[Morphological study of responses to mechanical stretching in fibroblasts derived from human periodontal ligaments]

Clonal cell lines established from human periodontal ligaments were used in vitro experiments to ascertain periodontal ligament responses, on the cellular level, to mechanical stretching. A procedure developed by Hasegawa et al. (1985) was used in applying mechanical stretching. Unstretched cultures were used as controls. All cultures were processed for investigations of fine structures, histochemical and cytochemical detection of ALPase activity, and localization of alpha-tubulin. Cultured cells to which mechanical stretching was intermittently applied showed little change in overall appearance, cell shape and arrangement, and distribution of alpha-tubulin. Although fine structural characteristics remained unchanged in both stretched and unstretched cultures, mechanical stretching force clearly increased the intensity of ALPase activity. Histochemical and cytochemical examinations indicated that the added intensity resulted from increases in numbers of cells demonstrating enzymatic activity.

Evidence of acute inflammation in the periodontal ligament subsequent to orthodontic tooth movement in rats

Experimental orthodontic tooth extrusion can result in red cell diapedesis through the PDL vascular wall. Diapedesis is an early sign of acute inflammation. At the ultrastructural level, red cell migration is demonstrated occurring through the endothelial junction of a postcapillary-sized venule. This phenomenon is considered to be indicative of unphysiological tooth loading.

[Study of the relationship between fibronectin and morphological changes in the early process of periodontal ligament formation]

The localization of fibronectin (FN) in the initial stage of periodontal ligament formation was examined immunohistochemically. This period was divided into four stages with respect to epithelial-mesenchymal interactions. FN was observed on the cell membrane of the follicular mesenchymal cells near the basement membrane of the epithelial root sheath outer layer (stage I). In the stages of contact between follicular mesenchymal cells and the epithelial cells of the outer layer (stage II) and those penetrating the intercellular space of the discontinuous epithelial cells of the root sheath (stage III), FN was observed on the cell membrane of follicular mesenchymal cells which was in contact with epithelial cells. Follicular mesenchymal cells which were in contact with the FN rich dentin surface had well-developed cytoplasmic organelles (stage IV). Nonstriated fibrils were seen close to the projection of mesenchymal cells elongating toward the dentin surface, and were oriented parallel to the projection. FN in the small fibrils was clearly observed in the area connected to the mesenchymal cells. The reaction of FN was less in the area where collagen fibrils were organized into bundles. A dense amount of FN was seen where the periodontal ligament crossed into the dentin surface collagen. It is considered that FN plays an important role in follicular mesenchymal cell penetration of the increasing intercellular space between epithelial cells, the differentiation into the fibroblast at the dentin surface, the formation and arrangement of the periodontal ligament, and the attachment of the periodontal ligament to the dentin surface.

[Histological study of cell attachment and proliferation of periodontal ligament cells on the tooth surface. Effect of the fibronectin application]

The purpose of this study was to examine the effect of fibronectin on cell attachment and the growth of cultured cells on the surface of the dentin. In the first experiment, dentin specimens were divided into following three groups: dentin surface polished with carborundum-point, carborundum-point and #150 sandpaper and carborundum-point, #150 sandpaper and #240 sandpaper. The roughness of the surface was measured with a profilometer (Surfcom e-st-sa) for the purpose of comparing differences among the three groups. The foregoing treated samples were added to cultures of periodontal ligament (PDL) cells and following fixation, the number of cells was counted under a light microscope and examination under a scanning electron microscope (SEM) was also performed. 1. Greater numbers of cells attached to the smooth surface (#240) than the rough surface. 2. SEM observations showed increased numbers of attached and proliferated cells on the smooth surface. In the second experiment, the dentin surfaces were polished with carborundum point, #150 and #240 sand paper. The dentin tube side was treated with fibronectin. MEM-treated samples not immersed in fibronectin were employed as controls. The foregoing treated root samples were cultured with PDL cells. Following fixation, the cells attached to the root surface were examined under the light microscope and using a SEM. 1. A significant increase in the number of the attached cells as observed after treatment with fibronectin. 2. SEM observation suggested PDL cells migrated more and proliferated more on the side treated with fibronectin. 3. Fibronectin application increased cell attachment and proliferation more on the smooth surface of dentin.

[S E M study of vascular architecture of periodontal ligament under chronic marginal periodontitis]

The present study was carried out by fabrication of microcorrosive resin cast to investigate the vascular changes of periodontium of dogs' mandibular incisors with severe mobility and deep pocket formation concomitant with suppuration and alveolar bone loss. With aid of the dissolution of soft tissues by protease, alveolar bone remained left with resin cast of specimen, which then was referred for scanning electron microscopic examination. Results were as follows: 1. The vasculature of inner gingival epithelium which originally appeared as a flat, mesh-like network underwent a conformational change and turned out to be a vasculature with glomerulus-like loops due to chronic inflammation. 2. No remarkable change was ever identified in vasculature of periodontal ligament surrounding cervix of tooth. 3. Certain parts of vasculature of periodontal ligament disappeared, which combining with the occlusion indicated the occurrence of occlusal trauma. 4. Exposed alveolar bone surface where the periodontal vasculature disappeared showed an amorphous, flat surface. Quite contrast to this, the surface of alveolar bone on which the vasculature is located appeared undergoing a resorptive process. 5. Accordingly, the damage occurred in periodontium was not merely due to chronic inflammation but to the accompanying occlusal trauma which was supposed to be a predominant factor.

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

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

[Ultrastructural study of initial attachment by human fibroblast-like cells on tooth roots in vitro]

The purpose of this study was to determine the longitudinal effect of demineralized treatment of root surfaces on initial attachment, growth and differentiation of human periodontal ligament fibroblast-like cells in vitro. Cementum and dentin fragments were prepared from intact extracted human teeth for orthodontic reason. The root fragments of one group were not demineralized. Those of the other groups were demineralized by either citric acid (pH = 1.0, 3 min) or EDTA (pH = 7.4, 30 min). Plastic sheets served as controls. Human periodontal ligament fibroblast-like cells were incubated on root fragments and plastic sheets. After incubation, the root fragments and plastic sheets were examined by electron microscopy. The collagen fibers were exposed to the root surface by demineralized root surface. The exposed collagen fibers showed an effect on the cell attachment and growth, and the cells produced collagen fibers in the extra-cellular space of the root surface. Demineralization of dentin fragments were more strongly affected in cell attachment, growth and differentiation than demineralization of cementum fragments. Citric acid demineralization of dentin fragments had a greater effect on cell attachment, growth and differentiation than EDTA demineralization of dentin fragments. The results suggest that citric acid demineralization of dentin fragments may provide the most effective dental surface for the establishment of connective tissue attachment after periodontal treatment.

Radioautographic study of [3H]mannose utilization during cementoblast differentiation, formation of acellular cementum, and development of periodontal ligament principal fibers

The formation of acellular cementum and the deposition of [3H]mannose-labeled extracellular matrix were studied in 14-day-old Sprague-Dawley rats. The sequential events of cementogenesis and periodontal ligament formation observed by light and electron microscopy were described from the stage of an intact root sheath to postcementogenesis. Ultrastructural examination of cementoblasts and periodontal ligament fibroblasts revealed [3H]mannose labeling of the Golgi apparatus at 10 minutes, collagen secretion granules at 30 minutes, and the extracellular matrix beginning at 30 minutes. The extracellular matrix between cementoblasts and dentin was heavily labeled at 1 and 4 hours. Newly formed principal fibers of the periodontal ligament were also heavily labeled at 4 hours. Fully differentiated cementoblasts exhibited the largest sectional profiles and the highest number of silver grains per unit area of cytoplasm. The morphologic and radioautographic data suggest that during the formation of acellular cementum, the cementoblast phenotype is expressed for a short period of time, after which cementoblasts appear to mix with the fibroblasts of the periodontal ligament.

Ultrastructure of epithelial rests of Malassez in human periodontal ligament

The cell rests in healthy periodontal ligament were studied by transmission electron microscopy. They consisted of clusters of cells surrounded by a basal lamina. These cells were characterized by an irregular nucleus with condensed heterochromatin, tonofilaments, relatively abundant mitochondria and poorly developed rough endoplasmic reticulum. They were connected to each other by desmosomes and gap junctions. Coated pits and vesicles were also seen at the periphery. In addition, a primary cilium accompanied by a centriole was often observed in association with the Golgi complex and rootlet-like structures. The findings suggest that the epithelial rests are more than a vestigial structure.

Comparison of trigeminal receptor location and structure in the periodontal ligament of different types of teeth from the rat, cat, and monkey

The periodontal ligament is richly innervated by mechanoreceptors whose cell bodies are located either in the trigeminal ganglion (TG) or the mesencephalic (MS) trigeminal nucleus. Both are sensitive to stretch of the ligament induced by tooth movement, but their thresholds, central connections, and functional significance differ. This study compared the location of TG and MS receptors in the periodontal ligament of cat teeth after labeling each by anterograde axonal transport. We also compared the location and ultrastructure of the feline TG receptors with labeled TG receptors in the periodontal ligament of monkey teeth and rat incisors in order to determine their location and ultrastructural properties. We found that the MS and TG receptors had a different distribution in the periodontal ligament of cat teeth; the MS terminals were concentrated below and next to the base of the roots, whereas the TG receptors were most numerous around the middle of the roots. The TG receptors of monkey teeth had a similar location to the feline TG receptors, but those of rat incisors were very different. Rat incisors are curved, continuously erupting teeth, and their TG receptors were located primarily on the lingual side in the alveolar (nonerupting) portion of the ligament. Ultrastructural comparisons found that most mechanoreceptors in the periodontal ligament of all the teeth had an unencapsulated branched Ruffini-like structure. The TG receptors in the rat incisor ligament were the largest; those of monkey had the most varied form. Some coiled or encapsulated receptors were found in the monkey and cat ligament, but not in the rat incisor ligament. The TG receptors appear to be located at sites that would be most easily stretched during tooth contact. The different sites and intensity of the stretch forces occurring during the use of different types of teeth may determine the variations in the size and location of the TG mechanoreceptors and of their associated support cells. The different distribution of MS receptors may contribute to their response thresholds and static properties, which differ from those of TG receptors.

Cell death and the regulation of populations of cells in the periodontal ligament

The contribution of cell death in regulating cellular populations of periodontal ligament was studied in young adult rats. Mandibular first molar periodontium was prepared for light-microscopic radioautography after a pulse of 3H-thymidine in 6 rats and for electron microscopy in 4 rats. The labeling index for 3H-thymidine and the density of fibroblast-like cells were computed from radioautographs. The percentages of dying or dead cells and macrophages were computed from electron micrographs. The labeling index of cells within 20 microns of bone and cementum was significantly lower (p less than 0.01) than the labeling index within the body of the periodontal ligament. The patterns of cellular density and indices of death were the inverse of the labeling indices. Macrophages were plentiful (% macrophages = 3.68% +/- 0.30) and were clustered around blood vessels (mean distance from blood vessel = 2.3 microns). However, only 10% of dying or dead cells were within 10 microns of blood vessels. These data show that death of cells in the periodontal ligament may, in part, balance production of cells by mitosis. The relationships between labeling index, index of death, and cellular density suggest that cells born in the middle of the periodontal ligament may migrate to regions of high cellular density near bone and cementum, and that they may die there. Macrophages do not appear to be associated with dying cells of the periodontal ligament.

An ultrastructural study of human epithelial rests of Malassez maintained in a differentiated state in vitro

Healthy human periodontal ligaments (PDL), obtained from the extracted teeth (premolars and third molars), were cultivated for 1-35 days, using a multi-purposes culture chamber (MPCC) equipped with various transparent membranes. The resting state of the epithelial rests of Malassez (ERM), similar to their in vivo counterparts, appeared as small islands or strands with scant cytoplasm containing poorly developed organelles. This state was most effectively maintained in MPCC with a cellophane sheet. MPCC with a Sartorius membrane filter permitted proliferation and emigration of ERM. Proliferating ERM were characterized by more profiles of rough endoplasmic reticulum and free ribosomes, new formation of actin-containing microfilaments, less prominent tonofilaments and desmosomes and loss of gap junctions. Most of these ultrastructural changes are manifested in epithelial cells during wound healing. The emigrating ERM from PDL explants, as well as occasional proliferating ERM within explants, consisted of two cell types--outer basal-like cells, as described above, and inner tonofilament-rich prickle-like cells, suggesting a propensity for differentiation of ERM. The results show the possibility of controlling the growth and differentiation of ERM through the MPCC culture environment.

Formation of a new fibrous attachment to human dental roots. A new vitro model for studying periodontal regeneration

This study was performed to improve currently employed in vitro models for the study of periodontal regeneration by using a porous filter upon which periodontal ligament cells were grown. Periodontal ligament cells were harvested and 0.3 mm root discs cut from three partially erupted and extracted third molar teeth of one patient. Experimental culturing was performed by seeding periodontal ligament cell suspensions on Puropor-200 filters supported by wire-mesh grids in Grobstein Petri dishes. The following day, an interdental space of 0.1 to 0.3 mm was created by gently placing two dental root discs upon the filter. Cultures were terminated after 42, 56, 112 and 124 days, and processed for light- and electron microscopy. Collagen fibril diameters were measured. Adjacent and often attached to large areas of cementum-lined root discs, a dense fiber fringe developed. This fiber fringe was not found on dentin-lined root discs. Although less organized, older cultures demonstrated a similar disc-culture interface, which depended upon the presence or absence of original root cementum. Collagen fibrils of early cultures had a mean diameter of about 42 nm, while in older cultures the diameters ranged from 47 to 68 nm. It is concluded that the fibrous matrix attached to cementum-lined root discs somewhat resembles the initial stages of the formation of dental root cementum in vivo.

Radioautographic demonstration of receptors for epidermal growth factor in various cells of the oral cavity

Mouse iodinated epidermal growth factor (EGF) was localized by light and electron microscopic radioautography in basal cells of oral epithelium, papillary cells of the enamel organ, periodontal ligament fibroblasts, preodontoblast precursor cells, and preosteoblasts of the alveolar bone of 13-day-old Sprague-Dawley rats. The specificity of binding in these cells was suggested by an observed reduction of about 90% in the labeling when excess unlabeled EGF was injected along with the 125I-EGF. In contrast, fully differentiated cells, such as ameloblasts, odontoblasts, and osteoblasts, were only poorly labeled. Quantitative analysis of the light microscopic radioautographs revealed that the papillary cells had the highest level of labeling (5.5 grains per 100 micron 2 of cell area). The significance of the rather high labeling of the preosteoblasts of the alveolar bone and the fibroblasts of the periodontal ligament is unknown. However, the well-known effect of EGF in producing precocious eruption of teeth may be a consequence of an effect on these two cell types.

Collagen phagocytosis by fibroblasts in the periodontal ligament of the mouse molar during the initial phase of hypofunction

This study was undertaken in order to determine whether hypofunction of teeth is associated with changes in collagen phagocytosis by fibroblasts of the periodontal ligament. In mice, the lower right molars were extracted and the animals killed one, two, three, four, or seven days later. The maxillary first molars with their surrounding periodontium were processed for electron microscopy and their periodontal ligament subjected to morphometric analysis. It was observed that, whereas the volume density of extracellular collagen in the ligament of the hypofunctional molars decreased from 50% to 30% during the course of the experiment, the fraction of fibrillar collagen ingested by the cells increased over two-fold. This increase was already manifest very shortly after the onset of the experiment and offers an explanation for the net loss of collagen fibrils from the extracellular space.

[Cells in the normal human periodontal ligament. An ultrastructural, histo-enzymological and immunocytochemical study on in vitro cultures]

Four cellular cultures from explants of human periodontal ligament were studied. In these cultures, cells were fusiform or stellate with a high percentage (5 to 10%) of round mitotic cells. The scanning electron microscope confirmed the simultaneous presence of flat cells in interphase and cells in prophase with microvilli and long filipodes and of round mitotic cells with microvilli and blebs. Histoenzymology disclosed in these cells high activities in oxidative enzymes and leucine aminopeptidase. Furthermore some cells showed an alkaline phosphatase activity. Immunocytochemistry detected in most of these cells intermediate vimentin filaments and the presence of type I and III collagen irregularly distributed among these cells. In transmission electron microscopy the elongated cells presented a clear nucleus, numerous endocytosic vesicles, ribosomes and longitudinal filaments. Variations were noted, especially in the quantity and quality of cell secretions, the fibroblasts secreting either the two type I and III collagen or only type I. The rare cells assuming alkaline phosphatase activity were atypical in possibly being provided with osteogenic potential.

Experimentally induced resorption cavities in rat molars

The incidence and ultrastructure of resorption cavities were studied in albino rat molars. The transseptal fiber system between the 1st and 2nd maxillary molars in 30 albino rats aged 50 days was transected by buccopalatal incision. Fifty approximal surfaces represented the experimental material. Unaffected interproximal areas and approximal surfaces of adjacent teeth as well as of 10 teeth from five healthy, unoperated rats served as controls. The rats scheduled for operation were assigned to experimental groups each comprising three or four animals. Following injury, the incisional wounds were allowed to heal for 1, 2, 4, 5, 6, 8, 10, 14 and 21 days. The animals were sacrificed by an overdose of pentothal sodium and specimens prepared for light and electron microscopy. Normal, healthy teeth showed no resorption cavities on tooth surfaces facing the interproximal area, in contrast to the observation that minor resorption cavities with cemental repair were regularly present on root surfaces facing periodontal ligament. Following surgical injury, extensive resorption cavities in dentin and cementum developed on experimental surfaces adjacent to the area of wound healing. Arrest of active resorption in some of the experimentally induced cavities had occurred in 14-day specimens. Repair of resorption cavities appeared to start by attachment of connective tissue fibers to exposed dentinal and cemental collagen. The ultrastructural observations indicate that initial fibril attachment to exposed collagen is mediated by a granular, coating material resembling minute deposits of afibrillar cementum.

Resorbing potential of different connective tissue types

Pieces of dentin were implanted into five different connective tissues in rats and examined with scanning electron microscopy after observation periods of up to 2 weeks. Dentin-oclast-like cells, apparently involved in resorption of the implants, were only seen associated with periosteum and periodontal membrane. These findings indicate that the resorbing potential of connective tissues is related to their ability to induce bone formation.

3H-mannose utilization by fibroblasts of the periodontal ligament

The synthesis, intracellular translocation, and secretion of mannose-containing glycoproteins(s) by periodontal ligament fibroblasts have been investigated by means of electron microscopic radioautography. Tritiated mannose was administered to young mice via jugular vein, and radioautographs were prepared at 5, 10, 20, and 35 minutes, 4 and 8 hours after injection. Analysis of electron microscopic radioautographs revealed a maximum labeling (94%) with 3H-mannose of the rough endoplasmic reticulum at 5 minutes. Labeling of the Golgi components started to increase from 10 minutes (14%) and reached a maximum level at 20 minutes (31.2%). At 35 minutes, secretion granules, dense bodies, profiles of intracellular collagen, and the cell surface were labeled. At 8 hours, most labelling (79.2%) was extracellular, and associated either with the collagenous matrix (43.7%) or the cell surface (35.5%). Cytoplasmic vesicles containing dense materials around collagen fibrils were also labeled at 8 hours. It is concluded that mannose is directly incorporated into the rough endoplasmic reticulum (RER), and that mannose-containing glycoprotein(s) are packaged in the Golgi apparatus into secretory granules. Mannose-containing glycoprotein(s) become distributed on the periodontal ligament (PDL) fibroblast cell surface, cytoplasmic dense bodies, and the extracellular matrix.

Ultrastructural and morphometric analyses of human cementoblasts and periodontal fibroblasts

In order to elucidate the cytological characteristics of human cementoblasts which distinguish them from periodontal fibroblasts, the periodontal ligament and gingival connective tissue attached to 37 extracted teeth from 27 patients (ages 10-67) were analyzed by electron microscopy coupled with a morphometric procedure. The cementoblasts largely consisted of either immature or resting types of collagen-producing cells (CPC), both of which were poor in the rough endoplasmic reticulum and Golgi complex; these organelles were well-developed in the relatively less common active cementoblasts. The cementoblasts consistently revealed a higher mean-volume-density per tissue unit than the fibroblasts and sometimes were grouped into clusters with the formation of junctional apparatuses. The relative volume of glycogen particles per cytoplasm was significantly higher in the cementoblasts, whereas the rough endoplasmic reticulum was higher in the fibroblasts. From the present study, it is suggested that the cementoblasts are functionally less active CPC than the periodontal fibroblasts.

Nuclear morphometric analysis of osteoblast precursor cells in periodontal ligament, SL-3 rats

Five small (55 days old, 196 +/- 5 g) (mean +/- SE) and five large (83 days old, 382 +/- 4 g) Sprague-Dawley strain, specific pathogen-free rats were exposed to a 7-day spaceflight and 12-h postflight recovery period. As measured in 3-micron sections, periodontal ligament (PDL) fibroblastlike cells were classified according to nuclear size: A + A' (40-79), B (80-119), C (120-169), and D (greater than or equal to 170 microns 3). Since the histogenesis sequence is A----A'----C----D----osteoblast, the relative incidence of A + A' to C + D is an osteogenic index. No difference in A + A' or C + D cells in small rats may reflect partial recovery of preosteoblast formation (A----C) during the 12-h postflight period. Large flight rats demonstrated increased numbers of A + A', indicating an inhibition of preosteoblast formation (A----C). At least in the older group, a 7-day flight is adequate to reduce PDL osteogenic potential (inhibition in PDL osteoblast differentiation and/or specific attrition of C + D cells) that does not recover by 12-h postflight.