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PubMedDate not supplied

Vascular endothelial growth factor (VEGF) in human tooth germ center.

Many oncogenis and tumour suppressor genes found inside normal and pathological cells are fundamental for the processes of development, proliferation and tissue differentiation. The purpose of our study is to show the presence and a possible relationship of the VEGF protein during different phases of the development of human dental germ centers. After cephalometric investigation in 8 orthodontic patients with a mean age of 13 years, (4 females and 4 males), hyperdivergence of the third molars were extracted. The 40 surgical samples were tested with monoclonal human anti-VEGFs antibodies carrying out a semi-quantitative analysis to look for a positive reaction. Reaction for anti-VEGF antibodies was detected in normal embryological tissues and in microvessels near odontogenic cells. During different phases of embryologic development of the dental bud our search showed intracytoplasmatic positive immunoreactions both in the ameloblastic and odontoblastic cells. Additionally, a positive reaction was observed for the VEGF protein in the cells of the stellate reticulum and in those endothelial tissue surrounding the microvessels in all the samples examined.

Adolescent↗
PubMed2001

Neural crest and tooth morphogenesis.

Mammalian teeth develop from two types of cells: stomodeal ectoderm, which forms ameloblasts, and cranial neural-crest-derived (ecto) mesenchyme cells, which form odontoblasts and cementoblasts. These two cell types, juxtaposed in the developing oral cavity, interact to control the entire process of tooth initiation, morphogenesis, and cytodifferentiation. Cell-cell signaling pathways and their target nuclear factors have been identified as key mediators of the progressively complex exchange of information between ectoderm and ectomesenchyme. The constantly changing direction of the reciprocal signaling and cell responses between ectoderm and ectomesenchyme enables cells to monitor their relative spatial positions and differentiated states continuously. The least understood of the early processes in tooth development are morphogenesis and patterning. From a seemingly uniform layer of oral ectoderm and underlying mass of ectomesenchyme, different types (shapes) of teeth develop in different positions. Tooth type is determined very early in development, before the overt onset of morphogenesis. Thus, the early ectoderm-ectomesenchyme cell interactions must in some way either create or respond to positional differences in the jaw primordia.

Activins↗
PubMed2001

Further observations on tertiary dentin in human deciduous teeth.

The structure of reparative tertiary dentin in human deciduous teeth has been studied. Reparative dentin is secreted by a new generation of odontoblast-like cells which have been subject to strong stimuli, e.g., trauma or deep active caries lesions with associated pulp inflammation. Ground sections of 25 teeth were prepared, and contact microradiographs were produced. Another 30 teeth were demineralized, embedded in paraffin, sectioned, and stained with hematoxylin and eosin. Some demineralized sections from each tooth were also studied in the scanning electron microscope. Most of the teeth showed some type of tertiary dentin formation. Mineralized tissue with a varied morphology was observed. In teeth which had been subject to trauma, the entire pulp chamber was sometimes obliterated. Mineralization seemed to start in the incisal region, and the central part of the pulp was the last part to be obliterated. Radiolucent voids and canals were seen. The organic matrix was dense and fibrous. In the pulp chamber and especially in the root canals, resorption had often occurred, indicating that signals giving rise to odontoclasts were also present. Resorption was often followed by deposition of various amounts of cementum-like repair tissue. The cells responsible for the formation of reparative dentin are believed to be subodontoblasts or undifferentiated ectomesenchymal cells. The varied morphology of the reparative dentin, observed in the pulp of the teeth examined, indicates that different stimuli lead to induction of hard-tissue-forming cells which produce different types of hard tissue.

Cementogenesis↗
PubMed1989

Developmental disturbances of the rat molar induced by two diphosphonates.

Very few reports have been published about the effects of diphosphonates on the cells and tissues of developing teeth. The present study was designed to investigate possible morphological changes in ameloblasts and odontoblasts and relate these changes to defects in the enamel surface of erupted teeth. Young rats were injected subcutaneously with single or multiple doses of HEDP or Cl2MDP (10 mg P/kg b.w.). Light microscopic examination of developing maxillary first molars showed that single injections of HEDP or Cl2MDP induced subameloblastic cysts between the secretory ameloblasts and the developing enamel. The ameloblastic lining of the cysts contained numerous calcified deposits. A few days after injection, hypoplasias were seen in the enamel in areas previously occupied by cysts. In the erupted teeth, scanning electron microscopic examination revealed enamel hypoplasias which were mainly localized on the mesial sides of the cusps. In addition to the previously mentioned disturbances, multiple injections resulted in more extensive cysts, some of which contained non-mineralized enamel matrix. Inhibition of the mineralization of dentin and alveolar bone was also noticed.

Ameloblasts↗
PubMed1996

Radioautographic study of the incorporation of (3H)-choline into the phospholipids of secretory ameloblasts and enamel of normal and essential-fatty-acid-deficient rats.

(3H)-choline, a precursor for phosphatidylcholine (PC) and sphingomyelin (SM), was injected into rats killed after 4, 24, 48, and 96 hrs. Radioautography carried out on malachite-green/aldehyde-fixed tissues demonstrated that labeled choline was incorporated into cells and further released into the extracellular matrix. In predentin, labeling decreased rapidly, whereas in dentin, silver grains formed a stable band. In contrast, labeling was still high at 48 and 96 hrs in secretory ameloblasts as well as in the forming enamel. This indicates that ameloblasts are actively involved in the synthesis of membranes. Membrane remnants of the ameloblasts could be released into the forming enamel. In rats fed with an essential fatty-acid-deficient (EFAD) diet for 42 days, (3H)-choline uptake was delayed and reduced in pulp cells and odontoblasts, and consequently the migration of labeled phospholipids into dentin. The influence of the EFAD diet on secretory ameloblasts was limited. No difference was detected between normally fed and EFAD-fed rats in the forming enamel.

Ameloblasts↗
PubMed1993

Dentinogenesis.

The formation of dentin, dentinogenesis, comprises a sophisticated interplay between several factors in the tissue, cellular as well as extracellular. Dentin may be regarded as a calcified connective tissue. In this respect, as well as in its mode of formation, it is closely related to bone. Using dentinogenesis as an experimental model to study biomineralization provides several practical advantages, and the results may be extrapolated to understand similar processes in other tissues, primarily bone. After describing dentin structure and composition, this review discusses items such as the morphology of dentinogenesis; the dentinogenically active odontoblast, transport, and concentrations of mineral ions; the constituents of the dentin organic matrix; and the presumed mechanisms involved in mineral formation.

Animals↗
PubMed1996

Dynamics of the pulpo-dentin complex.

Dentin has a relatively high water content due to its tubular structure. Once dentin is exposed, this intratubular water is free to move in response to thermal, osmotic, evaporative, or tactile stimuli. Fluid shifts across dentin are thought to cause sufficient shear forces on odontoblasts, nerve endings, nearby fibroblasts, and blood vessels to cause significant mechanical irritation, disruption, or damage, depending on the magnitude of the fluid shift. Even in the absence of fluid shifts, the water-filled tubules provide diffusion channels for noxious (i.e., bacterial products) substances which diffuse inward toward the pulp, where they can activate the immune system, provide chemotactic stimuli, cytokine production, and produce pain and pulpal inflammation. Viewed from this perspective, dentin is a poor barrier to external irritants. However, pulpal tissues react to these challenges by increasing the activity of nerves, blood vessels, the immune system, and interstitial fluid turnover, to make the exposed dentin less permeable either physiologically, via increased outward fluid flow, or microscopically, by lining tubules with proteins, mineral deposits, or tertiary dentin, thereby enhancing the barrier properties of dentin, and providing additional protection to pulpal tissues. These reactions involve dentin and pulp, both in the initiation of the processes and in their resolution. These responses of the dental pulp to irritation of dentin demonstrate the dynamic nature of the pulpo-dentin complex.

Bacterial Toxins↗
PubMed2002

Tissue engineering of complex tooth structures on biodegradable polymer scaffolds.

Tooth loss due to periodontal disease, dental caries, trauma, or a variety of genetic disorders continues to affect most adults adversely at some time in their lives. A biological tooth substitute that could replace lost teeth would provide a vital alternative to currently available clinical treatments. To pursue this goal, we dissociated porcine third molar tooth buds into single-cell suspensions and seeded them onto biodegradable polymers. After growing in rat hosts for 20 to 30 weeks, recognizable tooth structures formed that contained dentin, odontoblasts, a well-defined pulp chamber, putative Hertwig's root sheath epithelia, putative cementoblasts, and a morphologically correct enamel organ containing fully formed enamel. Our results demonstrate the first successful generation of tooth crowns from dissociated tooth tissues that contain both dentin and enamel, and suggest the presence of epithelial and mesenchymal dental stem cells in porcine third molar tissues.

Absorbable Implants↗
PubMed2003

Class II antigen-presenting dendritic cell and nerve fiber responses to cavities, caries, or caries treatment in human teeth.

Major histocompatibility complex (MHC) class II molecule-expressing cells are distributed in human dental pulp, and have been shown to accumulate beneath caries lesions. The responses of these cells and nerve fibers were analyzed under 5 different clinical conditions: shallow and deep experimental cavities, active and slow untreated caries, and treated caries. Under deep cavities, class II molecule-expressing dendritic cells displaced the injured odontoblasts during a period of one month, while such a response was not observed in shallow cavities and untreated or treated carious teeth. The class II molecules seen in the neural elements under active caries were no longer detectable in treated carious teeth. However, six months after treatment, clusters consisting of dendritic cells, T-lymphocytes, and nerve fibers still remained locally in the subodontoblastic area. These results indicate that dental pulps respond differently to cavity preparation and restoration between normal and caries conditions, and that immunoresponses persist for many months, even after caries treatment.

Adult↗
PubMed2003

Lipoteichoic acid up-regulates VEGF expression in macrophages and pulp cells.

Vascular endothelial growth factor (VEGF) is a potent inducer of angiogenesis, vascular permeability, and edema. Up-regulation of VEGF expression in the dental pulp may result in increased intra-pulpal pressure, and contribute to pain and irreversible tissue damage. Lipoteichoic acid (LTA) is an amphiphilic molecule from Gram-positive bacteria that has been associated with the pathogenesis of pulpitis. To investigate if LTA regulates expression of VEGF, we exposed mouse odontoblast-like cells (MDPC-23), undifferentiated pulp cells (OD-21), fibroblasts, or macrophages to streptococcal LTA, and evaluated VEGF expression by ELISA and RT-PCR. LTA induced up to a nine-fold increase in VEGF protein expression in macrophages, a 2.4-fold increase in MDPC-23, and a 1.6-fold increase in OD-21 as compared with controls. In contrast, LTA did not induce VEGF expression in fibroblasts. VEGF mRNA expression remained constant upon exposure to LTA, which suggests that VEGF regulation in these cells is primarily post-transcriptional. This work constitutes the first demonstration that lipoteichoic acid is sufficient to induce expression of a pro-angiogenic factor.

Analysis of Variance↗
PubMed2003

Adhesive resin induces apoptosis and cell-cycle arrest of pulp cells.

The application of an adhesive resin near or directly over the pulp was shown to induce pulp inflammation and lack of dentin regeneration. We hypothesize that the absence of dentin bridging is due to adhesive-resin-induced apoptosis of cells responsible for pulp healing and dentin regeneration. Mouse odontoblast-like cells (MDPC-23), undifferentiated pulp cells (OD-21), or macrophages (RAW 264.7) were exposed to SingleBond polymerized for 0-40 seconds. Annexin V and propidium iodide assays demonstrated that SingleBond induced apoptosis of MDPC-23, OD-21, and macrophages. The proportion of apoptotic cells was dependent on the degree of adhesive resin polymerization. Adhesive-resin-induced death of pulp cells was associated with activation of the pro-apoptotic cysteine protease Caspase-3. Interestingly, most cells exposed to adhesive resin that did not undergo apoptosis showed cell-cycle arrest. We conclude that an adhesive resin induces apoptosis and cell-cycle arrest of cells involved in the regeneration of the dentin-pulp complex in vitro.

Analysis of Variance↗
PubMed2004

Lactational exposure of Han/Wistar rats to 2,3,7,8-tetrachlorodibenzo-p-dioxin interferes with enamel maturation and retards dentin mineralization.

Exposure to environmental dioxins via mother's milk may be one causative factor of mineralization defects in children's teeth. A prerequisite for the completion of enamel mineralization is the removal of enamel matrix. To test the hypothesis that dioxins interfere with enamel maturation, we administered lactating Han/Wistar rats a single dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; 50 or 1000 micro g/kg) on the day after delivery and analyzed tissue sections of the pup heads at post-natal days (Pn) 9 and 22. By Pn22, the first and second molars of the exposed pups, but not controls, showed retention of enamel matrix. Predentin was thicker than normal. Immunostaining for the aryl hydrocarbon/dioxin receptor (AhR) and cytochrome P4501A1 (CYP1A1) in ameloblasts and odontoblasts was reduced, suggesting that TCDD interferes with tooth mineralization via AhR. Extinction of AhR may lead to abolition of CYP1A1 expression as a sign of impaired dental cell function.

Ameloblasts↗
PubMed2004

Nitric oxide synthase in healthy and inflamed human dental pulp.

Nitric oxide synthase (NOS) plays a significant role in the pathogenesis of pulpitis. In this study, we hypothesized the existence of endothelial (eNOS) and inducible (iNOS) enzyme isoforms in human dental pulp. Extracted third molar pulps were divided into groups based on clinical diagnosis: healthy, hyperemic, and irreversible pulpitis. We have localized the eNOS and iNOS by immunohistochemistry and have tested their mRNA expression by RT-PCR and protein levels by Western blots. eNOS is present in the endothelial cells and odontoblasts of the healthy pulp, but an elevation of eNOS mRNA and protein levels with a concomitant dilation of vessels was characteristic under pathological conditions. Healthy pulp tissue failed to exhibit any iNOS; however, acute inflammation enhanced the mRNA and protein levels of iNOS, mainly in the leukocytes. There are differences in localization and expression between eNOS and iNOS in healthy and inflamed dental pulp.

Adult↗
PubMed2005

Organized tooth-specific cellular differentiation stimulated by BMP4.

Mammalian teeth develop on the oral surface of the first pharyngeal arch by a series of reciprocal interactions between epithelial and mesenchymal cells. The embryonic first pharyngeal arch oral epithelium is able to induce tooth formation when combined with mesenchymal cells from the second pharyngeal arch, a region devoid of tooth development. Second pharyngeal arch mesenchyme is thus competent to form teeth if provided with the correct signals. First-arch oral epithelium expresses several signaling molecules that could be potential inducers of tooth development, including BMP4. The addition of BMP4 to intact second-arch explants resulted in the development of organized structures containing layers of cells that express marker genes of tooth-specific cells, odontoblasts and ameloblasts. Thus, although overt tooth development did not occur, BMP4 has the ability to stimulate organized differentiation of epithelial- and mesenchymal-derived dental-specific cells from non-dental primordia.

Ameloblasts↗
PubMed2005

Amelotin--a Novel Secreted, Ameloblast-specific Protein.

We aimed to analyze the differential gene expression in various murine dental tissues, expecting to find novel factors that are involved in tooth formation. We here describe the identification of a novel ameloblast-specific gene, amelotin (AMTN), by differential display polymerase chain-reaction (DD-PCR) analysis of microdissected ameloblasts, odontoblasts, dental pulp, and alveolar bone cells of 10-day-old mouse incisors. The conceptually translated protein sequence was unique and showed significant homology only with its human orthologue. The amelotin genes from mouse and human displayed a similar exon-intron structure and were expressed from loci on chromosomes 5 and 4, respectively, which have been associated with various forms of amelogenesis imperfecta. Expression of amelotin mRNA was restricted to maturation-stage ameloblasts in developing murine molars and incisors. Amelotin protein was efficiently secreted from transfected cells in culture. Taken together, our findings suggest that amelotin is a novel factor produced by ameloblasts that plays a critical role in the formation of dental enamel.

Alveolar Process↗
PubMed2006

Cloning, sequencing, and expression of the amelogenin gene in two scincid lizards.

Our knowledge of the gene coding for amelogenin, the major enamel protein, is mainly based on mammalian sequences. Only two sequences are available in reptiles. To know whether the snake sequence is representative of the amelogenin condition in squamates, we have studied amelogenin in two scincid lizards. Lizard amelogenin possesses numerous conserved residues in the N- and C-terminal regions, but its central region is highly variable, even when compared with the snake sequence. This rapid evolution rate indicates that a single squamate sequence was not representative, and that comparative studies of reptilian amelogenins might be useful to detect the residues which are really important for amelogenin structure and function. Reptilian and mammalian enamel structure is roughly similar, but no data support amelogenin being similarly expressed during amelogenesis. By performing in situ hybridization using a specific probe, we showed that lizard ameloblasts express amelogenin as described during mammalian amelogenesis. However, we have not found amelogenin transcripts in odontoblasts. This indicates that full-length amelogenin is specific to enamel matrix, at least in this lizard.

Ameloblasts↗
PubMed1975

Inhibition studies of alkaline phosphatase in hard tissue-forming cells.

The effects of the alkaline phosphatase inhibitors levamisole and R 8231 on p-nitro-phenylphosphatase, inorganic pyrophosphatase and adenosine triphosphatase (ATPase) activities in dentingenically active odontoblasts were studied. The p-nitrophenylphosphatase and inorganic pyrophosphatase activities were inhibited, while 40% of the ATP-splitting enzyme activity remained under the assay condition used. This finding, togeather with earlier studies, indicates that at least two different phosphatase are active at alkaline pH in hard tissue-forming cells; on nonspecific alkaline phosphatase and one specific ATPase. The ATPase activity is uninfluenced by ouabain and ruthenium red and is activated by Ca-2+ ions.

4-Nitrophenylphosphatase↗
PubMed1990

Immunohistochemical localization of glycosaminoglycans and proteoglycans in predentin and dentin of rat incisors.

We examined immunocytochemically the type and distribution of glycosaminoglycans and proteoglycans (PG) in predentin and dentin demineralized with EDTA after aldehyde fixation of rat incisors using (a) four monoclonal antibodies (1-B-5,9-A-2,3-B-3, and 5-D-4) which recognize epitopes in unsulfated chondroitin (C0-S), chondroitin 4-sulfate (C4-S), chondroitin 6-sulfate (C6-S), and keratan sulfate (KS) associated with the PG, and (b) monoclonal (5-D-5) and polyclonal antibodies specific for the core protein of large and small dermatan sulfate (DS) PG. Light microscope immunoperoxidase staining after pre-treatment of tissue sections with chondroitinase ABC localized the majority of stainable PG (C4-S, KS, DSPG, C0-S, and C6-S) in predentin and, to a lesser extent (C4-S and small DSPG), in the dentin matrix. The former site demonstrated relatively homogeneous PG distribution, whereas the latter site revealed that strong staining of C4-S and small DSPG was confined mostly to dentinal tubules surrounding odontoblastic processes, with only weak staining in the rest of the dentin matrix. These results indicate that there is not only a definite difference between PG of predentin and dentin but also a selective decrease in the concentration or alteration of these macromolecules during dentinogenesis and mineralization.

Animals↗