Inhibition of epithelial cell matrix metalloproteinases by tetracyclines

The effects of tetracyclines on periodontal epithelial cells were investigated by culturing cells from porcine rests of Malassez in the presence of oxytetracycline, doxycycline or one of two analogues of tetracycline bearing no antimicrobial activity. Matrix metalloproteinase activity produced by the epithelial cells was assayed by quantitation of radioactive gelatin degradation and by gelatin enzymography. The results show that all tested tetracyclines exerted a direct dose-dependent inhibitory effect on epithelial cell gelatinases. Furthermore, epithelial cells cultured with doxycycline, oxytetracycline and de-dimethylaminotetracycline in concentrations ranging from 1 to 50 micrograms/ml showed a marked reduction in secreted gelatinase activity when grown in alpha minimum essential medium in the absence of fetal calf serum. Viability of cells following this treatment, measured as lactate dehydrogenase activity released to the cell media, was not affected by the presence of any of these drugs at the concentrations used. Scanning electron microscopy revealed striking morphologic changes of the cells following treatment with tetracyclines in the absence of serum which include rounding, decreased intracellular contacts and increased intercellular spaces. No such effects were seen in cells cultured in the presence of serum. These results provide evidence that periodontal epithelial cells produce matrix metalloproteinases whose activities are inhibited by tetracyclines and their non-antimicrobial analogues at concentrations present in gingival crevicular fluid following tetracycline therapy. When used as adjuncts in periodontal therapy, tetracyclines may therefore inhibit epithelial cell mediated degradation of basement membrane and subepithelial connective tissue.

Cultural and morphological characteristics of human periodontal ligament cells in vitro

Primary cell lines from explants of human periodontal ligament were established in vitro to assess their suitability as test cells in a biocompatibility assay. They were maintained over nine passages. The constituent fibroblast-like cells (F-cells) were monitored throughout by light and electron microscopy. Although F-cells from several different donors displayed stable and consistent growth characteristics, after the ninth subculture changes in the fine structure suggested that some cells were undergoing differentiation or senescence. It is therefore recommended that cells from earlier passages be used in in vitro biocompatibility assays.

Periodontal repair or regeneration: structures of different types of new attachment

The present study details the structural and ultrastructural features of healing events between the regenerated periodontal ligament and the root surface after experimental periodontal disease. Experiments were performed on dogs, and the concept of guided tissue regeneration was tested using resorbable polyurethane membranes. Light microscopy, scanning- and transmission electron microscopy were employed to determine if healing events involve regeneration (ie, process by which the architecture and the function are completely renewed) or periodontal repair (ie, healing of a wound by tissue that does not fully restore the architecture of a part). Regeneration occurred in parts of the roots only if some original cementum remained on the root surface after root planing. Repair was observed if peripheral dentin was removed by root planing as this layer was not reestablished. In areas remote from the base of the defect, new collagen fibrils, synthesized by fibroblasts and oriented perpendicular to the root surface, were spliced with severed ends of Sharpey's fiber bundles of original cementum. If circumpulpal dentin was exposed, intermingling between new fibrils with dentinal matrix fibrils occurred. In areas near the base of the defect, the first event was the formation of a cementoid by a cementoblast monolayer and subsequent formation of intrinsic fibrils oriented parallel to the root surface. Afterwards, the cementoblast monolayer disintegrated and extrinsic fiber bundles became anchored in the new cellular mixed fiber cementum. In these areas, linkage between new cementum and pre-existing tissues always occurred by interfacial intermingling of the fibrils, regardless of whether new attachment occurred at circumpulpal dentin or original cementum.

Light and electron microscopic observations on rat molar periodontal ligament after intraperitoneal injection of vinblastine

The effect of intraperitoneal injection of Vinblastine sulfate on rat periodontal ligament was studied. Cells still synthetize collagen after 2 hours of the injection with evidence of loss of extracellular collagen fibers orientation. Tubular lysosome could not be detected after 2 hours with formation of lysosomal clusters in the cell center. After 4 hours of administration, evidences of cell degeneration were observed. The present study has shown that Vinblastine produces effect on fibroblasts as early as two hours after injection.

An immunohistochemical study examining the role of collagen type VI in the rodent periodontal ligament

The distribution of collagen types I and VI has been examined in the periodontal ligaments of rat incisor and molar teeth using cryosections and immunohistochemical staining procedures. The stain for collagen type I was uniform in all the ligaments examined. Uniform staining for collagen type VI was evident only in the ligament of the fully erupted molars, and the stain was absent from the mid-zone of the ligaments of the erupting molars and incisors. The staining pattern of the collagen type VI antibodies is consistent with previous reports which have suggested that the removal of collagen type VI precedes the degradation of major banded collagen fibrils in remodelling connective tissues. The removal of collagen type VI from the mid-zone of the incisor ligament may precede the remodelling events which facilitate tooth eruption.

Ultrastructure and histochemistry of the dental cuticle in adult periodontitis

This study examined the dental cuticle (DC) at the interface with cementum surface, as well as its relationship to the overlying subgingival plaque (SP), the so-called plaque-free zone (PFZ), the junctional epithelium (JE), and the coronal fibers of the residual periodontal ligament (PL) by transmission electron microscopy (TEM) and histochemistry. Material comprised of 41 extracted, adult periodontitis-affected teeth (AP). Following extraction, 20 teeth were fixed in 3% glutaraldehyde in 0.1M sodium cacodylate, post-fixed in 1% osmium tetroxide, embedded in araldite, decalcified in EDTA, re-embedded in araldite, and sectioned. En bloc histochemistry was undertaken on the remaining 21 teeth, using ruthenium red, alcian blue-lanthanum nitrate, or safranin-O, and processed as above. Results show that the DC covered the cementum surface from the SP to the JE, and formed an interface with these structures. No DC was observed at the interface with PL. Morphological variations in DC surface were observed at the interface with the SP and at the so-called PFZ where bacteria were always in close contact with or surrounded by the DC. At the interface with JE, the DC appeared homogeneous, although layers varying in electron density were distinguishable. Teeth treated histochemically revealed a positive reaction of DC and bacteria to the three methods, suggesting the presence of anionic polymers including glycoproteins in the DC. It was concluded that on adult periodontitis affected teeth, the DC always covers exposed cementum and may mediate bacterial adhesion, and adsorb components from the periodontal pocket.

Periodontal neural endings intimately relate to epithelial rests of Malassez in humans. A light and electron microscope study

The periodontal ligament was examined by light microscopy at 3 different levels (apical, intermediate, coronal) on the 4 root sides of 43 extracted teeth. Epithelial rests were localised and serial LM and EM sections showed a close apposition (up to 0.03 microns) between Ruffini-like and free nerve endings and the basal lamina of the epithelial cell rests. The neural structures were facing the epithelial cells, whereas the Schwann cells were oriented towards the outer connective tissue. The Ruffini-like corpuscles contained numerous mitochondria. Free nerve endings contained neurotubules, neurofilaments and some vesicles. The intimate association between both neuroectodermal structures could indicate a target function of epithelial cell rests during developmental periodontal ligament innervation. Recent immunohistological findings involving nerve growth factor receptors substantiate this hypothesis.

Cytochrome oxidase activity as a marker for periodontal sensory receptors in the rat

Cytochrome oxidase activity was explored histochemically in axon terminals of periodontal Ruffini endings of rat upper incisors at both the light- and electron-microscopic levels. Staining clearly demonstrated ramified structures in the alveolar half of the periodontal ligament. These structures resembled the profiles of the axon terminals of the periodontal Ruffini ending previously demonstrated by an immunohistochemical method for neurofilament protein. Histochemically at the electron-microscopic level, the ramified structures were identified as true Ruffini endings in which each axon terminal was filled with reactive mitochondria. Two types of mitochondria were distinguished with respect to the localization pattern of reaction products; almost all mitochondria were positive for cytochrome oxidase activity, with only a few negative. As the enzyme activity did not decrease after demineralization, the findings suggest that cytochrome oxidase is a useful marker enzyme for demonstrating sensory receptors in the periodontal ligament. Histochemical methods for cytochrome oxidase may contribute to the light- and electron-microscopic morphological analysis of periodontal sensory receptors.

Epithelial cell-fibroblast interactions: modulation of extracellular matrix proteins in cultured oral cells

A model system involving co-cultures of human gingival or periodontal ligament fibroblasts with mouse epithelial root sheath cells or human gingival epithelial cells was used to study epithelial cell-fibroblast interactions. Double-labeled immunofluorescence and microfluorometry were used to investigate the expression of extracellular matrix molecules of collagen type I (collagen I), type III (collagen III) and fibronectin in fibroblasts. When fibroblasts from either source were cultured alone, the fluorescence for collagen I and fibronectin ranged from strongly positive to almost negative. Collagen III staining was relatively weak compared with that of collagen I. After 2-3 days of co-culture, gingival fibroblasts and ligament fibroblasts adjacent to the mouse sheath cells exhibited enhanced intracellular fluorescence for collagen I and fibronectin. Very little change was observed for collagen III. Gingival fibroblasts cultured with gingival epithelial cells showed increased fluorescence for collagen I but decreased fluorescence for fibronectin. In contrast, the fluorescence intensity for both collagen I and fibronectin in ligament fibroblasts were reduced after 3 days of co-culture with gingival epithelial cells. Ultrastructural changes in fibroblasts co-cultured with mouse root sheath cells included increased Golgi cisternae and vesicles and an increased abundance of rough endoplasmic reticulum, polyribosomes, secretory vesicles and pinocytotic vesicles. Thus, the expression of extracellular matrix proteins and the metabolic activity of fibroblasts can be modulated by oral epithelial cells.

Distribution of undulin, tenascin, and fibronectin in the human periodontal ligament and cementum: comparative immunoelectron microscopy with ultra-thin cryosections

We studied the ultrastructural localization of three distantly related glycoproteins of the extracellular matrix, undulin, tenascin and fibronectin, in decalcified sections of human periodontal ligament (PL) and cementum. Undulin was associated with tightly packed major collagen fibrils and not with microfibrils, indicating that this protein may be involved in the supramolecular and functional organization of collagen fibrils into flexible bundles. Tenascin was found on globular masses between less densely packed collagen fibrils, thus displaying a pattern quite distinct from that of undulin. Fibronectin was noted in bulky material between the cross-striated fibrils, often surrounding individual fibrils like garlands, and in the microfibrillar meshwork extending from cross-striated fibrils. The three glycoproteins displayed a distinct and unique pattern of distribution in PL that can be correlated with their molecular structure and potential functions.

A T.E.M. stereological analysis of blood vessels and nerves in marmoset periodontal ligament following endodontics and magnetic incisor extrusion

Maxillary incisor fracture is a common dental injury. It is frequently treated by endodontic therapy, orthodontic extrusion, and a retention period. The aim of the study was to mimic this regime and stereologically quantify the vascular and neural reconstitution of the periodontal ligament (PDL). Ten marmosets (Callithrix jacchus) had the right maxillary incisor crown removed, root canal treatment, and magnetic incisor root extrusion of 1.2 mm. After incisor retention for 9 weeks, the animals were perfusion fixed for electron microscopy. The incisor PDL was sectioned at 250 micron intervals from the cervical to apical region and recorded for stereological evaluation. Further evaluations were conducted with a two-way analysis of covariance using program 3V of the BMDP-81 statistical software package. The total luminal PDL vascular volume was statistically unchanged. An increased occurred in the mean number of venous capillaries from 0.07 +/- 0.3 to 0.17 +/- 0.3 per 560 microns 2 of PDL (P < 0.05). Vessel wall and luminal volume of post-capillary-sized venules decreased from 1.64 to 1.03 per cent, and 5.32 to 3.04 per cent (P < 0.05), respectively. Mean luminal and abluminal diameters for post-capillary-sized venules were reduced (P < 0.05). Myelinated and unmyelinated axons showed no significant change in volume (Vv), length (Lv), or surface (Sv) densities. Axon number/unit, PDL area, and mean diameters demonstrated no statistical differences. Since the PDL demonstrated almost complete morphological re-establishment of the microvascular and axon systems, it is considered that this clinical treatment is a justifiable rationale.

Multinucleated fibroblastic cells in the periodontal ligaments of aged rats

Using 12- to 18-month-old rats, we examined the ultrastructural and cytochemical features of multinucleated fibroblastic cells (MFCs) in the periodontal ligament (PDL) of molars. In aged rats, the MFCs were distributed randomly in the PDL and exhibited cytoplasmic structural variations which were not dependent on the number of nuclei. There was a tendency for the MFCs to cluster in the PDL. The MFCs, rich in cytoplasmic organelles involved with procollagen synthesis such as rough endoplasmic reticulum and the Golgi apparatus, incorporated and secreted 3H-proline-labelled products. The MFCs also possessed many phagosomes containing intact collagen fibrils. These MFCs were apparently involved in phagocytosis and intracellular degradation of incorporated collagen fibrils. Phagosome-rich MFCs contain acid phosphatase activity in primary and secondary lysosomes, similar or stronger in intensity to that which can be demonstrated in mononuclear fibroblasts. However, unlike mononuclear fibroblasts, the MFCs did not exhibit alkaline phosphatase activity along their plasma membranes. These results suggest that MFCs demonstrate a range of fibroblastic cellular activity, including collagen phagocytosis, and that they may lack certain plasma membrane glycoproteins, which might explain the occurrence of multinucleation in these cells.

A TEM analysis of tissue channels in normal and orthodontically tensioned rat molar periodontal ligament

This investigation tested the hypotheses that (1) tissue channels (TC) exist in normal periodontal ligament (PDL) between the cervical and apical zones, and (2) orthodontic tooth tension alters their number and distribution within this region. A continuous 1.0 N tension was applied to the maxillary first molar for 30 minutes and ionic tracer precipitate used to analyse TC in unstained TEM sections. In normal PDL, the mean number of tissue channels (MNTC) was 0.10 +/- 0.01/micron 2 in the 0-2-microns PDL zone extending from the vessel wall, 0.09 +/- 0.02/micron 2 in the 2-4-microns zone, and 0.06 +/- 0.02/micron 2 in the 4-6 microns zone. Differences were not statistically significant. Extrusion increased the MNTC to 0.28 +/- 0.01/micron 2, 0.20 +/- 0.02/micron 2, and 0.16 +/- 0.02/micron 2, in the 0-2-, 2-4- and 4-6-microns zones, respectively (P < 0.001). For normal PDL in the tooth, middle and bone circumferential thirds the TC distribution were even. In the tensioned PDL, TC in the circumferential tooth third (0.20 +/- 0.02/micron 2), middle third (0.19 +/- 0.01/micron 2), and bone third (0.23 +/- 0.02/micron 2) increased significantly (P < 0.001) from normal ligament. The total increase in experimental MNTC was associated mainly with the post-capillary-sized venules, venous capillaries, and arterial capillaries. With progression from the cervical to apical regions the MNTC in control PDL failed to significantly fit a quadratic regression pattern. By contrast, tensioned PDL showed a marked regression pattern (P < 0.001) indicating a reduction in MNTC with vertical depth.(ABSTRACT TRUNCATED AT 250 WORDS)

Fine structure of adrenergic nerve fibers in human periodontal ligament

The presence of adrenergic nerve fibers was demonstrated ultrastructurally in the human periodontal ligament obtained from extracted premolar teeth from 8 young patients. The nerve endings were located close to arterioles. The results suggest that they seem to control blood flow in the human periodontal ligament.

A re-evaluation of the distribution of the elastic meshwork within the periodontal ligament of the mouse

The elastic properties of the periodontal ligament have been attributed, in part, to oxytalan fibers, as no other types of elastic fibers are described there. It has been difficult to study the periodontal elastic meshwork by standard microscopic techniques because it is partially obscured by the adjacent periodontal ligament collagen fibers. Our study employed methods which either completely or partially removed mandibular molar periodontal ligament collagen fibers, exposing a previously undescribed periodontal elastic meshwork. The periodontal elastic meshwork was composed of many elastin lamellae containing both peripheral microfibrils of regular arrangement and central microfibrils of irregular arrangement, which could only be demonstrated in oxidized tissues. Peripheral, regularly arranged bundles of microfibrils resembled oxytalan fibers, which were often adherent to the border of the elastin lamella. Elastin lamellae containing irregular microfibrils resembled elaunin fibers. These fibers probably enclosed either blood vessels, nerves or collagen fiber bundles. Peripheral microfibrils attached elaunin to cementum, alveolar bone, blood vessels, and principal periodontal collagen fibers. Thus, the periodontal elastic meshwork is composed of both oxytalan and elaunin fibers. Microfibrils attach elaunin fibers to the adjacent non-elastic tissue and also form bundles which traverse the periodontal ligament space and are probably the oxytalan fibers demonstrable by light microscopic techniques. This meshwork of oxytalan and elaunin fibers probably contributes to tooth support and maintenance of periodontal homeostasis by dissipating chewing forces and maintaining patency of periodontal blood vessels.

Immunohistological localization of cell adhesion proteins and integrins in the periodontium

The distribution of the cell adhesion proteins vitronectin, fibronectin, tenascin, and laminin as well as several integrin subunits, alpha 2, alpha 5, and alpha v, was studied in primate periodontal tissues. Full baboon mandibular sections were analyzed by immunohistochemical methods in order to localize the molecules studied in both soft and hard tissues. Vitronectin was associated with the connective tissue of the marginal gingiva, the periodontal ligament, as well as the endosteum and periosteum. A notable finding was the particularly high staining intensity of vitronectin in the periodontal ligament. Fibronectin was widely distributed in the periodontal connective tissue and was also localized to the pericellular matrix of osteocytes and blood vascular elements. Epithelial basement membranes stained positively for both fibronectin and tenascin. These proteins were also expressed in the periosteal and endosteal connective tissues and the periodontal ligament. The staining intensity for tenascin was higher in zones along the cementum and bone surfaces. Laminin was, characteristically, limited to basement membranes of epithelium and endothelium. The distribution of fibronectin, tenascin, and laminin is related to previous findings in other species. The localization of the several integrin alpha-subunits is also described in full baboon mandibular sections. The vitronectin receptor (alpha v) had a uniquely strong expression in osteoclasts of the alveolar bone and was found, at lesser intensity, on periodontal ligament fibroblasts. The fibronectin receptor alpha subunit, alpha 5, was also observed on osteoclasts, and, in addition, was widely distributed on fibroblasts, cementoblasts, and osteoblasts.(ABSTRACT TRUNCATED AT 250 WORDS)

Scanning electron microscopic observations of the periodontal ligament fibers and cells in rat molar teeth

The periodontal ligament of rat molar teeth was observed with scanning electron microscopy (SEM) using two different methods: NaOH maceration and KOH-collagenase treatments. Rat jaws with molar teeth were fixed, demineralized with 10% EDTA, and cut into several pieces. After maceration with 5% NaOH for 5 days at room temperature, the cellular elements were completely removed and the periodontal ligament fibers appeared as bundles of collagen fibrils. The fibers branched and anastomosed but did not spread fibrils randomly. In some regions near the alveolar bone, collagen fibrils circularly binding the fibers were found. When treated with 30% KOH for 7 to 10 minutes at 60 degrees C and with 0.1% collagenase, the periodontal ligament fibers were removed and the cells appeared as spindle and stellate shapes, and combined with the irregular cell processes of each other. Thus, the interaction between the periodontal ligament fibers and cells were three-dimensionally visualized by using the two different methods.

Morphology of neural endings in the human periodontal ligament: an electron microscopic study

The ultrastructure of sensory nerve endings in the human periodontal ligament from 43 extracted teeth was studied using serial sections. Three types of nerve endings were found: free nerve endings (FNE), Ruffini-like endings and lamellated corpuscles. Free nerve endings stem from unmyelinated or from myelinated nerve fibers. The endings contain neurotubuli, neurofilaments and vesicles. Ruffini-like receptors were mostly found in the apical part of the periodontal ligament. In these Ruffini-like receptors a particularly abundant concentration of mitochondria appears. In some cases desmosome-like junctions are present between neurite and ensheathing cell. Lamellated corpuscles were also found in the periodontal ligament. The lamellae are extremely endocytotic and are in close contact with each other.

Enhanced collagen phagocytosis by rat molar periodontal fibroblasts after topical application of lipopolysaccharide--ultrastructural observations and morphometric analysis

To investigate the effect of lipopolysaccharide (LPS) on phagocytic activity of collagen fibrils by periodontal fibroblasts, we studied rat molar gingival connective tissue and periodontal ligament under light and electron microscopy after topical application of LPS (5 mg/ml in physiological salt solution (PS)) on the gingival sulcus. Phagocytic activity of collagen fibrils by fibroblasts was evaluated by counting the number of collagen-containing vacuoles inside fibroblasts that were present within a defined area (1200 microns2). Values obtained from fibroblasts in the subepithelial connective tissue, the region near the alveolar crest, and the middle region of periodontal tissue were compared. Periodontal ligament fibroblasts showed increased phagocytosis of the collagen fibrils from 3 hours to 1 day after topical LPS application, but no differences were observed in the gingival tissue. The intracytoplasmic vacuoles containing collagen fibrils were of various sizes and shapes, showing positive for acid phosphatase and/or alkaline phosphatase reaction. Collagen phagocytic activity of the fibroblasts in the middle region of the periodontal ligament also increased after PS treatment. However, this was significantly less than that observed in LPS-treated animals (p less than 0.01). This study indicates that LPS may enhance the degradation of collagen by stimulating the phagocytic activity of the periodontal ligament fibroblasts.

In vitro formation of mineralized nodules by periodontal ligament cells from the rat

The purposes of this study were to determine whether periodontal ligament (PDL) cells are capable of producing mineralized nodules in vitro and to analyze ultrastructural features of the nodules. Rat PDL cells were obtained from coagulum in the socket at 2 days after tooth extraction and cultured at confluence in standard medium containing Dulbecco's Modified Eagle's Medium supplemented with 10% FBS and antibiotics. To test mineralized nodule formation, cells were further cultured for an additional 3 weeks in the standard medium containing (1) ascorbic acid (50 micrograms/ml) and sodium beta-glycerophosphate (10 mM), (2) ascorbic acid, sodium beta-glycerophosphate, and dexamethasone (5 microM), or (3) ascorbic acid alone. Cells were then fixed in 2.5% glutaraldehyde, postfixed in 1% OsO4, and prepared for light and electron microscopy. Three-dimensional nodules containing mineralized matrices were formed only when the cells were cultured in the presence of ascorbic acid and dexamethasone. They were composed of multilayered fibroblasts (up to 13 layers), and highly organized collagen fibrils with 64 nm cross-banding patterns between the cell layers. The fibroblasts in the nodules exhibited an elongated shape with a high degree of cytoplasmic polarity throughout the nodule, and have the morphological features of PDL fibroblasts as seen in vivo. Mineral deposition with needle-like crystals was initiated on collagen fibrils located in intercellular spaces of the upper cell layers and became increasingly heavier towards the bottom half of the nodules. X-ray microanalysis and electron diffraction analysis confirmed that mineral deposition contained calcium and phosphate in the form of immature hydroxyapatite.(ABSTRACT TRUNCATED AT 250 WORDS)

Innervation of the periodontal ligament in the dog with special reference to the morphology of Ruffini endings

The distribution and terminal formation of nerves in the periodontal ligament of dog incisors and canines were investigated by immunohistochemistry for neurofilament protein (NFP) and by electron microscopy. The NFP-immunoreactive nerve fibers were found to be densely distributed in the apical third of the periodontal ligament, while they were sparse in the coronal two thirds. Most of the nerve endings in the periodontal ligament showed a tree-like appearance and resembled those nerve endings demonstrated in the periodontal ligament of human and monkey under the category of free nerve endings. Presumable axon terminals of these were slightly thicker than preterminal portions, running along periodontal collagen fibers and tapering within them. In light microscopic images, at least, they differed from the Ruffini endings which are commonly seen in rodents, displaying a glove-like configuration with extremely expanded tips. Under the electron microscope, however, the tree-like endings of the dog appeared similar to the Ruffini endings of rodents: their terminals were filled with mitochondria, covered with a cytoplasmic process of a Schwann cell, and surrounded by collagen fibers. These ultrastructural findings, combined with the results of previous physiological studies suggest that the nerve endings demonstrated in the present study can be identified as Ruffini endings. It is even stressed that the dog-type of Ruffini ending can be regarded as a representative of the sensory receptors in the mammalian periodontal ligament. In addition to these endings, knobbed endings, corpuscular (lamellated and glomerular) endings, and free nerve endings were rarely encountered in the periodontal ligament of incisors and canines of the dog.

Osteogenic activity of cells from dental pulp, periodontal ligament, bone marrow and muscle in vitro: an ultrastructural study and alkaline-phosphatase activity

Dental pulp, periodontal ligament, bone marrow and muscle tissue from the same rat were cultured in vitro in order to investigate their osteogenic activity by transmission electron microscope. Immunohistochemical methods with various antibodies were utilized and alkaline-phosphatase (ALPase) activities of these cells were also measured biochemically. Dental pulp cells were stellate in shape, showed an intense ALPase reaction, and had lipid-like droplets. Periodontal ligament cells were composed of spindle fibroblasts and epithelial cells. The former revealed a positive reaction for ALPase and possessed microfilaments. Bone marrow cells were spindle shaped, resembling fibroblasts, but some of them were similar to osteoblasts. Muscle cells were long, slender in shape, and showed no positive reaction for ALPase. The cells from pulp tissue showed the highest activity of ALPase, followed by periodontal ligament and bone marrow; there was no activity in muscle tissue. All the cells except the epithelial-like cells of the periodontal ligament and muscle cells were positive in reaction with ALPase which is a marker for osteogenic cells, and vimentin which is a marker of fibroblastic characteristics. Osteogenic activity and cellular differentiation of these cells were discussed.

Bundle formation of principal fibers in rat molars

The bundling of principal fibers was investigated in tangential sections through the tooth-related portion in developing rat molars by light and electron microscopy. When root dentin calcification began, cross sections of principal fibers emerged as fibril aggregates in the narrow intercellular spaces in a densely packed population of periodontal ligament cells. Subsequently, these cells changed shape and location to widen the intercellular spaces. The fibril aggregates became thicker in these spaces. With root development, the collagen fibrils formed loosely aggregated bundles and the periodontal ligament cells extended cell processes between the bundles. The cell processes usually contained microfilaments suggestive of actin filaments, and as the cell processes extended and came in close apposition, they formed delimited compartments. These compartments appeared to be a sheath-like structure, and the loose fibril bundles developed into tight fibril bundles in the compartments. Finally the principal fibers consisted of many tight fibril bundles, which were partially or entirely surrounded by cell processes and cell bodies. The findings suggest that the sheath-like, cellular compartments cause the tight bundling of the principal fibers.

A possible mechanism of mechanoreception in Ruffini endings in the periodontal ligament of hamster incisors

The topographical relationship between Ruffini endings and the surrounding collagen fibers in the periodontal ligament of hamster incisors was investigated by means of both immunohistochemistry for neurofilament protein (NFP) and electron microscopy. Periodontal Ruffini endings, a type of stretch receptor, were present exclusively in the alveolar half of the periodontal ligament. Their axon terminals were densely and regularly associated with transverse collagen fibers, possibly forming a mechanoreceptive complex. Since blood sinuses with frequent anastomoses extended throughout the alveolus-related part, the densely innervated collagen bundles were separated from each other by the vascular spaces. Electron microscopic observation of specimens stained with tannic acid revealed a linkage between the axon terminals of the Ruffini endings and the surrounding collagen filaments. The axon terminals were enveloped by multiple layers of the basal lamina, which were penetrated by collagen filaments. The irregularly arranged collagen filaments were sandwiched between electron-dense laminae of the multilayered basal lamina. The possible mechanism of mechanoreception by the periodontal Ruffini endings is discussed on the basis of the immunohistochemical and ultrastructural findings.

An ultrastructural study comparing new gingival tissue attachment on chemically exposed fibrils and retained periodontal ligament

Successful periodontal healing has been demonstrated in animals following application of citric acid to exposed root surface. However, we have been unable to achieve comparable results on clinical patients. Accordingly, the present study, using monkeys, was designed to re-evaluate the degree of interdigitation of newly-formed gingival fibrils with ones exposed to citric acid compared to normal attachment tissues of the retained periodontal ligament. We found that superficial collagen fibrils in both cases suffer degradation following normal inflammation and healing secondary to flap surgery. On retained periodontal ligament tissues, this change was limited to superficial levels and newly-formed collagen fibrils were linked immediately with old ones. In contrast, when exposed collagen fibrils were conditioned by exposure to citric acid, the degradative change occurred more deeply, and healing was delayed. Thus, the citric acid may not be the best choice of root treatments in terms of promoting better gingival tissue attachment. Furthermore, the results indicated that fibrils preserved on the root should not be curetted as possible during flap surgery as they offer an improved chance for optimal reattachment.