An ultrastructural evaluation of the relationship between epithelial rests of Malassez and orthodontic root resorption and repair in man

Contrary to previous reports, epithelial cell clusters with ultrastructural features similar to classically defined epithelial rests of Malassez were found, for the first time, in areas of repairing orthodontic root resorption. These observations were made on the buccal root surface of premolars extracted for orthodontic purposes from adolescent patients who had required rapid maxillary expansion. Ultrastructurally, the epithelial clusters ranged in size from 2-8 cells and were characterized by the presence of true desmosomes (macula adherens) and tonofilaments. Certain ultrastructural features of the epithelial cell clusters indicate that they may be involved in mediating repair cementogenesis subsequent to migration into the resorption bay.

Occurrence of epidermal growth factor-binding sites during differentiation of cementoblasts and periodontal ligament fibroblasts of the young rat: a light and electron microscopic radioautographic study

Occurrence of epidermal growth factor (EGF)-binding sites during differentiation of cementoblasts and periodontal ligament (PDL) fibroblasts was investigated using radioautography after I. V. injection of 125I-EGF to 14-day-old rats. During differentiation of cementoblasts, a very low level of EGF-binding sites was present on the mesenchymal cells in dental follicle proper, precementoblasts, and cementoblasts. On the other hand, during differentiation of PDL fibroblasts, numerous EGF-binding sites were observed on the undifferentiated paravascular cells and on the perifollicular mesenchymes representing the major source of PDL fibroblast precursor cells. Also heavy labeling was observed throughout their differentiation to PDL fibroblasts, as well as during full synthetic activity as mature cells. Quantitative analysis of the light microscopic radioautographs revealed that these cells demonstrated approximately 4 grains per 100 microns 2 of cell area. These results suggest that EGF plays an important role in differentiation of PDL fibroblasts, but not in that of cementoblasts. Furthermore, the well-known in vivo effect of EGF in producing precocious eruption of teeth may be a consequence of a more extensive effect of EGF throughout differentiation of PDL fibroblasts as well as during full synthetic activity as mature cells.

Permanent teeth in hypophosphatasia: light and electron microscopic study

The changes in a permanent central incisor of a patient suffering from hypophosphatasia, were investigated light microscopically and compared with those of two of his primary teeth. In addition his other central incisor was studied with transmission and scanning EM. The changes in permanent teeth were similar to those of the primary dentition, including loss of cementum and the presence of deep resorption areas in dentin. Afibrillar cementum was detected with EM, and was attached to dentin surface. The presence of a thick layer of bacterial plaque was a prominent feature in all the teeth examined. A large number of bacteria was also found in resorption bays. It is suggested that bacteria may play an important role in the destruction of soft and hard tissues leading to loss of teeth in hypophosphatasia.

Immunohistochemical localization of laminin in the periodontal Ruffini endings of rat incisors: a possible function of terminal Schwann cells

Ruffini endings in the periodontal ligament of rodents are ensheathed by a special type of terminal Schwann cell with a particularly developed rough endoplasmic reticulum and Golgi apparatus, and further enveloped by a characteristic multi-layered structure. In order to reveal the functional significance of the structures, localization of a laminin molecule in the periodontal Ruffini endings of rats was immunohistochemically investigated at the levels of light and electron microscopy. Immunostaining using an anti-laminin serum clearly demonstrated the profiles of the Ruffini endings as well as those of the blood vessels. Ultrastructurally, reaction products for laminin were deposited in the entire thickness of the multi-layered structure, supporting the idea that this structure is derived from the basal lamina. The basal lamina, immunoreacting with laminin antiserum, was penetrated by periodontal collagen fibers, possibly serving as an adhesive device between the Ruffini endings and surrounding collagen fibers. The laminin immunoreactive materials were also recognized in the vesicles and caveolae of the terminal Schwann cells which tended to gather at the interstitial surface of the cells. The terminal Schwann cells are therefore believed to be directly involved in the formation of the multilayered basal lamina through the active production of its materials.

The electron microscopic immunolocalization of a copper-zinc superoxide dismutase in association with collagen fibers of periodontal soft tissues

Periodontal soft tissues were cleaved from freshly extracted human teeth. Tissues were then prepared for subsequent biochemical and morphological studies according to the following plan: 1) immediate immersion in liquid nitrogen for the biochemical assay of superoxide dismutase (SOD); 2) immediate fixation prior to routine preparation for routine transmission electron microscopy; 3) immediate fixation prior to preparation for electron microscopic immunohistochemistry. Biochemical analysis showed that the human periodontal ligament contained about twice as much SOD activity as human skin (dermis), but considerably less enzyme activity than that seen in red blood cells. Interestingly, periodontal SOD activity appeared to decrease with age. Immunohistochemistry localized enzyme activity to the periphery of matrix collagen fibrils and to the glycocalyx of tissue fibroblasts. The pathophysiology of this enzyme regarding inflammatory diseases such as periodontitis is discussed.

A quantitative study of the ultrastructure of fibroblasts within the enamel-related connective tissue of the rat incisor

A quantitative ultrastructural study was made of the fibroblasts of the enamel-related connective tissue and periodontal ligament of the rat incisor. The two populations of fibroblasts were very similar in morphology, the only difference found in the parameters measured being the increased number of microtubules in the enamel-related connective tissue. The data do not lend support to the idea that the fibroblasts of the periodontal ligament generate the eruptive force by their motility or contractility.

An assessment of the control of matrix turnover by a quantitative ultrastructural analysis of fibroblasts of the periodontal ligament in rats

A quantitative structural analysis of the synthetic and degradative organelles of fibroblasts of rat incisor and molar periodontal ligaments was conducted. The results showed that in these tissues which are reported to have significantly different rates of turnover of their functional matrix collagen the rate of synthetic activity was the same. However, there were differences in the pattern of degradation with the molar ligament having between 5 and 6 times more phagocytosed collagen than the incisor. It is suggested that post-synthesis processing may control collagen turnover rather than modulation of rates of synthesis.

Establishment of acellular extrinsic fiber cementum on human teeth. A light- and electron-microscopic study

The present study describes for the first time the development of early acellular extrinsic fiber cementum (AEFC) until its establishment on human teeth. Precisely selected premolars with roots developed to 50%-100% of their final length were prefixed in Karnovsky's fixative and most of them were decalcified in EDTA. Their roots were subdivided into about 10 blocks each, cut from the mesial and distal root surfaces. Following osmication, these blocks were embedded in Epon and sectioned for light- and transmission electron microscopy. Some blocks were cut non-demineralized. From semithin stained sections, the density of the collagenous fiber fringe protruding from the root surface was measured by using the Videoplan-system. After initiation of this fiber fringe and its attachment to the dentinal root surface followed by mineralization, the fringe gradually increased in length and subsequently became mineralized. Fringe elongation and the advancement of the mineralization front appeared to progress proportionally. Thus, in all stages of AEFC development, a short fiber fringe covered the mineralized AEFC. Its density remained constant, irrespective of AEFC thickness. The latter gradually increased and reached an early maximum of 15-20 microns in the cervical region. At this stage, the AEFC fringe appeared to fuse with the future dentogingival or other collagen fibers of the tooth supporting apparatus. Mineralization of the fringe commenced with isolated, spherical or globular centers, which later fused with the mineralization front and became incorporated in AEFC.

Initiation of acellular extrinsic fiber cementum on human teeth. A light- and electron-microscopic study

The development of acellular extrinsic fiber cementum (AEFC) has never before been studied in human teeth. We have therefore examined the initiation of AEFC in the form of a collagenous fiber fringe and its attachment to the underlying dentinal matrix, in precisely selected, erupting human premolars with roots developed to 50%-60% of their final length. Freshly extracted teeth were prefixed in Karnovsky's fixative, decalcified in EDTA and subdivided into about 10 blocks each, cut from the mesial and distal root surfaces, vertical to and along the root axis. The blocks were postfixed in osmium tetroxide, embedded in Epon and cut for light- and electron-microscopic investigation. Starting at the advancing edge of the root, within a region extending about 1 mm coronal to this edge, fibroblast-like cells were seen closely covering the external root surface. Along the first 100 microns from the root edge, these cells extended cytoplasmic processes and contacted the dentinal collagen fibrils. Between these cells and the dentinal matrix, new collagen fibrils and very short collagen fibers gradually developed. Within the second 100 microns from the root edge, this resulted in the formation of a cell-fiber fringe network. Newly formed fibers of the fringe were directly attached to the non-mineralized matrix containing dentinal collagen fibrils and could be distinguished from the latter by differences in fibril orientation. During the process of dentin mineralization, the transitional zone between the fiber-fringe base and the dentinal matrix, i.e., the future dentino-cemental junction, also mineralized. It is suggested that this fiber fringe is the base of AEFC, which later increases in thickness by fiber extension and subsequent mineralization.

Distribution of type I and type III collagen in the developing periodontal ligament of mice

In order to localize type I and type III collagen in developing periodontal ligament, immunofluorescent and immunoelectron microscopic examinations were undertaken. The materials used were the maxillary molars of CF1 mice, 13 days to 6 months old. The antibodies used were monospecific polyclonal antibodies against type I or type III collagen raised in rabbits or guinea pigs, respectively. Single- and double-staining methods were employed in immunofluorescent as well as immunoelectron microscopic examinations. In immunofluorescent examinations, during the development of the periodontal ligament, periodontal fibers showed intense and homogenous staining for both type I and type III collagen; while Sharpey's fibers in the alveolar bone showed a heterogenous staining in cross and longitudinal sections for both types of collagen. In immunoelectron microscopic examinations, fibrils of periodontal fibers showed positive staining for type I and type III collagen simultaneously and had characteristic cross-banding and had a large diameter (ranging 40 approximately 80 nm) which remained constant during development. Sharpey's fibers in the alveolar bone or in the cementum showed the same staining pattern as the periodontal fibers, except for an afibrillar area which showed negative staining for both type I and type III collagen. The results obtained suggest that periodontal fibers and Sharpey's fibers consist of cofibrils of at least type I and type III collagen.

Immunohistochemical localization of the matrix glycoproteins--tenascin and the ED-sequence-containing form of cellular fibronectin--in human permanent teeth and periodontal ligament

The expression of two matrix glycoproteins, tenascin and cellular fibronectin (cFN), has been studied in fully developed human permanent teeth, periodontal ligament, and alveolar bone, in both frozen and paraffin-processed material. Polyclonal antibodies to tenascin and a monoclonal antibody recognizing the ED sequence specific to at least some forms of cFN were used. Staining for both tenascin and cFN was positive in the dental pulp, odontoblastic layer, cementoblast-pre-cementum zone, and on the periosteal as well as endosteal surfaces of the alveolar bone. In the periodontal ligament, cFN was evenly distributed, whereas tenascin was accumulated in the attachment zones. Pre-dentin stained for tenascin but not for cFN. Mineralized dentin and cementum were tenascin- and cFN-negative. The relative staining intensity for tenascin was greater than that for cFN in the cementoblast-pre-cementum layer and in the attachment zones of the periodontal ligament, whereas cFN stained more intensely in the pulp. In frozen material, antigenicities were well-preserved. Paraffin processing facilitated precise recognition of tissue morphology, but the antigenicity of cFN was lost. The co-expression of tenascin and cFN in the dental pulp, cementogenic zone, and on the surfaces of the alveolar bone may reflect the ability of the cells to deposit mineralized tissue matrices. The pronounced expression of tenascin in the interfaces between mineralized and non-mineralized tissues suggests that it is functionally associated with mechanical stress and may thus have at least two distinct functions. The relative amounts of the two matrix glycoproteins may contribute to regulation of tissue structure.

Immunocytochemical localization of laminin in the epithelial rests of Malassez of immature rat molars

Immediately after disruption of Hertwig's root sheath, epithelial cells were found near the root apex, singly or in groups of two or three cells. They were irregular in shape with only a partial lining of basal lamina. Immunoreactivity for laminin was intense in the basal lamina and weak between projections of the epithelial cells. In 5-week-old rats, the epithelial rests consisted of about five cells and still had an incomplete basal lamina with collagen fibrils in the intercellular spaces. Immunoreaction products were seen in the basal lamina and diffusely in the intercellular spaces. The epithelial rests of 9-week-old rats had more cells, an almost complete lining of basal lamina, and narrowed intercellular spaces. Immunoreaction products were seen in the basal lamina but not in the intercellular spaces. These findings indicate the basal lamina is involved in the formation of the epithelial rests.

Possible involvement of bone cells in a new cementum formation

Cells from the gingival lamina propria, bone-derived granular tissues and periodontal ligament (PDL) were isolated after periodontal surgery and subsequently cultured in vitro. The resulting cells were defined as gingival cells, bone cells and PDL cells, respectively. Under a phase contrast microscope, the cultured cells exhibited a spindle and/or a polyhedral shape. On the basis of their appearance under an electron microscope, spindle-shaped cells and polyhedral-shaped cells were identified as fibroblasts and osteoblasts, respectively. Bone cells, a homogeneous population of osteoblasts, had a more rapid growth ability than PDL cells, which were a heterogeneous population of fibroblasts and osteoblasts. Of particular interest was that only bone cells produced bone matrix in the multilayers in vitro. These results support the hypothesis that the phenotype expressed by cells from the alveolar bone establishes a new concept for progenitor cells in the formation of cementum.

Sensory receptors in the periodontal ligament of hamster incisors with special reference to the distribution, ultrastructure and three-dimensional reconstruction of Ruffini endings

The innervation of the periodontal ligament in hamster incisors was investigated by means of immunohistochemistry for nervous-specific proteins and electron microscopy. The lingual periodontal ligament was found to be exclusively innervated by Ruffini endings which appeared to be most developed in this species among rodents; the labial periodontal ligament lacked them. The Ruffini endings occupied the alveolar half of the periodontal ligament, being intertwined with transverse collagen fibers. In electron microscopy, the Ruffini endings displayed expanded axon terminals filled with large-sized mitochondria. Three-dimensional reconstructions of the Ruffini endings at the electron microscopic level revealed complicated shapes for the axon terminals and a characteristic relationship with the associated terminal Schwann cells. The axon terminals were plate- or knob-shaped, the former being predominant. Each axon terminal was covered by thick Schwann sheaths derived from more than two terminal Schwann cells whose cell bodies were located apart from the axon terminals and contained a developed Golgi apparatus and rough endoplasmic reticulum. On the other hand, each terminal Schwann cell simultaneously extended their cytoplasmic processes to several axon terminals just like astrocytes. The thick Schwann sheath, for the most part, was covered by a multiple layer of basal lamina. These findings have aided us in understanding the entire structure of the periodontal Ruffini endings.

Cholinesterase activity in terminal Schwann cells associated with Ruffini endings in the periodontal ligament of rat incisors

A nonspecific cholinesterase activity was demonstrated in terminal Schwann cells associated with Ruffini endings in the periodontal ligament of rat incisors at the light and electron microscopic levels. The terminal Schwann cells are ultrastructurally characterized by a well-developed Golgi apparatus and rough endoplasmic reticulum. The cells in this study were positive for nonspecific cholinesterase, whereas ordinary Schwann cells associated with more proximal nerve fibers reacted negatively. The reaction products were densely deposited in the cisternae of the rough endoplasmic reticulum and along the nuclear envelop. A moderately intense labeling was found in the cytoplasmic extensions, in which the reaction products gathered in caveolae and vesicles. These findings indicate that nonspecific cholinesterase is a useful marker to distinguish terminal Schwann cells from ordinary Schwann cells and that the enzyme may be synthesized in the rough endoplasmic reticulum and conveyed toward the axon terminals. Since this enzyme has been known to be shared by the inner bulb of Pacinian corpuscles and the lamellar cells of Meissner's corpuscles, its possible involvement in mechanoreceptive functions in these specialized Schwann cells deserves further investigation.

[Electron microscopic observation for periodontal tissue regeneration after implantation of atelocollagen membrane]

The purpose of the present study was to clarify wound healing process of periodontal tissue following experimental flap surgery, when applied the guided tissue regeneration (GTR) technique using a cross-linked atelocollagen membrane (AM). Mucoperiosteal flaps were made on the palatal gingiva of maxillary first molars of rats. The cementum was removed by curettage in order to expose the dentin surface. An AM was implanted into the site of dissection in the experimental group, while the control group received no implantation. The resorption processes of AM and wound healing processes of exposed root surface in the experimental group were examined by electron microscopic observation, 1, 3, 5, 7, 14 and 21 days, and 2, 3 months after the implantation. While the wound healing processes of periodontal tissue in the control group were examined at the fine structural level, 2 and 3 months after the flap surgery. The results were as follows. At the resorption processes of AM, the early invasion of a large number of neutrophils appeared in the site of of implantation. Neutrophils were attracted to and adhered to the AM fibers over the first few days after. AM was resolved to fine fibrous structure by the neutrophils between 1 and 3 days. A large number of macrophages appeared in the implanted site between 3 and 7 days, and neutrophils subsided after 5 days. The implanted material was rapidly resolved be macrophages with active phagocytosis, sometimes forming giant cells. Fibroblasts were invading to peripheral gingival connective tissue and were development of microfilament were observed. The implanted materials were completely resolved after 14 days. In light microscopical findings, of the experimental group, epithelial downgrowth was markedly inhibited, fibrous bundles of the gingival connective tissue were clearly arranged vertical to the root surface and new cementum tissue deposited to the root surface after 21 days. At electron microscopic observation in early stage of healing, dens granular layer (d. g. l.) was presented to the dentin surface. After 2 or 3 months of the control group, high density fibrous layer increased to the root surface. Connective tissue fiber bundles were paralleled to the root surface. The above results indicate that the GTR technique using an atelocollagen membrane may provide an effective method to promote periodontal tissue regeneration after periodontal surgery.

[In vitro growth of periodontal ligament fibroblasts between bone and root slices]

In a first experiment the proliferation and growth kinetics of periodontal ligament fibroblast monolayers generated from human healthy (HPDL) and diseased (DPDL) periodontia were compared. In a second experimental series a periodontal ligament-like space was developed by laying a root slice inside a bony ring slice on the bottom of a tissue culture petri dish and leaving a space of about 0.5 mm between both structures. HPDL cells showed a higher proliferation rate than DPDL cells. Growing into the space between the slices, the PDL cells built up a matrix which was composed of cells and fibrils. HPDL cells built up the matrix more rapidly than DPDL cells.

Effects of tooth function on adjacent alveolar bone and Sharpey's fibers of the rat periodontium

There is little information about the effects of short-term non-hypo-, and hyperfunction of teeth on the 1) mineralization patterns of intrinsic and extrinsic (Sharpey's) fibers and 2) mean number and diameter of Sharpey's fibers of adjacent alveolar bone. The mineral density of intrinsic and Sharpey's fibers and the size and number of Sharpey's fibers could indicate the relative strength of the attachment of a tooth to bone in various functional situations. In the present study, non- and hypofunctional situations were created by selective extraction of right molar teeth of the rat; the contralateral teeth were placed in hyperfunction by the surgery. In non- and hypofunctionals, intrinsic and Sharpey's fibers of the crestal third of the alveolus were less densely mineralized than in hyperfunctionals or untreated controls. Mean Sharpey's fiber diameters were significantly greater and their mean number/unit area significantly less in non- than in hypo- or hyperfunctionals or untreated controls (P less than 0.001). Mean Sharpey's fiber diameters in hyperfunctionals were significantly less than in untreated controls (P less than 0.05). Hypofunction ameliorated the effects of nonfunction on mean diameter and number of Sharpey's fibers, but had little effect on the density of mineralization of either the intrinsic or Sharpey's fibers of the alveolus, suggesting that their mineralization may be controlled by factors other than occlusal forces from the adjacent teeth. Thus changes in the stress/strain environment within the periodontium, coincident to altered occlusal function of the adjacent teeth, rapidly affects the morphology of intrinsic and Sharpey's fibers of alveolar bone and ensures that adequate tooth support is maintained in the new functional situation.

[Experimental studies on morphological changes of microvascular architecture following the free gingival autograft on denuded alveolar bone]

The purpose of the present studies was to examine the healing process following the free gingival autograft placed on the recipient bed either with or without periosteum in 54 adult mongrel dogs with healthy periodontium. A recipient bed was prepared on denuded alveolar bone in a definite portion of the attached gingiva of the right maxillary canine tooth, and the graft was taken from the attached gingiva of the left maxillary canine and transplanted in the recipient bed. Morphological changes were observed by means of vascular corrosion casts on the postoperatively 3rd, 5th, 14th, 21st, 28th, 42nd, 56th and 84th day. The healing process following the free gingival autograft on the denuded alveolar bone showed that this graft survived in its margin by recirculation from the cut margin of the recipient bed, and in its center the necrotic tissue changed to granulation tissue, which gradually cicatrized. This was different from the healing process following the free gingival autograft on periosteum, in which the graft was survived entirely by recirculation from the vascular plexus of the periosteum on the recipient bed. This may help to restore the function proper.

Transmission electron microscopy of supra-alveolar periodontal healing of auto- and allotransplanted teeth in monkeys

An ultrastructural study of the supra-alveolar periodontal healing of auto- and allotransplanted teeth was performed in 4 immunologically unmatched green Vervet monkeys. Eight mature incisors were either auto- or allotransplanted. Non-transplanted adjacent incisors served as controls. Prior to transplantation the teeth were endodontically treated extraorally. Eight weeks after transplantation, biopsies including part of the tooth and the adjacent supra-alveolar tissues were taken, fixed, decalcified and processed for electron microscopy. A thin electron dense layer covered the root surface of the autotransplanted teeth. Most collagen fibres inserted into this electron-dense border, as well as into the underlying cementum. A similar relationship between the fibres and root surface was found in controls. On the allotransplanted teeth a layer of electron-dense granular material covered the root surface in the supra-alveolar area. Collagen fibres inserting into the electron-dense border were frequently observed. Fibroblasts were the predominant cell type in the connective tissue adjacent to all transplanted teeth. In autotransplants 2 morphotypes of fibroblasts were observed: 1) cells with dilated endoplasmic reticulum and swollen mitochondria; and 2) cells with normal characteristics of protein synthesis and secretion. The fibroblasts of the allografts were predominantly cells with dilated endoplasmic reticulum and swollen mitochondria. The results indicated some similarities in the healing between the root surface and connective tissue in the supra-alveolar portion of the roots of auto- and allotransplanted teeth.

A morphometric, electron microscopic analysis of tissue channels shown by ionic tracer in normal and tensioned rat molar apical periodontal ligament

A 1.0 newton continuous, extrusive load was applied to the right maxillary molar for 30 min to determine the presence of channels as shown by the distribution of tracer across the interstitial compartment of normal and tensioned PDL. Sodium ferrocyanide (1% w/v), perfused via the common carotid arteries, was the tracer probe and tris(ethylenediamine) cobalt III chloride (1% w/v) the precipitating ion. Left molar control PDL had an overall mean of 0.43 +/- 0.05/microns2 tissue channels at 0.2 microns from the vascular endothelium, and 0.15 +/- 0.04/microns2 at 7-8 microns. On the experimental side, the overall mean number of tissue channels was 0.65 +/- 0.13/microns2 at 0-2 microns and 0.19 +/- 0.07/microns2 at 7-8 microns. A significant depth effect (P less than 0.01) was present in the control and experimental interstitial tissues for tissue channels adjacent to the endothelium of different categories of vessel. Extrusion increased the tissue channel density adjacent to arterial capillaries (P less than 0.01), venous capillaries (P less than 0.01) and postcapillary-sized venules (P less than 0.01). These findings implicate these three types of vessel as being functionally important in fluid exchange across endothelial boundaries in the PDL.

Differential distribution and ultrastructural staining of oxytalan and elastic fibers in the periodontal ligament of Alligator mississippiensis

We have investigated ultrastructural cytochemical properties of elastic elements in Alligator periodontal ligaments decalcified with EDTA and stained with 1) the tannic acid-uranyl acetate (TA-UA) method for elastin in combination with elastase digestion; 2) the high iron diamine-thiocarbohydrazide-silver proteinate (HID-TCH-SP) method with prior treatment of specimens with either monopersulphate or cupric-sulphite reagent for the localization of disulphide- and/or sulphydryl-containing material (i.e., oxytalan fibers); and 3) HID-TCH-SP alone for sulphated complex carbohydrates. Many microfibrils accumulated to form either large or small bundles. Large bundles having a diameter of 2.50 +/- 1.10 microns (mean +/- SD; n = 50) each showed an apico-occlusal distribution, although small bundles measuring 0.63 +/- 0.13 microns (mean +/- SD; n = 50) in diameter each were exclusively localized in interstitial areas rich in vessels and nerves. The former bundles always lacked TA-UA reactivity and represented oxytalan fibers; the latter bundles frequently contained TA-UA-reactive elastase digestible components and were similar in appearance to immature elastic fibers or elaunin fibers. HID-TCH-SP after oxidation strongly stained both the oxytalan and elastic fiber microfibrils but stained the amorphous elastin very weakly or not all. In nonoxidized specimens, there was no definite HID-TCH-SP staining of microfibrils and the amorphous elastin, although adjacent matrix proteoglycans stained consistently. These results indicate that although there is a marked difference in the distribution and size of oxytalan and elastic fibers in Alligator periodontal ligaments, their associated microfibrils lack stainable sulphate groups but are enriched with disulphide and/or sulphydryl groups, as has been described in mammals.

[Ultrastructural and cytochemical studies of clonal cell lines in fibroblasts derived from human periodontal ligaments--establishment of clonal cell lines in fibroblasts from periodontal ligaments]

It has recently been suggested that fibroblasts in periodontal ligaments have cytochemical characteristics similar to those of osteoblasts and different from those of other connective tissues. The authors isolated clonal cell lines of fibroblast-like cells from human periodontal ligaments in order to clarify their nature. Digestion with collagenase and hyaluronidase was used to isolate the cells from a human periodontal ligament. The cells were then plated in a 96-hole microplate. A single cell in a conditioned medium containing 20%FBS was placed in each hole. From these single cells large colonies ware subcultured. Subculturing was done every 8 days until more than 20 successive generations had been produced. The method developed by Lowry et al. was used to determine the ALPase activity of the cultured cells. From the 768 cells cultured from human periodontal ligament, 7 clonal cell lines were isolated in vitro. Cultures of these clonal cell lines resulted in typical, spindle-shaped, fibroblast-like cells, all of which were homogeneous. Very high ALPase activity was observed in 4 of the 7 cell lines. Enzyme reaction products occurred mainly along cell membranes. These stable clonal cell lines provide suitable systems for in vitro studies related to morphological and functional analysis of fibroblasts in the periodontal ligament.

Collagen phagocytosis by cementoblasts at the periodontal ligament-cementum interface

The periodontal ligament-cementum interface of rat first molars was investigated by electron microscopy. Evidence supporting cementoblast phagocytosis of collagen fibrils of the periodontal ligament was found. In addition, collagen-containing vacuoles were frequently observed within cementoblasts in association with an acid phosphatase activity. The presence of acid phosphatase activity in these vacuoles suggested that intracellular degradation of collagen was occurring. Our results showed that cementoblasts exhibited collagen phagocytic activity and suggest that cementoblasts may play an important role in the physiological remodeling and metabolic breakdown of the collagen at the periodontal ligament-cementum interface.