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PubMed1984

Effect of 1-p-bromotetramisole on mineralization of hamster tooth germs in vitro: a light and electron microscopic study.

In culture, 10(-3)M 1-p-bromotetramisole (1-pBTM) inhibited mineralization of in vitro secreted enamel matrix in two-day old neonatal hamster first maxillary molar tooth germs. In contrast, in control tooth germs cultured without the inhibitor, new enamel and dentin matrices were secreted and subsequently mineralized in vitro. It is suggested that the arrested enamel matrix mineralization in vitro is a result of reduced phosphate uptake due to alkaline phosphatase inhibition by 1-pBTM. In addition, 1-pBTM induced accumulation of secretory granules in odontoblasts and ameloblasts, but not in the other cells. This is probably a specific effect of the inhibitor on these cells due to alkaline phosphatase inhibition.

Alkaline Phosphatase↗

PubMed1980

[Role of secretion in the dynamics of the maturation of predentin. Morphological, autoradiographic and freeze fracture study in the rat; changes induced by vinblastine].

Morphological and autoradiographic data give evidence that secretion take place at the odontoblast process level according to a lateral axis, perpendicular to the maturation axis of the predentine. Induced modifications with vinblastine sulphate emphasize the importance of the pericellular space (150--200 nm) while the disorganization of the collagen fiber arrangement suggests the presence of flows. We propose an hypothesis which connects all these facts.

Animals↗

PubMed1982

Ultrastructural changes in developing hamster molars during vitamin C deficiency in vitro.

Second day maxillary molars of hamsters were cultured during 4, 8 and 10 days in the presence or absence of 250 micrograms/ml vitamin C. After 8 days of culture without vit. C the basal lamina in the cervical loop region (proliferation zone) was locally disrupted; after 10 days it was completely absent or only remnants of it could be found. In the differentiation zone an abnormal amorphous predentine matrix was found during vit. C deficiency; from the 4th day on the basal lamina had changed in structure or ruptured prematurely. A role of the basal lamina in directing odontoblast differentiation is possible but was not actually demonstrated. It is suggested that the failure of the pre-ameloblasts to differentiate was due to changes in the extracellular matrix. The observations support a cell-matrix type of interaction for the differentiation of the ameloblast.

Ameloblasts↗

PubMed1981

[Diurnal layer formation in the incisor dentin of rodents].

The growth of dentin of the constantly growing lower incisors in rodents was studied using tetracycline as a vital marker of the growing parts of bones and teeth. In the common vole in nature the incisors grow in length at a rate of 490 micrometers per day; a basal-apical gradient of growth of the tooth walls in thickness was found: the minimal daily increment at the tooth base and the maximal in the apical third, it decreases again at the very apex. In the peripulp part of dentin of the apical incisor half there are diurnal layers seen both on polished sections and stained slides the formation of which correlates with the diurnal rhythm of skeleton growth. The diurnal dentin layers form in the apical incisor half only. The odontoblasts appear to begin to function rhythmically from the middle of their life on only. A similar phenomenon was found in a natural population of large-toothed redbacked voles. The topography of dentin layers in the laboratory rats is similar to that in the voles but the layers are not distinct and the basal-apical gradient of dentin growth is observed in young animals, rather than in the old ones.

Animals↗

PubMed1982

Morphological types of epithelial-mesenchymal cell contacts in odontogenesis.

During early stages of odontogenesis, differentiating ameloblasts form cytoplasmic processes which penetrate deeply into developing uncalcified dentine. Some of these cytoplasmic protrusions form close approximations or contacts with odontoblast processes. The contacts are of a variety of morphological types, but their membranes never fuse or form any known type of cell junction. The present results, together with those derived from other studies, suggest that the approximations or contacts may play a role in inductive mechanisms of the cytodifferentiation of odontogenic cells.

Ameloblasts↗

PubMed1995

The early distribution and possible role of nerves during odontogenesis.

Neural crest cells migrate along specific pathways to reach the mandibular and maxillary arches where they condense under specific areas of the ectoderm which will give rise to the primary and permanent dentition. In the mouse, the trigeminal ganglion becomes evident on E9 and the superior cervical sympathetic ganglion E13. Several studies have suggested that nerves in the vicinity of the developing teeth could influence the surrounding tissues and initiate tooth development, whereas other investigators have suggested that tooth development will proceed without an intact innervation. Innervation of the dental papilla has been reported as early as the cap stage in human teeth using an antibody to PGP 9.5. A large variety of putative neurotransmitters have been localized in the nerves of the dental pulp. Many of the putative neurotransmitters function in vasoregulation while others have unknown functions. A hypothesis is presented describing a possible signal transduction pathway between odontoblasts and nerve terminals.

Animals↗

PubMed1995

Contributions of heterospecific tissue recombinations to odontogenesis.

Determining the functions of cell surface and substrate adhesion molecules during heterospecific tissue recombinations constitutes a significant problem in biology. The developing tooth organ provides a fine model to pursue this problem, especially in the context of instructive epithelial-mesenchymal interactions. The interpretation of many experimental heterospecific tissue combinations is difficult because of the complexity of the embryonic systems. According to some authors, the expressed phenotype corresponds to the genotype of the epithelium; on the contrary, other studies have demonstrated the leading role of the mesenchyme. The importance of cranial neural crest in tooth morphogenesis has been established. Lizard teeth maintain a continuous morphogenetic field throughout life (polyphyodont). These tissues can be considered as biological models and are ideally suited to study neural crest cell differentiation. Oral cavity of chick embryos show a rudiment resembling the dental lamina of amphibian, reptilian and mammalian embryos, though further odontogenic interactions between the epithelial and mesenchymal tissues are not operating. Some authors have suggested that genes involved in tooth formation, which have remained silent in birds for more than 200 million years, can be activated by appropriate signals. Chick epithelium combined with mesenchyme from mouse molar tooth produced dental structures with differentiated ameloblasts depositing enamel matrix. Quail neural crest combined with lizard dental bud showed quail cells with odontoblastic processes. Combinants (quail ectoderm-lizard papilla, and quail ectoderm-rabbit embryo papilla) showed differentiated chimeric-tooth-like structures. However, controversy persists regarding the ability of avian epithelium to express the ameloblast phenotype and to secrete enamel protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Ameloblasts↗

PubMed1993

The influence of tissue pretreatment on the immunohistochemical demonstration of type I and III collagens and tenascin in fetal human tooth germs.

The influence of tissue pretreatment on the PAP immunostaining for type I and III collagens and tenascin was studied in formalin-fixed and paraffin-embedded human tooth germs at the 24th and 25th weeks of fetal life. Three variables were considered: the type of buffer used (PBS or Tris), pepsin digestion and the use of normal serum as a blocking agent prior to immunostaining. All three proteins needed an enzymatic digestion to be intensely revealed. Pepsin promoted, even at low concentrations, an intracellular staining of type I collagen in the secretory odontoblasts and in the pulpal fibroblasts. Normal serum partially blocked unspecific immunoreaction when polyclonal rabbit antibodies were used. The Tris buffer increased the staining intensity of the three macromolecules and revealed an unusual tenascin-like immunoreactivity in the ameloblasts. This study demonstrated that pepsin digestion and the use of normal serum and different buffers may influence the immunoreactivity of ECM proteins.

Buffers↗

PubMed1995

[Detection of the apoptosis-suppressing oncoprotein bcl-2 in ameloblastomas].

The product of apoptosis-suppressing oncoprotein bcl-2 can block apoptosis and result in the development of tumors. In this study, the expression of bcl-2 was observed in 40 cases of ameloblastomas by immunohistochemical staining. The results showed that the epithelium and reduced enamel epithelium of the enamel organ, the odontoblasts, basal cells of odontogenic cysts, normal oral epithelium and 90% (36/40) of ameloblastomas were positive for bcl-2, indicating that the expression of bcl-2 in odontogenic epithelium may be related to the degree of differentiation and proliferation of cells, the overexpression of bcl-2 may be associated with the development of ameloblastoma.

Ameloblastoma↗

PubMed1994

Degradation of the dental basement membrane during mouse tooth development in vitro.

During tooth development, the basement membrane is degraded at the late bell stage, but the developmental significance of this event is not known. Organ culture offers a method where developmental processes can be manipulated in controlled conditions. We cultured bell-stage tooth germs either in a chemically defined or a serum-containing medium and analyzed the degradation of the basement membrane by different methods. Type IV collagen was present throughout the dental basement membranes at the epithelial-mesenchymal interface at the onset of culture. After 10 days of culture, irrespective of the medium used, type IV collagen and laminin had disappeared from the cuspal areas but were present at the cervical loop. As was the case in vivo, the expression of 72 kDa type IV collagenase gene was intense in the differentiating preodontoblasts and in the odontoblasts during secretion of the first predentin matrix near the cuspal tips. Ultrastructural observations showed that the basal lamina had been removed in all cultured tooth organs. Also, the breakdown of the basement membrane occurred irrespective of the presence of mineral in the dentin matrix. Our observations suggest in contrast to earlier observations, that there are no major differences in basic events leading to dentino- and amelogenesis, when tooth organs are cultured in the presence or absence of serum.

Ameloblasts↗

PubMed1994

Pulpal response after complete crown preparation, dentinal sealing, and provisional restoration.

This study evaluated the acute pulpal healing response following preparation, etching, and sealing of the prepared vital dentin with a 4-methacryloxyethyl trimellitate anhydride (4-META) bonding system. Adult monkey teeth received crown preparations with chamfer margins, prepared with a diamond used at ultra high speed with water cooling. Vital dentin was etched with 10% citric acid-3% ferric chloride, rinsed, and sealed with 4-META system. A provisional crown was formed with a low-viscosity light-curing adhesive resin. Teeth were fixed and evaluated histopathologically. Pulpal responses at 3 days showed only minimal disruption of the odontoblastic zone. At 7 days, the pulps presented reorganizing odontoblastoid cells, and, at 10 days, the pulps showed new odontoblastoid cells with a thin rim of reparative dentin. Pulps of crown preparations that were etched and then sealed with the 4-META system presented healing patterns similar to those of pulps associated with Class V preparations lined with calcium hydroxide, observed in (previous) similar studies.

Acid Etching, Dental↗

PubMed1993

[Cellular kinetics and dental cytodifferentiations].

Several experimental results led to the hypothesis that odontoblast's and ameloblast's genetic programmes may determine a minimal number of cell cycles before overt differentiation can be triggered by specific, epigenetic, matrix-mediated interactions. The cell kinetic dependent maturation of the dental cells could imply transcriptional modifications of matrix molecules and paracrine factors involved in the control of the respective cytodifferentiations and of specific receptors conferring competence to the responding cells.

Ameloblasts↗

PubMed1993

[Lysosomal storage diseases, genetic or drug-induced? effect of glycosaminoglycan and sphingolipid disorders on dental tissues].

In vivo studies were carried out on dental tissues of rat incisor after a single injection of suramin, a drug which induces mucopolysaccharidosis-like disease. Accumulation of lysosome-like structures was seen in secretory ameloblasts and odontoblasts. In vitro studies on embryonic tooth germ buds showed similar changes when they were cultured in presence of suramin. Anti-phospholipid immunolabelling revealed a developmentally regulated temporo-spatial pattern. Radiolabeling with 3H-suramin indicated cytosolic and nuclear incorporation. The drug acting as polyanion interacted directly with predentine. 35S sulphate incorporation was impaired by the drug. Another lysosomal storage disease, the sphingolipidosis, Krabbe's disease was also investigated in human. Changes were observed in pulp cells and as a consequence in dentin. Enamel also displayed many changes. Pharmacological or genetically acquired diseases constitute models providing insights on the role played by glycosaminoglycans and phospholipids in biomineralization.

Ameloblasts↗

PubMed1995

Differential expression of the full-length and secreted truncated forms of EGF receptor during formation of dental tissues.

The developmental regulation of various receptor forms may be a key-element in the local fine tuning of growth factor effects. The present study focuses on the tissue- and stage-specificity of the alternative splicing of EGF receptor transcripts in the rat incisor. In situ hybridization, as well as light- and electron-microscopic immunolocalization were performed with a set of tools which enable us to discriminate the full-length and secreted truncated forms of EGF receptor. Our data show that, apart from a transient expression in differentiating odontoblasts, EGF receptor expression was predominantly observed in the dental epithelium. In the crown, the expression of the full-length EGF receptor was maximal during preameloblast proliferation and differentiation, decreased in differentiated ameloblasts, and remained low throughout enamel secretion. On the other hand, maturation stage ameloblasts, which regulate the final mineralization of enamel, express high levels of the full-length EGF receptor. In contrast with ameloblasts, epithelial supra-ameloblastic cells, which are not directly involved in the deposition of enamel matrix, showed an alternating predominance of the secreted truncated form during the secretion stage, and the full-length form during the maturation stage. The presence of the secreted truncated EGF receptor form was supported by the electron microscopic detection of extracellular aggregates of immunoreactive EGF receptor. Finally, Northern-blotting of enamel organ samples confirmed the presence of transcripts corresponding to mRNAs of both EGF receptor forms. During root formation, a decreasing gradient of full-length EGF receptor form expression was observed from the apical loop to the disrupting zone in root epithelium. The secreted truncated EGF receptor form was essentially detected in epithelial cells of the disrupting zone of root epithelium. During crown formation, the secreted truncated EGF receptor form, which appears to be synthesized by epithelial supra-ameloblastic cells and secreted toward ameloblasts, may competitively bind EGF receptor ligands and modify activation of the full-length EGF receptor.

Aging↗

PubMed1993

An experimental study of osteogenesis by autografted dental pulp, periodontal ligament, and bone marrow in vivo.

Osteogenic activity of autografted dental pulp, periodontal ligament, and bone marrow of rat in vivo was investigated. Immunolocalization of ALPase in situ was also studied. One month after the transplantation, osteodentin was formed in all the dental pulp transplants (100%), bone or cementum like tissues were created in 20% of periodontal ligament transplants, and bone like tissues were in 20% of bone marrow transplants. After two months, osteodentin was produced in all the dental pulp transplants (100%) and bone like tissue were in 50% of both periodontal ligament and bone marrow transplants. Immunohistochemically, positive reactions to ALPase in situ were detected in cells just below the odontoblast layers in dental pulp, surface layers of alveolar bone in periodontal ligament, and endosteal membrane of bone marrow space. From these results, it was suggested that the cells of these three kinds of tissue can be termed osteogenic-fibroblasts in vivo.

Alkaline Phosphatase↗

PubMed1997

Dentin and pulp response to Erbium:YAG laser ablation: a preliminary evaluation of human teeth.

OBJECTIVE: We determined the real effect of Erbium:YAG laser ablation on human teeth in vivo. SUMMARY BACKGROUND DATA: We advocated the idea that overheating of teeth, specially pulp damage can be avoided if correct laser parameters are used. METHODS: We evaluated human premolars scheduled for extraction during orthodontic treatment. Before tooth extraction, an oval cavity preparation was made with a pulsed Er:YAG laser. After extraction, the teeth were decalcified for 6 weeks. Routine staining with haematoxylin and eosin was performed on longitudinal section. One hundred seventy-two sections were prepared and examined in a light microscope. RESULTS: Under Er:YAG laser application, reduction of the dentin layer was observed. Dentinal tubules had a radial course up to the surface. No cracks or structural injury were observed. Inflammatory reaction in the pulp was not found. The vascularity of the pulp was normal. The odontoblasts were of the usual spindle-like or star-like cell shape. The cementum and epithelial attachment were healthy. No changes of structure or indications of inflammation were observed. CONCLUSIONS: The results of this in vivo experiment on human teeth confirm safety of Er:YAG laser ablation of enamel and dentin under the conditions described.

Adolescent↗

PubMed1996

Heterochronic quantitative microevolution: dental divergence in aboriginal Americans.

Studies of tooth crown morphology alone have proven valuable in defining human population differentiation. We test the hypothesis that quantitative comparisons of more complex whole tooth structure may prove informative in understanding human diversity. Three disparate populations in Native American genetic history were compared: Kodiak Island Western Eskimos, Peruvian Inca Amerindians, and Southeast Asians. Enamel depth (an increasing gradient extended from Southeast Asians to the Inca) and root parameters were the most discriminating variables. The observed microevolution appears to result from variation in timing of known X-linked, Y-linked, and autosomal genes that affect either ameloblast or odontoblast differentiation. The dental traits were sexually dimorphic, the effect being more pronounced in aboriginal Americans, with male teeth having robust roots and thin enamel compared to female. Southeast Asians were isometrically related. The prominence of sexual dimorphism and the importance of sex-linked genes in the determination of the dental phenotypes suggest that sexual selection was one evolutionary force acting on early Asian populations. Subsequently, the selection appears to have been relaxed in Southeast Asians. Observed divergence of tooth shape among the populations, i.e., differences in the appropriation process of tooth primordia, was mainly the consequence of genetic drift modulating heterochronic regulators of homeotic genes.

Analysis of Variance↗

PubMed1997

Expression patterns of bone morphogenetic proteins (Bmps) in the developing mouse tooth suggest roles in morphogenesis and cell differentiation.

Bone morphogenetic proteins (BMP) are secretory signal molecules which have a variety of regulatory functions during morphogenesis and cell differentiation. Teeth are typical examples of vertebrate organs in which development is controlled by sequential and reciprocal signaling between the epithelium and mesenchyme. In addition, tooth development is characterized by formation of mineralized tissues: the bone-like dentin and cementum as well as epithelially derived enamel. We have performed a comparative in situ hybridization analysis of the expression of six different Bmps (Bmp-2 to Bmp-7) starting from initiation of tooth development to completion of crown morphogenesis when dentine and enamel matrices are being deposited. Bmps-2, -4, and -7 were frequently codistributed and showed marked associations with epithelial-mesenchymal interactions. Their expression shifted between the epithelium and mesenchyme starting from the stage of tooth initiation. They were subsequently expressed in the enamel knot, the putative signaling center regulating tooth shape. Their expression domains prior to and during the differentiation of the dentine-forming odontoblasts and enamel-forming ameloblasts was in line with functions in regulation of cell differentiation and/or secretory activities of the cells. The expression of Bmp-3 was confined to mesenchymal cells, in particular to the dental follicle cells which give rise to the cementoblasts, forming the hard tissue covering the roots of teeth. Bmp-5 was expressed only in the epithelial ameloblasts. It was upregulated as the cells started to polarize and intense expression continued in the secretory ameloblasts. Bmp-6 was expressed only weakly in the dental mesenchyme during bud and cap stages. Our results are in line with regulatory functions of Bmps at all stages of tooth morphogenesis. Bmps-2, -4, and -7 are conceivably parts of signaling networks regulating tooth initiation and shape development. They as well as Bmp-5 may be involved in the induction and formation of dentine and enamel, and Bmp-3 in the development of cementum. The remarkable overlaps in the expression domains of different Bmp genes may implicate functional redundancy and/or formation of active heterodimers between different BMPs.

Animals↗