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PubMed1991

Differential expression of type I and type III collagen genes during tooth development.

Collagen gene expression during mouse molar tooth development was studied by quantitative in situ hybridization techniques. Different expression patterns of type I and type III collagen mRNAs were observed in the various mesenchymal tissues that constitute the tooth germ. High concentration for pro-alpha 1(I) and pro-alpha 2(I) collagen mRNAs were found within the osteoblasts. We found that the cellular content of type I collagen mRNAs in the odontoblasts varies throughout the tooth formation: whereas mRNA concentration for pro-alpha 1(I) collagen decreases and that of pro-alpha 2(I) increases, during postnatal development. Moreover, different amounts of pro-alpha 1(I) and pro-alpha 2(I) collagen mRNAs were observed in crown and root odontoblasts, respectively. Type III collagen mRNAs were detected in most of the mesenchymal cells, codistributed with type I collagen mRNAs, except in odontoblasts and osteoblasts. Finally, this study reports differential accumulation of collagen mRNAs during mouse tooth development and points out that type I collagen gene expression is regulated by distinct mechanisms during odontoblast differentiation process. These results support the independent expression of the collagen genes under developmental tissue-specific control.

Animals↗
PubMed2005

Rat enamel contains RP59: a new context for a protein from osteogenic and haematopoietic precursor cells.

We have recently identified a protein, RP59, in bone marrow cells and young osteoblasts, in cells involved in bone repair and in young erythroblasts and megakaryocytes. Here, we report immunohistochemical data at the light- and electron-microscope level indicating that RP59 is also present in newly secreted tooth enamel of the rat and in ameloblasts, the formative cells. In enamel matrix, RP59 was located proximal to secretory ameloblasts only, i.e. in newly secreted material. Distal enamel and enamel in association with maturation stage ameloblasts were unlabelled. Secretory ameloblasts contained RP59 in the matrix-proximal region including Tomes' processes, post-secretory ameloblasts in the cell-matrix interface. Western blotting of proteins from tooth germs identified RP59 as a band at 90 kD, co-migrating with RP59 from bone marrow and spleen. Antisera versus a chemically synthesised RP59 peptide and versus a bacteria-synthesised protein fragment reacted in the same manner. In situ hybridisation of tooth tissue revealed RP59 RNA specifically in ameloblasts. The reverse transcription/polymerase chain reaction method identified tooth RNA coding for RP59. Sequence analysis indicated that RP59 RNA from tooth and marrow had the same sequence. An internal sequence motif was found in rat RP59 resembling a signal implicated in secretion of the chicken "engrailed" gene product. The findings indicate that RP59 is a genuine product of ameloblasts and that it is secreted in the course of enamel formation together with other matrix components.

Ameloblasts↗
PubMed1997

The genetic control of early tooth development.

Most vertebrate organs begin their initial formation by a common, developmentally conserved pattern of inductive tissue interactions between two tissues. The developing tooth germ is a prototype for such inductive tissue interactions and provides a powerful experimental system for elucidation of the genetic pathways involved in organogenesis. Members of the Msx homeobox gene family are expressed at sites of epithelial-mesenchymal interaction during embryogenesis, including the tooth. The important role that Msx genes play in tooth development is exemplified by mice lacking Msx gene function. Msxl-deficient mice exhibit an arrest in tooth development at the bud stage, while Msx2-deficient mice exhibit late defects in tooth development. The co-expression of Msx, Bmp, Lefl, and Activin beta A genes and the coincidence of tooth phenotypes in the various knockout mice suggest that these genes reside within a common genetic pathway. Results summarized here indicate that Msxl is required for the transmission of Bmp4 expression from dental epithelium to mesenchyme and also for Lefl expression. In addition, we consider the role of other signaling molecules in the epithelial-mesenchymal interactions leading to tooth formation, the role that transcription factors such as Msx play in the propagation of inductive signals, and the role of extracellular matrix. Last, as a unifying mechanism to explain the disparate tooth phenotypes in Msxl- and Msx2-deficient mice, we propose that later steps in tooth morphogenesis molecularly resemble those in early tooth development.

Ameloblasts↗
PubMed1991

A developing complex odontome associated with delayed premolar formation.

Delayed development of a bicuspid in the right premolar region of the mandible was observed radiographically in a 16-year-old male patient following surgical removal of a developing odontome. Whilst odontomes are commonly associated with a failure of eruption of permanent teeth, this case was unusual in that there was both failure and marked delay of adjacent permanent tooth germ development, suggesting that the odontome was associated with a regional disturbance of odontogenic tissues in the neonatal period.

Adolescent↗
PubMed1989

[Combined surgical orthodontic therapy in a patient with multiple agenesis].

After a wide analysis of the problems concerning biology and integration of autogenic transplantation of tooth germs, the Authors present a clinical case of monolateral agenesis of two premolars, with the transfer of the second premolar germ from one side to an other, suggesting some technical details in flap scalloping.

Abnormalities, Multiple↗
PubMed1992

Effects of ascorbate-deficiency on collagen secretion and resorption in cultured mouse incisor germs.

The effects of ascorbic acid deficiency on mouse incisors, grown in vitro, has been investigated at the histological and cytological levels. In this model, continuously growing mouse incisors are characterized by the existence of different type of predentin-dentin matrix on its lingual (root-analogue) and labial (crown-analogue) surface and the absence of enamel on the lingual surface. Our observations indicated that ascorbate-deficiency affected the behavior of mouse tooth germs in vitro: odontoblast differentiation was disturbed and morphological evidence for odontoblast-mediated collagen resorption were observed. An abnormal amorphous predentin-dentin matrix existed and the basement membrane was prematurely disrupted. The dentin mineralization, as well as functional differentiation of ameloblasts were strongly hampered. Chronic deficiency led to disorganization of the dental tissues.

Absorption↗
PubMed1996

Expression of neurotrophin receptors during rat tooth development is developmentally regulated, independent of innervation, and suggests functions in the regulation of morphogenesis and innervation.

Low-affinity neurotrophin receptor (LANR) and trk receptor tyrosine kinases (trks) serve as low- and high-affinity receptors for neurotrophins. Besides promoting the development and maintenance of the mammalian nervous system, it has been suggested that neurotrophins may have broader functions in the development of non-neuronal tissues. To evaluate the possible roles of neurotrophic factors in tooth development, we performed a detailed examination of the expression patterns of neurotrophin receptors during development of the rat tooth from initiation to completion of crown morphogenesis. mRNA expression was studied by in situ hybridisation and LANR protein was localised by immunohistochemistry. Furthermore, dissected tooth germs were cultured in vitro to examined the role of trigeminal innervation in the expression of neurotrophin receptors. mRNAs for LANR, trkB, and trkC, but not trkA, were detected in developing teeth. LANR and the truncated form of trkB, which lacks the intracellular tyrosine kinase domain, were expressed throughout tooth morphogenesis and their expression patterns were largely non-overlapping and changed spatio-temporally. trkC was expressed after birth, and it was restricted to dental papilla mesenchyme. The expression of all receptors correlated with the development of innervation, but, in addition, the expression of LANR and trkB appeared to be associated with cell differentiation and epithelial-mesenchymal interactions. The patterns of LANR, trkB, and trkC in teeth which underwent morphogenesis in organ culture were similar to those in vivo, which indicates that the expression of these neurotrophin receptors is not regulated by and does not depend on trigeminal innervation. The data suggest that neurotrophin receptors have roles in the development of tooth innervation, but that they also have non-neuronal, organogenetic functions.

Aging↗
PubMed1995

Epithelial-mesenchymal signaling during tooth development.

Classic studies on experimental embryology have shown that organ development in an embryo is largely regulated by so called inductive tissue interactions which mostly take place between epithelial and mesenchymal tissues. Also in the developing tooth, both morphogenesis and cell differentiation are governed by such interactions. Characteristic features of epithelial-mesenchymal interactions are that they are sequential and reciprocal, i.e. "induction" appears to consist of a chain of signaling events between the tissues. During the last decade, the expression patterns of numerous molecules have been studied in developing organs by in situ hybridization and immunohistology. Many of them have been associated with epithelial-mesenchymal interactions, and it is apparent that same molecules participate in regulation of morphogenesis in a number of different organs. Transcription factors such as Msx-1, Msx-2 and Egr-1, growth factors, including TGF beta's, BMPs, and FGFs, and structural proteins such as syndecan and tenascin are expressed in transient, time and space-specific patterns in many organ rudiments, including the tooth. We have shown by tissue recombination studies that the expression of certain molecules is indeed regulated by epithelial-mesenchymal interactions in the early tooth germ. In particular, during the early stages of morphogenesis, when the dental epithelium induces the condensation of mesenchymal cells around the epithelial bud, the expression of many genes is upregulated in the condensed mesenchyme. Previous experimental tissue recombination studies have indicated that at the same time the capacity to instruct tooth morphogenesis shifts from the dental epithelium to the dental mesenchyme.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Expression of the neural cell adhesion molecule (NCAM) during second- and third-molar development in the mouse.

Distribution of the neural cell adhesion molecule (NCAM) during the development of the mandibular second- and third-molars of the mouse was studied by indirect immunofluorescence techniques. At the initial stage, NCAM was intensely expressed by the mesenchymal cells surrounding the dental lamina, and by the cap stage NCAM expression by the mesenchymal cells became restricted to the dental follicle. After that, in addition to the follicular mesenchyme, some cells in the basal part of the dental papilla showed NCAM-immunoreactivity for a while after the hard tissue formation had started. During root formation, the follicular cells lost NCAM first from the level of the cervical root and later from the coronal part, while an additional NCAM positive area appeared deep in the dental papilla. Even after the teeth had erupted, NCAM was expressed in the tissue surrounding the apical root and in the pulp core. During the initial and bud stages, the pattern of NCAM expression in the second and third molars was different from that in the first molar, where NCAM was found only after the late bud stage; while from the cap stage onward, it changed in the same sequence as in the first molar. The different pattern of NCAM expression implies that there is a difference in developmental events between the early stages of the first and the other two molars. On the other hand, the common sequence of NCAM expression in the tooth germs later than the cap stage suggests that NCAM plays an essential role in the formation of the basic structure of the teeth and periodontal tissues.

Animals↗
PubMed2006

Proliferation and apoptosis in early molar morphogenesis-- voles as models in odontogenesis.

Proliferation and apoptosis play crucial roles in the development of multicellular organisms. Their precise balance is necessary for tissue homeostasis throughout life. The developing dentition is a suitable model to study proliferation and apoptosis during embryogenesis, but the corresponding studies have been carried out principally in the mouse. The present study aimed to examine proliferation and apoptosis in the vole (Microtus sp., Rodentia) during the early morphogenesis of the first upper molar and compare it to what is known from the mouse. To this end, apoptosis and proliferation were investigated using histology and computer-aided 3D reconstruction. Mitoses accumulated predominantly in the developing cervical loop. Apoptosis during early odontogenesis showed highly specific spatio-temporal patterns in the dental epithelium. Apoptotic bodies were localised in non-dividing cell populations. They accumulated in the same places as described in the mouse: antemolar vestiges (ED 12.5 15.5), enamel knot (ED 14.5 15.5), stalk and palatally along the whole first molar tooth germ longitudinal axis (ED 15 - 15.5). Early tooth development in the field vole, including the distribution of apoptosis and mitosis, is very similar to that reported in the mouse, with the exception of the antemolar region. The microtine antemolar vestige is preserved longer than the murine one. It is conceivable that additional distinct differences in morphogenetic processes appear later in tooth development.

Animals↗
PubMed1994

Localization of ornithine decarboxylase in mouse teeth. An in vitro and in vivo study.

Ornithine decarboxylase (ODC), a key enzyme in polyamine biosynthesis, and thus in tissue growth and development, has been localized in mouse dental tissues, in vivo as well as in vitro by light and electron microscopic autoradiography with radiolabeled alpha-difluoromethylornithine ([3H]DFMO). Mandibular first molar germs from day-18 fetuses were incubated in vitro in the presence of [3H]DFMO and processed for autoradiography. For ODC localization in vivo, 3-day old puppies received [3H]DFMO by injection. As controls, puppies were injected either with unlabeled DFMO, or with cycloheximide before administration of isotope. Kidneys and mandibles were excised and processed for autoradiography. In vitro, labeling was found in all cell types of the tooth germ, but with a more intense labeling in ameloblasts and odontoblasts. In both these, radioactivity decreased from the tip of the cusps to the cervical loop. In vivo the binding of [3H]DFMO in cells of the ameloblast and odontoblast lineages, respectively, showed a gradual increase form the posterior end of the incisor to its anterior end. The distribution of radioactivity in the kidney was in accordance with findings by others. Both the kidney and tooth cell labeling decreased strongly after cycloheximide treatment. The results show that ODC is expressed in tooth-forming cells, and that ODC is not only present in differentiating cells but occurs at higher amounts in mature, secreting cells. The findings suggest that polyamines have a central role in tooth development.

Aging↗
PubMed1976

Cell division and cytodifferentiation of odontoblasts.

The chronological delay of overt cytodifferentiation of odontoblasts in isochronal and heterochronal associations between inner dental epithelium and preameloblasts was analysed. The in vitro action of FUdR of tooth germs was summarised. The respective role of cell interaction and specific cell cycle was discussed.

Animals↗
PubMed1979

Structure and formation of ankylosis in Xenopus laevis.

The structure of ankylotic teeth in Xenopus laevis was studied by light, transmission, and scanning electron microscopy as well as by microradiography in decalcified and undecalcified specimens. The mature teeth of Xenopus laevis are calcified from the crown to the base, fused to the jaw bone, and have no uncalcified area, such as a fibrous ring separating the tooth into the crown and pedicle. Microradiography shows that the mature tooth and jaw bone appear as an X-ray opaque area, except for the basal region of the dentine. This region is composed of an X-ray translucent area and an X-ray opaque thin layer on the lingual side of the translucent area. The mature tooth is composed of two differently calcified areas: (1) a highly calcified area, which makes up almost all of the tooth and contains a thin layer of the basal dentine on the lingual side, and (2) a lowly calcified basal dentine, which is fused to the jaw bone. Therefore, the lowly calcified area does not completely separate the dentine and jaw bone. Repeating banding patterns among the collagen fibrils differ among the dentine-forming area and the matrices of dentine and jaw bone. During the formation of ankylosis of the tooth germ, collagen bundles in the dentine-forming area accumulate directly on the surface of the jaw bone. Consequently, the mature teeth of Xenopus laevis fuse to the jaw bone directly without the mediation of the other structures.

Animals↗
PubMed2003

Ultrastructure of basement membranes in monkey and shark teeth at an early stage of development.

The basement membrane, which separates the inner enamel epithelium from the dental papilla in the early stages of tooth development, is known to play a significant role in odontogenesis. In this review article, this basement membrane was described in detail based on our recent findings with the use of high-resolution electron microscopy. Tooth germs of a monkey (Macaca fuscata) and a shark (Cephaloscyllium umbratile) were processed for thin-section observations. During the early stage of development, the basement membrane of the inner enamel (dental) epithelium was composed of a lamina lucida, lamina densa, and much wider lamina fibroreticularis. At higher magnification, the lamina densa in both species was made up of a fine network of cords, which are generally the main constituents of the basement membranes. In the monkey tooth, the lamina fibroreticularis was rich in fibrils, which were now characterized as basotubules, 10-nm-wide microfibril-like structures. The space between the basotubules was filled with a cord network that extended from the lamina densa. Dental papilla cell processes were inserted into the lamina fibroreticularis, and their surface was closely associated with numerous parallel basotubules via 1.5- to 3-nm-wide filaments. In the shark tooth during its early stage of development, the basotubules were absent in the lamina fibroreticularis and only narrow extensions, 60-90 nm wide and 1-2 microm long, of the cord network of the lamina densa were present. The dental papilla cells were immobilized by means of the binding of their processes to the extensions. These results indicate that basement membranes in both monkey and shark teeth at early stage of development are specialized for functions as anchoring and firm binding, which are essential for the successful differentiation of the odontoblasts.

Animals↗
PubMed1987

[Post-natal development of tooth structures in Didelphis albiventris].

The post-natal development of tooth germs has been studied in the opossum or South American marsupial (Didelphis albiventris) between the 2nd and 10th week. Dentinogenesis starts around the 3rd week. The enamel which begins to appear at this stage is deposited until the 8th-10th week. At 10 weeks, the enamel enters the maturation phase. It is unlikely that enamel tubules in these marsupials have a cellular origin. No specific histochemical reaction predicts their appearance which is observed in the mature tooth. This fact suggests that their origin is related either to enamel maturation or to the beginning of tooth function. The mineralizing dentine front presents on the one hand calcospherites where peritubular dentine is formed before intertubular dentine, and on the other hand a radiating mineralizing structure. These two aspects are exceptional in Vertebrates.

Amelogenesis↗
PubMed1983

Evolution and development of the dentition.

The genetic code that produces human teeth began to develop in primitive vertebrates around 500 million years ago. Some parts of the information appear to have been very stable, particularly the mineralized matrices, while others have evolved. The development of tooth shape and tooth number are very rigidly controlled by genes in each species and are responsive to relatively rapid genetic selection by the environment, as are bone shape and associated soft tissues. Their developmental independence is reflected in the ability of the embryonic tooth bud to develop in vitro. Part of the genetic control of tooth size and shape is correlated with the genetic control of size and shape of the jaws, but the jaws are more responsive to environmental variables modifying individual development than are the teeth. There are recognized mutations producing changes in teeth which act at all levels of control, the development of the embryonic bud, the morphogenesis of the bell stage, the production of enamel and dentin and the formation of the roots. The mechanisms of this genetic control are at the molecular and submolecular levels which are just beginning to be examined. Tooth germs are a good system for study of these processes, and changes in our knowledge will lead to increased understanding of the variation of teeth and its relation to the structure of other tissues both normal and abnormal.

Animals↗
PubMed2005

Tooth development included in the multifocal jaw lesions of Langerhans cell histiocytosis.

Many cases demonstrating the oral manifestations of Langerhans cell histiocytosis (LCH) have been reported; however, tooth development in jaw lesions has rarely been mentioned. This paper reports the case of a 3-year-old Japanese girl with LCH suffering from multiple osteolytic lesions of the skull and jaw bones. She was referred to our paediatric clinic because of swelling of the mucogingival folds in the upper and lower primary molar regions. The patient responded well to steroid therapy and the osteolytic lesions resolved. There was an accompanying development of permanent tooth germs included in the lesions. Langerhans cell histiocytosis in children usually has a long-term clinical course and paediatric dentists should be involved with oral health care for affected patients.

Bicuspid↗
PubMed1987

Nerve growth to tooth buds after homotopic or heterotopic autotransplantation.

Feline permanent incisor tooth buds (bell stage) were autotransplanted to mandibular alveolar sockets (homotopic site) or to the submandibular subcutis or the leg (heterotopic sites). This was done in 34 kittens aged 1-2 months. After survival times of 3-8 months the animals were fixed by glutaraldehyde perfusion. A total of 56 mineralized teeth, which had developed at the recipient sites, were removed, demineralized and processed for light microscopic (LM) general evaluation. Fourty-four teeth, which were judged to be grossly normal in the LM, were selected for electron microscopic (EM) analysis with respect to the occurrence of pulpal nerve fibres. The highest proportion of normal teeth (16 of 16) was obtained from the alveolar site, followed by the submandibular (11 of 14) and hindlimb (17 of 26) sites. Most of the grossly normal grafts possessed pulpal axons (37 of 44). The alveolar grafts were all innervated and exhibited a largely normal appearance qualitatively and in terms of percentage of myelinated fibres. The proportion of innervated pulps was lower among the heterotopic mandibular (10 of 11) and hindlimb (11 of 17) grafts. In addition, signs of nerve fibre degeneration appeared more frequently at the heterotopic sites. On the basis of these findings, and in view of the results of other workers, we conclude that tooth germs are attractive targets for all divisions of the trigeminal nerve and for cutaneous nerves outside the trigeminal system. However, the morphological picture tends to become increasingly abnormal with increasing distance from the normal locus.

Alveolar Process↗