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

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

Effects of aging on oxytalan fibre in mouse periodontal ligament

The reactions of periodontal tissues to the mechanical stimulation of teeth seem to be different in patients of different ages. Although the effects of aging on other structures of the periodontal tissues, i.e., collagen fibre, bone, and cementum, have been reported, there is very little information available concerning the effects of aging on periodontal oxytalan fibre, which is reportedly the only elastic element in the human periodontal ligament. The purpose of this research was to clarify the aging related changes in the distribution of oxytalan fibres in the periodontal ligament of mice. Histological sections of the periodontal ligament of the lower first molar of 10-week-old (control group) and 1-year-old (aged group) ICR mice were specifically stained for oxytalan fibres with aldehyde fuchsin after preoxidization, and observed by light microscopy and confocal laser scanning microscopy (CLSM). In the aged group, oxytalan fibres seemed to be more prevalent around blood vessels in comparison with the control group. Furthermore, CLSM clearly showed that oxytalan fibres in the aged group were relatively more tortuous and complex than those in the control group. This tortuosity and complexity might imply that the oxytalan fibres in aged mice have lost a considerable amount of their original elasticity. While further study of these changes is required, these results may help orthodontists to establish better treatment strategies and methods for adult orthodontic patients.

An ultrastructural study of the effects of bisphosphonate administration on osteoclastic bone resorption during relapse of experimentally moved rat molars

This study was designed to clarify the effects of systemic administration of bisphosphonate, pamidronate, on the bone resorbing activity of osteoclasts during relapse of rat molars, after experimental movement. An elastic band was inserted between the upper first and second molars of 7-week-old rats and removed 21 days later. At 1 day before elastic band removal, bisphosphonate was administered via a tail vein. After elastic band removal, the rats were further maintained for 0, 5, or 10 days. The relapse of the first molars was studied by means of light and scanning-electron and transmission-electron microscopy. When an elastic band was removed, the mean interdental distance between the first and second molars in all rats was approximately 435 micrometer. In the control rats, it had decreased to 108 micrometer by day 5 and 57 micrometer by day 10. In these control rats, numerous osteoclasts appeared along the alveolar bone surface in the compressed side of the periodontal ligament of first molars. Administration of bisphosphonate significantly inhibited the prominent decrease in interdental distance. In these rats, it averaged 313 micrometer at day 5 and 115 micrometer at day 10. In bisphosphonate-treated rats, osteoclasts aggregated mainly in vascular canals of alveolar bone but were occasionally observed along the alveolar bone surfaces facing the periodontal ligament. Administration of bisphosphonate also induced structural changes, such as disappearance of ruffled borders and cytoplasmic polarity, in osteoclasts. A degenerated osteoclast was also observed in a bisphosphonate-treated rat. However, bisphosphonate induced no structural changes in osteoblasts, osteocytes, or periodontal ligament fibroblasts. These results suggest that a single systemic administration of bisphosphonate decreases the extent of initial relapse in experimentally moved rat molars via a mechanism involving impairment of the structure and resorptive functions of osteoclasts.

Presence of oxytalan fibers in human regenerated periodontal ligament

The aim of the present study was to investigate whether oxytalan fibers are formed in the regenerated human periodontal ligament. 6 patients, each of them exhibiting an advanced intrabony defect, were treated with a bioresorbable membrane according to the GTR-principle. Following a healing period of 6 months, the teeth were extracted together with their surrounding soft and hard tissues and subsequently fixed in 10% buffered formalin. Following decalcification in EDTA, the specimens were embedded in paraffin and 8-microm histological sections were cut in the mesio-distal direction, parallel to the long axes of the teeth. The sections were stained with hematoxylin and eosin, or with the oxone-aldehyde-fuchsin-Halmi staining method and examined in the light microscope. A regenerated periodontal ligament containing newly-formed oxytalan fibers was observed in all specimens. Many of them inserted into the newly formed cementum on the root surface. It is concluded that oxytalan fibers are formed de novo in human regenerated periodontal ligament tissue.

Transmission and scanning electron microscopic analysis of mineralized loci formed by human periodontal ligament cells in vitro

Fibroblasts isolated from human periodontal ligament (PDL) were cultured under a medium supplemented with ascorbic acid, beta-glycerophosphate and dexamethasone. The cultures were assessed for their ability to elaborate a mineralized matrix. Cell cultures stained positive when analyzed for alkaline phosphatase activity throughout the culture period. After about 3 weeks in culture, the cells produced a calcified matrix. Light microscopy showed formation of clusters of different shapes and sizes. Von Kossa staining revealed mineral deposits as amorphous brown-black precipitates. Transmission electron microscopy showed cells in multilayers and mineralized formations in close association with a dense network of collagen fibers. Scanning electron microscopy revealed smooth formations rising over the cultures with an abundant fiber matrix. We conclude that human PDL fibroblasts can be induced to form a mineralized matrix which shares features with bone mineralized matrix but most likely represents a more immature type of in vitro mineralization. Moreover, the present study further supports the osteoblastic potential of these cells.

Cellular roles in relapse processes of experimentally-moved rat molars

This histological study was designed to clarify the relapse processes of rat molars following orthodontic tooth movement by the Waldo method. An elastic band was inserted between the upper first and second molars, and removed either 7 or 21 days later. The relapse processes of first molars were examined at 1 or 4 days after completing the 7-day-insertion and at 5 or 10 days after the end of the 21-day-insertion. At the end of the 7-day-insertion period, the mean interdental space was 158 microns, but decreased rapidly, reaching 44 microns by 1 day after removal, and 16 microns by day 4. In the periodontal ligament (PDL) compressed by elastic band insertion, partial hyalinization and/or mineralization occurred. The stretched PDL consisted of irregularly-distributed, thin principal fibres, approximately 2.4 microns in diameter. On days 1 and 4 after removal, osteoclasts, macrophage-like cells and fibroblast-like cells were localized around hyalinized tissues, but thick principal fibres, approximately 3.8 microns in diameter, were regularly distributed throughout the PDL proper. The mean interdental space after the 21-day-insertion was 536 microns, but this had decreased to 108 microns by day 5, and 71 microns by day 10. On day 5 after removal, numerous osteoclasts were evenly distributed in the compressed PDL, while thick principal fibres, approximately 3.5 microns, were present in the stretched PDL. These results suggest that, during relapse of experimentally-moved rat molars, (i) rapid remodelling of the PDL and surrounding alveolar bones is the main cause of tooth relapse and (ii) hyalinized and/or mineralized tissues occurred by compression are rapidly resorbed by osteoclasts, macrophage-like cells and fibroblast-like cells.

The structure and function of periodontal ligament cells in acellular cementum in rat molars

To elucidate the structure and function of periodontal ligament cells at the periodontal ligament-cementum interface in advanced acellular cementogenesis, the cervical regions of molars in rats aged 6 weeks were observed by light and electron microscopy. The light and transmission electron microscopy showed the periodontal ligament cells to be elongated between dense, well-developed principal fibers. The transmission and scanning electron microscopy showed that these cells extended wing-like projections from the lateral surface, forming cylindrical compartments surrounding the principal fibers. In addition, finger-like projections extended toward the cementum from the cementum-facing ends. The main results suggest the following: at the periodontal ligament-cementum interface, the periodontal ligament cells maintain the architecture of the principal fibers by means of extracellular compartments. The arrangement of finger-like projections results in the formation of acellular cementum containing only Sharpey's fibers as a fibrous component.

[The responses of the microvasculature of the periodontal ligament to horizontal force]

OBJECTIVE

The purpose of this study is to examine the responses of the microvasculature in periodontal ligament(PDL) to horizontal force.

METHODS

Using ink injections and celloidin embed, serial sections were cut, then observed by light micrascope, quantitative analysis was conducted by the picture-analysis instrument. Vascular corrosion casts were prepared and examined by scanning electron microscopy. The forth premolars of dogs were pulled by 200 g force in a mesial direction for two hours, and the pressure effects in different positions were demonstrated.

RESULTS

The section area of the microvasculature per unit PDL area is obvious larger on the tension sides than on the pressure sides. There is not an obvious distinction on the pressure sides between the experiment groups and control groups. However, there are clear distinctions in the one-third of cervical, and apical segment on the tension sides between the experiment groups and control groups.

CONCLUSION

The microvascular changes in PDL had importance to the cushioning effect of PDL when a teeth received a kind of force in a short-time.

Type VI collagen is associated with microfibrils and oxytalan fibers in the extracellular matrix of periodontium, mesenterium and periosteum

Type VI collagen was immunolocalized in several soft connective tissues at the light and electron microscopic level. Positive labeling was found in all tissues examined, periodontal ligament, gingiva, mesenterium and periosteum. The labeled structures could be divided into 2 categories: microfibrils intermingling with collagen fibrils, and those that formed bundles (oxytalan fibres and elastin-associated microfibrils). Control sections incubated with antibody preabsorbed to purified type VI collagen, or with non-immune antibody, proved to be negative. Our observations indicate that the structural organization of type VI collagen varies from small microfibrillar structures associated with the collagen and elastin fibre systems to highly ordered parallel arrays of oxytalan bundles.

Changes in the cytoskeleton of cells within the periodontal ligament and dental pulp of the rat first molar tooth during ageing

The periodontal ligament and dental pulp connective tissues are foetal-like, and their process of ageing may therefore differ from other tissues of mesenchymal origin. Several studies have already highlighted the lack of age changes in the extracellular matrix (ECM), but more needs to be known about cellular changes. For this study, tissues from the first molar teeth of Wistar rats aged 12 wk and 104 wk were compared by immunolocalisation of cytoskeletal components. Tissues from the first molar were immunostained, employing a panel of 16 monoclonal antibodies against cytokeratins, vimentin, F-actin and tubulin. Within the pulp, labelling for vimentin in both odontoblasts and pulpal fibroblasts and F-actin in the cell processes of odontoblasts was detected at both ages but with marked reduction in labelling in the older tissue. Within the periodontal ligament, vimentin labelling was weaker in the aged tissue, especially nearer the cementum. More significantly, the fibroblasts of the aged periodontal ligament expressed cytokeratin 19. In contrast to reports of little age change to the ECM, the cells of the pulp, and particularly the periodontal ligament, show marked changes to their cytoskeletal components.

Formation of reparative acellular extrinsic fiber cementum in relation to implant materials installed in rat periodontium

The aim of the present study was to determine the nature of the cells associated with the formation of reparative acellular extrinsic fiber cementum (AEFC). Calcifying collagen membranes, hydroxyapatite particles and/or non-resorbable ePTFE membranes were implanted in lesions made in the periodontium of the rat mandibular incisor. The incisor was prevented from erupting further, and the animals were killed after 1-8 wk. In the first week, next to cells with a fibroblastic phenotype, epithelial cells (ECs) migrating out of the reduced enamel epithelium were among the cells colonizing the wounds. From 2 wk on, the ECs showed regressive changes and disappeared. Along mineralized implant surfaces, a basophilic layer enriched in osteopontin (but without detectable amelogenin) was deposited. After 3 wk (when ECs were no longer present) the healing tissue transformed into a well-organized PDL-like tissue, and AEFC started to develop. Along the non-mineralizing ePTFE membranes, AEFC did not form except in regions where small calcified bodies were present. It is concluded that reparative AEFC layers are formed only along calcified surfaces. The cells associated with this reparative activity are periodontal ligament cells with a fibroblastic phenotype.

Coexpression of calretinin and parvalbumin in Ruffini-like endings in the rat incisor periodontal ligament

The coexpression of calretinin- (CR) and parvalbumin-immunoreactivities (irs) was examined in oro-facial tissues of the rat. Nerve fibers coexpressing these calcium-binding proteins (CaBPs) were observed in the lingual periodontal ligament of incisors but not other tissues. In the part of periodontal ligament adjacent to the alveolar bone, such nerve fibers left nerve bundles and formed bush-like endings, i.e., they ramified repeatedly and terminated with one to four twigs. An immunoelectron microscopic method indicated that these endings were identical to Ruffini-like endings, 4% of trigeminal neurons retrogradely labeled from the inferior alveolar nerve coexpressed CR- and parvalbumin-irs. The present observations suggest that the coexpression of these CaBPs may be a specific marker for low-threshold mechanoreceptors in the trigeminal ganglion.

Immunocytochemical demonstration of beta 1-subunit of Na+/K(+)-ATPase in the mechanoreceptive Ruffini-like endings of the rat incisor ligament

The localization of one of the isoforms of Na+/K(+)-ATPase, the beta 1-subunit, was investigated in the periodontal Ruffini endings of rat incisors by light- and electron-microscopic immunocytochemistry. Immunoreactivity for the rat beta 1-subunit followed the pattern of dendritic terminal arborization in the alveolar half of the lingual periodontal ligament. Ultrastructurally, the reaction products were localized in dilatations of axons, possibly the terminals of Ruffini-like endings in the periodontal ligament. No immunoreactivity was seen in Schwann cells. The immunostaining results support the view that the beta 1-subunit of Na+/K(+)-ATPase is the predominant isoform in sensory neurones, and that this protein is a useful marker for periodontal Ruffini-like endings.

Biomechanical and morphological studies on the periodontal ligament of the rat molar after treatment with alpha-amylase in vitro

Biomechanical properties and morphological features of the rat molar periodontal ligament were examined after treatment with alpha-amylase. Treatment with alpha-amylase induced dose-dependent decreases in the maximum shear stress, tangent modulus, and failure strain-energy density of the periodontal ligament; in addition, it weakened the alcian-blue staining of the periodontal ligament and exposed periodontal collagen fibrils as revealed by scanning electron microscopy. Azan staining and polarized microscopic observations of the periodontal collagen fibers were not markedly different between the control and alpha-amylase treated specimens. These results suggest that decreases in the strength of the periodontal ligament due to alpha-amylase digestion are largely due to removal of interfibrillar substances such as acid glycosaminoglycans and neutral polysaccharides from the periodontal ligament. It is also suggested that the interaction of the interfibrillar substances with collagen fibrils is involved the biomechanical properties of the periodontal ligament.

Quantitative morphology of dermal elastic fibers system of the human face during aging

Human skin has various distributions and arrangements of elastic fiber (EF). Previous reports did not clearly show the distribution of EF in the face skin because of various contents during aging. In this study, a color image analyzer indicated distribution of elastic, oxytalan, and muscle fibers in human face skin. During aging the muscle fiber size and the content of the EF decreased in the modiolus and inferior labial regions of the human skin, and the ratio of the EF was lower than that of oxytalan fiber measured areas. That is, the dimension of oxytalan fiber may reflect the content of EF, and muscle has a role in the distribution of the EF in human face skin. In the deeper regions, small and large EF bundles were found near the sheath of gland and muscles. Therefore, face movement might be an important aspect to maintaining the EF content of human face skin.

Formation of an alternate lamellar pattern in the advanced cellular cementogenesis in human teeth

The formation of an alternate lamellar pattern in the advanced stage of cellular cementogenesis in human molars was examined by light and electron microscopy. In longitudinal ultrathin sections, longitudinally oriented intrinsic fibril bundles appeared in close and parallel association with slender processes of cementoblasts on the cementum. Where transversely oriented intrinsic fibril bundles appeared, cementoblasts formed indentations to enclose the fibril bundles. Cytoplasmic fragments were also enclosed in the indentations. Scanning electron microscopy indicated that cementoblasts have developed two types of processes on their cementum-facing side - ridge- and finger-like. The cementoblasts formed groove-like compartments by ridge-like processes in cooperation with other cementoblasts. The compartments formed groups, and in each group the compartments were arranged in the same direction. The finger-like processes were arranged in parallel with the ridge-like processes in the compartments. These observations suggest that: (1) slender processes and cytoplasmic fragments are longitudinally and transversely cut finger-like processes, respectively; (2) the cellular indentations are transversely cut groove-like compartments; (3) the cementoblasts regulate the intrinsic fiber arrangement by the two types of processes; (4) the cementoblasts move the two types of processes synchronously and periodically to cause an alternate change in the intrinsic fiber arrangement. This dynamic sequence results in the alternate lamellar pattern of cellular cementum.

Expression of TrkB-like immunoreactivity in non-neural cells of rat periodontal ligament

The Trk family, a group of high-affinity neurotrophin receptors, is divided into three subtypes, TrkA, TrkB and TrkC. These were originally found in neural elements, and are involved in neural development, maintenance and survival. Recent studies have shown that non-neural cells in vitro also express mRNA encoding some neurotrophin receptors. In our preliminary study, TrkB-like immunoreactivity (LI) was found in the various non-neural cells in the rat periodontal ligament. The present study was undertaken to clarify which cell types express Trk-LI, in particular two types of TrkB-LI, in the periodontal ligament of mature rats, using an immunocytochemical technique with polyclonal antibodies. Intense full-length TrkB-LI was clearly recognized in non-neural cells such as fibroblasts, osteoclasts, odontoclasts and cementoblasts as well as in neural elements. Relatively large cells with many cytoplasmic processes were also frequently immunopositive for full-length TrkB. Immunocytochemistry for TrkB[TK-], a truncated type, also demonstrated a similar immunostaining pattern to that of full-length TrkB in non-neural periodontal cells, and intense positive reactions in endothelial cells. Some non-neural cells were positive for TrkA and TrkC. These findings suggest that neurotrophic factors, the ligands of the Trk family, have certain effects on the proliferation and/or differentiation of non-neural cells, as well as on their neurotrophic functions.

The roles of periodontal ligament mechanoreceptors in the reflex control of human jaw-closing muscles

Controlled mechanical stimuli were applied to an upper central incisor tooth in 19 human subjects and the resulting reflexes in the ipsilateral masseter muscle were examined electromyographically. In most cases the force profile of the stimuli consisted of a ramp leading to a sustained plateau at an intensity of 1 N. In addition 1 N tap stimuli were employed in some subjects. The 1 N ramp stimuli with a rise time of < or = 20 ms consistently evoked a single, short-latency (approximately 12 ms), inhibitory reflex which was often followed by an excitatory wave. The ramp stimuli with shorter rise times produced larger responses than those produced by ramp stimuli with longer rise times. By contrast the tap stimuli elicited a sequence of responses consisting of inhibitory-excitatory-inhibitory-excitatory components. The first inhibitory and excitatory responses evoked by tap stimuli had latencies similar to those of the responses evoked by the ramp stimuli. The latencies of the inhibitory responses evoked by 1 N ramps with rise times ranging between 2.5 and 20 ms did not vary significantly with the rise time. Consistent with this observation it was found that the median threshold force for evoking the short-latency inhibitory reflex was only 0.25 N. This was significantly less than the threshold for the excitatory response (median: 0.75 N). The responses to ramp-plateau forces were not dependent on the level of preloading of the tooth (at least within the range tested: < 0.25 to 1 N). These findings provide evidence that mechanoreceptors in the periodontal ligament contribute to the control of human jaw-closing muscles, notably to short-latency reflex responses. It may be concluded that the additional reflex responses produced by tapping stimuli result from the activation of receptors elsewhere due to vibration.

Different localizations of growth-associated protein (GAP-43) in mechanoreceptors and free nerve endings of adult rat periodontal ligament, dental pulp and skin

Distributions of growth-associated protein-43 (GAP-43) in the periodontal ligament and dental pulp of adult rats were studied by light and electron microscopy. The mature periodontal ligament and dental pulp contained numerous GAP-43-positive neural elements, comprising periodontal Ruffini endings and thin nerve fibers, but expression patterns differed among the kinds of nerves. In the periodontal ligament of rat molars, immunoelectron microscopy revealed that GAP-43 like immunoreactivity in the Ruffini ending, an essential mechanoreceptor, was confined to the Schwann sheaths around the axon terminals and was not in the axon terminals themselves, unlike free endings that revealed axonal GAP-43. However, the lamellar Schwann cells associated with the cutaneous receptors did not exhibit any GAP-43 like immunoreactivity though they were intensely reactive for low affinity nerve growth factor receptor (p75-NGFR), a marker for lamellar Schwann cells in mechanoreceptors. The characteristically uniform expression of GAP-43 in the Schwann lamellae that surround the Ruffini mechanoreceptors of rat molar ligament suggests that Schwann cells are involved in the GAP-43 mediated plasticity of these receptors. On the other hand, the pulpal nerves were filled with the reaction products in their axonal spaces, suggesting the potential for neuronal plasticity during normal function and after tooth injury.

Microvascular luminal volume changes in aged mouse periodontal ligament

Data for the microvascular bed in the aged periodontal ligament have not been established. This investigation tested the hypothesis that the luminal microvascular volume decreased in the aged ligament. Mice 35 days old and one year old were vascular-perfused and the mandibular first molar periodontal ligament processed for electron microscopy. Tissue quadrats from each circumferential third ligament region were recorded at 150-microns intervals from the alveolar crest to the apex for randomized sampling of blood vessel lumina. The data were analyzed with a generalized linear model at the p < 0.01 level for the interaction of the aging effect with differences across regions. Stereological parameters were established for vessel lumen volume, and for surface and length densities. Mean ligament width decreased from 119.9 +/- 16.94 (micron +/- SE) in young mice to 60.0 +/- 10.58 (micron +/- SE) in aged mice. The luminal volume of 8.63 +/- 1.37 (% +/- SE) in young ligament increased to 9.83 +/- 2.14 (% +/- SE) in aged ligament. Collecting venules and the combined group of arterio-venous anastomoses with terminal arterioles showed a two-fold increase in luminal volume density (p < 0.01). In aged ligament, regional shifts affected the microvascular bed distribution, but these changes were not consistent across regions, or with depth. The average cross-sectional tissue area served per capillary decreased from 2117 microns 2 to 1451 microns 2 for young and old. Average ligament thickness served per capillary dropped from 52.5 microns to 27.5 microns. These reductions in average diffusion distances indicated a change in the quality of the diffusion barrier with age.

Changing expression of intermediate filaments in fibroblasts and cementoblasts of the developing periodontal ligament of the rat molar tooth

The distributing of vimentin and cytokeratin intermediate filaments within the cells of the dental follicle and developing periodontal ligament is described during eruption of the rat 1st molar tooth. Alcohol-fixed tissues from animals ranging from neonates to 12 wk old were cryosectioned, immunolabelled with monoclonal antibodies against vimentin and a range of cytokeratins and examined by indirect immunofluorescence. Vimentin was observed in follicular and periodontal ligament fibroblasts in all animals and at all stages of eruption. It was also observed in cementoblasts after disruption of the epithelial root sheath (of Hertwig) which is responsible for determining the shape of the developing root. Prior to eruption, cytokeratins were restricted to epithelial components of the developing tooth, including the root sheath. However, they were seen in cementoblasts on disruption of the root sheath at 2 wk and in periodontal ligament fibroblasts at 3 wk after birth, when the tooth was erupting but had not reached occlusion. On occlusion (at 4 wk), fibroblasts no longer labelled for cytokeratins but cementoblasts associated with acellular cementum formation continued to express them. These results demonstrate temporal and spatial changes within the cells of the developing periodontal connective tissues and suggest that the appearance of cytokeratins in periodontal fibroblasts and cementoblasts may be related to mechanical changes during tooth eruption. Further, the results suggest different origins for cementoblasts associated with cellular and acellular cementum formation.

Cellular cementogenesis in rat molars: the role of cementoblasts in the deposition of intrinsic matrix fibers of cementum proper

The formation of intrinsic fibers was examined in the advanced stage of rat cellular cementogenesis by light and electron microscopy. Using scanning electron microscopy, cementoblasts showed wing-like processes, partly encircling principal fibers. At the cementum-facing side of the cells these processes showed segmentation into finger-like processes, arranged in parallel with the cementum surface. Transmission electron microscopy showed many cytoplasmic fragments around intrinsic fibers at the cementum surface. These fragments contained microtubules and collagenous secretory granules that were arranged in parallel with the cementum surface and the intrinsic fibers. The wing-like processes contained microtubules and secretory granules that were arranged perpendicularly to the cementum surface and in parallel with the principal fibers. These observations suggest that: (1) the cytoplasmic fragments are cross-sectioned finger-like processes; (2) cementoblasts secrete intrinsic fibers from the finger-like processes and additional principal fibers from the wing-like processes; (3) cementoblasts constantly shorten their wing-like processes by forming finger-like processes. This development starts at the side facing the cementum and proceeds towards the periodontal ligament. With the segmentation, the cementoblasts change the arrangement of secretory granules to secrete intrinsic fibers around preformed principal fibers.

Functional characteristics of gingival and periodontal ligament fibroblasts

In periodontal surgery, healing after guided tissue regeneration (GTR) may be explained by differences in functional activities of gingival and periodontal ligament fibroblasts (GF and PDLF). Several studies in vitro have supported this hypothesis, but much remains to be defined. In the present work, gingival and periodontal ligament fibroblasts derived from five healthy subjects were isolated and compared in vitro. The morphology of the cells was observed under scanning electron microscopy (SEM). Several extracellular matrix components (ECM) were studied to compare the effects on fibroblast attachment, proliferation, and protein synthesis. Several biochemical markers were examined in both cellular extract (CE) and conditioned medium (CM). We also examined the muscle differentiation markers alpha-smooth muscle actin, desmin, and smooth-muscle myosin. Finally, we studied the effects of epithelial cells on the proliferation and protein synthesis of the two types of fibroblasts. GF and PDLF appeared identical under the SEM. All ECM components enhanced attachment; however, while collagen types I and IV promoted the attachment of GF, gelatin, laminin, and vitronectin promoted that of PDLF. Most ECM components increased the proliferation rate of GF and the biosynthetic activity of PDLF. The biochemical markers were similarly distributed between the two cell types, except for alkaline phosphatase, which was detected only in the CE of PDLF. Both GF and PDLF strongly expressed alpha-smooth-muscle actin and were negative for desmin; only PDLF were positive for smooth-muscle myosin. Epithelial cells increased the proliferation of both GF and PDLF but had no effect on their biosynthetic activity. These in vitro results may better explain the in vivo functional differences between GF and PDLF.

Changes in the fibre arrangement of the rat incisor periodontal ligament in relation to various loading levels in vitro

The relationship between the fibre arrangement of the periodontal ligament and the load-deformation behaviour was investigated at various loading levels. Transverse sections of the rat incisor were loaded in the eruptive direction in vitro and the deformation fixed at predetermined loads. Sections were prepared at these deformation levels. The periodontal ligaments were examined by polarized-light and scanning-electron microscopy. At the initial ("toe') part of the load-deformation curve, the periodontal fibres were gradually pulled and bent towards the direction of loading; their wavy pattern and periodic dark and bright bands became indistinct. At the next, linear part of the curve, the running direction of the fibres changed gradually until they were straightened and stretched. At the yielding part of the curve, the periodontal fibres began to rupture. Ruptured fibres adhering to the bone surface returned to their original obliquity and showed periodic dark and bright bands. The fibrous components of the rat incisor periodontal ligament thus transmit forces to bone at the linear part of the curve when the tooth is axially loaded.

Mechanical stretching of periodontal ligament fibroblasts--a study on cytoskeletal involvement

To investigate molecular aspects of the mechanism(s) involved in orthodontic tooth movement, periodontal ligament fibroblasts (PDL) were isolated and grown on culture dishes with a flexible bottom. The cells were stimulated by stretching the bottom of the culture dishes and whole cell extracts were prepared and subjected to sodium dodecyl sulfate polyacrylamide (SDS-PAGE) electrophoresis, electrotransferred to nitrocellulose membrane and immunoprobed with antibodies specific for vimentin and alpha- and beta-tubulin. No apparent alterations in the expression profile of the above mentioned major cytoskeletal elements were evident after mechanical stretching. Moreover, immunofluorescence against the same proteins revealed no changes in their topographical organisation between stretched and unstretched cell cultures.