Expression and role of epidermal growth factor receptors during differentiation of cementoblasts, osteoblasts, and periodontal ligament fibroblasts in the rat

Biopotentials of Collagen Scaffold Impregnated with Plant-Cell-Derived Epidermal Growth Factor in Defective Bone Healing

The combination of scaffolds with recombinant human epidermal growth factor (rhEGF) protein can enhance defective bone healing via synergistic activation to stimulate cellular growth, differentiation, and survival. We examined the biopotentials of an rhEGF-loaded absorbable collagen scaffold (ACS) using a mouse model of calvarial defects, in which the rhEGF was produced from a plant cell suspension culture system because of several systemic advantages. Here, we showed a successful and large-scale production of plant-cell-derived rhEGF protein (p-rhEGF) by introducing an expression vector that cloned with its cDNA under the control of rice α-amylase 3D promoter into rice calli (Oryza sativa L. cv. Dongjin). Implantation with p-rhEGF (5 μg)-loaded ACSs into critical-sized calvarial defects enhanced new bone formation and the expression of osteoblast-specific markers in the defected regions greater than implantation with ACSs alone did. The potency of p-rhEGF-induced bone healing was comparable with that of Escherichia coli-derived rhEGF protein. The exogenous addition of p-rhEGF increased the proliferation of human periodontal ligament cells and augmented the induction of interleukin 8, bone morphogenetic protein 2, and vascular endothelial growth factor in the cells. Collectively, this study demonstrates the successful and convenient production of p-rhEGF, as well as its potency to enhance ACS-mediated bone regeneration by activating cellular responses that are required for wound healing.

The Roles of SIBLING Proteins in Dental, Periodontal and Craniofacial Development

The majority of dental, periodontal, and craniofacial tissues are derived from the neural crest cells and ectoderm. Neural crest stem cells are pluripotent, capable of differentiating into a variety of cells. These cells can include osteoblasts, odontoblasts, cementoblasts, chondroblasts, and fibroblasts which are responsible for forming some of the tissues of the oral and craniofacial complex. The hard tissue forming cells deposit a matrix composed of collagen and non-collagenous proteins (NCPs) that later undergoes mineralization. The NCPs play a role in the mineralization of collagen. One such category of NCPs is the small integrin-binding ligand, N-linked glycoprotein (SIBLING) family of proteins. This family is composed of dentin sialophosphosprotein (DSPP), osteopontin (OPN), dentin matrix protein 1 (DMP1), bone sialoprotein (BSP), and matrix extracellular phosphoglycoprotein (MEPE). The SIBLING family is known to have regulatory effects in the mineralization process of collagen fibers and the maturation of hydroxyapatite crystals. It is well established that SIBLING proteins have critical roles in tooth development. Recent literature has described the expression and role of SIBLING proteins in other areas of the oral and craniofacial complex as well. The objective of the present literature review is to summarize and discuss the different roles the SIBLING proteins play in the development of dental, periodontal, and craniofacial tissues.

The promotion function of Berberine for osteogenic differentiation of human periodontal ligament stem cells via ERK-FOS pathway mediated by EGFR

Coptidis Rhizoma binds to the membrane receptors on hPDLSC/CMC, and the active ingredient Berberine (BER) that can be extracted from it may promote the proliferation and osteogenesis of periodontal ligament stem cells (hPDLSC). The membrane receptor that binds with BER on the cell surface of hPDLSC, the mechanism of direct interaction between BER and hPDLSC, and the related signal pathway are not yet clear. In this research, EGFR was screened as the affinity membrane receptor between BER and hPDLSC, through retention on CMC, competition with BER and by using a molecular docking simulation score. At the same time, the MAPK PCR Array was selected to screen the target genes that changed when hPDLSC was simulated by BER. In conclusion, BER may bind to EGFR on the cell membrane of hPDLSC so the intracellular ERK signalling pathways activate, and nuclear-related genes of FOS change, resulting in the effect of osteogenesis on PDLSC.

Epithelial rests of Malassez: from latent cells to active participation in orthodontic movement

Introduction:

The epithelial rests of Malassez (ERM) represent a group of cells in the periodontal ligament classically consisting of latent or quiescent structures associated with pathological processes. However, recent evidence shows that these structures cannot be considered only as cellular debris. The ERM is a major tissue structure, with functions in maintaining the homeostasis of periodontal tissue, including the maintenance of orthodontic movement.

Objective:

The present literature review aims at presenting the potential functions of ERM, with emphasis on orthodontic movement and the functional structure of the periodontium.

Conclusion:

ERM cells have a functional activity in modulation of orthodontic movement, trough their potential for differentiation, maintenance functions and the capacity of repairing periodontium.

F-spondin negatively regulates dental follicle differentiation through the inhibition of TGF-β activity

OBJECTIVE

F-spondin is an extracellular matrix (ECM) protein that belongs to the thrombospondin type I repeat superfamily and is a negative regulator of bone mass. We have previously shown that f-spondin is specifically expressed in the dental follicle (DF), which gives rise to the periodontal ligament (PDL) during the tooth root formation stage. To investigate the molecular mechanism of PDL formation, we investigated the function of f-spondin in DF differentiation.

DESIGN

The expression patterning of f-spondin in the developing tooth germ was compared with that of periodontal ligament-related genes, including runx2, type I collagen and periostin, by in situ hybridization analysis. To investigate the function of f-spondin during periodontal ligament formation, an f-spondin adenovirus was infected into the bell stage of the developing tooth germ, and the effect on dental differentiation was analyzed.

RESULTS

F-spondin was specifically expressed in the DF of the developing tooth germ; by contrast, type I collagen, runx2 and periostin were expressed in the DF and in the alveolar bone. F-spondin-overexpresssing tooth germ exhibited a reduction in gene expression of periostin and type I collagen in the DF. By contrast, the knockdown of f-spondin in primary DF cells increased the expression of these genes. Treatment with recombinant f-spondin protein functionally inhibited periostin expression induced by transforming growth factor-β (TGF-β).

CONCLUSION

Our data indicated that f-spondin inhibits the differentiation of DF cells into periodontal ligament cells by inhibiting TGF-β. These data suggested that f-spondin negatively regulates PDL differentiation which may play an important role in the immature phenotype of DF.

Are Cementoblasts a Subpopulation of Osteoblasts or a Unique Phenotype?

Experimental studies have shown a great potential for periodontal regeneration. The limitations of periodontal regeneration largely depend on the regenerative potential at the root surface. Cellular intrinsic fiber cementum (CIFC), so-called bone-like tissue, may form instead of the desired acellular extrinsic fiber cementum (AEFC), and the interfacial tissue bonding may be weak. The periodontal ligament harbors progenitor cells that can differentiate into periodontal ligament fibroblasts, osteoblasts, and cementoblasts, but their precise location is unknown. It is also not known whether osteoblasts and cementoblasts arise from a common precursor cell line, or whether distinct precursor cell lines exist. Thus, there is limited knowledge about how cell diversity evolves in the space between the developing root and the alveolar bone. This review supports the hypothesis that AEFC is a unique tissue, while CIFC and bone share some similarities. Morphologically, functionally, and biochemically, however, CIFC is distinctly different from any bone type. There are several lines of evidence to propose that cementoblasts that produce both AEFC and CIFC are unique phenotypes that are unrelated to osteoblasts. Cementum attachment protein appears to be cementum-specific, and the expression of two proteoglycans, fibromodulin and lumican, appears to be stronger in CIFC than in bone. A theory is presented that may help explain how cell diversity evolves in the periodontal ligament. It proposes that Hertwig’s epithelial root sheath and cells derived from it play an essential role in the development and maintenance of the periodontium. The role of enamel matrix proteins in cementoblast and osteoblast differentiation and their potential use for tissue engineering are discussed.

FGF-2 induces the proliferation of human periodontal ligament cells and modulates their osteoblastic phenotype by affecting Runx2 expression in the presence and absence of osteogenic inducers

The exact phenotype of human periodontal ligament cells (hPDLCs) remains a controversial area. Basic fibroblast growth factor (FGF-2) exhibits various functions and its effect on hPDLCs is also controversial. Therefore, the present study examined the effect of FGF-2 on the growth and osteoblastic phenotype of hPDLCs with or without osteogenic inducers (dexamethasone and β-glycerophosphate). FGF-2 was added to defined growth culture medium and osteogenic inductive culture medium. Cell proliferation, osteogenic differentiation and mineralization were measured. The selected differentiation markers, Runx2, collagen type I, α1 (Col1a1), osteocalcin (OCN) and epidermal growth factor receptor (EGFR), were investigated by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Runx2 and OCN protein expression was measured by western blotting. FGF-2 significantly increased the proliferation of hPDLCs, but did not affect alkaline phosphatase activity. RT-qPCR analysis revealed enhanced mRNA expression of Runx2, OCN and EGFR, but suppressed Col1a1 gene expression in the absence of osteogenic inducers, whereas all these gene levels had no clear trend in their presence. The Runx2 protein expression was clearly increased, but the OCN protein level showed no evident trend. The mineralization assay demonstrated that FGF-2 inhibited mineralized matrix deposition with osteogenic inducers. These results suggested that FGF-2 induces the growth of immature hPDLCs, which is a competitive inhibitor of epithelial downgrowth, and suppresses their differentiation into mineralized tissue by affecting Runx2 expression. Therefore, this may lead to the acceleration of periodontal regeneration.

Expression and effects of epidermal growth factor on human periodontal ligament cells

Repair of damaged periodontal ligament (PDL) tissue is an essential challenge in tooth preservation. Various researchers have attempted to develop efficient therapies for healing and regenerating PDL tissue based on tissue engineering methods focused on targeting signaling molecules in PDL stem cells and other mesenchymal stem cells. In this context, we investigated the expression of epidermal growth factor (EGF) in normal and surgically wounded PDL tissues and its effect on chemotaxis and expression of osteoinductive and angiogenic factors in human PDL cells (HPDLCs). EGF as well as EGF receptor (EGFR) expression was observed in HPDLCs and entire PDL tissue. In a PDL tissue-injured model of rat, EGF and IL-1β were found to be upregulated in a perilesional pattern. Interleukin-1β induced EGF expression in HPDLCs but not EGFR. It also increased transforming growth factor-α (TGF-α) and heparin-binding EGF-like growth factor (HB-EGF) expression. Transwell assays demonstrated the chemotactic activity of EGF on HPDLCs. In addition, EGF treatment significantly induced secretion of bone morphogenetic protein 2 and vascular endothelial growth factor, and gene expression of interleukin-8 (IL-8), and early growth response-1 and -2 (EGR-1/2). Human umbilical vein endothelial cells developed well-formed tube networks when cultured with the supernatant of EGF-treated HPDLCs. These results indicated that EGF upregulated under inflammatory conditions plays roles in the repair of wounded PDL tissue, suggesting its function as a prospective agent to allow the healing and regeneration of this tissue.

Effect of FDC-SP on the phenotype expression of cultured periodontal ligament cells

INTRODUCTION

Recently, a novel protein, follicular dendritic cell secreted protein (FDC-SP), has been identified in human periodontal ligament (PDL) tissue and a biomolecular study suggested that the expression of FDC-SP might be associated with the expression of the PDL phenotype. The purpose of this study was to test the effect of FDC-SP on the proliferation and phenotype of PDL cells.

MATERIAL AND METHODS

Periodontal ligament cells obtained following the 3(rd) passage were exposed to various concentrations of FDC-SP. The cell proliferation was monitored by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide(MTT) assay. Then, as a measure of osteogenic activity, the alkaline phosphatase (ALP) activity was recorded after 4, 7, and 14 days using p-nitrophenylphosphate as a substrate. Finally, total RNA was extracted and RT-PCR was performed for gene analysis.

RESULTS

The results indicated that PDL cells exposed to 50 ng/ml FDC-SP could proliferate more rapidly. RT-PCR results showed that the mRNA expression of epidermal growth factor receptor (EGFR) was obviously upregulated and the mRNA expression of osteocalcin (OCN) and bone sialoprotein (BSP) were downregulated in PDL cells exposed to FDC-SP. Moreover, two groups of PDL cells exposed to FDC-SP showed a significant decrease of ALP activity during all the culture days.

CONCLUSIONS

In sum, the findings observed in this study suggest that FDC-SP in PDL cells could positively affect the proliferation and act as a fibroblastic phenotype stabilizer by inhibiting their differentiation into mineralized tissue-forming cells.

Epidermal growth factor (EGF) transfection of human bone marrow stromal cells in bone tissue engineering

A novel therapeutic approach for the treatment of bone defects is gene therapy assisted bone tissue engineering using bone marrow stromal cells (hBMSC). The aim of this study was to investigate the influence of human epidermal growth factor (hEGF) on proliferation and alkaline phosphatase (AP) activity of primary hBMSC in vitro. hBMSC cultures were achieved by explantation culture of bone chips. Following exposure to 0-10 ng recombinant hEGF (rhEGF)/ml cell numbers were determined by automated cell counting and cell bound AP activity was measured spectrophotometrically. hBMSC were transfected with hEGF plasmids and the proliferative effect was studied by cocultivation of transfected and untreated cells using porous cell culture inserts. The persistence of hEGF expression even after cell transfer was studied by the generation of possibly osteogenic constructs introducing transfected hBMSC in fibrin glue and bovine cancellous bone. The maximum increase in proliferation (156 +/- 7%) and AP activity (220 +/- 34%) was detected after exposition to 10 ng rhEGF/ml. In the separation chamber assay transfected cells produced hEGF concentrations up to 3.6 ng/ml, which induced a mean proliferation increase of 93% which could be significantly inhibited by a neutralizing hEGF antibody. Further, EGFsecretion of transfected hBMSC in 3D-culture was verified. Recombinant and transgenic hEGF stimulate proliferation of primary hBMSC in vitro. Lipotransfection of hBMSC with hEGF plasmids allows the transient and site directed delivery of biologically active transgenic hEGF. The introduction of mitogenic, angiogenic and chemoattractive factors in gene therapy assisted bone tissue engineering is discussed by the example of EGF.

The KK-Periome database for transcripts of periodontal ligament development

The periodontal ligament (PDL) is a strong connective tissue that surrounds the tooth root, absorbs occlusal forces, and functions as a sense organ. PDL originated from dental follicle (DF), which possessed mesenchymal progenitors in the developing tooth germ. However, as specific marker genes for PDL and DF are currently unavailable, the molecular mechanisms of PDL development are yet to be clarified. To facilitate the identification of such genes, we have previously established a transcriptome database of the human PDL (the KK-Periome database) and screened for specific genes expressed during PDL development. Initial screening of the database revealed two marker genes for distinguishing DF and PDL. The KK-Periome database thus appears to offer a useful resource for investigating genes involved in PDL development.

Regulatory mechanisms of periodontal regeneration

The periodontal ligament, located between the cementum and the alveolar bone, has a width ranging from 0.15 to 0.38 mm. Regeneration and homeostasis of the periodontal ligament are highly significant functions in relation to periodontal therapy, tooth transplantation or replantation, and orthodontic tooth movement. The purpose of this review is to discuss the regulatory mechanisms of regenerative and homeostatic functions in the periodontal ligament based on currently published studies and also on our own experimental data. We consider the capability of the ligament tissue to promote or to suppress calcification in connection with bone and cementum formation and the maintenance of the periodontal ligament space. Also discussed are the involvement of the periodontal ligament tissue in the regenerative ability, cell proliferation, growth and differentiation factors, extracellular matrix proteins, homeostatic phenomena, function of Malassez epithelial rests, tooth movement, or occlusal loading. Regulatory mechanisms for regeneration and homeostasis of the periodontal ligament are hypothetically proposed.

A cell line with characteristics of the periodontal ligament fibroblasts is negatively regulated for mineralization and Runx2/Cbfa1/Osf2 activity, part of which can be overcome by bone morphogenetic protein-2

The periodontal ligament (PDL) is a connective tissue located between the cementum of teeth and the alveolar bone of the mandibula. It plays an integral role in the maintenance and regeneration of periodontal tissue. The cells responsible for maintaining this tissue are thought to be fibroblasts, which can be either multipotent or composed of heterogenous cell populations. However, as no established cell lines from the PDL are available, it is difficult to assess what type of cell promotes all of these functions. As a first step to circumvent this problem, we have cloned and characterized cell lines from the PDL from mice harboring a temperature-sensitive SV 40 large T-antigen gene. RT-PCR and in situ hybridization studies demonstrated that a cell line, designated PDL-L2, mimics the gene expression of the PDL in vivo: it expresses genes such as alkaline phosphatase, type I collagen, periostin, runt-related transcription factor-2 (Runx2) and EGF receptor, but does not express genes such as bone sialoprotein and osteocalcin. Unlike osteoblastic cells and a mixed cell population from the PDL, PDL-L2 cells do not produce mineralized nodules in the mineralization medium. When PDL-L2 cells were incubated in the presence of recombinant human bone morphogenetic protein-2 alkaline phosphatase activity increased and mineralized nodules were eventually produced, although the extent of mineralization is much less than that in osteoblastic MC3T3-E1 cells. Furthermore, PDL-L2 cells appeared to have a regulatory mechanism by which the function of Runx2 is normally suppressed.

Analysis of quantitative trait locus effects on the size and shape of mandibular molars in mice

While >50 genes have been found to influence the development of teeth in mice, we still know very little about the genetic basis for the adaptive characteristics of teeth, such as size and shape. We applied interval mapping procedures to Procrustes size and shape data obtained from 10 morphological landmarks on the mandibular molar row of the F(2) progeny from a cross between the LG/J and SM/J strains of mice. This revealed many more QTL for molar shape (18) than for molar centroid size (3), although levels of dominance effects were comparable among QTL for size and shape. Comparisons of patterns of Procrustes additive and dominance shape effects and ordination of QTL effects by principal components analysis suggested that the effects of the shape QTL were dispersed among the three molars and thus that none of these molars represents a genetically distinct developmental structure. The results of an analysis of co-occurrence of QTL for molar shape, mandible shape, and cranial dimensions in these mice suggested that many of the QTL for molar shape may be the same as those affecting these other sets of characters, although in some cases this could be due to effects of closely linked genes.

Gingival, dermal, and periodontal ligament fibroblasts express different extracellular matrix receptors

BACKGROUND

Fibroblasts are the predominant cells of the periodontal ligament and the gingiva and have important roles in the function and regeneration of the tooth support apparatus. The goal of this study was to investigate the possible differences in the adhesion properties and expression of extracellular matrix (ECM) receptors among different fibroblast populations.

METHODS

The adhesion of gingival (GF), dermal (DF), and periodontal ligament fibroblast (PDLF) cultures to ECM proteins (fibronectin, laminin, vitronectin, RGD peptide, collagen type I, and collagen type IV) adsorbed to tissue culture plastic was evaluated fluorometrically. Quantitative reverse transcription-polymerase chain reactions (RT-PCR) were performed using primers specific for 19 integrin subunits to quantify ECM receptor transcript expression.

RESULTS

Our data demonstrated that GF and PDLF adhere to vitronectin and collagen types I and IV more avidly than do DF. PDLF adhered well to laminin, whereas GF and DF did not. Quantitation of integrin expression demonstrated that the different fibroblast types expressed different integrin transcripts, further demonstrating their innate differences.

CONCLUSIONS

The 3 fibroblast types studied behave differently and expressed different ECM receptors. However, gingival fibroblasts and periodontal ligament fibroblasts are more similar in their attachment and integrin expression than either is to dermal fibroblasts. Therefore, experiments using DF will not necessarily be valid for oral tissues.

Response of periradicular tissues to growth factors introduced into the surgical site in the root-end filling material

AIM

The objective of this study was to evaluate the healing of the periradicular tissues when exogenous growth factors were delivered to the respected root-end. The healing response was compared with that when Diaket was used as a control.

METHODOLOGY

Non-surgical root canal treatment was performed on mandibular teeth in mongrel dogs. Surgical treatment followed and included root-end resection and root-end cavity preparation. Insulin-like growth factor in combination with platelet-derived growth factor, or fibroblast growth factor alone, were then placed in the root-end preparations on a polylactic acid carrier (Atrisorb) with or without the incorporation of the carrier tetracalcium phosphate. The healing was evaluated at 60 days with regard to presence of inflammatory response, bone regeneration, periodontal ligament formation and cementum formation.

RESULTS

Osseous regeneration in the excisional would and periodontal formation were significantly greater when Diaket was used as the root-end filling material. Likewise, cementum deposition occurred significantly more frequently in the Diaket group (P < 0.05). The polylactic carrier Atrisorb remained in the surgical sites for the duration of the study.

CONCLUSIONS

The use of specific growth factors, FGF and a combination of IGF/PDGF, delivered to the prepared root end in a collagen carrier did not initiate the desired periradicular tissue response of regeneration. Diaket, as used in this study, did stimulate a periradicular tissue response compatible with regeneration.

Expression of transforming growth factor-beta 1 (TGF-beta1) in the developing periodontium of rats

Transforming growth factor-beta 1 (TGF-beta1) has been reported to be expressed within several tissue compartments of developing molar crowns and therefore is implicated in tooth development. Additionally, TGF-beta1 may also play a crucial role in tissue repair and regeneration. The aim of this study was to determine the distribution of TGF-beta1 in the developing periodontal attachment apparatus (cementum, periodontal ligament, and alveolar bone) in Lewis rats. Animals aged 3, 6, and 12 wks were killed, their mandibles removed, fixed, demineralized, and processed in paraffin. The localization of TGF-beta1 in tissues was detected by polyclonal goat antibodies against human TGF-beta1 by means of immunoperoxidase techniques. TGF-beta1 messenger RNA was detected by in situ hybridization with a cocktail oligonucleotide probe. Cell counts were determined for analysis of the percentage of cells stained positive for TGF-beta1. Results revealed that TGF-beta1 was expressed in the developing alveolar bone, periodontal ligament, and cementum at all stages of tissue development studied. Staining was stronger at sites of cementum and alveolar bone compared with the periodontal ligament. Intensity of the positive staining, based on 3 grades, indicated a similarity between the tissues obtained from different ages, but varied between several cell types. Cementoblasts and osteoblasts stained more strongly than fibroblasts. Large numbers (approximately 90%) of the osteocytes in developing bone expressed TGF-beta1; however, in mature bone, fewer osteocytes stained for TGF-beta1. The percentages of positively stained cementoblasts, osteoblasts, and fibroblasts in the periodontal space were greater at the apical portion than at the cervical portion of the root. TGF-beta1 mRNA was expressed in osteoblasts, some bone marrow cells, cementoblasts, and fibroblasts. This study indicates that TGF-beta1 may play an important role in the modulation of tissue formation and development of the periodontium.

Immunolocalization of epithelial and mesenchymal matrix constituents in association with inner enamel epithelial cells

After crown formation, the enamel organ reorganizes into Hertwig's epithelial root sheath (HERS). Although it is generally accepted that HERS plays an inductive role during root formation, it also has been suggested that it may contribute enamel-related proteins to cementum matrix. By analogy to the enamel-free area (EFA) in rat molars, in which epithelial cells express not only enamel proteins but also "typical" mesenchymal matrix constituents, it has been proposed that HERS cells may also have the potential to produce cementum proteins. To test this hypothesis, we examined the nature of the first matrix layer deposited along the cervical portion of root dentin and the characteristics of the associated cells. Rat molars were processed for postembedding colloidal gold immunolabeling with antibodies to amelogenin (AMEL), ameloblastin (AMBN), bone sialoprotein (BSP), and osteopontin (OPN). To minimize the possibility of false-negative results, several antibodies to AMEL were used. The labelings were compared with those obtained at the EFA. Initial cementum matrix was consistently observed at a time when epithelial cells from HERS covered most of the forming root surface. Cells with mesenchymal characteristics were rarely seen in proximity to the matrix. Both the EFA matrix and initial cementum exhibited collagen fibrils and were intensely immunoreactive for BSP and OPN. AMEL and AMBN were immunodetected at the EFA but not over the initial cementum proper. These two proteins were, however, present at the cervical-most portion of the root where enamel matrix extends for a short distance between dentin and cementum. These data suggest that epithelial cells along the root surface are likely responsible for the deposition of the initial cementum matrix and therefore, like the cells at the EFA, may be capable of producing mesenchymal proteins.

Developmental appearance and distribution of bone sialoprotein and osteopontin in human and rat cementum

BACKGROUND

Bone sialoprotein (BSP) and osteopontin (OPN), two major noncollagenous proteins (NCPs) in collagen-based mineralized tissues, have been implicated in mineral deposition and cell- and matrix-matrix interactions during root development. However, their role in cementogenesis is still a subject of debate. Since distribution of proteins is indicative of function, we have analyzed their temporo-spatial appearance in relation to that of cementum collagen.

METHODS

Human premolars and rat molars at various stages of root development characterized by differing rates of formation were fixed in aldehyde and embedded in epoxy and LR White resin. Sections were processed for ultrastructural analysis and postembedding colloidal gold (immuno)cytochemistry.

RESULTS

Incubations with antibodies against BSP and OPN and with lectins recognizing prominent sugars in these proteins generally revealed similar labeling patterns in both human and rat teeth, with gold particles accumulating mainly in the interfibrillar spaces. The lectin Helix pomatia, specific for N-acetyl-D-galactosamine, was distinctive in that it consistently reacted with human cementum, but only sporadically labeled rat cementum. Regardless of both the species and the stage of root development, mineralization initiated in mantle predentin in association with distinct foci immunoreactive for BSP and OPN. In human teeth, the deposition of cementum collagen began before the start of dentin mineralization and thus prior to any detectable labeling for BSP and OPN. However, at early stages of root formation in the rat, cementum collagen appeared after BSP and OPN accumulated on the root surface, whereas at advanced stages the deposition of cementum collagen, BSP and OPN coincided.

CONCLUSIONS

The temporo-spatial differences in the appearance of BSP and OPN relative to cementum collagen correlate well with known differences in the speed of root elongation and explain the variable appearance of the dentino-cemental junction. The data reveal no causal relationship between BSP and OPN and the differentiation of cementoprogenitor cells and indicate that the distribution of collagen fibrils ultimately determines the amount and pattern of accumulation of these NCPs. There also is no consistent planar accumulation of BSP and OPN between dentin and cementum such as the cement lines found between "old" and "new" bone. It is concluded that the interlacement of collagen fibrils at the dentino-cemental junction, across which mineralization spreads, represents the primary attachment mechanism between cementum and dentin.