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.