A STUDY OF THE ONTOGENETIC ORIGIN OF HUMAN PERMANENT TOOTH GERMS.
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Entomology↗
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Immunolocalization of connexin 43 in the tooth germ of the neonatal rat.
Rabbit polyclonal antibodies to amino acids 346-360 of connexin 43, the 'heart' gap junction protein, were employed to immunolocalize connexin 43 gap junctions in the neonatal rat molar tooth germ. Connexin 43 appears early in the differentiation of both ectodermally derived and ectomesenchymally derived cells of the developing tooth. Connexin 43 immunoreactivity is present in the epithelial components of the enamel organ, including the area of the proximal and distal junctional complexes of the ameloblast layer, and the stratum intermedium, stellate reticulum and outer enamel epithelium. Secretory odontoblasts and developing alveolar bone also display a pattern of connexin 43 immunostaining. Both the epithelial and ectomesenchymally-derived components of the developing tooth acquire connexin 43 channels in a manner that correlates with cell differentiation. In addition, three regions can be defined by connexin 43 immunostaining: the epithelia of the enamel organ that are derived from the oral epithelium, the odontoblast layer derived from the ectomesenchyme, and the alveolar bone. The results suggest that connexin 43 may provide the mechanism for functional compartmentalization of the tissues associated with tooth formation. Compartmentalization suggested by connexin 43 expression could play important roles in the development and functions of these tissues.
Animals↗
[Replantation and transplantation of teeth and tooth germs].
Replantation as well as the transplantation of autologous and homologous teeth or tooth buds were carries out ot utilize teeth which had been knocked out of their alveolus due to trauma and/or, if indicated, to close diastemas and aesthetically and functionally satisfactory teeth. These procedures are briefly described here and illustrated with a few cases.
Adolescent↗
Diazo-oxo-norleucine (DON)-induced alterations in the extracellular matrix of the mouse tooth germ.
In a previous study we have shown that the glutamine analogue diazo-oxo-norleucine (DON) inhibits the differentiation of mesenchymal cells into odontoblasts in the developing tooth. In the present study we have studied the effect of DON on the formation of the extracellular matrix by using light microscopic autoradiography and transmission electron microscopy. The inhibition of odontoblast differentiation was accompanied by alterations in the extracellular matrix at the epithelio-mesenchymal interface. The interface was reduced in space and filled with filamentous material, and the organization of collagen fibers in more advanced tooth germs was disturbed. DON also reduced the incorporation of [35S]sulphate into the basement membrane region, whereas no marked change was observed in the incorporation of [3H]fucose. These results suggest that DON affected the cell--matrix interaction which is believed to control the differentiation of odontoblast.
Animals↗
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↗
Functional fixation of autotransplanted tooth germs by using bioresorbable membranes.
OBJECTIVE: The purpose of this study was to evaluate the contribution of a bioresorbable membrane placement to the healing of immature teeth after autotransplantation of tooth buds. STUDY DESIGN: Six cases were selected: 2 transplantations of wisdom teeth, 2 for premolar agenesis, 1 for ectopia, and 1 premolar in an incisor position. The crown of each tooth germ and the marginal alveolar bone were covered with a resorbable membrane. RESULTS: The radicular edification was nearly complete, neither ankylosis nor inflammatory resorption was observable, the pulp vitality was preserved, and the periodontal integration was identical to that of other teeth. The membrane ensured contention and stabilization of the transplant, allowed functional stimulation, permitted protection of the coagulum and periodontal cells, and kept the epithelium at a distance. CONCLUSIONS: The transplantations of immature teeth were improved by the use of a resorbable membrane, which caused an optimal functional fixation of the transplanted tooth.
Absorbable Implants↗
Gene expression profiling of ameloblastoma and human tooth germ by means of a cDNA microarray.
The molecular and genetic characteristics of ameloblastoma are still poorly understood. We analyzed gene expression in fresh-frozen ameloblastomas and human fetal tooth germs, using a cDNA microarray. Thirty-four genes exhibited significant changes in expression levels in the ameloblastoma. Eleven genes were overexpressed more than three-fold, and 23 genes were underexpressed to below 0.4 of the control level. The oncogene FOS was the most overexpressed gene (from eight- to 14-fold), followed by tumor-necrosis-factor-receptor 1 (TNFRSF1A). Genes for sonic hedgehog (SHH), TNF-receptor-associated-factor 3 (TRAF3), rhoGTP-ase-activating protein 4 (ARHGAP4), deleted in colorectal carcinoma (DCC), cadherins 12 and 13 (CDH12 and 13), teratocarcinoma-derived growth-factor-1 (TDGF1), and transforming growth-factor-beta1 (TGFB1) were underexpressed in all tumors. In selected genes, a comparison between cDNA microarray and real-time RT-PCR confirmed similar relative gene expression changes. The gene expression profile identifies candidate genes that may be involved in the origination of ameloblastoma and several genes previously unidentified in relation to human tooth development.
Adolescent↗
Influence of iron upon the development of tetracycline-treated mouse tooth germs in vitro (1).
The inhibitory action of tetracycline on the development of embryonic mouse incisors cultured in vitro was examined. Explants exposed to tetracycline were severely inhibited in development. In contrast, tooth germs cultured in the presence of both tetracycline and iron escaped inhibition and attained a stage of development which compared favorably with the controls.
Animals↗
[Tooth germ transplantation or gap closure--a comparative study in the loss of the first molar].
In our study 37 transplanted and 33 mesialized molars by orthodontics were clinically and radiologically compared. The teeth moved by orthodontics showed a better long-term prognosis. As vital teeth with functioning periodontal structures and only slightly shortened roots they were equivalent to healthy teeth. However, the disadvantage of orthodontic space closure is the requirement of a good compliance due to long treatment time. The prognosis of maintaining a transplanted tooth germ is uncertain. One third of the teeth showed an altered periodontium with resorption areas. The danger of a continuing resorption, as well as a late external resorption is still a risk after a long period of time and can eventually lead to tooth loss. As a treatment alternative, germ transplantation may serve as a replacement of a single missing 6-year-molar in adolescence. Orthodontic space closure is indicated at any age with an existing dysgnathia, the loss of several first molars, the loss of space and mesial tipping of the second molars.
Adolescent↗
[Resorption of the 1st permanent molars through the tooth germs of premolars].
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Humans↗
[Clinical and experimental animal studies on the autotransplantation of tooth germs (IV)].
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Animals↗
Histochemical studies of acid and alkaline phosphatases in rat tooth germs with undecalcified resin-embedded specimens.
A novel technique for the histochemical demonstration of acid phosphatase (AcPase) and alkaline phosphatase (AkPase) in hard tissues has been proposed. Fresh, unfixed, undecalcified samples of rat tooth germs and surrounding structures were embedded in LR Gold resin at -20 degrees C. Sections of 2 microns were taken and subsequently processed for enzyme histochemistry. AkPase reaction product appeared as strong linear staining outlining cell boundaries and was present in the enamel organ, dental pulp, and osteoblast cells. Tartrate-resistant AcPase staining was seen exclusively in the osteoclasts of developing alveolar bone. Our results demonstrated that the use of unfixed, undecalcified LR Gold resin-embedded specimens for histochemistry is a novel technique which may be of value for certain studies when decalcification of specimens is undesirable. The technique appears to give good preservation of enzyme activity combined with the ability to prepare sections with excellent morphological detail.
Acid Phosphatase↗
Ultrastructure of in-vitro recovery of mineralization capacity of fluorotic enamel matrix in hamster tooth germs pre-exposed to fluoride in organ culture during the secretory phase of amelogenesis.
The recovery of mineralization capacity of fluorotic enamel matrix was investigated in 3-day-old hamster first molar tooth germs already pre-exposed in organ culture to 10 parts/10(6) F- for 24 h during the secretory phase. The germs were then cultured for another 24 h in a fresh medium without F-. The unmineralized fluorotic enamel matrix secreted in vitro eventually mineralized in the absence of F- but the orientation of the crystals compared to those in the fluorotic enamel was disturbed, especially in the younger regions of the enamel nearest cervical-loop in which the underlaying fluorotic enamel was most hypermineralized; but least disturbed in the more mature parts of the enamel organ in which the fluorotic enamel was less hypermineralized. The subsequent culture in F(-)-free medium did not abolish or reduce the degree of hypermineralization induced by F- treatment during the initial 24 h of culture. It seems that in vitro the inhibitory effect of F- on enamel matrix mineralization during the secretory phase is completely reversible when the ion is removed from the matrix environment, i.e. F(-)-induced synthesis and secretion of defective enamel matrix is not the cause of the lack of matrix mineralization. The F(-)-induced hypermineralization seems to be irreversible.
Amelogenesis↗
Ultrastructure of the effects of calcitonin on the development of mouse tooth germs in vitro.
Mandibular first molars, from 17-day-old embryos, were cultivated in control medium or medium containing 0.1, 0.01 or 0.001 unit/ml of calcitonin (CT) for periods up to 10 days. In untreated tooth germs, cells of the dental papilla differentiated into pre-odontoblasts up to 4 days and predentine was seen on day 6. Cells treated with 0.1 unit/ml of CT differentiated into pre-odontoblasts up to 4 days, but no predentine was formed even after 10 days in culture. With 0.01 unit/ml, cells differentiated into odontoblasts, and had already secreted predentine a few days earlier than the untreated group. With 0.001 unit/ml, the developing germs were similar to the control explants during the entire 10-day cultivation period. The proportional area of rough endoplasmic reticulum to cytoplasm of the odontoblasts was low at 0.1 unit/ml of CT and high at 0.01 unit/ml compared to the untreated explants.
Animals↗
Effect of methotrexate on cell proliferation in developing hamster molar tooth germs in vitro.
Amongst the most frequently used drugs for the treatment of acute lymphoblastic leukaemia (ALL) belongs methotrexate (MTX), an inhibitor of pyrimidine (thymidine) synthesis. We examined effects of MTX on cell proliferation during tooth morphogenesis in organ culture by exposing hamster molar tooth germs to 10(-7) to 10(-3) M MTX for 24 h. In the presence of serum, only the highest concentration of MTX (10(-3) M) induced a small, nonsignificant decrease in cell mass without histological changes but, unexpectedly, increased uptake of [3H]thymidine. In serumless conditions increase in cell mass (dry weight) and incorporation of [3H]thymidine was lower than in serum-supplemented conditions. Exposure to MTX in serumless conditions reduced the increase in cell mass even further without histological changes and, again, strongly enhanced incorporation of [3H]thymidine to the same proportion as measured in the serum-supplemented cultures exposed to MTX. The data suggest that only exposure to high levels of MTX reduces proliferation activity, shown by reduction in cell mass. The enhanced [3H]thymidine uptake under MTX exposure was explained by blockage of the internal biosynthesis of thymidine, by which action more radiolabel was taken up from the medium. The data also suggest that serum contains (growth) factors that stimulate cell proliferation, thereby increasing cell mass and [3H]thymidine incorporation.
Animals↗
An autoradiographic study of calcium movement in the enamel organ of rat molar tooth germs.
The distribution and movement of calcium through the enamel organ and into the forming enamel was studied in 6-day-old rats, intravenously injected with 45Ca. To prevent dislocation of radiocalcium in the specimens, the tooth germs were rapidly frozen/freeze-substituted and processed for 45Ca autoradiography under dry conditions. At 30 s after the 45Ca injection, there was a decrease in labelling intensity progressing from the overlying connective tissue to the enamel organ and, in the secretory ameloblasts, from the proximal to distal cytoplasm. The most intense labelling was in the enamel matrix, where it was restricted to the superficial layer extending approx. 15 microns below the surface. At later times the density of silver grains over the connective tissue decreased considerably, whereas secretory ameloblasts showed an increasing intensity in the distal portions. Enamel had the heaviest labelling: the width of the labelled enamel increased gradually to only 40 microns from the surface 60 min after the injection. The use of wet emulsion over similarly prepared sections caused a severe dislocation of radiocalcium in the specimens. These findings confirm the rapid penetration of systemically administered calcium to newly formed enamel, probably due to isotopic exchange. A relatively slow diffusion through the enamel organ and into the surface layer of enamel suggests that net transport of calcium through the enamel organ is transcellular.
Ameloblasts↗
Ultrastructural study of fluoride-induced in-vitro hypermineralization of enamel in hamster tooth germs explanted during the secretory phase of amelogenesis.
The effects of fluoride (5, 10 and 20 parts/10(6) F-) were studied in vitro with light and electron microscopy in 5-day-old hamster maxillary second molar tooth germs explanted when most of the ameloblasts are in the secretory phase, and cultured for 24 h in the presence of F-. F- at all doses investigated induced hypermineralization of that enamel which had been secreted in vivo just prior to exposure to F-. The most intense hypermineralization was in the aprismatic enamel near the cervical loop region, where the in-vivo enamel layer was thinnest and gradually decreased (but was not abolished) with the increasing thickness of in-vivo formed enamel in the more mature parts of the enamel organ. The fluoride-induced hypermineralization in the aprismatic enamel layer did not stain at all with dilute toluidine blue solution and was therefore indistinguishable from the underlying dentine in light micrographs. The hypermineralization was due to growth in thickness of the enamel crystals, which in the aprismatic enamel layer resulted in a lateral fusion of all the enamel crystals. Thus fluoride administered during the secretory phase of enamel formation decontrols or even abolishes enamel crystal growth in length and promotes crystal growth in thickness so producing the hypermineralization of the pre-fluoride enamel. Enamel matrix secreted in the presence of fluoride did not mineralize.
Amelogenesis↗
Expression of basement membrane components in the dental papilla mesenchyme of monkey tooth germs--an immunohistochemical study.
The present work, which employs indirect immunoperoxidase methods, demonstrates electron microscopic localization of three major basement membrane (BM) components--type IV collagen, laminin, and heparan sulfate proteoglycan--at the early stages of odontogenesis in tooth germs of the Japanese macaque (Macaca fuscata). Intense immunostaining for each examined component occurred at the interface between the inner enamel epithelium and the dental papilla mesenchyme. At higher magnification, immunoreaction products were observed both in the lamina densa and lamina fibroreticularis. Fuzzy substances occurring very close to the lamina fibroreticularis manifested moderate immunoreactivity. In addition, immunostaining took place in the dental papilla mesenchyme. The dental papilla cells located close to the BM demonstrated immunoreactive material mainly on plasma membranes facing the BM. Reaction products were also observed in large concavities formed in some areas of the cell surfaces; and small, immunopositive vesicles occurred close to the plasma membrane. Immunoreaction products could be found in the cisternae of the rough endoplasmic reticulum of some mesenchymal cells. These findings suggest that dental papilla mesenchymal cells may produce the three major BM components and those of the components that are incorporated into the dental BM--particularly into the lamina fibroreticularis--during tooth development.
Animals↗