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PubMed1983

Cementogenesis and soft tissue attachment after citric acid treatment in a human. An electron microscopic study.

The four maxillary incisors and two maxillary premolars of a 25-year-old male patient were used to study epithelial and connective tissue attachment 67 days and 164 days after flap surgery and cutting of an horizontal intradentinal groove near the buccal cervical region. Three teeth were topically conditioned for 3 minutes with citric acid pH = 1. The three other teeth were used as controls. The histologic examination was carried out in double-blind conditions; the examiners did not know which specimens were acid treated until the end of the study. Two of the three cases treated with citric acid showed improved healing conditions, when compared to the controls; a more coronal position of the epithelial attachment in the dentin nick as well as a relatively important gain in connective tissue attachment. Two types of connective tissue attachment were observed. The first consisted of an attachment to dentin, without cementum formation and was characterized by a mineralization of decalcified dentin collagen spliced with collagen, newly secreted by fibroblasts. The second type involved cementum formation. Topical citric acid treatment, however, can not be considered as a completely reliable clinical procedure since in one experimental case the type of attachment observed was not better than that seen in the control.

Adult↗
PubMed1995

Models for the study of cementogenesis.

Cementum is a mineralized tissue that acts to connect the periodontal ligament to the tooth root surface. Its composition is very much like bone, being comprised mainly of type I collagen, inorganic mineral and noncollagenous proteins, however the origin of the cells and factors necessary for cementum formation have yet to be elucidated. Our laboratory has focused on the role that adhesion molecules, and their cell surface receptors, play in the formation of cementum and tooth root. In order to study this, we used a mouse molar as a model system. This system enabled us to study the formation of four distinct mineralized tissues; bone, cementum, dentin and enamel at various stages of their development. For these studies, we initiated experiments to examine potential cementoblast progenitor cells, in vitro. As a first step, we show that dental papilla and dental follicle cells, n vitro, obtained from molar tissues at day 21 of development, induce mineralized nodules, in vitro. In addition, we obtained tissues from mice where defects in root development may exist and determined bone sialoprotein (BSP) protein expression, a mineralized tissue specific adhesion molecule, in such tissues. As discussed here, we found that osteopetrotic (op/op) mice have delayed and/or defective root development and BSP does not localize in the dental tissues, at day 33 of development. In addition, dentin formation was defective and odontoblasts appeared immature, based on morphological examination. In contrast, the day 33 control molars demonstrated positive staining for BSP localized to root cementum, with normal formation of dentin.

Amelogenesis↗
PubMed2000

Parathyroid hormone-related protein regulates extracellular matrix gene expression in cementoblasts and inhibits cementoblast-mediated mineralization in vitro.

Parathyroid hormone-related protein (PTHrP) has been implicated in regulating tooth eruption and/or development. Formation of cementum, a mineralized tissue covering the tooth root surface, is a critical biological event for tooth root development. To test the hypothesis that PTHrP targets cementoblasts (CMs) and acts to regulate cementogenesis, CM cell lines were established and their responsiveness to PTHrP stimulation was determined, in vitro. First, subclones were derived from two immortalized murine cell populations that contained CMs; SV-CM/periodontal ligament (PDL) cells were obtained from the root surface of first mandibular molars of CD-1 mice and immortalized with SV40 T-antigen (TAg), and OC-CM cell population was established from OC-TAg transgenic mice in which their cells harbor an osteocalcin (OC and/or OCN) promoter-driving immortal gene SV40 TAg. Based on our previous in situ studies, CM subclones were identified as cells expressing bone sialoprotein (BSP) and OCN transcripts, while PDL cell lines were designated as cells lacking BSP and OCN messenger RNA (mRNA). CMs exhibited a cuboidal appearance and promoted biomineralization, both in vitro and in vivo. In contrast, PDL cells (PDL subclones) displayed a spindle-shaped morphology and lacked the ability to promote mineralized nodule formation, both in vitro and in vivo. Next, using these subclones, the effect of PTHrP on cementogenesis was studied. CMs, not PDL cells, expressed PTH/PTHrP receptor mRNA and exhibited PTHrP-mediated elevation in cyclic adenosine monophosphate (cAMP) levels and c-fos gene induction. PTHrP stimulation repressed mRNA expression of BSP and OCN in CMs and blocked CM-mediated mineralization, in vitro. Collectively, these data suggest that CMs possess PTH/PTHrP receptors and, thus, are direct targets for PTHrP action during cementogenesis and that PTHrP may serve as an important regulator of cementogenesis.

Animals↗
PubMed2004

Immunolocation of proteoglycans and bone-related noncollagenous glycoproteins in developing acellular cementum of rat molars.

To elucidate the roles of proteoglycans of (PGs), bone sialoprotein (BSP), and osteopontin (OPN) in cementogenesis, their distribution was investigated in developing and established acellular cementum of rat molars by an immunoperoxidase method. To characterize PGs, antibodies against five species of glycosaminoglycans (GAGS), chondroitin-4-sulfate (C4S), chondroitin-6-sulfate (C6S), unsulfated chondroitin (C0S), dermatan sulfate (DS), and keratan sulfate (KS) were used. Routine histological staining was also applied. With onset of dentin mineralization, the initial cementum appeared on the dentin surface as a hematoxylin-stained fibril-poor layer. Subsequently, primitive principal fibers attached to the initial cementum. As the acellular cementum containing extrinsic fibers covered the initial cementum, the intal cementum formed the cemento-dentinal junction. Following immunohistochemistry at the earliest time of cementogenesis, the initial cementum was intensely immunoreactive for C4S, C6S, C0S, BSP, and OPN. After the initial cementum was embedded, neither the cemento-dentinal junction nor the cementum was immunoreactive for any GAG species. However, the cementum was immunoreactive for any GAG species. However, the cementum and cemento-dentinal were consistently immunoreactive for BSP. Although the cemento-dentinal junction was consistently immunoreactive for OPN, the remaining cementum showed no significant immunoreactivity. Thus, initial acellular cementogenesis requires a dense accumulation of PGs, BSP, and OPN, which may be associated with the mineralization process independently of collagen fibrils and initial principal fiber attachment.

Animals↗
PubMed1993

The development of cellular cementum in rat molars, with special reference to the fiber arrangement.

To elucidate how intrinsic and extrinsic fibers are arranged during cementogenesis, rat cellular cementum was observed in various developmental stages by light and electron microscopy. As cementogenesis progressed, the periodontal ligament cells showed characteristics of collagen-secreting cells, wing-like processes, and delimited extracellular compartments. The principal fibers were organized into substantial bundles in these compartments. The organization of extrinsic and intrinsic fibers progressed in parallel with the extracellular compartmentalization. The main results suggest the following. (1) The extracellular compartments formed by periodontal ligament cells regulate the three-dimensional architecture of the principal fibers. (2) The compartments formed by cementoblasts are essential for the formation of the typical intrinsic-extrinsic fiber structures. When the cementoblasts move away from the cementum surface or are embedded in the cementum, these cells retract the processes that have encircled the principal fibers. At the same time, these cells secrete intrinsic fibers around the principal fibers. This results in the typical intrinsic-extrinsic fiber structures. (3) In the early stage when the cellular compartmentalization is not established, both the intrinsic and extrinsic fibers are irregularly arranged.

Animals↗
PubMed1994

Comparative study of the initial genesis of acellular and cellular cementum in rat molars.

The initial genesis of acellular and cellular cementum was examined in rat molars by light and electron microscopy. Before root dentinogenesis, flattened dental follicle cells formed compartments by regularly arranged cellular processes which demarcated collagen fibril bundles oriented in parallel with the root long axis in both of the two kinds of cementum. After this stage, compartments disappeared from the dental follicle cells, which became elongated and polarized, with the cytoplasmic side facing toward the root surface in the acellular cementogenesis. Fibril bundles, oriented in parallel with the root long axis, decreased in number, and principal fibers appeared. Some principal fibers were attached on the first acellular cementum. Observations suggested that the fibril bundles, which had been oriented in parallel with the root long axis, were reoriented to merge into the principal fibers. In cellular cementogenesis, the dental follicle cells continued to hold the fibril bundles in cellular compartments. The regular processes were transformed into randomly oriented, finger-like processes. At the same time, fibers, which may be secreted from the finger-like processes, appeared around the preformed fibril bundles oriented in parallel with the root long axis. The different cellular behavior may result in the different fiber arrangement of acellular and cellular cementum.

Age Factors↗
PubMed1997

The modulatory role of cementum matrix on osteoblastic cells in vitro.

The formation of new cementum is an important issue in clinical periodontology, as cementum is required to provide attachment for newly formed periodontal tissues to the root surface. In this study a model of cementogenesis in vitro was used in order to test the effects of root surface demineralization on the migration, attachment and formation of a cementum-like tissue by osteoblastic cells cultured on cementum and to test the specificity of cementum matrix in modulating those effects by comparison of root co-cultures with bone co-cultures. It was demonstrated that root surface demineralization did not significantly alter the orientation, number and attachment of cells to the root co-cultures. The results also demonstrated that cementum and bone matrix appear to behave differently in culture, as seen by their distinct action on the morphological profile of the attached cells and the extracellular matrix deposited by these cells. These results demonstrate that although cementum matrix appears to stimulate the production of cementum-like tissue, this action is not confined to cementum matrix alone, since a similar material was also deposited on dentine and bone surfaces. Thus, these results do not support a specific action of cementum matrix on the modulation of the cementoblast phenotype. The use of co-cultures of neonatal rat calvaria cells with root slices represents a promising model of cementogenesis in vitro; however, studies should be undertaken towards the identification of markers to distinguish between cementoblast and osteoblast phenotypes in order to further validate this model.

Animals↗
PubMed2004

Immortalization of cementoblast progenitor cells with Bmi-1 and TERT.

UNLABELLED: A cementoblast progenitor cell line designated BCPb8 was successfully isolated from dental follicle cells immortalized with Bmi-1 and hTERT. BCPb8 showed the potential to differentiate into cementoblasts on implantation into immunodeficient mice. BCPb8 was confirmed to be the first established cementoblast progenitor cell line and will provide a useful model for investigating cementogenesis. INTRODUCTION: The dental follicle is the mesenchymal tissue surrounding the developing tooth germ. During tooth root development, progenitor cells present in the dental follicle are believed to play a central role in the formation of periodontal components (cementum, periodontal ligament, and alveolar bone). However, little more is known about the biology of these progenitors. Previously, we observed that cultured bovine dental follicle cells (BDFCs) contained putative cementoblast progenitors. To further analyze the biology of these cells, we attempted to isolate cementoblast progenitors from immortalized BDFC through expression of the polycomb group protein, Bmi-1, and human telomerase reverse transcriptase (hTERT). MATERIALS AND METHODS: BDFCs were transduced with replication-deficient retroviruses carrying human Bmi-1(LXSN-Bmi-1), and hTERT (LXSH-hTERT) for immortalization. Single cell clones were established from immortalized BDFC, and differentiation into cementoblasts was assessed by implantation into immunodeficient mice. RESULTS AND CONCLUSION: BDFCs expressing Bmi-1 and hTERT showed an extended life span-90 population doublings more than normal BDFCs-and still contained cells with the potential to differentiate into cementoblasts on implantation into immunodeficient mice. From these cells, we established a clonal cell line, designated BCPb8, which formed cementum-like tissue that was reactive to the anti-cementum-specific monoclonal antibody 3G9 and expressed mRNA for bone sialoprotein, osteocalcin, osteopontin, and type I collagen on implantation. Thus, by using Bmi-1 and hTERT, we succeeded in immortalizing cementoblast progenitor cells from BDFC without affecting differentiation potential. The BCPb8 cell line is the first immortalized clonal cell line of cementoblast progenitors and could be a useful tool not only to study cementogenesis but also to develop regeneration therapy for patients with periodontitis.

Animals↗
PubMed2004

Effect of sustained gene delivery of platelet-derived growth factor or its antagonist (PDGF-1308) on tissue-engineered cementum.

BACKGROUND: Cementum, a mineralized tissue lining the tooth root surface, is destroyed during the inflammatory process of periodontitis. Restoration of functional cementum is considered a criterion for successful regeneration of periodontal tissues, including formation of periodontal ligament, cementum, and alveolar bone. Short-term administration of platelet-derived growth factor (PDGF) has been shown to partially regenerate periodontal structures. Nonetheless, the role of PDGF in cementogenesis is not well understood. The aim of the present study was to determine the effect of sustained PDGF gene transfer on cementum formation in an ex vivo ectopic biomineralization model. METHODS: Osteocalcin (OC) promoter-driven SV40 transgenic mice were used to obtain immortalized cementoblasts (OCCM). The OCCM cells were transduced with adenoviruses (Ad) encoding either PDGF-A, an antagonist of PDGF signaling (PDGF-1308), a control virus (green fluorescent protein, GFP), or no treatment (NT). The transduced cells were incorporated into polymer scaffolds and implanted subcutaneously into severe combined immunodeficient (SCID) mice. The implants were harvested at 3 and 6 weeks for histomorphometric analysis of the newly formed mineralized tissues. Northern blot analysis was performed to determine the expression levels of mineral-associated genes including bone sialoprotein (BSP), OC, and osteopontin (OPN) in the cell-implant specimens at 3 and 6 weeks. RESULTS: The results indicated mineralization was significantly reduced in both the Ad/PDGF-A and Ad/PDGF-1308 treated specimens when compared to the NT or Ad/GFP groups at 3 and 6 weeks (P<0.01). In addition, the size of the implants treated with Ad/PDGF-A and Ad/PDGF-1308 was significantly reduced compared to implants from Ad/GFP and NT groups at 3 weeks (P<0.05). At 6 weeks, the size of implants and mineral formation increased in NT, Ad/GFP, and Ad/PDGF-A groups, while the Ad/PDGF-1308 treated implants continued to decrease in size and mineral formation (P<0.01). Northern blot analysis revealed that in the Ad/PDGF-A treated implants OPN was increased, whereas OC gene expression was downregulated at 3 weeks. In the Ad/PDGF-1308 treated implants, BSP, OC, and OPN were all downregulated at 3 weeks. At 3 weeks, the Ad/PDGF-A treated implants contained significantly higher multinucleated giant cell (MNGC) density compared to NT, Ad/GFP, and Ad/PDGF-1308 specimens. The MNGC density in NT, Ad/GFP, and Ad/PDGF-A treated groups reduced over time, while the Ad/PDGF-1308 transduced implants continued to exhibit significantly higher MNGC density compared with the other treatment groups at 6 weeks. CONCLUSIONS: The results showed that continuous exposure to PDGF-A had an inhibitory effect on cementogenesis, possibly via the upregulation of OPN and subsequent enhancement of MNGCs at 3 weeks. On the other hand, Ad/PDGF-1308 inhibited mineralization of tissue-engineered cementum possibly due to the observed downregulation of BSP and OC and a persistence of stimulation of MNGCs. These findings suggest that continuous exogenous delivery of PDGF-A may delay mineral formation induced by cementoblasts, while PDGF is clearly required for mineral neogenesis.

Animals↗
PubMed2001

The developmental biology of cementum.

In conclusion, we have reviewed an extensive literature on early cementogenesis and performed a detailed morphological and molecular analysis to illustrate and verify key issues in the current debate about epithelial and mesenchymal contributions to root cementum. We have demonstrated that prior to cementogenesis, Hertwig's epithelial root sheath disintegrates and dental follicle cells penetrate the epithelial layer to invade the root surface. Our studies confirmed that HERS became disrupted or disintegrated prior to cementum deposition. We visualized how mesenchymal cells from the dental follicle penetrated the HERS bilayer and deposited initial cementum, while immediately adjacent epithelial cells were separated from the root surface by a basal lamina and did not secrete any cementum. Human specimen from the Gottlieb collection indicated that HERS was removed from the root surface prior to cementum deposition. Our in situ hybridization and immolocalization data revealed that both amelogenin mRNAs and enamel proteins were restricted to the crown enamel and were absent from the root surface and from the cervical-most ameloblasts adjacent to the root margin. On Western blots, cementum protein extracts did not cross-react with amelogenin antibodies. Our studies in conjunction with our literature review together confirmed the classical theory of cementum as a dental follicle derived connective tissue that forms subsequent to HERS disintegration.

Ameloblasts↗
PubMed1992

The role of osteonectin in human tooth development: an immunohistological study.

We investigated immunohistologically 160 teeth and dental germs in various stages of tooth development taken from human individuals (13th week of pregnancy to the 24th year of life) to study the osteonectin expression in dental hard tissue. In the course of dentinogenesis, the predentin, the odontoblasts, and their cell processes show a positive osteonectin staining reaction. During cementogenesis, osteonectin is synthesized by cement-producing fibroblasts, cementoblasts, and cementocytes. The expression of osteonectin during dentinogenesis and cementogenesis is closely related to the development of the respective calcified tissue. All cells of the inner and outer enamel epithelium, the cells of the stratum reticulare and stratum intermedium, the ameloblasts, and the enamel substance are osteonectin negative, just as dentin and cement are. The results of this study indicate one important physiological role of osteonectin as a protein associated with the formation of collagen containing mineralizing tissues like human bone, as well as human dentin and cement.

Adolescent↗
PubMed2005

Molecular cloning, expression and immunolocalization of a novel human cementum-derived protein (CP-23).

Cementum is a unique mineralized connective tissue that covers the root surfaces of the teeth. The cementum is critical for appropriate maturation of the periodontium, both during development as well as that associated with regeneration of periodontal tissues, IU; however, one major impediment to understand the molecular mechanisms that regulate periodontal regeneration is the lack of cementum markers. Here we report on the identification and characterization of one such differentially human expressed gene, termed "cementum protein-23" (CP-23) that appears to be periodontal ligament and cementum-specific. We screened human cementum tumor-derived cDNA libraries by transient expression in COS-7 cells and "panning" with a rabbit polyclonal antibody against a cementoblastoma conditioned media-derived protein (CP). One isolated cDNA, CP-23, was expressed in E. coli and polyclonal antibodies against the recombinant human CP-23 were produced. Expression of CP-23 protein by cells of the periodontium was examined by Northern blot and in situ hybridization. Expression of CP-23 transcripts in human cementoblastoma-derived cells, periodontal ligament cells, human gingival fibroblasts and alveolar bone-derived cells was determined by RT-PCR. Our results show that we have isolated a 1374-bp human cDNA containing an open reading frame that encodes a polypeptide with 247 amino acid residues, with a predicted molecular mass of 25.9 kDa that represents CP species. The recombinant human CP-23 protein cross-reacted with antibodies against CP and type X collagen. Immunoscreening of human periodontal tissues revealed that CP-23 gene product is localized to the cementoid matrix of cementum and cementoblasts throughout the entire surface of the root, cell subpopulations of the periodontal ligament as well as cells located paravascularly to the blood vessels into the periodontal ligament. Furthermore, 98% of putative cementoblasts and 15% of periodontal ligament cells cultured in vitro expressed CP-23 gene product. Cementoblastoma cells and periodontal ligament cells contained a 5.0 kb CP-23 mRNA. In situ hybridization showed strong expression of CP-23 mRNA on cementoblast, cell subpopulations of the periodontal ligament and cells located around blood vessels into the periodontal ligament. Our results demonstrate that CP-23 represents a novel, tissue-specific-gene product being expressed by periodontal ligament subpopulations and cementoblasts. These findings offer the possibility to determine the cellular and molecular events that regulate the cementogenesis process during root development. Furthermore, it might provide new venues for the design of translational studies aimed at achieving predictable new cementogenesis and regeneration of the periodontal tissues.

3' Untranslated Regions↗