Response of periodontal ligament cells to orthodontic force: ultrastructural identification of proliferating fibroblasts

Histochemical examination of cathepsin K, MMP1 and MMP2 in compressed periodontal ligament during orthodontic tooth movement in periostin deficient mice

The purpose of this study was to investigate immunolocalization of collagenolytic enzymes including cathepsin K, matrix metalloproteinase (MMP) 1 and 2 in the compressed periodontal ligament (PDL) during orthodontic tooth movement using a periostin deficient (Pn-/-) mouse model. Twelve-week-old male mice homozygous for the disrupted periostin gene and their wild type (WT) littermates were used in these experiments. The tooth movement was performed according to Waldo's method, in which elastic bands of 0.5 mm thickness were inserted between the first and second upper molars of mice under anesthesia. At 1 and 3 days after orthodontic force application, mice were fixed with transcardial perfusion of 4 % paraformaldehyde in 0.1 M phosphate buffer (pH 7.4), and the first molars and peripheral alveolar bones were extracted for histochemical analyses. Compared with WT mice, immunolocalization of cathepsin K, MMP1 and MMP2 was significantly decreased at 1 and 3 days after orthodontic tooth movement in the compressed PDL of Pn-/- mice, although MMP1-reactivity and MMP2-reactivity decreased at different amounts. Very little cathepsin K-immunoreactivity was observed in the assessed regions of Pn-/- mice, both before and after orthodontic force application. Furthermore, Pn-/- mice showed a much wider residual PDL than WT mice. Taken together, we concluded that periostin plays an essential role in the function of collagenolytic enzymes like cathepsin K, MMP1 and MMP2 in the compressed PDL after orthodontic force application.

[Transplantation of impacted canines]

Techniques for dental transplantation today are taking better advantage of the potential for healing of the periodontal ligament than in the past and have reduced the risk of ankylosis and root resorption to below 1.5%. The resulting improvement in prognosis has made it possible to more confidently plan procedures that include orthodontic treatment. Transplantations can offer a good end result in certain clinical situations that would otherwise be difficult to manage: ectopic teeth, transpositions, tooth trauma sequellae, advanced decay or advanced periodontitis, implanted hard to treat impacted teeth, and idiopathic ankylosis. This article describes the biological principles for transplantation using double periodontal ligament stimulation, explains the surgical techniques and provides several examples to expand on the treatment of impacted canines, whether or not they present with idiopathic ankylosis. Dental ankylosis is the fusion of the bone with the root. The idiopathic type occurs spontaneously before the eruption of the affected tooth. The etiology is unknown. Because the tooth becomes part of the process of osseous remodeling, it is progressively resorbed and then replaced by bony tissue. This process takes place rather quickly and weakens the tooth. Additionally, an early diagnosis makes it possible to plan a transplantation under favorable circumstances, as that is the only way to halt the ankylosis and to achieve an adequate implantation. In rare cases, the location of the ankylosis is surgically accessible and can be eliminated before resuming orthodontic traction.

Idiopathic ankylosis-resorption: diagnosis and treatment

Dental ankylosis involves the fusion of root to bone. The idiopathic form occurs spontaneously before the eruption of the tooth concerned. Etiology is unknown. As the tooth becomes part of the bone-remodeling process, it is gradually resorbed and is replaced by bony tissue. The process is quite rapid and weakens the tooth. Thus, early diagnosis makes it possible to perform a graft in optimal conditions, this being the only means of severing the ankylosis and achieving adequate eruption. In some rare cases, the ankylotic point of fusion can be reached surgically and can be eliminated before orthodontic traction is initiated.

Comparison of dentoalveolar morphology in WT and P2X7R KO mice for the development of biomechanical orthodontic models

It has been suggested that the absence of the P2X7 receptor affects long bone morphology, and that one of the cytokines dependent on its activation may also affect tooth morphology. P2X7R KO (knockout) were compared with C57B/6 WT mice (background strain) to identify differences in a maxillary molar and surrounding bone. Nineteen WT and 12 KO mouse maxillae were scanned and 3D-reconstructed using microCT. Tooth dimensions were measured and 3D bone morphometry was conducted. A finite element model was constructed based on the results. No statistically significant differences were found in dentoalveolar characteristics between the two mouse types. A single finite element model of the tooth can be used to mechanically represent both strains. P2X7R does not have a major effect on alveolar bone or tooth morphology. The P2X7R effects are site-specific.

Establishment of Periodontal Ligament Cell Lines from Temperature-Sensitive Simian Virus 40 Large T-antigen Transgenic Rats

Orthodontic tooth movement is controlled by various cell types in the periodontal ligament (PDL). Mechanical stresses, such as orthodontic force, are thought to induce differentiation of the mesenchymal cells in the PDL into osteoblasts and cementoblasts. The details of the process of differentiation, however, are not known, in part because adequate in vitro systems for their study do not yet exist. The purpose of this study was to establish and characterize immortalized PDL cell lines derived from the PDL of transgenic rats harboring the temperature-sensitive simian virus 40 T-antigen gene (TG rats). The PDL was removed from the molar roots of TG rats and incubated in tissue culture. Outgrowth cells from the PDL explant were passaged and cloned, depending on the shape of the colonies formed. The cell lines thus established were analyzed by reverse transcription-polymerase chain reaction for expression of type-I collagen, osteopontin, fibronectin, alkaline phosphatase (bone type), bone sialoprotein, the receptor activator of NF-kappa B ligand, and osteoprotegerin. In addition, the capacity for formation of mineralized nodules was assessed by incubating cells in calcification-promoting medium at 37 degrees C. A total of 15 stable cell lines were successfully established and characterized. These cell lines were classified into six groups based on their pattern of gene expression at 33 degrees C. Moreover, three of these clones were capable of forming calcified nodules. In conclusion, differential gene expression was demonstrated in 15 established PDL cell lines. Some cells had the potential to differentiate into cell types found in mineralized tissues, such as osteoblasts and cementoblasts, as well as cells expressing molecules that regulate osteoclast differentiation.

Tooth auto-transplantation with double periodontal ligament stimulation to replace periodontally compromised teeth

BACKGROUND

The healing process of autotransplantation puts 2 different tissues in competition: the ligament on the root surface and the bone tissue of the alveolus. This study shows the effects of a protocol with 2 surgical stages, which promote ligament repair, inhibit adhesion between bone and dental root, and reduce the occurrence of the ankylosis-root resorption phenomenon.

METHODS

Forty-three patients, 33 to 73 years old, received 47 transplantations of mature teeth (including retained teeth) during a 5-year period. During the first surgical step, the transplanted tooth is extracted, measured, immediately replaced in its origin site, and maintained with an original suture technique. The alveolus to which the tooth will be transplanted is adapted after extraction of the periodontally compromised tooth. The second surgery occurs at day 14, when regeneration of periodontal ligament (PDL) is at a maximum (first stimulation). The tooth is transplanted in its new alveolus and retained using the same suture technique to avoid a rigid splint and to create mechanical stimulation of the PDL (second stimulation).

RESULTS

The results were 95.75% positive with normal PDL, with a 4.25% failure rate (transplant loss) and no ankylosis. Mean probing reduction was 8.37 +/- 3.0 mm. Mean radiographic bone gain was 7.73 +/- 4.32 mm.

CONCLUSIONS

This study suggests that auto-transplantation with double PDL stimulation can be a viable treatment in clinical practice, especially to replace teeth with large periodontal lesions, deep furcation defects, and/or root fractures. This study shows the high potential of stimulated PDL to regenerate alveolar bone and periodontal structures in severe destruction sites.

Bisphosphonate modulates proliferation and differentiation of rat periodontal ligament cells during wound healing

BACKGROUND

Periodontal ligament (PL) width is precisely maintained throughout the lifetime of adult mammals, but the biological mechanisms that regulate the spatial locations of the cell populations for bone, cementum, and PL are unknown.

METHODS

As bisphosphonates induce ankylosis in mouse molar teeth, we used ethane-1-hydroxy-1, 1-bisphosphonate-(HEBP, Etidronate; Didronel) in combination with a periodontal window wound model to identify those cell populations involved in the regulation of PL width during the reformation of cellular domains after wounding. Four groups of Wistar rats were wounded by drilling through the alveolar bone and extirpation of the PL. Rats were administered HEBP for 1 week and then sacrificed or allowed to recover for an additional week prior to sacrifice. Control rats were sacrificed after 1 or 2 weeks. One hour prior to sacrifice, rats were injected with 3H-thymidine to label proliferating cells. Tissue sections were immunohistochemically stained for osteopontin (OPN) or bone sialoprotein (BSP) or were prepared for in situ hybridization (BSP) to identify extra- and intracellular expression of these non-collagenous bone proteins associated with periodontal healing.

RESULTS

HEBP treatment for 1 week induced a twofold increase in the thickness of the alveolar bone matrix in which weak immuno-staining for OPN and BSP mRNA signal was seen. During the recovery phase the increased bone width was reduced but was still considerably thicker than in control (P < 0.001). OPN staining as well as the BSP mRNA signal were much more intense than at 1 week. HEBP induced a > 40% reduction of PL width which returned to normal dimensions following the recovery phase. HEBP also modulated PL cell proliferation and differentiation: PL cell counts and labelling indices were reduced fivefold after 1 week of HEBP but returned to control values after the recovery phase. In controls, PL cells did not express OPN and BSP, but after HEBP treatment, and particularly after the recovery phase, PL cells expressed both of these markers intensely. In contrast, gingival and pulp connective tissues that were contiguous with the PL were not stained for OPN and did not express BSP mRNA after HEBP treatment.

CONCLUSIONS

While wounding induced transient increases of proliferation which were followed by repopulation of the extirpated tissue, the effects of HEBP on cell differentiation were independent of wounding. HEBP modulates the differentiation of PL cells and recruits cells that contribute to alveolar bone formation and loss of PL width homeostasis. Conceivably, bisphosphonates could be used therapeutically to selectively alter the differentiation of PL cells and promote the formation of alveolar bone and cementum.

Preparation of unfixed and undecalcified frozen sections of adult rat periodontal ligament during experimental tooth movement

The upper first molars of adult male rats were moved for 7 days and unfixed, undecalcified frozen sections of the molar periodontal ligament were prepared and observed. The upper jaws of the rats were immersed rapidly in liquid nitrogen and sectioned with a cryostat using a super hard knife. Five micrometer serial sections were cut, collected, freeze-dried and observed with both light and scanning electron microscopy. Electron probe microanalysis (EPMA) was also performed on the sections. On the tension side of the periodontal ligament, periodontal fibers were stretched and the osteoblasts were aligned on the osteoid, which showed metamasia with the toluidine blue stain. On the pressure side where the periodontal ligament was extremely compressed, tissue degeneration was caused by tooth movement and the osteoclasts were observed on the bone surface adjacent to the degenerating tissues. Scanning electron microscopy revealed a network arrangement of the collagen fiber bundles on the tension side, but not on the pressure side of the periodontal ligament. The spectrum obtained from EPMA of the osteoid demonstrated X-ray (Ka) peaks of Na, P, S, K and Ca.

Histochemical demonstration of acid phosphatase activity in terminal Schwann cells associated with Ruffini endings in the periodontal ligament of rat incisors

Histochemical staining for acid phosphatase, a marker for lysosomal elements, distinguished rounded, intensely reactive cells from less reactive fibroblasts and osteoblasts in the lingual periodontal ligament. The highly reactive cells were located exclusively in the alveolar half of the ligament. Double staining for acid phosphatase and S-100 protein confirmed that these reactive cells were identical with the terminal Schwann cells associated with periodontal Ruffini endings. Electron microscopically, reaction products for acid phosphatase were observed in the lysosomes and Golgi apparatus in the paranuclear cytoplasm of the terminal Schwann cells. As the terminal Schwann cells associated with the Ruffini endings are assumed to be capable of synthesizing exportable proteins, acid phosphatase in this type of cell may be involved in the processing of macromolecules in synthetic and/or secretory pathways.

Tooth movement

This article reviews the evolution of concepts regarding the biological foundation of force-induced tooth movement. Nineteenth century hypotheses proposed two mechanisms: application of pressure and tension to the periodontal ligament (PDL), and bending of the alveolar bone. Histologic investigations in the early and middle years of the 20th century revealed that both phenomena actually occur concomitantly, and that cells, as well as extracellular components of the PDL and alveolar bone, participate in the response to applied mechanical forces, which ultimately results in remodeling activities. Experiments with isolated cells in culture demonstrated that shape distortion might lead to cellular activation, either by opening plasma membrane ion channels, or by crystallizing cytoskeletal filaments. Mechanical distortion of collagenous matrices, mineralized or non-mineralized, may, on the other hand, evoke the development of bioelectric phenomena (stress-generated potentials and streaming potentials) that are capable of stimulating cells by altering the electric charge on their membrane or their fluid envelope. In intact animals, mechanical perturbations on the order of about 1 min/d are apparently sufficient to cause profound osteogenic responses, perhaps due to matrix proteoglycan-related "strain memory". Enzymatically isolated human PDL cells respond biochemically to mechanical and chemical signals. The latter include endocrines, autocrines, and paracrines. Histochemical and immunohistochemical studies showed that during the early places of tooth movement, PDL fluids are shifted, and cells and matrix are distorted. Vasoactive neurotransmitters are released from periodontal nerve terminals, causing leukocytes to migrate out of adjacent capillaries. Cytokines and growth factors are secreted by these cells, stimulating PDL cells and alveolar bone lining cells to remodel their related matrices. This remodeling activity facilitates movement of teeth into areas in which bone had been resorbed. This emerging information suggests that in the living mammal, many cell types are involved in the biological response to applied mechanical stress to teeth, and thereby to bone. Essentially, cells of the nervous, immune, and endocrine systems become involved in the activation and response of PDL and alveolar bone cells to applied stresses. This fact implies that research in the area of the biological response to force application to teeth should be sufficiently broad to include explorations of possible associations between physical, cellular, and molecular phenomena. The goals of this investigative field should continue to expound on fundamental principles, particularly on extrapolating new findings to the clinical environment, where millions of patients are subjected annually to applications of mechanical forces to their teeth for long periods of time in an effort to improve their position in the oral cavity.(ABSTRACT TRUNCATED AT 400 WORDS)

Membrane-bound intracellular collagen fibrils in fibroblasts and myofibroblasts of regenerating rabbit calcaneal tendons

The ultrastructures of 33 rabbit calcaneal tendons were studied to determine (1) whether vacuolar fibrils are present in three regions of tendons undergoing normal healing after tenotomy and repair, and (2) to stimulate collagen synthesis via functional loading, and hence determine the effect of loading on the presence of vacuolar fibrils in healing tendons. In all the loaded tendons, electron microscopy revealed membrane-bound collagen fibril equivalents in sections of neotendon obtained from the site of tenotomy, and in sections of tendon segments proximal and distal to the site of surgery. Similar vacuolar fibrils were visualized in sections of the proximal and distal segments of the non-loaded regenerating tendons, and also in sections of neotendons formed at the site of tenotomy after 12 and 15 days of healing without functional loading. No such fibrils were visualized in the non-tenotomized normal control tendons. These findings indicate that chemical agents and disease are not necessary to induce the appearance of intracytoplasmic fibrils in vivo and that functional loading augments the presence of fibril-bearing vacuoles in regenerating tendons.

Effect of force level on synthesis of type III and type I collagen in mouse interparietal suture

Nine-week-old Swiss male white mice were divided into groups killed after time intervals of force application of six h, and one, three, five, seven, ten, 14, 21, and 28 days. Each group had 45 animals: three control, three sham-operated, and three experimental animals for each of the five force levels: 50 g, 35 g, 25 g, 15 g, and 5 g. The experimental animals had helical springs placed surgically in their calvaria for expansion of the interparietal suture. The sham-operated animals received inactive springs. Control animals were at the same age as the experimental and sham-operated animals. After death, the amount of sutural expansion was measured, and the calvaria with the implanted springs were explanted into Trowell-type organ culture dishes. [14C]-glycine was added for two h after 60 min of culture for all explants. The rate of suture expansion was directly proportional to the force value of the tensile stress, and a maximum 2.0-mm expansion was achieved for all force levels by the 28th day. Sutural collagen was solubilized by limited pepsin digestion, and radiolabeled types I and III alpha-chains were separated by SDS-PAGE, visualized fluorographically, and measured densitometrically. All the experimental and sham-operated animals responded with a rapid rise followed by an almost equally rapid fall in the proportion of newly-synthesized type III collagen before becoming stabilized for the rest of the experimental period at a level that was significantly higher than that of the control and sham-treated animals of the same age.(ABSTRACT TRUNCATED AT 250 WORDS)

Collagen remodeling in wound healing by gingival fibroblasts in vitro

Collagen degradation by fibroblasts was studied in the absence of other cell types to improve our understanding of the mechanisms by which fibroblasts digest collagen. Human gingival fibroblasts were cultured in α -MEM medium for eight weeks. Incisional wounds were made in the fibroblast cultures, and the cells were fixed by different procedures at two days post-wounding. Collagen remodeling has been investigated by tracer experiments and by cytochemical demonstration of acid and alkaline phosphatase activity at the ultrastructural level and stereological analysis in experimental wound-healing in vitro.

The results showed that fibroblasts in the wounded zone exhibited high collagen phagocytic activity, and indicate that fibroblasts have a fundamental role to play in collagen remodeling in wound repair in vitro. This in vitro experimental system is also suggested as a useful model for the analysis of collagen remodeling in wound-healing by fibroblasts.

Localization of acid phosphatase activity in collagen-secreting and collagen-resorbing fibroblasts

The ultrastructural localization of acid phosphatase (ACPase) activity was examined in cultured human gingival fibroblasts in the formative and resorptive phases. In the collagen-secreting fibroblasts, weak ACPase activity was demonstrated in the lysosomes, inner Golgi cisternae, and condensing vacuoles, and none was found in the Golgi-associated endoplasmic reticulum-lysosome system (GERL), presecretory granules, or secretory granules. On the contrary, collagen phagocytosis induced strong ACPase activity in the GERL, which was in addition to the weaker activity found in the same sites as those in the collagen-secreting cells. At the same time, collagen secretion was suppressed, and dense elongated secretory bodies associated with ACPase activity accumulated within the cells. When collagen fibrils had been interiorized in whole or in part within the phagosomes, primary lysosomes derived from the Golgi-GERL complex then fused with them to form phagolysosomes. Collagen degradation occurred within these bodies. The observations indicate significant differences in ACPase activity used as a marker for lysosomal enzyme activities in the different functional phases of fibroblasts. These results suggest that fibroblasts work only one way at a given time, viz., collagen synthesis or collagen degradation.

Effect of tensile force magnitude on release of cranial suture cells into S phase

An in vitro model was used to study the effect of tensile force magnitude and duration on cell proliferation in cranial suture tissue. Helical springs were calibrated to deliver specific magnitudes of force to rat midsagittal suture in organ culture. The explants were incubated for time periods ranging from 1 to 48 hours. The in vitro model system facilitates study of the effects of a single parameter of an applied force on suture tissue without the interference of the complicated craniofacial anatomy. Specifically, the influence of tensile force magnitude and duration on DNA synthesis was investigated. Using autoradiography, cells incorporating tritiated thymidine were counted, indicating cells released into DNA synthesis (S) phase.

Proliferation and differentiation sequence of osteoblast histogenesis under physiological conditions in rat periodontal ligament

To define the mechanism of osteoblast histogenesis, nuclear morphometry was utilized as a marker for precursor cell differentiation. One hour after 3H-thymidine injection, groups of 7-week-old rats were killed at hourly intervals over one complete 24-hr photoperiod (LD 12:12). S-phase and mitosis were assessed in autoradiographs of 3-micron sections of molar periodontal ligament (PDL) adjacent to a physiological bone-forming surface. Labeled nuclei were divided into four categories according to morphometry of nuclear size: A (40-79 micron3), B (80-119 micron3), C (120-169 micron3), and D (greater than or equal to 170 micron3) cells. C and D cells synthesize DNA during the light and divide in the following dark phase; the rhythm for A cells is the opposite. B cells demonstrated no preference and were subsequently determined to be nonosteogenic. Compared to A cells the S-phase photoperiod of C and D cells (combined) is approximately a one-to-one reciprocal relationship, suggesting two proliferating progenitors in series. Based on arrest points in the histogenesis sequence, five compartments are defined: 1) A cells, less differentiated, self-perpetuating precursors; 2) A' cells, committed osteoprogenitors; 3) C cells, G1 stage preosteoblasts; 4) D cells, G2 stage preosteoblasts; and 5) Ob cells, morphologically distinct osteoblasts. Minimal elapsed time for the A----A'----C----D----Ob sequence is about 60 hr (five alternating dark/light cycles). A stress/strain-mediated increase in nuclear volume (A'----C) is an important, rate-limiting step in osteoblast differentiation.

Autoradiographic and cytochemical studies of phagocytic cells in selected fibre tracts of the mouse periodontium

Proliferative and protein synthetic activities of phagocytic cells of specific fibre tracts of the periodontium of C57Bl mice were employing autoradiographic techniques; these were combined with a histochemical technique for horseradish peroxidase (HRP) as a marker for phagocytic activity. Animals were injected either with [3H]thymidine as a marker for proliferative activity, or with [3H]proline as a marker for protein synthetic activity prior to HRP injection. Blocks from the maxillae of experimental and control animals were fixed, decalcified, and sectioned at 50 micrometers. These were incubated with HRP localization media, dehydrated and flat embedded in Epon 812 wafers. The entire length of the periodontium, including adjacent tooth and bone, were selectively cut from the wafers, mounted on epoxy blocks and serially sectioned at 2 micrometers. Slides containing these sections were then dipped in NTB-3 nuclear track emulsion, and after appropriate exposure times, were developed and post-stained. Sections were examined microscopically, employing an ocular grid, and phagocytic cells within each area examined were delineated as either 'fibroblast-like' (FL cells) or 'endothelial/macrophage-like' (EML cells) according to criteria such as morphology, location, orientation and proximity to a vascular channel. They were then subclassified as labelled or unlabelled with respect to the autoradiographic markers. The thymidine labelling index obtained for non-phagocytic FL cells was 3.09%; this was more than twice that for phagocytic FL cells (1.35%). Similarly phagocytic FL cells in all regions studied incorporated less than half as much [3H]proline as did their non-phagocytic counterparts. This was determined by silver grain counts over HRP-stained and unstained cells using a matched pair system. In addition, the variation of the relative number of phagocytic FL cells in specific fibre tracts suggested a relationship to functional demand. The distribution of these cells was closely related to experimentally determined rates of protein turnover. Phagocytic FL cells have a markedly reduced proliferative rate and synthesize proline-containing proteins at a reduced rate. This may reflect protein production primarily for the purpose of cell maintenance. These findings are consistent with the presence of subpopulations of fibroblasts (or fibrocytes) developmentally or functionally modified for phagocytosis; alternatively, this could signify modulation of fibroblasts from primarily biosynthetic activities to degradative functions in response to varying microenvironmental conditions.

Nuclear size as a cell-kinetic marker for osteoblast differentiation

A nuclear morphometric assay for preosteoblasts is introduced as a cell-kinetic technique, applicable to routine histological preparations of mineralized tissue. Because this method is a morphological marker for osteoblast precursor cell differentiation, it provides a new dimension for determining the mechanism of osteoblast histogenesis. Osteoblast precursors of the periodontal ligament are a mixed population of progenitors, kinetically separable into two distinct groups according to nuclear size. Preosteoblasts, the immediate proliferating precursors of osteoblasts, have large nuclei (greater than 170 micrometers3) and are derived from relatively undifferentiated fibroblastlike cells, which have smaller nuclei (less than 80 micrometers3). Increase in nuclear volume, during G1 phase of the cell cycle, is apparently a morphological manifestation of change in genomic expression. This key event in preosteoblast differentiation is related to mechanical stress/strain and may be an important rate-limiting step in osteoblast histogenesis.