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PubMed1995

Characterization of protein kinases involved in dentinogenesis.

Protein phosphorylation and dephosphorylation control many different cell functions as well as responses to internal and external signals. It has also been shown that highly phosphorylated acidic proteins have an important role in matrix mediated biomineralization, perhaps functioning as nucleators for crystal formation. Dentine phosphoprotein (DPP) is one of such proteins which is exclusively synthesized by the odontoblast cells and therefore a likely candidate to play a significant role in normal and abnormal dentine biomineralization. These studies are directed at characterizing the protein kinases involved in dentinogenesis and in particular the enzyme(s) responsible for DPP phosphorylation. In this report we present data which indicate that there are several different types of kinases in the odontoblast-enriched dental papilla mesenchyme (DPM), some of which can phosphorylate DPP, such as casein kinase I and II. However, a different DPP-kinase activity was identified. This enzyme(s) appears to be different from other reported kinases, and it is the only kinase that can phosphorylate both phosphorylated DPP and enzymatically dephosphorylated DPP.

Acid Phosphatase↗
PubMed1975

[Morphogenesis and structure of teleost teeth (Salmo fario L.)].

Tooth formation has been studied in the fry and adult trout (Salmo fario L.) in order to describe their structure and investigate the links between histogenetic and architectural features. Odontoblasts show typical polarized kinetics during their activity; they shrink back from the tooth wall they have elaborated, without leaving any cytoplasmic process (Tomes' fibres); so the dentine in a characteristic way lacks any cellular or canalicular inclusion, at any stage of its development. The tooth as a whole grows from an apical to basal direction; its organic matrix is formed of coarse fibres from the pulp, and fine collagenous fibres formed by the odontoblastic layer. These various fibrillar systems assume definite orientations. Mineralization was studied by fluorescent markers and microradiography. The external apical part of the tooth is hypermineralized, but its structure and pattern of deposition would make it closer to a dentinal differentiation (enameloid) than to an ectodermal enamel. The ameloblasts of the inner epithelium are high, very polarized and active cells, but their participation in tooth tissue formation has not been definitely demonstrated.

Ameloblasts↗
PubMed2000

Expression of amelogenins in developing embryonic and neonatal rat teeth.

OBJECTIVE: Tooth enamel is formed by ameloblasts, which are derived from epitheliums and secrete an extracellular matrix containing a complex arrangement of protein components. The epithelial component, referred to as the enamel organ, contains a layer of cells that secrete an organic matrix that biomineralizes to become tooth enamel. Adjacent ectomesenchyme cells differentiate to become dentinproducing odontoblasts. These two mineralized matrices form the crown of the vertebrate tooth. Therefore, amelogenins play a critical role in tooth enamel formation. We have examined the expression patterns and tissue distribution of amelogenins in their developmental stages in order to build a foundation for further study. METHODS: Amelogenin expression patterns and tissue distribution in developing teeth of embryonic (E17E19) and neonatal (1 to 9 days old) Wistar rats were examined by immunohistochemistry. RESULTS: Positive immunostaining for amelogenin was first observed in the late embryonic stage, E18. The highest level of amelogenin was noted in neonatal secretary ameloblasts, fully engaged in enamel matrix deposition (3 to 5 days old). After that, amelogenin expression continued at a lower level (6, 7, 8 days old). There was no amelogenin staining observed in the maturation stage of development (9 days old). CONCLUSIONS: Amelogenin expression occurs as early as the polarization stage of pre-ameloblasts. Amelogenin was also expressed, but at a low level, in post-secretary stages of amelogenesis. Odontoblasts did not contain detectable amelogenin.

Ameloblasts↗
PubMed1975

Studies on dentin 2. transient vasodentin in the incisor teeth of a rodent (perognathus longimembris).

Vascular inclusions regularly occur in the lingual dentin of the constantly erupting teeth of the pocket mouse (P. longimembris). The inclusion of a capillary loop and surrounding perivascular tissues is associated with odontoblasts whose cytodifferentiation is relatively immature. These same cells produce dentinal tubules which are more irregular in their course, more arborescent, with more lateral branches, wider in diameter and less numerous than are the tubules of the labial orthodentin. The patent vascular inclusions are surrounded by a broad halo of incompletely mineralized dentin. With further maturation complete obliteration of the vessels occurs, accompanied by complete dental matrix mineralization. A literature review supports the contention that vasodentinogenesis is related operationally to lower stages of odontoblastic cytodifferentiation although the processes by which this occurs are not yet clear.

Animals↗
PubMedDate not supplied

Comparison of pulp responses to resin composites.

Diverse reports have described how various types of adhesive systems cause disastrous pulp necrosis, chronic severe inflammation or failure to stimulate any pulp reactions. This article reports on the effects of five common adhesive systems and how they compare in terms of pulp injury as measured by odontoblast survival or dentin regeneration and reactionary dentin formation. One hundred and thirty Class V pulp, non-exposed cavities were prepared in non-human primate teeth and were restored with five different adhesive systems. After a period of time between 3 and 172 days, the teeth were extracted, fixed, processed and examined histomorphometrically. Bacterial microleakage was detected with McKays stain and inflammation was categorized according to the International Organization for Standardization (ISO) criteria. The number of odontoblasts and the area of reactionary dentin were measured. Pulp reactions of all adhesive systems were generally minimal, although some systems permitted bacterial microleakage in 33% of restorations, and some other systems were associated with pulp inflammation in 22% of restorations. These observations suggest that adhesive systems provide acceptable biocompatibility, however, there is strong potential for improvement.

Analysis of Variance↗
PubMed1992

Investigation of the role of Von Korff fibers during murine dentinogenesis.

The existence and significance of Von Korff fibers during early dentinogenesis are still very controversial. The purpose of the present study was to re-examine the questions of the existence, nature and significance of Von Korff's fibers using light microscopy and immunohistochemistry. Specimens were obtained from 3 days-old CD-I mice and mandibles were carefully dissected under constant irrigation and immediately fixed in 10% neutral buffered formalin for light microscopy. Sections were treated or not with collagenase prior to silver staining. For immunohistochemistry, specimens were fixed in 95% ethanol and embedded in paraffin. Sections were reacted with goat anti-human-bovine type I or type III collagen and a rhodamine (RITC) labelled rabbit anti-goat IgG was then reacted as a secondary antibody. Slides were then examined under a Zeiss II photomicroscope equipped with epifluorescence. Our results have confirmed the presence of argyrophilic material concentrated at the periphery of the dental papilla and stretching from the subodontoblastic layer to the future dentino enamel junction. The distribution of type III collagen was very similar to the distribution of the silver staining at the cervical loop area. Type I collagen distribution was different and concentrated in areas where odontoblasts were fully differentiated. Our study showed that Von Korff fibers are not artefactual. We have established the presence of an apical compartment containing type I collagen fibers and a basal compartment containing type III collagen to explain the image of continuous silver staining crossing the entire thickness of the odontoblast layer.

Animals↗
PubMedDate not supplied

Composite cure and pulp-cell cytotoxicity associated with LED curing lights.

This study compared the cure and pulp-cell cytotoxicity of composites polymerized with light-emitting diode (LED) and halogen-based light curing units. A mini-filled resin composite (Tetric Ceram, Vivadent), two LED (E-light [EL], GC and Freelight [FL], 3M-ESPE), a conventional halogen (Max [MX], Dentsply) and a high-intensity halogen light (Astralis 10 [AS], Vivadent) were evaluated. Cure associated with the different lights was determined by measuring the top and bottom surface hardness (KHN; n = 5) of 2-mm thick specimens using a digital microhardness tester (load = 500 gf; dwell time = 15 seconds). Pulp-cell cytotoxicity was assessed using a direct contact method involving incisor tooth slices dissected from 28-day old Wistar rats maintained in Dulbecco's Modified Eagle's Medium (DMEM) and 1% agarose. The bottom surfaces of the cured composite specimens (7-mm diameter and 2-mm deep) were placed in contact with the openings of each tooth slice. After incubation in 5% CO2 atmosphere at 37 degrees C for 48 hours, the tooth slices were fixed, demineralized and processed for histological examination. Pulp fibroblasts and odontoblasts were counted histomorphometrically at 400x magnification within a 1500 microm2 area using a computerized micro-imaging system. Eighteen readings were obtained for each curing light. Data was subjected to ANOVA/Scheffe's test and Pearson's correlation at significance level 0.05 and 0.01, respectively. At the top surfaces, the cure with AS was significantly greater than the other curing lights, with MX and FL being significantly greater than EL. At the bottom surfaces, MX, AS and FL had significantly better cure than EL. Specimens cured with MX were less cytotoxic than those polymerized with other curing lights. Specimens cured with AS and EL were significantly less cytotoxic than FL. Composite cure and cytotoxicity associated with LED lights is device dependent. Composite cure was not correlated to pulp-cell cytotoxicity. The response of pulpal fibroblasts to unreacted/leached components of composites differs somewhat from odontoblasts.

Analysis of Variance↗
PubMed2004

[Induction of transforming growth factor-beta 1 and dentin non-collagen proteins on tissue engineering pulp].

OBJECTIVE: To study the influence of transforming growth factor-beta 1 (TGF-beta 1), dentin non-collagen proteins (dNCPs) and their complex on tissue engineering pulp system. METHODS: Collagen I and dentin powder were used to construct the system of pulp cells in 3-dimensional culture, dentin powder was added in the gel. The tissue engineering pulp were divided TGF-beta 1 group, dNCPs group, TGF-beta 1/dNCPs group and control group. After 3, 6 and 14 days, the appearance and the differentiation of pulp cells were observed by HE staining and immunohistochemical staining respectively. RESULTS: Collagen I could form netted collagen gel construction. Growing condition of pulp cells in gel was similar to that of pulp cells in vivo. After the TGF-beta 1 and dNCPs were added, the pulp cells had some characteristics of odontoblasts and had unilateral cell process after culture 6 days. Pulp cells arranged with parallel columnar and form dentin-pulp-like complex after 14 days. Immunohistochemical staining showed dentin salivary protein (DSP) began to express in some cells. The number of positive cell was most in the TGF-beta 1 group. No positive cells were detected in the control group. CONCLUSION: The transforming growth factor-beta 1 and non-collagen proteins can stimulate the pulp cells to transform into odontoblasts to some extent, which promote the formation of tissue engineering pulp.

Animals↗
PubMed1992

Mineral-associated adhesion proteins are linked to root formation.

There is a general agreement that the extracellular environment plays a critical role in controlling cell behavior. Thus, significant research efforts have focused on understanding the effects of extracellular matrix proteins on cell function. In particular we have focused on determining the role of adhesion proteins in the regulation of root formation. Using an OPN antibody, 2arN (generously provided by Drs Craig and Denhardt), the expression of OPN during root formation was determined. OPN (osteopontin) is a bone-associated adhesion protein. OPN was expressed in the dental follicle region of molars obtained from 3 day old CD-1 mice, but was not expressed in the odontoblast layer. In contrast by day 8, positive staining was noted in the odontoblast layer, as well as in the area of Hertwig's epithelial root sheath. However, at this same time point no positive labeling for 2arN was observed in the enamel organ or in the dental papillae cells. By day 15 positive staining for OPN was seen in the area of the periodontal ligament, as well as the region of primary deposition of extracellular matrix onto dentin. Also determined was the ability of fibronectin, OPN and dentin sialoprotein (DSP) to promote the attachment of dental ectomesenchymal cells, in vitro. Interestingly, these cells attached remarkable well on bacteriological dishes (control) in the absence of an adhesion protein. DSP did not increase cell attachment beyond that observed for control cells. In contrast, both fibronectin and OPN enhanced cell attachment. These studies, while preliminary indicate that OPN is expressed in a unique fashion during root development, thus suggesting a regulatory role for such adhesion proteins during root formation.

Animals↗
PubMed2004

[Enamelin transcriptional expression in developing postnatal rat tooth germ].

OBJECTIVE: To observe the transcriptional expression of enamelin in developing postnatal rat first mandibular molar germs, for further studies of functions of enamelin in enamel development and mineralization. METHODS: Tissue slices of first mandibular molar germ of rat 1, 3, 7, 10, 14 days after birth were prepared. The enamelin mRNA expression was identified by in situ hybridization. RESULTS: Enamelin mRNA was observed in both ameloblast and odontoblast in 1-10 day old rat postnatal first mandibular molar germs. Enamelin mRNA appeared very weakly at 1st day, and increased through 3rd day, reached the maximum at 7th day, and reduced at 10th day and became negative at 14th day postnatally; while the expression of enamelin mRNA in odontoblast maintained lower from 1st to 10th day and negative at 14th day postnatally. CONCLUSION: Enamelin gene transcriptional expression lasts from preameloblast to maturation ameloblast, which suggests that enamelin may participate in the development of enamel and mantle dentin.

Ameloblasts↗
PubMed2005

Effect of a fluoride-releasing one-step adhesive system on monkey pulp tissue.

PURPOSE: The purpose of this study was to evaluate the pulpal response of a fluoride-releasing one-step adhesive in nonexposed monkey teeth. MATERIALS AND METHODS: Cervical Class V cavities were prepared in monkey teeth. The cavities were divided into three groups of different restorative materials. A one-step adhesive (SI-IB551, Shofu) was applied to the teeth, and the cavities were filled with a resin composite (Beautifil, Shofu). In the other two groups, a two-step adhesive (Imperva FluoroBond, Shofu) together with either a resin composite (Beautifil) or a glass-ionomer cement (Fuji II, GC) was placed in the cavities. The teeth were then extracted after 3, 30, and 90 days, fixed in 10% buffered formalin solution, and prepared according to routine histological techniques. Five-micrometer sections were stained with hematoxylin and eosin, or Brown & Brenn gram stain for bacterial observation. Four histological features, odontoblastic change, inflammatory cell infiltrate, reparative dentin formation, and the bacterial staining, were evaluated and compared. The results were compared statistically with significance defined as p < 0.05 (Kruskall-Wallis test). RESULTS: Disarrangement of the odontoblasts and slight inflammatory cell infiltrations were the main initial reactions, while deposition of reparative dentin was the major long-term reaction in all groups. No statistically significant differences in the four histological features were seen among the restorative materials placed in the cavities (p > 0.05). No serious pulpal inflammatory reactions, such as necrosis or abscess formation, were observed in any of the experimental groups. CONCLUSION: The one-step adhesive showed acceptable biological compatibility with the monkey pulp, whereas the pulpal response to the system was minimally different from that of the glass-ionomer cement or the two-step self-etching adhesive.

Animals↗
PubMed2006

[Transcriptional regulation of dentin sialophosphoprotein by c-Jun/c-Fos].

OBJECTIVE: To investigate the role of c-Jun and c-Fos as transcriptional factors in regulation of dentin sialophosphoprotein (DSPP) gene by a promoter-luciferase reporter gene construct in odontoblast cell line MDPC-23. METHODS: Endogenous c-Jun or c-Fos protein was determined by immunocytochemistry. The role of c-Jun or c-Fos in transcription of DSPP was investigated in co-transfection experiments using promoter-luciferase reporter gene construct containing the sequence between -791 bp and +54 bp of mouse DSPP gene. RESULTS: c-Jun and c-Fos was expressed by MDPC-23 cells, and located in the nucleus of MDPC-23 cells. Overexpression of c-Jun or c-Fos significantly inhibited luciferase activity of DSPP promoter. CONCLUSION: These findings suggest c-Jun and c-Fos down-regulated the transcription of DSPP gene as a transcriptional factor in odontoblast.

Animals↗
PubMedDate not supplied

[The lamina limitans. Its scanning electron microscopic aspects].

Many researches agree in maintaining that all the membraneous structure visible in the most external parts of the dental tubules must be considered not ad cytoplasmatic membranes of the odontoblastic processes but as an extracellular organic matrix which in certain conditions may appear detached from the internal wall of the tubule and simulated a superimposable aspect like that of an odontoblastic extension. The aim of this study was to examine at the SEM the state of this organic component in normal conditions and after demineralization with citric acid. Therefore the entire teeth of young people were fixed in formalin and dissected by fracturing. Some of the samples were demineralized with a citric acid solution. All the samples were dehydrated and metallized for the observation at SEM. Demineralization made the peritubular dentine disappear and expose inside every tubule a sheet-like structure which extended all along the tubules. The samples which were not demineralized did not demonstrate a similar structure because of their tight adhesion to the internal wall surface. This kind of formation which other researchers calls "lamina limitans" because of its high content of glycosaminoglycans might be a key factor in controlling the formation of peritubular dentine and tubular sclerosis and it will surely lead to further interesting research.

Decalcification Technique↗
PubMedDate not supplied

[Interactions between the extracellular matrix and the cell surface determine tooth morphogenesis and the cellular differentiation of the dental mesenchyme].

A series of reciprocal interactions between epithelial and mesenchymal tissues control the morphogenesis and cell differentiation in the developing tooth. The molecular mechanisms operating in these interactions are, however, unknown at present. Structural components of the extracellular matrix (ECM) affect cellular behavior in the embryo and appear to be involved also in these regulatory processes. The ECM molecules exert their effects on cells through binding to specific matrix receptors on the cell surface. This review article summarizes our findings on the distribution patterns during tooth development of the ECM glycoproteins, fibronectin and tenascin, and of the cell surface proteoglycan, syndecan, which functions as a receptor for interstitial matrix. Based on the observed changes in these distribution patterns and on experimental evidence, roles for these molecules in epithelial-mesenchymal interactions during tooth development are suggested. Fibronectin and tenascin are enriched in the dental basement membrane at the time of odontoblast differentiation. These matrix glycoproteins may be involved in the cell-matrix interaction which controls differentiation of the dental mesenchymal cells into odontoblasts. Tenascin and syndecan are accumulated in the dental mesenchyme during bud stage of development. We have shown in tissue recombination experiments that the presumptive dental epithelium induces the expression of tenascin and syndecan in mesenchyme. We suggest that these molecules are involved in cell-matrix interactions, which regulate mesenchymal cell condensation during the earliest stages of tooth morphogenesis.

Basement Membrane↗
PubMed1979

The role of ascorbic acid on the structural integrity of developing tooth germs.

Tooth germs grown in ascorbate deficient medium for up to 20 days underwent progressive and widespread changes. Proliferation and differentiation of preameloblasts and preodontoblasts progressed normally. Newly differentiated odontoblasts, however, became vacuolated when they began secreting: this suggested a metabolic disturbance. Failure to maintain differentiated odontoblasts, ameloblasts and pulpal cells resulted in aberrant dentin matrix, cessation of dentin production, and finally overall structural collapse with loss of normal morphology. Biochemical studies then were undertaken to define the lesion involved. The relative rate of collagen synthesis in ascorbate deficient cultures was comparable to that of ascorbate supplemented cultures, but the collagen was found to be underhydroxylated. In this state it would be unstable at 37 degrees and subject to preferential degradation. This correlates with the observation that a major fraction of the hydroxyproline in the scorbutic cultures was found in the medium as small molecular weight peptides. The overall effect of ascorbate deficiency was to deprive the tooth germ of the normal quality and quantity of collagen resulting in the characteristic histological and structural abnormalities observed. Flattening and deterioration due to structural failure most likely resulted from abnormal extracellular matrix synthesis in the supportive pulp and dentin due to the aberrant collagen.

Animals↗
PubMed1989

[Incorporation of 3H-cortisol into the dental pulp and the induced changes].

The incorporation of labelled hydrocortisone (3H-cortisol) in the dental pulp of Wistar rats has been tested using autoradiography. Light microscopy showed that an hour after injection the hormone is incorporated in the nuclei of the odontoblasts, subodontoblastic and endothelial cells of the dental pulp. It was also demonstrated at the ultrastructural level that a 4 week-treatment with high rates of hydrocortisone (16 and 32 mg/kg) at the time of rat intensive growth induces degeneration of the odontoblasts, pulp connective tissue cells and capillaries. High rates of hydrocortisone thus induces a decrease in the protective and reparative responses of rat molar pulp.

Animals↗
PubMed1979

The time scale of tooth development and replacement in Xenopus laevis (Daudin).

One hundred and seventy two larval specimens of Xenopus laevis were reared in such a way that their rates of development (as measured by external criteria) were similar, and so the course of dental development could be examined histologically in a cross sectional study. In this way the events of tooth development were observed, and a time scale constructed for these events. The teeth took an average time of 26 days to develop, erupt and become ankylosed to the bony pedestal, after which each tooth was in a functional position for only about 7 days. Individual tooth replacement was assessed to occur about every 16 days. By comparing the number and size of the odontoblasts responsible for dentinogenesis in 18 months old adult Xenopus laevis with the odontoblasts in the larval specimens, the conclusion was drawn that, despite the larger size of the adult teeth, the time involved in their development and replacement may well be of similar duration to the smaller larval teeth. The significance of the findings for the Zahnreihen Theory is discussed.

Animals↗
PubMed1978

A fine structural study of coronal and root dentinogensis in the mouse: observations on the so-called 'von Korff fibres' and their contribution to mantle dentine.

The fine structure of mantle dentine formation has been studied in the mouse molar. No evidence was found for the presence of collagenous von Korff fibres arising from the dental papilla, passing between odontoblasts and fanning out to form the collagenous matrix of mantle detine. Instead, large collagen fibrils were first demonstrable in the matrix peripheral to the dential aspect of an extensive junctional complex system occurring at the necks of the odontoblasts. The orientation of the fibres was at right angles to the future amelo-dentinal junction in coronal dentinogenesis, but parallel to the root surface in radicular dentinogenesis. These large collagen fibrils formed the mantle dentine. It is concluded that von Korff fibres, as strictly defined, are artefacts. Photographs in the literature purporting to show von Korff fibres are attributable to obliquity of section. Also, is suggested that the difference in fibril orientation in coronal and root mantle dentine is the reason for the conflicting opinions on the pattern of fibril orientation in this tissue.

Animals↗