Odontoblast differentiation and the formation of the odontoblast layer

SVCT2-GLUT1-mediated ascorbic acid transport pathway in rat dental pulp and its effects during wound healing

Ascorbic acid (AA; vitamin C) plays a crucial role in the biosynthesis and secretion of collagen to produce the organic matrix of hard tissues. Nevertheless, the detailed mechanism by which AA induces reparative dentinogenesis is still unknown. This study aimed to investigate the pathway and function of AA during wound healing in a rat pulpotomy model. Sodium-dependent vitamin C transporter (SVCT) 2 and glucose transporter (GLUT) 1 were detected in odontoblasts, endothelial cells, and nerve fibers in normal pulp tissues. SVCT2 and GLUT1 were also expressed in odontoblast-like cells in pulpotomized tissues of Wistar rats, and immunopositive cells of SVCT2 were significantly increased at 5 days after pulpotomy (p < 0.05). By contrast, osteogenic disorder Shionogi (ODS) rats, which cannot generate AA, also expressed SVCT2 and GLUT1 in normal and wound healing conditions. However, in ODS rats, when compared with the AA-addition group, the formation of dentin bridges in the AA-loss group was not evident, a layer of osteopontin was significantly increased beneath the wound surface (p < 0.05), and alpha smooth muscle actin at the odontoblast-like cells observed along this layer was significantly increased (p < 0.05), but not Nestin. Moreover, the amounts of type 1 collagen generated in the reparative dentin and beneath the wound healing site were significantly diminished (p < 0.05). Macrophages expressing CD68 and CD206 increased beneath the wound site. Hence, AA may be involved in odontoblast-like cell differentiation and anti-inflammatory response during dental pulp wound healing. Our results provide new insights into the function of AA through SVCT2 and GLUT1 in reparative dentinogenesis and may help in developing new therapeutic targets for dental pulpal disease.

Effects of rice fermented extracts, "Sake Lees", on the functional activity of odontoblast-like cells (KN-3 cells)

This study was designed to investigate the effects of Sake Lees extracts (SLE, Sake Kasu) on the functional activity of odontoblastic cells and tooth pulp of the rats. For in vitro studies, a rat clonal odontoblast-like cell line, KN-3 cells were cultured. SLE significantly decreased KN-3 cell proliferation, but showed no significant cytotoxicity. SLE effects on several protein productions of KN-3 cells were compared with PBS. SLE and PBS increased alkaline phosphatase (ALP), dentin sialoprotein (DSP), and osterix in a day-course dependent manner, while SLE increased the induction of ALP on day 9-21 and DSP on day 15-21. SLE also increased Runx2 expression on day 3 and 9 compared to PBS. Alizarin Red stainings revealed that SLE showed a subtle increase in mineralization of KN-3 cells on day 15 and 21. A histological investigation was conducted to assess if SLE induced reparative dentin formation after direct capping at the exposed tooth pulp in rats, suggesting that SLE could increase the reparative dentin formation more than PBS. These findings suggest that Sake Lees could have functional roles in the alterations of odontoblastic activity, which might influence the physiology of the tooth pulp.

Ultrastructural studies of developing egg tooth in grass snake Natrix natrix (Squamata, Serpentes) embryos, supported by X-ray microtomography analysis

The egg tooth development is similar to the development of all the other vertebrate teeth except earliest developmental stages because the egg tooth develops directly from the oral epithelium instead of the dental lamina similarly to null generation teeth. The developing egg tooth of Natrix natrix changes its curvature differently than the egg tooth of the other investigated unidentates due to the presence of the rostral groove. The developing grass snake egg tooth comprises dental pulp and the enamel organ. The fully differentiated enamel organ consists of outer enamel epithelium, stellate reticulum, and ameloblasts in its inner layer. The enamel organ directly in contact with the oral cavity is covered with periderm instead of outer enamel epithelium. Stellate reticulum cells in the grass snake egg tooth share intercellular spaces with the basal part of ameloblasts and are responsible for their nutrition. Ameloblasts during egg tooth differentiation pass through the following stages: presecretory, secretory, and mature. The ameloblasts from the grass snake egg tooth show the same cellular changes as reported during mammalian amelogenesis but are devoid of Tomes' processes. Odontoblasts of the developing grass snake egg tooth pass through the following classes: pre-odontoblasts, secretory odontoblasts, and ageing odontoblasts. They have highly differentiated secretory apparatus and in the course of their activity accumulate lipofuscin. Grass snake odontoblasts possess processes which are poor in organelles. In developing egg tooth cilia have been identified in odontoblasts, ameloblasts and cells of the stellate reticulum. Dental pulp cells remodel collagen matrix during growth of the grass snake egg tooth. They degenerate in a way previously not described in other teeth.

The role of insulin-like growth factors in modulating the activity of dental mesenchymal stem cells

Regenerative treatment protocols are an exciting prospect in the management of oral pathology, as they allow for tissues to be restored to their original form and function, as compared to the reparative healing mechanisms which currently govern the outcomes of the majority of dental treatment. Stem cell therapy presents with a great deal of untapped potential in this pursuit of tissue regeneration, and, in particular, mesenchymal stem cells (MSCs) derived from dental tissues are of specific relevance with regards to their applications in engineering craniofacial tissues. A number of mediatory factors are involved in modulating the actions of dental MSCs, and, of these, insulin like growth factors (IGFs) are known to have potent effects in governing the behavior of these cells. The IGF family comprises a number of primary ligands, receptors, and binding proteins which are known to modulate the key properties of dental MSCs, such as their proliferation rates, differentiation potential, and mineralisation. The aims of this review are three-fold: (i) to present an overview of dental MSCs and the role of growth factors in modulating their characteristics, (ii) to discuss in greater detail the specific role of IGFs and the benefits they may convey for tissue engineering, and (iii) to provide a summary of potential for in vivo clinical translation of the current in vitro body of evidence.

M2 Phenotype Macrophages Colocalize with Schwann Cells in Human Dental Pulp

Macrophages are immune cells with high plasticity that perform many functions related to tissue injury and repair. They are generally categorized as 2 functional phenotypes: M1 (proinflammatory) and M2 (anti-inflammatory and prohealing). To investigate the role of macrophages in human dental pulp, we examined the localization and distributional alterations of macrophages in healthy dental pulp as well as during the reparative process of pulp capping with mineral trioxide aggregate (MTA) and in cariously inflamed pulp of adult human teeth. We also quantified the populations of M1/M2 macrophages in healthy dental pulp by flow cytometric analysis. CD68⁺CD86⁺ cells (M1 phenotype) and CD68⁺CD163⁺ cells (M2 phenotype) were 2.11% ± 0.50% and 44.99% ± 2.22%, respectively, of 2.96% ± 0.41% CD68⁺ cells (pan-macrophages) in whole healthy dental pulp. Interestingly, M2 phenotype macrophages were associated with Schwann cells in healthy pulp, during mineralized bridge formation, and in pulp with carious infections in vivo. Furthermore, the M2 macrophages associated with Schwann cells expressed brain-derived neurotrophic factor (BDNF) under all in vivo conditions. Moreover, we found that plasma cells expressed BDNF. Coculture of Schwann cells isolated from human dental pulp and human monocytic cell line THP-1 showed that Schwann cells induced M2 phenotypic polarization of THP-1 cell-derived macrophages. The THP-1 macrophages that maintained contact with Schwann cells were stimulated, leading to elongation of their cell shape and expression of M2 phenotype marker CD163 in cocultures. In summary, we revealed the spatiotemporal localization of macrophages and potent induction of the M2 phenotype by Schwann cells in human dental pulp. M2 macrophages protect neural elements, whereas M1 cells promote neuronal destruction. Therefore, suppressing the neurodestructive M1 phenotype and maintaining the neuroprotective M2 phenotype of macrophages by Schwann cells may be critical for development of effective treatment strategies to maintain the viability of highly innervated dental pulp.

Fisiopatología de los odontoblastos: una revisión

Los odontoblastos son células post-mitóticas de origen mesenquimal dispuestas en forma de palizada en la periferia de la pulpa dental y responsables de la formación de la dentina. Los odontoblastos derivan de la cresta neural y su diferenciación es la consecuencia de las interacciones epitelio-mesénquima entre las células de la papila dental y el epitelio dental interno. Este trabajo tiene como objetivo revisar los aspectos fisiológicos y patológicos de los odontoblastos, comprendiendo su origen, mecanismos de diferenciación y propiedades funcionales. Se realizó una búsqueda electrónica de literatura desde el año 2000 hasta Febrero de 2018, seleccionando 2889 artículos, de los cuales 52 artículos fueron analizados y discutidos. Los resultados exponen el origen, etapas y los factores relacionados con la diferenciación odontoblástica, junto con los aspectos principales de la organización estructural y funciones que desempeñan los odontoblastos. Esta revisión demuestra mediante la evidencia científica actual como los estudios concernientes a los odontoblastos se focalizan en comprender los mecanismos en la formación de la dentina reparativa, la respuesta inmunitaria y su rol en los procesos de inflamación y dolor. Trabajos futuros deberán esclarecer las diferentes señales involucradas en los procesos fisiopatológicos celulares y moleculares llevados a cabo por los odontoblastos. 

Characterization of Odontoblast-like Cell Phenotype and Reparative Dentin Formation In Vivo: A Comprehensive Literature Review

INTRODUCTION

The primary aim was to explore the criteria used in characterization of reparative cells and mineralized matrices formed after treatment of pulp exposures, and the sequence of relative events. The secondary aim was to evaluate whether the reparative events depend on the experimental model species, age, and therapeutic intervention.

METHODS

A literature search of databases using different combinations of the key words was undertaken. Data analysis was based only on studies having histological or histochemical assessment of the pulp tissue responses. The search yielded 86 studies, 47 capping material-based and 39 bioactive application-based experiments, which provided data on morphological or functional characterization of the mineralized matrices and the associated cells.

RESULTS

In 64% of capping material-based and 72% of bioactive application-based experiments, a 2-zone mineralized matrix formation (atubular followed by tubular) was detected, whereas characterization of odontoblastic differentiation is provided in only 25.5% and 46.1% of the studies, respectively. In 93.3% of the studies showing odontoblast-like cells, differentiated cells were in association with tubular mineralized matrix formation. Analyses further showed that cell- and matrix-related outcomes do not depend on experimental model species, age, and therapeutic intervention.

CONCLUSIONS

The evidence of the reviewed scientific literature is that dental pulp cells secrete a dentin-like matrix of tubular morphology in relation to primitive forms of atubular or osteotypic mineralized matrix. Furthermore, data analysis showed that dental pulp cells express in vivo the odontoblastic phenotype, and secrete matrix in a predentin-like pattern, regardless of the model species, age, and therapeutic intervention used.

Characterization of Dental Pulp Myofibroblasts in Rat Molars after Pulpotomy

INTRODUCTION

Myofibroblasts express alpha smooth muscle actin (α-SMA) and play a critical role in wound healing. Myofibroblast differentiation is controlled by the joint actions of transforming growth factor beta 1 (TGF-β1) and the extradomain A fibronectin splice variant (EDA-FN). Currently, the contribution of myofibroblasts to dental pulp healing is unknown. Therefore, we analyzed expressional characteristics of α-SMA-positive cells and investigated TGF-β1, EDA-FN, and α-SMA expression levels after pulpotomy to better understand dental pulp healing.

METHODS

The maxillary first molars of 8-week-old Wistar rats were pulpotomized with mineral trioxide aggregate. After 1 to 14 days, localization and colocalization of α-SMA, rat endothelial cell antigen-1 (as a marker of endothelial cells), neuron-glial antigen 2 (as a marker of perivascular cells), prolyl-4-hydroxylase (P4H, as an additional marker of myofibroblasts), and EDA-FN were analyzed using immunohistochemistry and double immunofluorescence. Time-course changes in the messenger RNA expression levels of TGF-β1, EDA-FN, and α-SMA were evaluated using quantitative real-time polymerase chain reaction analysis.

RESULTS

Spindle-shaped α-SMA-positive cells transiently appeared after pulpotomy. These cells initially emerged in the pulp core on day 3 and then accumulated at the wound site by day 5. These cells were isolated from rat endothelial cell antigen-1 positive cells and did not express neuron-glial antigen 2 but did express P4H. The messenger RNA levels of TGF-β1, EDA-FN, and α-SMA were significantly up-regulated after pulpotomy. EDA-FN and α-SMA were colocalized at the wound sites on day 5.

CONCLUSIONS

In association with up-regulation of TGF-β1 and EDA-FN expression, α-SMA and P4H double-positive cells accumulated at the wound sites after pulpotomy. This suggests that myofibroblasts participate in dental pulp healing.

DSPP Is Essential for Normal Development of the Dental-Craniofacial Complex

The craniofacial skeleton is derived from both neural crest cells and mesodermal cells; however, the majority of the bone, cartilage, and connective tissue is derived from the neural crest. Dentin sialophosphoprotein (DSPP) is a precursor protein that is expressed by the connective tissues of the craniofacial skeleton, namely, bone and dentin with high expression levels in the dentin matrix. Gene ablation studies have shown severe dental defects in DSPP-null mutant mice. Therefore, to elucidate the role of DSPP on the developing dental-craniofacial complex, we evaluated phenotypic changes in the structure of intramembranous bone and dentin mineralization using 3 different age groups of DSPP-null and wild-type mice. Results from micro-computed tomographic, radiographic, and optical microscopic analyses showed defective dentin, alveolar and calvarial bones, and sutures during development. The impaired mineralization of the cranial bone correlated well with low expression levels of Runx2, Col1, and OPN identified using calvarial cells from DSPP-null and wild-type mice in an in vitro culture system. However, the upregulation of MMP9, MMP2, FN, and BSP was observed. Interestingly, the null mice also displayed low serum phosphate levels, while calcium levels remained unchanged. Alizarin red and von Kossa staining confirmed the dysfunction in the terminal differentiation of osteoblasts obtained from the developing calvaria of DSPP-null mice. Immunohistochemical analysis of the developing molars showed changes in Runx2, Gli1, Numb, and Notch expression in the dental pulp cells and odontoblasts of DSPP-null mice when compared with wild-type mice. Overall, these observations provide insight into the role of DSPP in the normal development of the calvaria, alveolar bone, and dentin-pulp complex.

Analysis of gene expression during odontogenic differentiation of cultured human dental pulp cells

OBJECTIVES

We analyzed gene-expression profiles after 14 day odontogenic induction of human dental pulp cells (DPCs) using a DNA microarray and sought candidate genes possibly associated with mineralization.

MATERIALS AND METHODS

Induced human dental pulp cells were obtained by culturing DPCs in odontogenic induction medium (OM) for 14 day. Cells exposed to normal culture medium were used as controls. Total RNA was extracted from cells and analyzed by microarray analysis and the key results were confirmed selectively by reverse-transcriptase polymerase chain reaction (RT-PCR). We also performed a gene set enrichment analysis (GSEA) of the microarray data.

RESULTS

Six hundred and five genes among the 47,320 probes on the BeadChip differed by a factor of more than two-fold in the induced cells. Of these, 217 genes were upregulated, and 388 were down-regulated. GSEA revealed that in the induced cells, genes implicated in Apoptosis and Signaling by wingless MMTV integration (Wnt) were significantly upregulated.

CONCLUSIONS

Genes implicated in Apoptosis and Signaling by Wnt are highly connected to the differentiation of dental pulp cells into odontoblast.

Tertiary dentinogenesis with calcium hydroxide: a review of proposed mechanisms

Calcium hydroxide has been used extensively in dentistry for a century. Despite its widespread use as a pulp-capping agent, its mechanisms of action still remain ambiguous. Understanding its modes of action will lead to a broader understanding of the mechanisms associated with induced dentinogenesis and help in optimizing the currently available agents to target specific regenerative processes to obtain the best possible clinical outcomes. A literature search relating to mechanisms of dentinogenesis of calcium hydroxide up to December 2011 was carried out using pubmed and MEDLINE database searches as well as manual searching of cross-references from identified studies. Resulting suggestions regarding dentinogenic mechanisms of calcium hydroxide range from direct irritating action of the material to induction of release of biologically active molecules. The purpose of this article is to discuss various mechanisms through which calcium hydroxide may induce tertiary dentinogenesis in the light of observations made in included studies.

Reparative dentinogenesis induced by mineral trioxide aggregate: a review from the biological and physicochemical points of view

This paper aims to review the biological and physicochemical properties of mineral trioxide aggregate (MTA) with respect to its ability to induce reparative dentinogenesis, which involves complex cellular and molecular events leading to hard-tissue repair by newly differentiated odontoblast-like cells. Compared with that of calcium hydroxide-based materials, MTA is more efficient at inducing reparative dentinogenesis in vivo. The available literature suggests that the action of MTA is attributable to the natural wound healing process of exposed pulps, although MTA can stimulate hard-tissue-forming cells to induce matrix formation and mineralization in vitro. Physicochemical analyses have revealed that MTA not only acts as a "calcium hydroxide-releasing" material, but also interacts with phosphate-containing fluids to form apatite precipitates. MTA also shows better sealing ability and structural stability, but less potent antimicrobial activity compared with that of calcium hydroxide. The clinical outcome of direct pulp capping and pulpotomy with MTA appears quite favorable, although the number of controled prospective studies is still limited. Attempts are being conducted to improve the properties of MTA by the addition of setting accelerators and the development of new calcium silicate-based materials.

The location and characteristics of two populations of dental pulp cells affect tooth development

This study investigated the characteristics of two dental pulp cell populations during the early stages of crown formation in porcine teeth. A transplantation method was developed to reproduce epithelial cell-mesenchymal cell interactions during odontogenesis (tooth development). The technique allowed two types of cells/tissue to be combined in vivo. Populations of cells localized in the cervical loop epithelium region, dental pulp horn, and dental pulp core chambers were isolated and dissociated into single cells. Each population was examined for its gene-expression pattern using both semiquantitative and quantitative reverse transcription-polymerase chain reaction (RT-PCR) analyses, and for its tissue-formation capability by combining the cervical loop epithelial cells with either pulp horn cells or pulp core cells on biodegradable collagen scaffolds that were subsequently examined using histology and immunohistology. Gene-expression patterns showed that pulp horn cells were more mature than pulp core cells. Cervical loop epithelial cells combined with pulp horn cells mainly reconstituted dentin-cementum structures. By contrast, cervical loop epithelial cells combined with pulp core cells reconstituted enamel-dentin structures. These results suggest that mesenchymal cells residing in a specific location of the pulp possess a specific tissue-formation potential when combined with epithelial cells.

Factors influencing the expression of dental extracellular matrix biomineralization

The forming tooth organ provides a number of opportunities to investigate the cellular and molecular biology of cell-mediated extracellular matrix (ECM) biomineralization. Regulatory processes associated with tooth formation are being investigated by identifying when and where cell adhesion molecules (CAMs), substrate adhesion molecules (SAMs), dentine phosphoprotein and enamel gene products are expressed during sequential developmental stages. In vitro organotypic culture studies in serumless, chemically-defined medium, have shown that instructive and permissive signalling are required for both morphogenesis and cytodifferentiation. Intrinsic developmental instructions (autocrine and paracrine factors) act independently of long-range hormonal or exogenous growth factors and mediate morphogenesis from the initiation of the dental lamina to the crown stages of tooth development. This review summarizes the results of studies using experimental embryology, recombinant DNA technology and immunocytology to elucidate mechanisms responsive to instructive epithelial-mesenchymal interactions associated with ameloblast differentiation, odontoblast differentiation, and dentine and enamel ECM biomineralization.

An immunohistochemical study of the expression of heat-shock protein-25 and cell proliferation in the dental pulp and enamel organ during odontogenesis in rat molars

OBJECTIVES

The aim of this study is to clarify the functional significance of heat-shock protein (HSP)-25 during tooth development.

DESIGN

We compared the expression of HSP-25 in the dental epithelial and mesenchymal cells with their proliferative activity during odontogenesis in rat molars on postnatal days 1-100 by immunohistochemistry using anti-HSP-25 and anti-5-bromo-2'-deoxyuridine (BrdU) for cell proliferation assay.

RESULTS

On day 1, BrdU-immunoreactive cells were densely located in the inner enamel epithelium in the cervical loop and intercusped areas and the dental pulp adjacent to them, whereas HSP-25-immunoractivity (IR) was restricted to the cusped area where odontoblasts and ameloblasts had already differentiated. Subsequently, BrdU-IR shifted in the apical direction to be localized around Hertwig's epithelial root sheath during days 5-30, never overlapping with concomitantly apically-shifted HSP-25-IR. On days 60-100, BrdU-immunoreactive cells were hardly recognizable in the dental pulp, where HSP-25-IR was exclusively localized in the odontoblast layer. Furthermore, the odontoblast- and ameloblast-lineage cells exhibited two steps in the expression of HSP-25 throughout the postnatal stages: first, dental epithelial and pulpal mesenchymal cells showed a weak IR for HSP-25 after the cessation of their proliferative activity, and subsequently odontoblasts and ameloblasts consistently expressed an intense HSP-25-IR.

CONCLUSION

Odontoblast- and ameloblast-lineage cells acquire HSP-25-IR after they complete their cell division, suggesting that this protein acts as a switch between cell proliferation and differentiation during tooth development. The consistent expression of HSP-25-IR in the formative cells may be involved in the maintenance of their functional integrity.

Immunolocalization of fibroblast growth factor-2 (FGF-2) in the developing root and supporting structures of the murine tooth

Epithelio-mesenchymal interactions are active during the development of the root of the tooth and are regulated by a variety of growth factors, such as fibroblast growth factors. FGF-2, 3, 4, and 8 have all been shown to play a role in the development of the crown of the tooth, but less is known about the factors that govern root formation, particularly FGF-2. The aim of this study was thus to elucidate the spatial and temporal expression of FGF-2 in the root of the developing tooth, as this growth factor is believed to be a mediator of epithelio-mesenchymal interactions. Parasagittal sections of the maxillary and mandibular arches of post-natal mice were utilized and the roots of the molar teeth were studied. Immunocytochemistry utilizing an antibody to FGF-2 was performed on sections of teeth at various stages of development. Intense immunostaining for FGF-2 was observed in differentiating odontoblasts at the apical end of the tooth and in the furcation zone of the developing root at all the stages examined. FGF-2 localization was also observed in cementoblasts on post-natal days 16, 20 and 24. The pattern of localization of FGF-2 in the developing root suggests that this growth factor may participate in the signaling network associated with root development.

The dentinogenic effect of mineral trioxide aggregate (MTA) in short-term capping experiments

AIM

The objective of the present experiment was to study the early pulpal cell response and the onset of reparative dentine formation after capping application of MTA in mechanically exposed pulps.

METHODOLOGY

Thirty-three teeth from three dogs, 12-18 months of age were mechanically exposed via class V cavities. Light pressure was applied to control haemorrhage. ProRoot MTA (Dentsply Simfra, Paris) was placed at the exposure site and light pressure was applied with a wet cotton pellet. The cavities were restored with amalgam and the pulpal tissue reactions were assessed by light and electron microscopy (transmission and scanning) after healing intervals of 1, 2 or 3 weeks.

RESULTS

A homogenous zone of crystalline structures was initially found along the pulp-MTA interface, whilst pulpal cells showing changes in their cytological and functional state were arranged in close proximity to the crystals. Deposition of hard tissue of osteotypic form was found in all teeth in direct contact with the capping material and the associated crystalline structures. Formation of reparative dentine (tubular matrix formation in a polar predentine-like pattern by elongated polarized cells) was consistently related to a firm osteodentinal zone.

CONCLUSIONS

The present experiments indicate that MTA is an effective pulp-capping material, able to stimulate reparative dentine formation by the stereotypic defensive mechanism of early pulpal wound healing.

A mineralizing rat dental pulp cell subline expressing collagen type I and dentin sialoprotein-phosphophoryn transcripts

A mineralizing rat dental pulp cell subclone, termed M2H4, was selected from single-cell cloning of the rat dental pulp cell line RPC-C2A by screening confluent single-cell cultures for their ability to undergo mineralization. To induce mineralization, confluent single-cell cultures were treated for 8 d with ascorbic acid followed by the addition of inorganic phosphate to a final concentration of 4 mM for an additional 3 d. Confluent M2H4 subclones were shown by immunofluorescence and electron microscopy to form collagen type I fibrils. Furthermore, using reverse transcriptase-polymerase chain reaction, this subclone was found to be capable of expressing dentin sialoprotein-phosphophoryn (DSP-PP) transcripts, an odontoblast-specific marker. Thus, this newly identified mineralizing rat M2H4 subclone possesses odontoblast-like characteristics and can serve as an in vitro model for examining the role of DSP and PP in the formation of mineralized dentin.

Crown morphology and pattern of odontoblast differentiation in lower molars of tabby mice

The Tabby mutation leads to abnormal crown morphology in the developing molars. To identify cusps which were altered in number, size, and position in the first lower molars of mutant mice, we analyzed the patterning of odontoblast differentiation using morphological criteria on serial sections and 3D reconstructions. In wildtype mice, polarized and functional odontoblasts were first observed in the median L2 and B2 cusps, then in the distal cusps L3 and B3, and finally in L1, B1, and 4. In Tabby mice, terminal differentiation of odontoblasts was retarded by 24-36 hours compared with wild-type mice. Polarized odontoblasts first appeared in the most mesial part of the tooth and progressively extended distally. The mesial part of the M1 in Tabby fetuses may correspond to the L2, B2 area from wild-type mice. The ante-molar dental primordium observed in some samples would thus represent remnants of cusps L1 and B1.

Dentin regeneration in vital pulp therapy: design principles

The nature and specificity of the mechanisms by which the amputated dentin-pulp interface is therapeutically healed determine the properties of the barrier at this site and play a critical role in the outcome of vital pulp therapy. Healing of the dentin-pulp complex proceeds either by natural repair-which results in defensive hard-tissue formation, or therapeutically regulated dentin regeneration, which aims to reconstitute the normal tissue architecture at the pulp periphery. Progress in biomedical research opens new directions for the design of biologically effective pulp therapies. Application of biocompatible and biodegradable carrier vehicles for local delivery of signaling molecules in pulp-capping situations showed induction of fibrodentin/reparative dentin formation, but often at the expense of underlying pulp tissue. An alternative pre-clinical model aiming to reconstitute normal tissue architecture directly at the dentin-pulp interface should be designed on the basis of the direct induction of odontoblast-like cell differentiation and reparative dentin formation at the pulp-capping material interface. Experimental data clearly showed that pulpal cells can differentiate directly into odontoblast-like cells in association with specific extracellular matrices (dentinal or fibrodentinal matrix) or TGF beta 1-containing artificial substrates. Dentin-induced dentinogenesis can be used as a master plan for the achievement of new therapeutic opportunities. In the present study, several short-term experimental studies on dog teeth for potential direct induction of odontoblast-like cell differentiation at the surface of rhTGF beta 1-containing artificial substrates (Millipore filters, hydroxyapatite granules, calcium hydroxide, pure titanium) failed to induce any specific reparative dentinogenic effects.

Teeth outside the mouth in teleost fishes: how to benefit from a developmental accident

Evolution proceeds by the selection of characters that enhance survival rates so that the long-term outcome for a species is better adaptation to its environment. These new characters are "accidentally" acquired, mostly through mutations leading to modifications of developmental events. However, changes that lead to the ectopic expression of an organ are rare and, whereas their subsequent selection for a new role is even more rare, such a scenario has apparently occurred for denticles in some teleost fish. Small, conical denticles are present, mainly on the dermal bones of the head, in a few, unrelated lineages of living teleosts. Here, I show that the morphology and structure of the denticles in Atherion elymus, an atheriniform, is similar to those of teeth inside the oral cavity. These denticles are not derived evolutionarily from odontodes of early vertebrates, nor do they represent a re-expression as such (i.e., a long-lasting ability to make odontodes outside the oral cavity). Teeth and odontodes are homologous organs but the origin of the denticles is to be found in teeth, not in odontodes. The denticles are simply teeth that form outside the mouth, probably derived from a sub-population of odontogenically pre-specified neural crest cells. These "accidental" extra-oral teeth have arisen independently in these lineages and were selectively advantageous in a hydrodynamic context.

Expression of dentin sialoprotein (DSP) and other molecular determinants by a new cell line from dental papillae, MDPC-23

The purpose of this study was to characterize the molecular expression of a spontaneously immortalized and cloned cell line (MDPC-23) derived from 18-19 day CD-I fetal mouse molar dental papillae to determine if these cells were odontoblast-like. Western blots showed that a protein band, at approximately 105 kDa, reacting positively with anti-DSP antibodies and co-migrating with mouse DSP, was present in lysates of cells from passages 7, 37 and 77, in serum-free conditioned medium from passage 37 cells, and in mouse dentin extract. A minor band at 55 kDa was also apparent in cell lysates. Using a cDNA probe for a 486bp mouse DSP coding sequence, DSP or DSP-PP mRNA expression was detected by Northern analysis as well as Southern analysis after RT-PCR in all three passages. It was also shown that in these cells 1,25 (OH)2 vitamin D3 upregulated both osteopontin and osteocalcin mRNA, and dexamethasone downregulated alkaline phosphatase and alpha2(I) collagen mRNA. Thus, MDPC-23 cells express proteins which are common to mineralizing tissue. The expression of DSP and DSP-PP strongly suggests that this cell line is from the odontoblast lineage.

Odontoblast commitment and differentiation

Histological and cytological organization confer specificity to the odontoblasts. These postmitotic, neural crest derived, polarized cells are aligned in a single layer at the periphery of the dental pulp and secrete the organic components of predentin-dentin. The developmental history of these cells demands a cascade of epigenetic signalling events comprising the acquisition of odontogenic potential by neural crest cells, their patterning in the developing jaws, the initiation of odontogenesis through interaction with the oral epithelium, commitment, and tooth-specific spatial distribution of competent preodontoblasts able to overtly differentiate. Recent experimental investigations are critically summarized, many open questions are stressed, and current hypotheses concerning the control of terminal odontoblast differentiation are outlined.Key words: odontoblast, neural crest, oral ectoderm, differentiation.

Effects of recombinant basic fibroblast growth factor, insulin-like growth factor-II and transforming growth factor-beta 1 on dog dental pulp cells in vivo

The effects of recombinant basic fibroblast growth factor (bFGF), insulin-like growth factor (IGF)-II and transforming growth factor (TGF)-beta 1 on dental pulp cells were investigated by light and transmission electron microscopy after their implantation for 1 and 3 weeks at central sites of mechanically exposed pulps in dog molar and canine teeth. The implants were Millipore filters that have been soaked with solutions containing 100 or 500 ng/ml of bFGF or IGF-II or 100 ng/ml of TGF-beta 1. Control filters were soaked with dog albumin. No changes in cell organization or matrix synthesis were seen after implantation of control filters. Groups of columnar, polarized cells with numerous mitochondria and Golgi elements or elongated cells unassociated with any matrix deposition were demonstrated after 1 or 3 weeks, respectively, in close proximity to the filters that had been soaked with bFGF solution; at a distance from these implants enhanced formation of an osteotypic matrix was seen beneath the exposure site. No particular response was found in close proximity to the filters that had been soaked with IGF-II solution after 1 or 3 weeks implantation but thick zones of osteodentine were found beneath the exposure site and at adjacent circumferential dentine sites. Numerous elongated, polarized cells with long cytoplasmic extensions invading the filter pores were consistently seen after 1 week in close proximity to the filters that had been soaked with TGF-beta 1 solution. After 3 weeks implantation of these filters, deposition of a tubular matrix surrounding the implants was seen in association with the highly elongated odontoblast-like cells, while enhancement of circumferential dentine formation was also found at adjacent peripheral sites. These experiments demonstrate that TGF-beta 1 when implanted for short term periods at central pulp sites exerted dentine-specific effects, inducing differentiation of odontoblast-like cells and stimulating primary odontoblasts. Implantation of bFGF and IGF-II did not result in reparative dentine formation, but did stimulate osteotypical matrix deposition at a distance from the implants.

Cell proliferation in developing human dental pulp. A combined flow cytometric and immunohistochemical study

Information concerning cell proliferation and differentiation in dental pulp may be important to understand tooth response to exogenous stimuli. Since few data concerning human dental pulp are available, we have investigated the growth fraction and the localization of proliferating cells in pulp tissue of third molars of young adult human males and females, using flow cytometry and immunohistochemistry. Flow cytometric analysis demonstrates a low proliferative activity of pulp tissue that appears to be confined to radicular pulp, as revealed by immunohistochemical detection of proliferating cells. No polyploid or aneuploid cell populations could be identified, and G2-blocked cells, if any, represented a negligible cell population. Odontoblasts, cells of the sub-odontoblastic layer, and cells of coronal pulp were found to be not proliferating under normal conditions. These data provide the basis for future investigations on proliferative activity and regenerative potentiality of human pulp cells in experimental and clinical situations.

Dentin sialoprotein (DSP) transcripts: developmentally-sustained expression in odontoblasts and transient expression in pre-ameloblasts

Dentin sialoprotein (DSP), a 53 kDa glycoprotein, is believed to be present exclusively in dentin. Using rat and mouse digoxigenin labeled (DIG)-DSP and 35S-DSP riboprobes, and in situ hybridization techniques, we have studied the presence of DSP mRNA at specific developmental stages of dentinogenesis. In mouse and rat molars and incisors, DSP transcripts were localized in young odontoblasts associated with early stages of predentin formation, as well as in mature odontoblasts, cells with cytoplasmic extensions embedded in the forming dentin. No DSP transcripts were detected in dental pulp, enamel organ, ameloblasts, epithelial root sheath, Meckel's cartilage, alveolar bone or tibia. Furthermore, no DSP mRNA was observed in other soft tissues including heart, lung, kidney, intestine, eye, and muscle. In addition to the intense and prolonged expression by odontoblasts, DSP mRNA was transiently expressed by pre-ameloblasts in both developing molars and incisors. These observations are consistent with the results of previous immunohistochemical studies (1). The transient expression of DSP in pre-ameloblasts across from young odontoblasts suggests an involvement of DSP in epithelial-mesenchymal interactions that are crucial to later stages of tooth development.

Expressions of c-jun and jun-B proto-oncogenes in odontoblasts during development of bovine tooth germs

c-jun and jun-B genes are among the nuclear proto-oncogenes induced by growth factors such as the TGF-beta superfamily and play important roles in cell differentiation. These gene products enhance expressions of proteins including osteocalcin, alkaline phosphatase, and collagens. On the other hand, it is well-known that the TGF-beta superfamily affects odontoblast differentiation, and that differentiated odontoblasts express extracellular and membrane proteins as described above. However, there are few reports of factors that participate in the transcriptional regulation of odontoblasts. Especially, little is known about the expression of c-jun and jun-B genes. In this study, we focused on the examination of expressions of c-jun and jun-B genes in dental papillae of bovine tooth germs. Using in situ hybridization, we found that these genes were expressed only in the odontoblastic lineage, but not in other dental papilla cells. Levels of c-jun and jun-B mRNAs increased along the gradient of differentiation of odontoblasts. These levels of c-jun mRNAs were maintained in both young and mature odontoblasts. However, unlike the c-jun gene, expression of the jun-B gene became sparse in mature odontoblasts compared with young odontoblasts. For further analysis, Northern hybridization of total RNA extracted from differentiated odontoblasts was performed for the examination of levels of jun-B mRNAs, indicating that levels of jun-B mRNAs of mature odontoblasts were clearly less than those of young odontoblasts. These results suggest that c-jun and jun-B genes may participate in the transcriptional regulation of odontoblasts of bovine tooth germs, and may control the odontoblast phenotype. Furthermore, our results suggest that these genes can be markers of odontoblasts during dentinogenesis; especially, high expression of jun-B gene can be a marker of young odontoblasts that start to form the new dentin matrix.

Detection of sugar residues in rabbit embryo teeth with lectin-horseradish peroxidase conjugate: II. A light microscopal study

The cellular distribution and changes of sugar residues during tooth development in embryos of the rabbit Oryctolagus cuniculus were investigated by using horseradish peroxidase-conjugated lectins (lectin-HRP). The lectins SBA, ECA, and LTA show no binding to any region of the dental cap and bell stages, whereas BS-1 and UEA-1 bind to dental cells at both stages. Appropriate control studies confirmed the specificity of the binding of the lectins. At cap stage, the lectins BS-1 and UEA-1 show moderate binding to the (pre)-ameloblast and (pre)-odontoblast cells. These results suggest that the acetylgalactosamine and alpha-L-fucose residues present in (pre)-ameloblasts and (pre)-odontoblasts, respectively, are common to determined but relatively undifferentiated cells capable of forming matrices of hard tissues. Since the odontoblast and ameloblast express dentin and enamel, respectively, it can be speculated that the abundance of these residues in these cells might be associated with the maintenance of the capacity of the cells to produce such matrices. At the bell stage, the odontoblasts display considerable amounts of alpha-L-fucose, whereas alpha-L-fucose is poorly localized in ameloblasts. However, ameloblasts contain significant quantities of N-acetylgalactosamine, whereas only a diffuse positivity for this carbohydrate is apparent in odontoblasts. The marked changes of the glycosylation pattern of these glycoconjugates might indicate that they play a role during the cell-to-cell interaction and might also be involved in the odontoblastic and ameloblastic functional activity. Such a possibility is entirely speculative until specific in vitro experiments are conducted.

An in vitro model of human dental pulp repair

Pulp tissue responds to dentin injury by laying down reactionary dentin secreted by existing odontoblasts or reparative dentin elaborated by odontoblast-like cells that differentiated from precursor cells in the absence of inner dental epithelium and basement membrane. Furthermore, growth factors or active dentin matrix components are fundamental signals involved in odontoblast differentiation. In vitro, dental pulp cells cultured under various conditions are able to express typical markers of differentiation, but no culture system can re-create pulp response to dentin drilling. This paper reports the behavior of thick slices from human teeth drilled immediately after extraction and cultured from 3 days to 1 month. Results show that the damaged pulp beneath the cavity is able to develop, in vitro, some typical aspects correlated to tissue healing, evidenced by cell proliferation (BrdU-positive cells), neovascularization (positive with antitype-IV collagen antibodies), and the presence of functional (3H proline-positive) cuboidal cells close to the injured area. After 30 days of culture, elongated spindle-shaped cells can be seen aligned along the edges of the relevant dentin walls, whereas sound functional odontoblasts are well-preserved beneath healthy areas. This tissue recovery leads us to believe that such a culture model will be a useful system for testing factors regulating pulp repair.

Hair matrix germinative epidermal cells confer follicle-inducing capabilities on dermal sheath and high passage papilla cells

Low passage cultured dermal papilla cells from adult rats stimulate complete hair follicle neogenesis when re-implanted into heterotypic skin. In contrast, cultured sheath cells are non-inductive despite sharing other behavioural characteristics (a common lineage and in situ proximity) with papilla cells. However, since sheath cells can behave inductively in amputated follicles after regenerating the papilla, this poses the question of what influences the sheath to papilla cell transition? During reciprocal tissue interactions specific epidermal cues are crucial to skin appendage development, and while in vivo assays to date have focussed on dermal interactive influence, our aim was to investigate epidermal potential. We have previously observed that hair follicle epidermal cells display exceptional interactive behaviour when combined with follicle dermal cells in vitro. Thus in the present study, hair follicle germinative, outer root sheath or skin basal epidermal cells were separately combined with each of three non-inductive dermal cell types (high passage papilla, low passage sheath or fibroblast) and then implanted into small ear skin wounds. The sheath/germinative and papilla/germinative cell implants repeatedly induced giant vibrissa-type follicles and fibres. In complete contrast, any single cell type and all other forms of recombination were consistently non-inductive. Hence, the adult germinative epidermal cells enable non-inductive adult dermal cells to stimulate hair follicle neogenesis, effectively, by altering their ‘status’, causing the sheath cells to ‘specialise’ and the ‘aged’ papilla cells to ‘rejuvenate’.

Immunolocalization of fibronectin during reparative dentinogenesis in human teeth after pulp capping with calcium hydroxide

Exposed dental pulp is known to possess the ability to form a hard-tissue barrier (dentin bridge). The exact mechanisms by which pulp cells differentiate into odontoblasts in this process are unknown. Fibronectin has been demonstrated to play a crucial role in odontoblast differentiation during tooth development. This study tested the hypothesis that fibronectin is involved in the initial stages of replacement odontoblast differentiation and reparative dentin formation. We observed its immunohistochemical localization during dentin bridge formation in human teeth, after pulp was capped with calcium hydroxide [Ca(OH)2]. One day after the capping, precipitation of crystalline structures was observed at the TEM level in association with cell debris at the interface between the superficial necrotic zone and underlying pulp tissue. This layer of dystrophic calcification showed positive reaction for fibronectin, and pulp cells appeared to be closely associated with this layer, seven to ten days post-operatively. At 14 days, an alignment of cells, some of which were elongated and odontoblast-like, was observed adjacent to the fibronectin-positive irregular matrix. Between the cells, corkscrew fiber-like fluorescence was visible. At 28 days, the irregular fibrous matrix was followed by the formation of tubular dentin-like matrix lined with odontoblast-like cells. Therefore, it would seem that fibronectin associated with the initially formed calcified layer might play a mediating role in the differentiation of pulp cells into odontoblasts during reparative dentinogenesis, after pulp was capped with Ca(OH)2.

Effects of a functional agar surface on in vitro dentinogenesis induced in proteolytically isolated, agar-coated dental papillae in rat mandibular incisors

In an attempt to study the effects of a three-dimensional agar surface on in vitro dentinogenesis both in the growing end and in incisally cross-cut pulp, the possible expression of odontoblast phenotype was investigated morphologically, autoradiographically and immunohistochemically. Explants were incubated for 8 days. In the growing end, during the last 4 days, mitotic cells differentiated into [3H]-thymidine-labelled, tubular matrix-forming cells. In cross-cut pulp, however, during the first 4 days, mitotic cells differentiated into [3H]-thymidine-labelled, tubular matrix-forming cells. Electron microscopy demonstrated that, in both regions, tubular matrix-forming cells had characteristics similar to those of primary odontoblasts. When agar was incubated alone, exogenous fibronectin was deposited on it rapidly. After 12 h, endogenous fibronectin appeared on explant peripheral cells. Collagen and materials reacting positively to periodic acid-Schiff (PAS) were first interposed between agar and explant after 4 days. After 8 days, an inner immunonegative layer corresponding to materials reacting positively to PAS or toluidine blue and an outer immunopositive layer of fibronectin or collagen were visible adjacent to the rows of elongated columnar cells. In the presence of Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP), a competitive inhibitor of attachment of cells to fibronectin, explants became detached from the agar surface, and no dentinogenesis occurred. These results indicate that, when in contact with an agar surface that becomes modified by fibronectin and/or by a complex of fibronectin with deposited matrix, dental mesenchymal cells progressively differentiate into tubular matrix-forming cells. Possibly the functional agar surface has the important role of providing a foothold for cell attachment, which is the first step towards in vitro odontoblast differentiation. This system of inducing tubular matrix-forming cells constitutes a useful model for the study of in vitro dentinogenesis.

Application of immunocytochemistry for detection of proliferating cell populations during tooth development

BACKGROUND

The production of monoclonal antibodies to cell cycle-related molecules provides the basis for immunochemical studies on cell kinetics.

METHODS

Immunocytochemistry permits the tissue localization of replicating cells, whereas flow cytometry defines the exact position of immunoreactive cells in the cell cycle and ensures a quantitative analysis of the growth fraction. Bromo-deoxyuridine-antibody can be used to reveal S phase-traversing cells, whereas the immunoreactivity for the Proliferating Cell Nuclear Antigen defines the G1, S, and G2-M subpopulations of the cell cycle.

RESULTS

Odontogenic cells produce secretory products (e.g., enamel and dentine matrix proteins and growth factors) and express receptors and oncogenes during specific stages of their differentiation.

CONCLUSIONS

The simultaneous detection of cell cycle-related antigens and differentiation markers using double immunochemical staining may be useful to clarify the role of putative regulatory molecules in the control of cell growth during odontogenesis, thus unveiling molecular mechanisms that regulate developmental dynamics.

Electron microscopic study on interodontoblastic collagen fibrils in amputated canine dental pulp

The purpose of this research was to study the presence and the ultrastructural features of interodontoblastic collagen fibrils and their contribution to the formation of reparative dentin in dog incisors and premolars for a period of 30 days following experimental pulpotomy. On the seventy day after pulp exposure and capping with calcium hydroxide, short cylindrical-shaped cells collected at the coronal end of the vital pulp tissue. Many collagen fibrils were synthesized in the intercellular spaces and in the direction of the long axis of these cells. On the fourteenth day, large bundles of collagen fibrils were observed in the intercellular spaces of young odontoblasts. These bundles spread out in a fan-shaped arrangement. On the thirtieth day, the odontoblasts formed a tubular dentin matrix. Small numbers of twisted collagen bundles crossed the distal junctional complex of the odontoblast cell bodies and entered the dentin matrix.

The soft connective tissues of the gingiva and periodontal ligament: are they unique?

The connective tissues of the gingiva and periodontal ligament share a common embryonic development from cells of the cranial neural crest. This review paper describes the relationship of these tissues in tooth germ initiation, development and eruption.

Induction of odontoblast-like cell differentiation in dog dental pulps after in vivo implantation of dentine matrix components

The effects of dentine extracellular matrix components on dental mesenchymal cells were studied by light and transmission electron microscopy after their implantation at central sites of mechanically exposed pulps in dog molar teeth. The implants were Millipore filters that had been soaked with solutions containing 30 or 300 micrograms/ml of an EDTA-soluble fraction of rabbit incisor dentine. Control filters were soaked with dog albumin or phosphate buffered saline. Columnar, polarized cells were consistently seen after 8 days in close proximity to the filters coated with both concentrations of dentine matrix components. Characteristic features of these polarized cells included widened cisternae of the rough endoplasmic reticulum, a rich microfilamentous network in the long cytoplasmic extensions invading the filter pores and numerous cytoplasmic bodies. These cells also showed evidence of functional as well as cytological differentiation. Polarized processing of secretory granules could be observed after 8 days' implantation, and also the presence of matrix vesicles and deposition of a fine, collagenous matrix into the filters apically to the distal end of the cytoplasmic processes. After 24 days' implantation, secretion of a tubular matrix could be consistently seen in association with the odontoblast-like cells. No changes in cell organization or matrix synthesis were seen after implantation of control filters. These studies demonstrate that bioactive components present in the EDTA-soluble dentine matrix fraction are able to directly induce cell polarization and apical secretion of tubular matrix when implanted in contact with dental pulp cells at sites remote from the odontoblast layer.

A new biological approach to vital pulp therapy

Molecular biology is providing opportunities to develop new strategies or agents for the treatment of a wide variety of diseases. The availability of large amounts of highly purified proteins produced by recombinant DNA techniques is an obvious example. Recent evidence has implicated proteins belonging to the bone morphogenetic protein (BMP) subgroup of the transforming growth factor beta supergene family in tooth formation and dentinogenesis. It has long been known that bone and dentin contain bone morphogenetic protein activity. Recently, recombinant human BMP-2, -4, and -7 (also known as OP-1), have been shown to induce reparative dentin formation in experimental models of large direct pulp exposures in permanent teeth. The manner in which these agents act appears unique. New reparative dentin replaces the stimulating agents applied directly to the partially amputated pulp. Hence, the new tissue forms contiguous with, largely superficial to, and not at the expense of the remaining vital pulp tissue. This suggests a therapeutic approach permitting the induction of a predetermined and controlled amount of reparative dentin. Additionally, OP-1 has been associated with the formation of reparative dentin after application to a freshly cut but intact layer of dentin. These findings may provide future clinicians with additional options for the treatment of substantially damaged or diseased vital teeth.

Teeth and tooth nerves

(1) Although our knowledge on teeth and tooth nerves has increased substantially during the past 25 years, several important issues remain to be fully elucidated. As a result of the work now going on at many laboratories over the world, we can expect exciting new findings and major break-throughs in these and other areas in a near future. (2) Dentin-like and enamel-like hard tissues evolved as components of the exoskeletal bony armor of early vertebrates, 500 million years ago, long before the first appearance of teeth. It is possible that teeth developed from tubercles (odontodes) in the bony armor. The presence of a canal system in the bony plates, of tubular dentin, of external pores in the enamel layer and of a link to the lateral line system promoted hypotheses that the bony plates and tooth precursors may have had a sensory function. The evolution of an efficient brain, of a head with paired sense organs and of toothed jaws concurred with a shift from a sessile filter-feeding life to active prey hunting. (3) The wide spectrum of feeding behaviors exhibited by modern vertebrates is reflected by a variety of dentition types. While the teeth are continuously renewed in toothed non-mammalian vertebrates, tooth turnover is highly restricted in mammals. As a rule, one set of primary teeth is replaced by one set of permanent teeth. Since teeth are richly innervated, the turnover necessitates a local neural plasticity. Another factor calling for a local plasticity is the relatively frequent occurrence of age-related and pathological dental changes. (4) Tooth development is initiated through interactions between the oral epithelium and underlying neural crest-derived mesenchymal cells. The interactions are mediated by cell surface molecules, extracellular matrix molecules and soluble molecules. The possibility that the initiating events might involve a neural component has been much discussed. With respect to mammals, the experimental evidence available does not support this hypothesis. In the teleost Tilapia mariae, on the other hand, tooth germ formation is interrupted, and tooth turnover ceases after local denervation. (5) Prospective dental nerves enter the jaws well before onset of tooth development. When a dental lamina has formed, a plexus of nerve branches is seen in the subepithelial mesenchyme. Shortly thereafter, specific branches to individual tooth primordia can be distinguished. In bud stage tooth germs, axon terminals surround the condensed mesenchyme and in cap stage primordia axons grow into the dental follicle.(ABSTRACT TRUNCATED AT 400 WORDS)

Temperature sensitive simian virus 40 large T antigen immortalization of murine odontoblast cell cultures: establishment of clonal odontoblast cell line

During tooth formation instructive epithelial-mesenchymal interactions result in the cytodifferentiation of ectomesenchymal cells into odontoblasts which produce the dentin extracellular matrix (DECM). The purpose of our study was to establish a stable murine odontoblast cell line by immortalization of odontoblasts using retrovirus transfection. In order to accomplish this goal, we utilized a previously characterized odontoblast monolayer cell culture system supportive of odontoblast cytodifferentiation from dental papilla mesenchyme (DPM), expression and secretion of a DECM and dentin biomineralization. First mandibular molars from E-18 Swiss Webster mice were dissected, the DPM isolated, and pulp cells dissociated. Pulp cells (5 x 10(5)/well) were plated as monolayers and grown in alpha-MEM supplemented with 10% FCS, 100 units/ml penicillin and streptomycin, 50 micrograms/ml ascorbic acid. Cultures were maintained for 6 days at 37 degrees C in a humidified atmosphere of 95% air and 5% CO2, with media changes every two days. Immortalization was performed using a recombinant defective retrovirus containing the temperature sensitive SV-40 large T antigen cDNA and the neomycin (G418) resistance gene recovered from CRE packaging cells. Cultures were infected for 24 h with CRE conditioned medium containing 8 micrograms/ml of polybrene, the media was replaced with selective media containing 300 micrograms/ml of G418, and the cultures incubated at 33 degrees C for one month with media changes every 3-5 days. Neomycin resistant cells were cloned by serial dilution to single cells in 96-well culture plates and grown in selection medium at 33 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Response of odontoblast-like cells to hydroxyapatite ceramic granules

In this study the inductive influence of hydroxyapatite ceramic (HAC) granules on preodontoblast differentiation was investigated. Dental papilla cells harvested from upper molar tooth germs were implanted intramuscularly in a pouch created for this purpose. Six months after surgery tooth-root-like bodies had developed with pulp-like cavities in the specimens in which dental papilla cells had been implanted with and without HAC. These bodies consisted of regular tubular dentine in the central part, fibrodentine peripherally and sometimes osteodentine. HAC was haphazardly enclosed in these root-like bodies, whereas the implantation of HAC alone had no effect.

Cultured incisors display major modifications in basal lamina deposition without further effect on odontoblast differentiation

Matrix-mediated epithelio-mesenchymal interactions play a crucial role in the control of dental cytodifferentiations. Ultrastructural observation of the epithelio-mesenchymal junction in cultured embryonic mouse molars showed discrete zones with duplicated or multilayered basal laminae. The use of synthetic peptides demonstrated that the process was RGD*-independent, did not involve the YIGSR* sequence present on laminin and could occur spontaneously. Cultured incisors showed a similar but much more dramatic multiplication of the basal laminae. Furthermore, the deposition of multilayered basal laminae was specific for the labial aspect of the tooth and could be detected after 6 h of culture. Despite these alterations, preodontoblasts differentiated and gradients of differentiation were maintained, suggesting that among basement membrane constituents, the basal lamina itself does not play a critical role. More important is the inner dental epithelium which may still control odontoblast differentiation by means of diffusible molecules able to reach surface receptors expressed by preodontoblasts or matrix receptors underlying the basal lamina. Gradients of odontoblast differentiation could result from a progressive acquisition of competence by preodontoblasts.

Identification of regulatory elements necessary for the expression of the COL1A1 promoter in murine odontoblasts

Recent studies have indicated that odontoblasts and osteoblasts have unique regulatory mechanisms that control COL1A1 gene expression. We are currently examining the regulation of COL1A1 gene expression in odontoblasts and have produced transgenic mice containing various collagen promoter constructs fused to the indicator gene, chloramphenicol acetyl transferase (CAT). Mandibular first molars were removed from jaws of transgenic mice. Some teeth were assayed for CAT activity (CAT diffusion assays), others were fixed and prepared for immunohistochemistry (CAT antibodies). Our results indicate the CAT activity was present in tooth germs containing promoter constructs longer than 1.719 kb. Immunoreactivity to CAT was confined to the odontoblast cell layer. No CAT activity was present in tooth germs containing a 1.670 kb construct. These data suggest that there are important regulatory elements located between -1.719 kb and -1.670 kb on the collagen promoter in odontoblasts. Examination of sequences in this region of the promoter demonstrates consensus with those known to be involved with binding of translation products of homeobox genes.