal ligament. After treatment with PI-PLC, the loss of ALP activity in the periodontal ligament was observed histochemically, and the loss of ALP activity in the fibroblasts as well as in the collagen fiber bundles and fibrils was observed cytochemically. These results strongly indicate that the bond between ALP and the collagen fibers is also dependent on PI.

[Effects of tobacco on proliferation and attachment of human periodontal ligament fibroblast]

OBJECTIVE

To evaluate the effects of nicotine and tobacco extract (ST) on PDLFs morphology, structure, proliferation and attachment.

METHODS

PDLFs were cultured in the presence of nicotine and ST at various concentration. The cell changes in the morphology and structure were examined by histological and transmission electrical microscope (TEM). The growth and attachment of cell were measured by MTT method.

RESULTS

The size of the cells became smaller gradually and their shapes changed from shuttle type to oval or round when the concentration of nicotine and ST increased, the polarity of the cells was in disorder, ultrastructure showed that the organelles, especially rough-surfaced endoplasmic reticulum and golgi complex decreased in number, microtubule and microfilaments were disassembled, the nuclei became fewer or shrunk, the growth and attachment were dose-dependently inhibited.

CONCLUSIONS

Nicotine and ST can change PDLFs' morphology and structure, they may inhibit the growth and attachment through disruption of the cytoskeleton, suggesting nicotine and ST may have pathological role on human periodontitis.

Evaluation of a soybean product fujiflavone P40 as an antiosteoporotic agent in rats

The preventive effects of Fujiflavone P40 (a soybean isoflavone product) against both bone loss and periodontal alteration were evaluated using an ovariectomized rat model. Rats were divided into five groups: sham-operated (Sham), ovariectomized (OVX), OVX given Fujiflavone P40, OVX given 17beta-oestradiol, and OVX given the vehicle for 17beta-oestradiol, respectively. Fujiflavone P40 contains 46.6% isoflavones which consist of 24.1% daidzin, 16.5% glycitin and 5.9% genistin. Administration of Fujiflavone P40 to OVX rats suppressed the body weight gain until 5 weeks. Fujiflavone P40 also decreased total and high-density lipoprotein (HDL) cholesterols and triglyceride level of OVX rats, significantly. After 7 weeks, Fujiflavone P40 did not recover the coarsened fibre of the periodontal ligament. The ovariectomy decreased the uterine weight by 78%. The administration of 17beta -oestradiol recovered the weight loss by 99%, while Fujiflavone P40 restored it by 33%. The ovariectomy decreased the tibial bone mineral density (BMD) by 22%. The administration of 17beta-oestradiol to OVX rats recovered the tibial BMD decrease by 100%, while Fujiflavone P40 recovered it by 78%. The results suggest that Fujiflavone P40 may be useful as a preventive agent for osteoporosis.

Attachment of human periodontal ligament fibroblasts to 3 different root-end filling materials: Scanning electron microscope observation

OBJECTIVE

The attachment behavior of the human periodontal ligament (PDL) fibroblasts to root-end filling materials (amalgam and Super-EBA) was compared in vitro to gutta-percha by means of scanning electron microscope.

STUDY DESIGN

Amalgam and Super-EBA were placed in a prepared cavity of root slices of freshly extracted human teeth and evaluated freshly prepared. Root slices of teeth with cold-burnished gutta-percha filling with AH26 sealer were used for comparison. The root slices were placed in tissue culture cluster, and 1 mL of cell suspension was added carefully over the root slice. They were incubated at 37 degrees C and 100% humidity for 4, 24, and 72 hours.

RESULTS

Results showed that the cold-burnished gutta-percha provides a better substrate than amalgam and Super-EBA for cell growth and attachment. Amalgam was the most toxic material, showing early manifestation of cell injury.

CONCLUSION

It was concluded that the composition and surface texture of the substrate have an influence on the morphology and the attachment of the PDL fibroblasts. It is suggested that cell attachment and morphology might reflect the biocompatibility of the substratum.

[Epithelial cell rests of Malassez: tissue, cell, and molecular biology]

This review presents an analysis of the current data on the structural and functional organization and biological significance of epithelial cell rests of Malassez (ERM), which are formed by persisting fragments of epithelial (Hertwig) sheath that participates in the tooth root development. ERM, found within the periodontal ligament, undergo intensive age-related involution and are traditionally described as small clusters of functionally inactive cells. Meanwhile, recent findings are indicative of high functional activity of ERM which are both producers of and targets for various cytokines, growth factors, adhesive substances, their receptors and other biologically active molecules. It is suggested that ERM participate in sustaining the optimal conditions for the normal functioning and regeneration of periodontium structural components. When periodontal tissue homeostasis is disturbed, ERM may grow up and acquire the capacity to destroy the surrounding tissues.

Ciliated fibroblasts in mouse connective tissues: a comparison between methods for estimating their frequency

The frequency of ciliated fibroblasts in skin, gingiva, molar and incisor periodontal ligaments and incisor enamel-related periodontium of the mouse was estimated by straight counting or by methods based on the probability of observing a basal body in relation to other cell structures. Transmission electron microscopy of ultra-thin sections mounted in single slot grids was used. The results obtained with these methods differed, but indicated that periodontal ligament fibroblasts from molars or incisors generally had a higher ciliation index than the fibroblasts from skin and gingiva. These differences may not be real since the detection of cilia and/or centriolar structures seems to depend very much upon the plane of sectioning relative to the long axis of the fibroblasts, a situation which favours the more regularly arranged periodontal fibroblasts. This arrangement makes the periodontal tissues, particularly those of rodent incisors, a valuable model for studying ciliation in vivo because of the prompt response to experimental manipulation.

Polarized light microscopic analyses of collagen fibers in the rat incisor periodontal ligament in relation to areas, regions, and ages

We prepared decalcified sagittal sections (20 microm thick) from the incisal, middle, and basal regions of the mandibular incisor of male Wistar rats aged 2, 6, 12, and 24 months, and examined the sections using polarized light microscopy. Most of the birefringent fibers appeared to run obliquely across the periodontal ligament. Birefringent fibers running parallel to the long axis of the incisor were also found in the intermediate area of the ligament. Similar fiber architecture was observed in all four age groups. Quantitative analysis showed that the retardation values of collagen were higher in the bone- and tooth-related areas and lower in the intermediate area of the ligament. The values for the bone- and tooth-related areas increased from the basal toward the incisal regions in all four age groups. Age-related changes in the retardation values were found only in the incisal region of the incisor. In the incisal region, the values for the bone- and tooth-related areas increased markedly from 2-24 months of age, whereas those for the intermediate area increased slightly but significantly with age. Our findings indicate that the degrees of molecular organization and alignment of collagen fibers in the bone- and tooth-related areas of the ligament are higher than those in the intermediate area and increase near the incisal region and with age. It is also suggested that the collagen fibers in the intermediate area remain immature along the long axis of the incisor throughout the life span of the animal.

Caiman periodontium as an intermediate between basal vertebrate ankylosis-type attachment and mammalian "true" periodontium

The teeth of many fish, amphibia, and reptiles are attached to the alveolar bone via ankylosis. In contrast, mammalian periodontia are characterized by a gomphosis, an attachment of the tooth root in the alveolar bone socket via periodontal ligament fibers. Among the reptiles, the crocodilians are the only group featuring a gomphosis-type connection between tooth root and alveolar bone, while in other reptiles tooth-root and jawbone are connected via ankylosis. The purpose of the present study was to compare several key features of the crocodilian periodontium with those of the mammalian and noncrocodilian reptile periodontium. As experimental models for our study we chose the periodontium of newborn geckos (Hemidacylus turcicus), juvenile caimans (Caiman crocodilus crocodilus), and 10-day-postnatal Swiss-Webster mice (Mus musculus) as representative models for noncrocodilian reptiles, crocodilian reptiles, and mammals. The caiman periodontium emerged as an intermediary between the mineral-free mouse ligament and the mineralized gecko ankylosis-type attachment. Caiman ligament fibers were less organized than mouse ligament fibers but featured distinct fasciae surrounding ligament fiber bundles. Caiman Hertwig's epithelial root sheath (HERS) was similarly perforated as mouse HERS and distinctly different from the continuous gecko HERS. Both caiman and mouse HERS covered the entire tooth root length, while in the gecko HERS was limited to the coronal portion of the root, allowing for cementoid-mediated ankylosis at the apical tip of the root. We interpret our data to indicate distinct differences in mineral distribution, periodontal ligament fiber organization, and HERS distribution between noncrocodilian reptiles, crocodilian reptiles, and mammals. Mineral deposits in the caiman ligament may reflect an evolutionary position of the caiman periodontium between ankylosis and gomphosis.

Participation of bacterial biofilms in refractory and chronic periapical periodontitis

The aim of this study was to examine morphologically the participation of extraradicular biofilm in refractory periapical periodontitis. Six teeth and five extruded root filling gutta-percha points associated with refractory periapical periodontitis were investigated by scanning electron microscope. In nine of 11 samples examined, bacterial biofilms were seen at the extraradicular area. The gutta-percha surface was covered with glycocalyx-like structures, and filaments, long rods, and spirochete-shaped bacteria were predominant in the extraradicular sites. Planktonic cells, which were filaments and spirochete-shaped bacteria, emigrated from the glycocalyx structures in some spots. In the extracted teeth, biofilm consisting of both bacteria and glycocalyx-like structures were observed on the periapical root surfaces. Next to the residual periodontal ligament, a few filaments, rods, and fusiforms were attached on the healthy cementum surface. The present findings suggested that bacterial biofilms formed in the extraradicular areas were related to refractory periapical periodontitis.

Development of oxytalan fibers in the rat molar periodontal ligament

Although oxytalan fibers are known to be a ubiquitous component of the periodontal ligament, little information has been available concerning their organization in the developing periodontal ligament. In the present study, growth and distribution of oxytalan fibers were examined in the developing periodontal ligament of rat molars aged 11, 14, 19, 21 and 28 days. A quantitative analysis of the fibers was made and the spatial relationship between the fibers and blood vessels was studied by means of a three-dimensional reconstruction of serial sections. At the beginning of root formation, oxytalan fibers appeared at first as dot-like structures around the root sheath as well as in areas very close to blood vessels. These structures were resolved in the electron microscope to be made up of 12-nm-wide microfibrils in the vicinity of the surface of the cells of the root sheath. In the process of development, these dot-like structures elongated into entities with helical appearances. As the development further proceeded, longer oxytalan fibers were produced in the apico-occlusal direction along with blood vessels. Quantitative analysis showed that an increase in oxytalan fibers coincided with an increase in the density of the vascular network in the developing periodontal ligament. Based on the results of the present study, the role of oxytalan fibers in the developing periodontal ligament may be in the maintenance of the integrity of the vascular system as previously suggested.

A unique localization of mechanoreceptors in the periodontal tissue of guinea pig teeth

This study describes the unique distribution of Ruffini endings (RE) in the periodontal tissues of the guinea pig teeth with special references to their presence in the enamel-related aspects of the continuously growing incisors and molars. In guinea pig incisors, immunohistochemistry for PGP 9.5 and glia specific S-100 protein revealed a condensed distribution of well-developed RE in the bone-related part of the lingual periodontal ligament as has been reported in many other rodents. In most cases, some RE-like nerve elements characterized by dendritic ramification and rounded terminal Schwann cells were found to be located in the labial, enamel-related regions, where no periodontal ligament-like fiber arrangement was established. In the molar periodontal ligament, well-developed RE-like nerve elements were also distributed in the enamel-related part, but in intimate relation to thick periodontal fiber bundles inserted in the cementum pearls grown on the enamel surface. In some cases, few RE were located in the apical region of the alveolar socket, where no periodontal fiber bundles could be identified. Our data provide the first morphological evidence of the presence of RE-like nerve elements in the enamel-related, fibrous connective tissue of continuously erupting rodent incisors. These data indicate that RE in guinea pig periodontal tissues have variable spatial correlation to the surrounding fibers, implicating their diverse mechanoreceptive properties depending on the anatomical location.

Scanning electron microscopic observation of microvasculature in periodontium

In this study, vascular resin cast models in the periodontium of beagle dogs were prepared and three-dimensional observation of the relationship between the gingiva and periodontal ligament (PDL) vascular network was performed. After the perfusion of Ringer's solution and fixative, synthetic resin was injected from the inferior alveolar arteries. Soft tissue was digested by proteinase solution and specimens were examined under scanning electron microscope (SEM). The gingival vascular network (GVN) in the region facing the teeth consisted of sulcular and junctional epithelium. The vascular network of the sulcular epithelium (SE) had a renal glomerulus-like form and the junctional epithelium (JE) consisted of squamous mesh. The gingival sulcular fluid exudated from the vascular network directly beneath the JE, and leukocytes permeated from the vascular network beneath the epithelium. Thus, we considered that the GVN performs an important function in the protection against the inflammation. Periodontal ligament had a polygonal mesh vascular network that was anastomosed to the venous plexus of alveolar bone through Volkmann's canals (VC). When occlusal force was applied, the blood in the periodontal vessels flowed out through VC into the bone marrow, and when the force was removed, it flowed backward into the PDL. This blood transfer acted as an absorber against occlusal force. Our findings suggest that the blood vessels of the gingiva perform an important function in defending against inflammation, while the blood vessels of the PDL play a key role in absorbing occlusal force.

[The ultrastructure changes of nerve fibers in pressure side of periodontal ligament during orthodontic tooth movement in rats]

OBJECTIVE

To observe the ultrastructure changes of nerve fibers in pressure side of periodontal ligament during orthodontic tooth movement (OTM) in rats.

METHODS

The left maxillary of fifteen rats molar was moved mesially by an appliance for 2 days, 1 week, 2 weeks and 3 weeks. The ultrastructure changes of nerve fibers in pressure side of the periodontal ligament in rats were observed with electron microscope.

RESULTS

The thick myelinated axon was degenerated after 2 days of OTM and not recovered after 3 weeks of OTM; the number of thin unmyelinated axons was increased after 2 days of OTM. It reached a maximum after 1 week of OTM and recovered after 3 weeks of OTM. Only part of thin unmyelinated was slightly degenerated. At the same time, some of the thin myelinated axons were slightly degenerated and partly demyelinated.

CONCLUSION

The nerve fibers were involved in periodontal tissue remodelling.

Ultrastructure of cementum and periodontal ligament after continuous intrusion in humans: a transmission electron microscopy study

An ultrastructural study of the cementum and periodontal ligament (PDL) changes after continuous intrusion with two different and controlled forces in humans was carried out. Twelve first upper premolars, at stage 10 of Nolla, orthodontically indicated for extraction from six patients (mean age 15.3) were used. They were divided into three experimental groups, distributed intra-individually as follows: control (not moved), continuously intruded for 4 weeks with 50 or 100 cN force, utilizing a precise biomechanical model with nickel titanium super-elastic wires (NiTi-SE), which were developed and calibrated individually. The teeth were extracted, fixed, decalcified, and conventionally processed for examination in a Jeol 100 CX II transmission electron microscope. Evident signs of degeneration of cell structures, vascular components, and extracellular matrix (EM) of cementum and PDL were observed in all the intruded teeth, with more severe changes towards an apical direction and in proportion to the magnitude of force applied. Resorptive areas and an irregular root surface of the intruded teeth were noticed, according to the same pattern described above. Concomitant, areas of repair were also revealed in the cementum and PDL although the magnitude of forces remained the same throughout the experimental period. Thus, a reduction of continuous force magnitude should be considered to preserve the integrity of tissues.

Transplantation of labeled periodontal ligament cells promotes regeneration of alveolar bone

Regeneration of damaged periodontal tissues is mediated by periodontal cells, but a major sub-population comprises highly differentiated cells that do not renew. To overcome the loss of specialized cell types caused by disease, various therapeutic approaches including cell transplants have been developed to promote cell re-population in periodontal tissues. As previous transplantation studies used unlabeled cells, that are indistinguishable from host cells, it has been difficult to assess the contributions of transplanted cells to the healing processes. To track the fate and differentiation of rat periodontal cells transplanted into periodontal wounds, we used collagen-coated fluorescent beads as a permanent endocytosed marker, or cells constitutively expressing beta-galactosidase. We assessed osteogenic cell differentiation with immunohistochemical staining for osteopontin and bone sialoprotein. Cells were transplanted into periodontal wounds created in Sprague--Dawley male rats that are null for beta-galactosidase. Defects were allowed to heal spontaneously (controls), or were closed with collagen implants mixed with beta-galactosidase-positive (Lac-Z) periodontal cells, or closed with collagen implants mixed with periodontal cells loaded with fluorescent beads. Animals were killed at 1 and 2 weeks after surgery and tissues were prepared for morphometric assessment and immunostaining for osteopontin (OPN) and bone sialoprotein (BSP). Transplanted cells were easily distinguished by fluorescent beads or by beta-galactosidase-positive expression and were distributed throughout the regenerating periodontal ligament (PL) and alveolar bone. At 1 week after wounding, animals treated with beta-galactosidase-positive cells exhibited a slightly higher percentage of labeled cells in the PL compared with the fluorescent bead-labeled cell implant group (2% vs. 1% respectively; P > 0.2). At Week 2 percentages of labeled cells were slightly increased in the regenerating PL (approximately 3% for both groups, P > 0.2). In regenerating alveolar bone at 1 week, animals that were treated with beta-galactosidase-positive cells and fluorescent bead-loaded cells exhibited approximately 30% and 25% of labeled cells respectively. At 2 weeks after wounding there was an increase in the percentage of transplanted beta-galactosidase-positive cells (approximately 39% at week 2; P < 0.05), but not of transplanted cells with fluorescent beads (approximately 25% at week 2). In sites with transplanted cells there were higher percentages of OPN positive and BSP positive cells in nascent bone and more newly formed bone than in controls (>40%; P < 0.05). Transplantation of beta-galactosidase-positive cells or cells loaded with fluorescent beads is a useful method for assessing the fate and differentiation of periodontal cells in vivo. Fluorescent beads, however, are diluted at mitosis and this method underestimates the percentage of transplanted cells. As transplanted periodontal cells in both groups promoted regeneration of alveolar bone, cell transplantation could improve the restoration of periodontium destroyed by periodontitis.

Pathology of the desmoplastic ameloblastoma

Desmoplastic ameloblastoma is a rare variant of ameloblastoma and only 54 cases have been previously reported in the English literature. We report ten cases of desmoplastic ameloblastoma of the jaw observed between 1972 and 1998 and discuss the pathogenesis of the tumor. Eight of the ten tumors were located in the anterior region of the jaw. Radiographically, six cases showed mixed radiolucent/radiopaque appearance with ill-defined margins and the other four cases lacked typical findings of ameloblastomas. The tumors were located mainly in the alveolar region and occupied the tooth-bearing area, without tooth resorption or impacted teeth. Histologically, the desmoplastic ameloblastomas were characterized by extensive stromal desmoplasia, and small tumor nests of odontogenic epithelium were scattered in the stroma. Oxytalan fibers stained by potassium monopersulfate-aldehyde fuchsin were demonstrated in the stroma of all desmoplastic ameloblastomas. From these findings, we presumed that the desmoplastic ameloblastomas might have developed in the periodontal membrane.

A role for decorin in the structural organization of periodontal ligament

Decorin is a small leucine-rich proteoglycan that interacts with several matrix molecules, including various types of collagen and growth factors, and suppresses the growth of neoplastic cells by an epidermal growth factor (EGF) receptor-mediated pathway. Decorin is abundantly expressed in the periodontal connective tissues during development and tissue maintenance. In periodontal disease, which is one of the most common diseases in the human kind, the level of decorin is decreased in the periodontal connective tissue. Abnormal expression of decorin may also associate with certain inherited disorders that involve increased susceptibility to severe periodontal disease in the early childhood. Therefore, we investigated the periodontal tissues of mice with targeted disruption of the decorin gene. Gross and microscopic analyses showed that decorin-deficient mice appeared to have normal tooth development and eruption, and there were no signs of periodontal disease. However, electron microscopic analysis revealed abnormal morphology and organization of the collagen fibrils in the periodontal ligament. The number of periodontal ligament fibroblasts in the decorin-deficient mice was also increased about two-fold as compared with the wild-type mice. In cell culture, ectopic overexpression of decorin in NIH 3T3 fibroblasts or decorin added exogenously to periodontal fibroblasts suppressed cell growth. However, blocking the EGF receptor tyrosine kinase activity did not prevent the decorin-elicited growth suppression in periodontal fibroblasts. Additionally, decorin did not induce a marked increase in the relative expression of p21 mRNA in periodontal fibroblasts. Therefore, decorin appeared to regulate growth of normal periodontal fibroblasts by a mechanism distinct from that reported for neoplastic cells. The findings demonstrate that decorin plays a role in the organization of collagen fibrils and regulates cell proliferation in the periodontal ligament.

Alterations in the periodontium after ovariectomy in rats: the effects of a Japanese herbal medicine, Chujo-to

Ovariectomy-induced changes on the periodontium (gingiva, alveolar bone, and periodontal ligament) in rats and the preventive effects of a Japanese herbal medicine, Chujo-to, were studied for a period of 49 days. The rats were divided into five groups: sham-operated (sham), ovariectomized (OVX), OVX given Chujo-to, OVX given 17beta-oestradiol, and OVX given the vehicle for 17beta-oestradiol, respectively. After the test period, the bone mineral content (BMC) of the mandibular condyle in OVX rats was similar to those in both sham rats and the OVX rats treated with either Chujo-to or 17beta-oestradiol. However, the scanning electron microscopic (SEM) analyses revealed that the periodontal ligament of the OVX rats and the OVX rats treated with Chujo-to became more coarse than that of the sham rats or the rats treated with 17beta-oestradiol. The surface of the alveolar bone in the OVX rats appeared to contain numerous small granules, which were not present in the sham rats and the rats treated with either Chujo-to or 17beta-oestradiol. These results suggest that ovariectomy caused alterations in the peridontium, but Chujo-to had a preventive effect on the surface architecture of the alveolar bones.

Time-related changes in periodontal mechanoreceptors in rat molars after the loss of occlusal stimuli

The effect of a loss of occlusal stimuli upon the distribution and structure of the periodontal mechanoreceptors of the rat mandibular molar was examined after extracting opposing molars. The hypofunctional periodontal ligament narrowed significantly two weeks after tooth extraction, associated with an altered morphology of the Ruffini endings that showed typical dendritic profiles in normal controls. At four weeks and later periods after extraction, the Ruffini endings-including those without light microscopic changes demonstrated unusual ultrastructural features such as the eccentric localization of mitochondria along the axonal membrane and loss of other cell organelles, unusual elongation of axonal microprojections, or a deep invagination of the Schwann sheath into the axoplasm. Immunoreactivity for the growth-associated protein-43 (GAP-43) in the Ruffini endings was restricted to the Schwann element in both the normal and hypofunctional periodontal ligament, but the reaction was weaker and even negligible in some cases in the latter ligament. The present results suggest that occlusal stimuli are essential for maintaining the structural integrity of the periodontal ligament, including that of periodontal mechanoreceptors. A decreased immunoreactivity for GAP-43 in the Schwann sheaths supports the notion of a possible functional alteration in the Ruffini endings that showed no structural abnormality.

Developmental changes of the vasculature in the periodontal ligament of rat molars: a scanning electron microscopic study of microcorrosion casts

Vascularization of the periodontal ligament was examined in developing upper first molars of rats from 5 to 30 d after birth with light and scanning electron microscopy. Formation of the vascular network in the periodontal ligament (PDL) started with the beginning of root formation. The PDL vessels derived from the basal region of the tooth germ ran parallel to the long axis of the root and connected with the vascular network of the enamel organ at the cervical end. The boundary of these 2 networks was initially indistinct but became clearer with the progress of root formation. The PDL vessels further elongated longitudinally and connected with each other by lateral branches to form a coarse mesh. Other vessels derived from the alveolar bone via Volkman's canals also contributed to the vascular construction of the PDL. The vessels from the alveolar bone provided branches to the existing mesh of the PDL. Consequently, the vascular network of the PDL consisted of vessels from 2 sources: 1 derived from the basal region of the tooth germ, and the other from the alveolar bone. The density of the vascular network reduced with the progress of root formation, especially at the middle part of the root, but the mesh at the apical region maintained a basket-like structure.

Neurocalcin-immunoreactive primary sensory neurons in the trigeminal ganglion provide myelinated innervation to the tooth pulp and periodontal ligament

The distribution of neurocalcin-immunoreactive (NC-ir) primary sensory neurons was examined in the trigeminal ganglion (TG), mesencephalic trigeminal tract nucleus (Mes5) and intraoral structures. NC-ir primary sensory neurons were located in the TG but not the Mes5. The coexpression study demonstrated that virtually all NC-ir TG neurons exhibited S100-immunoreactivity (-ir). In the tooth pulp, NC-ir nerve fibers were observed in the subodontoblastic and odontoblastic layers. Immunoelectron microscopic and retrograde tracing methods revealed that myelinated pulpal axons derived from the TG mostly exhibited the ir. In the periodontal ligament, bush-like endings showed NC-ir. These endings were morphologically identical to Ruffini-like endings. The present study suggests that NC-ir trigeminal primary sensory neurons have their cell bodies in the TG. Their peripheral axons are probably myelinated. Such neurons include pulpal nociceptors and low-threshold mechanoreceptors.

A histological and electron-microscopic study of the architecture and ultrastructure of human periodontal tissues

The structure of periodontal tissues is still far less understood than their clinical relevance would demand. Here the periodontal ligament and radicular cementum in healthy human teeth were studied by light microscopy, transmission and scanning electron microscopy. These observations showed that the extracellular matrix of periodontal ligament is composed of a loose plexus of wavy collagen fibrils immersed in a highly hydrated interfibrillar matrix. Only close to their cemental insertion do these fibrils gather in thick, parallel fascicles (Sharpey's fibres). As these cross the mineralization front, they become infiltrated by the mineral phase and continue directly with the cementum matrix. Sharpey's fibres, "extrinsic" and "intrinsic" fibres all appear to be the same fibres, which bend and branch repeatedly during their course within the thickness of the cementum. Because of its physical continuity with the cementum, a limited portion of the periodontal ligament approximately corresponding to the length of Sharpey's fibres remains unaffected by enzymatic digestion of the interfibrillar matrix while the rest of the ligament is completely dissolved. The findings here indicate that the periodontal ligament and dental cementum join by a continuity rather than a contiguity of structures; that the collagen-mineral relation in cementum has distinctive features in comparison to other hard tissues; that extrinsic and intrinsic fibres of cementum and the adjoining portion of periodontal ligament form a structural, mechanical and metabolic unit distinct from the central, more metabolically active portion of the periodontal ligament.

The effects of attachment factors on initial attachment of human periodontal ligament fibroblasts on different root surfaces: a light and scanning electron microscopic study

This study was aimed to test the effect of fibronectin (FN), vitronectin (VN) and a fibronectin analog (fibronectin-like engineered protein) on the attachment of periodontal ligament cells to mechanically-treated and mechanically non-treated periodontally involved and non-diseased root surfaces in vitro. Periodontal ligament fibroblasts were incubated with a total of 44 periodontally diseased and non-diseased root slices which had been treated in the following manner: 1) FN applied to mechanically-treated and non-treated root slices, 2) VN applied to mechanically-treated and non-treated root slices, 3) FN-like engineered protein applied to mechanically-treated and non-treated root slices, and 4) mechanically-treated and non-treated root slices. After the 1 hour incubation period in a humidified atmosphere of 95% air and 5% CO2 at 37 degrees C, the adherence of the fibroblasts was determined using light microscopy with an ocular grid system and orientation was evaluated by scanning electron microscopy. The results indicated that the number of attached cells to non-diseased cementum sites was significantly greater than the number of attached cells to diseased cementum sites for all of the groups (p < 0.05). Likewise, the number of attached cells to mechanically-treated diseased cementum sites was significantly greater than the number of attached cells to mechanically-non-treated diseased cementum sites (p < 0.05). Our findings suggest that these attachment factors cannot promote cell attachment to different cementum sites.

Re-innervation in the canine periodontal ligament of replanted teeth using an antibody to protein gene product 9.5: an immunohistochemical study

The re-innervation process in the periodontal ligament of replanted canine teeth was examined by immunohistochemistry for protein gene product 9.5 (PGP 9.5), a general marker for neurons, and by electron microscopy. Within 1 week of replantation, the periodontal fibers had regenerated, filling the narrow spaces between the alveolar bone and the root surface around the cervical and apical regions. Near the root apex, however, no PGP 9.5-immunopositive nerve fibers were found in the regenerated periodontal ligament except for those in the alveolar half of the ligament. At 2 weeks after replantation, many nerve fibers positive for PGP 9.5 had ascended the periodontal ligament from the thick nerve bundles located near the root apex. Fine nerve endings showing complicated ramification were also present in the apical region. By 3 or 4 weeks after replantation, the vascular network was regenerated and principal periodontal fibers were re-established throughout the entire length of the periodontal ligament. The extensively ramified PGP 9.5-immunopositive structures had increased in thickness and density and showed characteristic tree-like profiles by 3 weeks. Electron microscopy confirmed that most of these structures were Ruffini-like endings, and demonstrated that such nerve terminals were almost regenerated by 4 weeks post-replantation. These results indicated that, in the periodontal ligament of replanted canine teeth, the regeneration of the nerve fibers including mechanosensory receptors first showed signs of regeneration by 2 weeks following tooth replantation and proceeded rapidly thereafter. Regeneration of the periodontal ligament including fiber architecture as well as vascular and neural elements was almost complete by 4 weeks after replantation.