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The study reveals a lack of histomorphogenesis in New Zealand white rabbit teeth. The teeth development was examined through sequential histological segments in 24 rabbits from prenatal ages (E19, E21, E23, E25, and E28), neonates (E30), and postnatal age (1 week and 2 weeks); (three animal specimens at each age stage). Rabbit teeth first appeared at 19 days of prenatal life (E19) as an ectodermal epithelial thickening on each side of the mouth opening. At E21, the bud of upper incisor tooth appeared as an epithelial bud, which composed of many condensed epithelium cells, was simply identified from the larger with less condensed vestibular lamina, and was surrounded by mesenchymal connective tissue while the lower incisor took the cap stage. At (E23), tooth regular construction is formed from enamel, dentine, and pulp cavity. Peg incisor appearance (supplementary and assistant incisors) is visible at the lingual surface of the upper major incisor. Teeth prenatal development went through successive stages like initiation, bud, cap, late bell, maturation, and crown stages. The first initiation phase of tooth formation was seen as ectodermal epithelial cell collection at (E19). Bud stage saw on upper incisor tooth, while in cap structure in lower incisor teeth at (E19). A cap-formed tooth is composed of the enamel organ and fundamentally dense mesenchymal tissue. Enamel organs are segmented into three distinct layers: the external tooth enamel epithelial, the internal tooth enamel epithelial, and finally the stellate reticular layer. The cement layer covered teeth all around on enamel on both the labial and lingual sides while not contacting the dentine on the lateral side, forming enamel space. Teeth develop consistently all through life; they have expanded enamel thickness; they are diphyodont teeth; they have two continuous dentitions; they are deciduous and perpetual, with long crown teeth and an open root. [ABSTRACT FROM AUTHOR]

Statement of the Problem: Enamel organ (EO) is an ectodermal derived structure, which is involved in the different aspects of tooth development. Tooth development shares the same regulatory molecules and genes expressed in other developing organs. Endothelin- 1 (ET-1) and Endothelin A receptor (ETAR), (ET-1/ETAR) axis, are involved in differentiation of embryonic stem cells and organ development.Purpose: The present study aimed to investigate the ET-1 and ETAR expression profiles during the development of human primary tooth EO with the relatively large sample size.Materials and Method: In this experimental study, 33 human fetuses aged from 13 to 23 weeks (3 samples from each fetal age) were collected. The samples were divided into three age groups (

Background: Tooth development involves reciprocal interactions between the oral epithelium and ectomesenchyme. The inner layer cells of the enamel organ (EO), known as the inner enamel epithelium (IEE), undergo differentiation into preameloblasts and subsequently mature ameloblasts. These ameloblasts play a crucial role in the secretion of enamel matrix proteins, including amelogenin. This experimental study aimed to analyze the expression profile of amelogenin in various histological structures of human primary developing teeth, employing a relatively large sample size. Methods: This experimental study included 33 human fetuses aged between 13 and 23 weeks, with three samples obtained from each gestational age. The samples were categorized into three age groups of ≥13 and

Statement of the Problem: Enamel organ (EO) is an ectodermal derived structure, which is involved in the different aspects of tooth development. Tooth development shares the same regulatory molecules and genes expressed in other developing organs. Endothelin- 1 (ET-1) and Endothelin A receptor (ETAR), (ET-1/ETAR) axis, are involved in differentiation of embryonic stem cells and organ development. Purpose: The present study aimed to investigate the ET-1 and ETAR expression profiles during the development of human primary tooth EO with the relatively large sample size. Materials and Method: In this experimental study, 33 human fetuses aged from 13 to 23 weeks (3 samples from each fetal age) were collected. The samples were divided into three age groups (<16 weeks, <19 weeks, ≥19 weeks) and cut for hematoxylin and eosin (H&E) and immunohistochemistry (IHC) staining. A two-way ANOVA test was conducted to examine the expression levels of ET-1 and ETAR in different layers of human primary tooth EO. The statistical significance was assumed at p ≤ 0.05. Results: There were statistically significant differences between the expression levels of ET1/ETAR axis in the four-layered human primary tooth EO in different fetal ages (13-23 weeks). Besides, there were significant differences between the expression levels of ET1/ETAR axis in all layers of human primary enamel organ and types of teeth. Conclusion: Due to the profile of expression of ET-1/ETAR axis, it can be concluded that this axis contributes to the differentiation of all human primary EO layers and secretion of enamel. ET-1/ETAR axis is one of the signaling molecules, which may have crucial roles in tooth development. [ABSTRACT FROM AUTHOR]

The Notch pathway is an ancient, evolutionary conserved intercellular signaling mechanism that is involved in cell fate specification and proper embryonic development. The Jagged2 gene, which encodes a ligand for the Notch family of receptors, is expressed from the earliest stages of odontogenesis in epithelial cells that will later generate the enamel-producing ameloblasts. Homozygous Jagged2 mutant mice exhibit abnormal tooth morphology and impaired enamel deposition. Enamel composition and structure in mammals are tightly linked to the enamel organ that represents an evolutionary unit formed by distinct dental epithelial cell types. The physical cooperativity between Notch ligands and receptors suggests that Jagged2 deletion could alter the expression profile of Notch receptors, thus modifying the whole Notch signaling cascade in cells within the enamel organ. Indeed, both Notch1 and Notch2 expression are severely disturbed in the enamel organ of Jagged2 mutant teeth. It appears that the deregulation of the Notch signaling cascade reverts the evolutionary path generating dental structures more reminiscent of the enameloid of fishes rather than of mammalian enamel. Loss of interactions between Notch and Jagged proteins may initiate the suppression of complementary dental epithelial cell fates acquired during evolution. We propose that the increased number of Notch homologues in metazoa enabled incipient sister cell types to form and maintain distinctive cell fates within organs and tissues along evolution. [ABSTRACT FROM AUTHOR]

Background: Tooth development involves reciprocal interactions between the oral epithelium and ectomesenchyme. The inner layer cells of the enamel organ (EO), known as the inner enamel epithelium (IEE), undergo differentiation into preameloblasts and subsequently mature ameloblasts. These ameloblasts play a crucial role in the secretion of enamel matrix proteins, including amelogenin. This experimental study aimed to analyze the expression profile of amelogenin in various histological structures of human primary developing teeth, employing a relatively large sample size. Methods: This experimental study included 33 human fetuses aged between 13 and 23 weeks, with three samples obtained from each gestational age. The samples were categorized into three age groups of ≥13 and <16 gestational weeks (g.w.), <19 g.w., as well as ≥19 and ≤ 23 g.w. Hematoxylin and eosin staining, as well as immunohistochemistry staining, were performed on the samples. To assess the expression level of amelogenin in different histological structures of human primary teeth, a two-way ANOVA test was employed. The statistical significance threshold was set at P≤0.05. Results: There were statistically significant differences regarding the expression level of amelogenin in various histological structures of human primary teeth in different fetal ages (13-23 weeks), except for the maxillary central incisor and mandibular central incisor. Conclusion: Due to the profile of expression of amelogenin, it can be concluded that amelogenin expression could be associated with ameloblast and odontoblast differentiation, as well as enamel and dentin matrix deposition. In addition, the results of this study may shed light on the role of the cervical and coronal portions of the EO as stem cell reservoirs. [ABSTRACT FROM AUTHOR]

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Dens invaginatus (DI) is a rare developmental defect in dentistry that results from invagination of the enamel organ into the dental papilla during tooth formation. However, such morphology presents cases that challenge treatment and diagnosis because of the morphology of the canal. The present study reports a case of DI in a 12-year-old boy showing a very unusual clinical and radiographic appearance of maxillary lateral incisors. The flowable composite was used to seal the invagination, and an etchant and a bonding agent were used as part of the preventative or prophylactic clinical therapy that was implemented in this instance. This offers a secure and efficient substitute therapy. This method has the potential to yield the greatest results for patients by combining expertise from endodontics and restorative dentistry., Competing Interests: Human subjects: Consent was obtained or waived by all participants in this study. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work., (Copyright © 2024, Patekar et al.)

The morphological and possible functional interactions between the connective tissue and enamel organ cells were examined during the maturation phase of enamel formation, using immunohistochemical techniques. Decalcified mandibular sections (10 µm) including incisors were used from Wistar rats ages 10–12 weeks. Sections were incubated with one or two primary antibodies targeting cell cytoskeleton (vimentin, α-actin, α-tubulin), dendritic marker (OX6), gap junctions (cx-43), enzymes (nitric-oxide synthase (nos1) and cyclooxygenase (cox1)), and the ion transporters (Na+/H+ exchanger (NHE1) and Na+/Ca2+ exchanger (NCX)) for 24 h, before incubation with the appropriate conjugated fluorescent secondary antibodies. Sections were examined by fluorescence microscopy. Haematoxylin–eosin slides were also employed. Cellular heterogeneity and morphological modulations were identified within enamel organ cells and connective tissue covering suggesting complex cellular interactions and indicating a new functional concept and possible complementary role during enamel maturation. Also, some ion transportation activity, and nos1 and cox1 signalling pathways have been identified, indicating intercellular communication between these regions. A hypothesis is suggested, to explain the morphological modulation of ameloblasts and papillary cells during enamel maturation which functions to increase the transporting membrane surface area to accomplish faster and bulker ion transportation to achieve controlled pH and to direct Ca2+ towards enamel. [ABSTRACT FROM AUTHOR]

Evidence has shown that miRNAs could play a role in dental fluorosis, but there is no study has investigated the global expression miRNA profiles of fluoride-exposed enamel organ. In this study, we analysed the differentially expressed (DE) miRNAs between fluoride-treated and control enamel organ for the first time and found several candidate miRNAs and signaling pathways worthy of further research. Thirty Wistar rats were randomly distributed into three groups and exposed to drinking water with different fluoride contents for 10 weeks and during the gestation. The three groups were a control group (distilled water), medium fluoride group (75 mg/L NaF), and high fluoride group (150 mg/L NaF). On the embryonic day 19.5, the mandible was dissected for histological analysis, and the enamel organ of the mandibular first molar tooth germ was collected for miRNA sequencing (miRNA-seq) and quantitative real-time PCR analysis (qRT-PCR). Typical dental fluorosis was observed in the incisors of the prepregnant rats. In addition to the disorganized structure of enamel organ cells, 39 DE miRNAs were identified in the fluoride groups compared with the control group, and good agreement between the miRNA-seq data and qRT-PCR data was found. The functional annotation of the target genes of 39 DE miRNAs showed significant enrichment in metabolic process, cell differentiation, calcium signaling pathway, and mitogen-activated protein kinase(MAPK) signaling pathway terms. This study provides a theoretical reference for an extensive understanding of the mechanism of fluorosis and potential valuable miRNAs as therapeutic targets in fluorosis.

Background/Objective: The present article is between the fewest that describe the expression of desmosomal proteins in human tooth organ and to implicate desmosome and its components in tooth morphogenesis. Although present in all epithelia, desmosomes are particularly down regulated in undifferentiated, dedifferentiated and malignant cells. Methodology: In the present article, using immunohistochemical staining, we report the expression patterns of 6 desmosomal components; Desmoplakin, plakoglobin, desmoglein, plakophilin-1, plakophilin-2, and plakophilin-3. The dental, oral and ectodermal epithelia were investigated in 7 and 9 weeks' human embryos. Results: The expression of these components appeared to associate with cell differentiation, stage of development and epithelial type. The fundamental desmosomal proteins, desmoplakin, plakoglobin and desmoglein, produced almost identical profiles, suggesting that desmosomes are absent or under developed in negative and weak reacting areas respectively. Whilst the accessory component plakophilin-1 was always absent, plakophilin-2 and -3 were strongly labeled in the embryonic epidermis and moderately expressed in the oral epithelium. In the developing enamel organ, gradients of fundamental protein expressions were produced being strong towards the oral epithelium and weak/negative around the inner enamel epithelium. These gradients were also produced using antibodies to plakophilin-2 and -3 although the majority of enamel organ cells were unlabeled. Conclusion: Mirror image symmetry was foundwas found for the distribution patterns of these markers. Furthermore, the left-right asymmetry was found both for the maxillary and mandibular tooth germs, thus bringing further evidence implicating desmosome and its components in the mechanisms regulating tooth morphogenesis.

We herein report that deletion of mTOR in dental epithelia caused defective development of multiple cell layers of the enamel organ, which culminated in tooth malformation and cystogenesis. Specifically, cells of the stellate reticulum and stratum intermedium were poorly formed, resulting in cystic changes. The pre-ameloblasts failed to elongate along the apical-basal axis and persisted vigorous expression of Sox2 and P63, which are normally downregulated during cytodifferentiation. Expression of amelogenic markers was also attenuated in mutants. Cell proliferation and cell sizes in mutants were significantly reduced over time. Importantly, we found reduced amounts and aberrant aggregations of cytoskeletal components in mutants, along with attenuated expression of cytoskeleton regulator Cdc42 , whose epithelial deletion causes a similar phenotype. Moreover, disruption of actin assembly in an organ culture system affected cell proliferation and cytodifferentiation of tooth germs, supporting a causative role of mTOR-regulated cytoskeleton dynamics for the observed phenotype of mTOR mutant mice. In further support of this view, we showed that mTOR overactivation caused increased cytoskeletal component synthesis and assembly, along with accelerated cytodifferentiation in the enamel organ. Finally, we demonstrated that mTOR regulated enamel organ development principally through the mTORC1 pathway. • mTOR deletion causes enamel organ defects and tooth malformation. • mTOR is required for cell adhesion, proliferation and differentiation in the enamel organ. • mTOR regulates cytoskeleton dynamics in the enamel organ. • mTOR regulates enamel organ development principally through mTORC1. [ABSTRACT FROM AUTHOR]

Amelogenin proteins are a major component of the developing enamel matrix, and are likely to have a key role in the control of enamel biomineralization. The heterogeneity of amelogenin is in part due to alternative splicing of the amelogenin RNA transcripts. Several patterns of alternative splicing have been described in mouse, bovine, porcine, and human enamel, with all alternatively spliced products having homologous 5' and 3' sequences within the coding regions. In these studies, we have used anchored PCR to identify alternatively spliced amelogenin cDNA sequences in the rat. We found amelogenin cDNAs that could be divided into two groups based on their 3' sequence. Group 1 cDNAs had a novel terminal sequence that has not been previously identified, while group 2 cDNAs were similar to those previously identified in other animal species. We identified a sequence, identical to the novel 3' amelogenin cDNA sequence, in rat genomic DNA downstream from the previously identified exon 7. The putative amelogenin proteins predicted for the two groups differed in their predicted isoelectric points, with the novel group 1 proteins having a more basic isoelectric point.

Цель; определить и сравнить концентрацию кальция и фосфора в интерстициальной жидкости тканей зачатка (пульпы, эмалевого органа) и фолликулярной жидкости по ходу центробежного перемещения. Материал и методы. Изучен состав интерстициальной жидкости пульпы, эмалевого органа и фолликулярной жидкости 23 зубных зачатков. Для биохимического анализа образцов использован ферментативно-фотоколориметрический метод на биохимическом полуавтоматическом анализаторе «Stat Fax 3300». Результаты. В интерстициальной жидкости пульпы концентрация кальция в 1,7 раза больше, чем в плазме, в 3 раза выше, чем в эмалевом органе, и в 7 раз больше, чем в фолликулярной жидкости. Средняя концентрация фосфора в пульпе в 10 раз выше, чем в плазме крови. Заключение. Выявлено весьма значимое различие концентраций остеотропных элементов в интерстициальных жидкостях изученных структур. Доказано, что концентрация кальция и фосфора убывает по ходу движения постулируемого потока жидкости от пульпы зачатка к перифолликулярному пространству. Повышение концентрации изученных элементов в интерстиции пульпы по сравнению с плазмой крови свидетельствует о способности пульпы концентрировать данные элементы и таким путем обеспечивать минерализацию обызвествленных тканей зуба и до его прорезывания.

Odontogenic ameloblast-associated (ODAM) belongs to the secretory calcium-binding phosphoprotein (SCPP) gene cluster. It is expressed by the epithelial ameloblasts during the accrued mineralisation of enamel and by cells of the junctional epithelium (JE), a specialised portion of the gingiva that plays a critical role in periodontal health. In both cases, ODAM localises at the interface between the cells and the tooth surface. It is also present among the cells of the JE, and is distinctively highly expressed in many epithelial tumours. ODAM has been proposed to be a matricellular protein implicated in the adhesion of epithelial cells to tooth surfaces, and possibly in mediating cell status. To gain further understanding of the role of ODAM, we have created an Odam knockout (KO) mouse by deleting coding exons 2-6. Inactivation of the gene was verified by Southern blot, PCR, real-time qPCR and loss of immunostaining for the protein. Young Odam KO mice showed no readily apparent phenotype. No significant differences were observed in enamel volume and density, rod-interrod organisation, and its attrition. However, in older animals, the JE presented some detachment, an increase in inflammatory infiltrate, and apical down-growth. In addition, its regeneration was delayed following a gingivectomy challenge. Our results indicate that inactivation of Odam expression has no dramatic consequence on enamel but the phenotype in older animals replicates some JE changes seen during human periodontal disease. Altogether, our results suggest that ODAM plays a role in maintaining integrity of the JE.

Statement of the Problem: Enamel organ (EO) is an ectodermal derived structure, which is involved in the different aspects of tooth development. Tooth development shares the same regulatory molecules and genes expressed in other developing organs. Endothelin- 1 (ET-1) and Endothelin A receptor (ETAR), (ET-1/ETAR) axis, are involved in differentiation of embryonic stem cells and organ development., Purpose: The present study aimed to investigate the ET-1 and ETAR expression profiles during the development of human primary tooth EO with the relatively large sample size., Materials and Method: In this experimental study, 33 human fetuses aged from 13 to 23 weeks (3 samples from each fetal age) were collected. The samples were divided into three age groups (<16 weeks, <19 weeks, ≥19 weeks) and cut for hematoxylin and eosin (H&E) and immunohistochemistry (IHC) staining. A two-way ANOVA test was conducted to examine the expression levels of ET-1 and ETAR in different layers of human primary tooth EO. The statistical significance was assumed at p ≤ 0.05., Results: There were statistically significant differences between the expression levels of ET-1/ETAR axis in the four-layered human primary tooth EO in different fetal ages (13-23 weeks). Besides, there were significant differences between the expression levels of ET-1/ETAR axis in all layers of human primary enamel organ and types of teeth., Conclusion: Due to the profile of expression of ET-1/ETAR axis, it can be concluded that this axis contributes to the differentiation of all human primary EO layers and secretion of enamel. ET-1/ETAR axis is one of the signaling molecules, which may have crucial roles in tooth development., Competing Interests: The authors declare that they have no conflicts of interests., (Copyright: © Journal of Dentistry.)

Objective: To analyse the immunohistochemical expression of ameloblastin in the bell stage of tooth germ and compare with ameloblastoma to determine the level of differentiation of tumour cells. Study design: This study included eleven human tooth germs with four in the early and seven in the late bell stage, and six selected archival tissue samples of ameloblastomas were studied using haematoxylin and eosin, Masson's trichrome and ameloblastin. Results: All eleven tooth germs reacted positively to ameloblastin with a characteristic inverted and sequential pattern of expression in the acellular zone of the dental papilla and enamel organ. Of the six cases of ameloblastoma, five cases showed a variable level of expression of ameloblastin in the tumour cells, whereas in one case, ameloblastin was negative in the tumour cells but positive in the stromal fibrous tissue collar. Conclusion: Expression of ameloblastin in human tooth germ is related to differentiation and mineralization, and it correlates with the state of differentiation of the tumour cells in ameloblastoma. [ABSTRACT FROM AUTHOR]

Background/Objective: The present article is between the fewest that describe the expression of desmosomal proteins in human tooth organ and to implicate desmosome and its components in tooth morphogenesis. Although present in all epithelia, desmosomes are particularly down regulated in undifferentiated, dedifferentiated and malignant cells. Methodology: In the present article, using immunohistochemical staining, we report the expression patterns of 6 desmosomal components; Desmoplakin, plakoglobin, desmoglein, plakophilin-1, plakophilin-2, and plakophilin-3. The dental, oral and ectodermal epithelia were investigated in 7 and 9 weeks' human embryos. Results: The expression of these components appeared to associate with cell differentiation, stage of development and epithelial type. The fundamental desmosomal proteins, desmoplakin, plakoglobin and desmoglein, produced almost identical profiles, suggesting that desmosomes are absent or under developed in negative and weak reacting areas respectively. Whilst the accessory component plakophilin-1 was always absent, plakophilin-2 and -3 were strongly labeled in the embryonic epidermis and moderately expressed in the oral epithelium. In the developing enamel organ, gradients of fundamental protein expressions were produced being strong towards the oral epithelium and weak/negative around the inner enamel epithelium. These gradients were also produced using antibodies to plakophilin-2 and -3 although the majority of enamel organ cells were unlabeled. Conclusion: Mirror image symmetry was foundwas found for the distribution patterns of these markers. Furthermore, the left-right asymmetry was found both for the maxillary and mandibular tooth germs, thus bringing further evidence implicating desmosome and its components in the mechanisms regulating tooth morphogenesis. [ABSTRACT FROM AUTHOR]

Summary The continuity of epithelial tissue is collapsed by tooth eruption. The junctional epithelium (JE) is attached to the tooth surface by hemidesmosomes, which constitutes the front-line defense against periodontal bacterial infection. JE constitutively expresses intercellular adhesion molecule-1 (ICAM-1), and neutrophils and lymphocytes penetrate into JE via interaction between ICAM-1 and LFA-1 expressed on the surface of these migrating cells. JE also expresses cytokines and chemokines. These functions of JE are maintained even in germ-free condition. Therefore, the constitutive expression of adhesion molecules, cytokines, and chemokines might be used not only for anti-pathogenic defense but also for maintaining the physiological homeostasis of JE. In this review, we have mainly focused on the structural and functional features of JE, and discussed the function of intraepithelial lymphocytes in JE as a front-line anti-microbial defense barrier and regulator of JE hemostasis. [ABSTRACT FROM AUTHOR]

The Hey family (also known as Chf, Herp, Hesr, and Hrt) is a set of Hairy/Enhancer of Split-related basic helix-loop-helix type transcription factors. Hey1 , Hey2 , and HeyL have been identified in mammals. Although Hey proteins are known to regulate cardiovascular development, muscle homeostasis, osteogenesis, neurogenesis, and oncogenesis, their roles in tooth development have been largely obscure. Therefore, this study aimed to clarify detailed spatiotemporal expression patterns of Hey1 and Hey2 in developing molars and incisors of mice by section in situ hybridization. Hey1 and Hey2 were not significantly expressed in tooth germs at epithelial thickening, bud, and cap stages during molar development. In the dental epithelium in molars at the bell stage and incisors, Hey2 transcripts were restricted to the undifferentiated inner enamel epithelium and down-regulated in preameloblasts and ameloblasts. On the other hand, Hey1 was mainly expressed in preameloblasts and down-regulated in differentiated ameloblasts. Both genes were not significantly expressed in other dental epithelial tissues, including the outer enamel epithelium, stellate reticulum, and stratum intermedium cells. In the dental mesenchyme, Hey1 was intensely transcribed in the subodontoblastic layer of the dental pulp in both molars and incisors, whereas Hey2 was barely detectable in mesenchymal components. Our data implied that Hey2 function is restricted to transient amplifying cells of the ameloblast cell lineage and that Hey1 plays a role in the composition of the subodontoblastic layer, in addition to ameloblast differentiation. These findings provide novel clues for the better understanding of tooth development. [ABSTRACT FROM AUTHOR]

Objectives Nectins are immunoglobulin-like cell–cell adhesion molecules and are of four types, namely, nectin-1, nectin-2, nectin-3, and nectin-4. Cleft lip/palate-ectodermal dysplasia is caused by a mutation in the nectin-1 gene locus. However, nectin-1-deficient (KO) mice only show mild tooth defects. This study determined the intracellular localization of nectins in mouse mandibular incisors to identify their heterophilic interactions during amelogenesis. Methods Nectin localization was determined by performing immunohistochemical analysis with confocal microscopy. Nectin gene expression was determined by performing quantitative reverse transcription-PCR. Phenotypes of nectin-2 - KO mice were examined by performing micro-computed tomography, histological analysis, and organ culture. Results We found that mRNA levels of nectin-1 and nectin-3 genes were higher than those of nectin-2 and nectin-4 genes in mouse enamel organs. Nectin-2 and nectin-4 were strongly expressed at the apical adherens junctions of secretory-stage ameloblasts, whereas nectin-1 and nectin-3 were distributed between the basal adherens junction of maturation-stage ameloblasts and the stratum intermedium and papillary layers. Nectin-2-KO mice showed normal mandibular tooth shape, incisor surface pigmentation, and histology. Moreover, organ cultures of the tooth organs of nectin-2-KO mice proceeded normally. Conclusion These results indicate that nectins show graded and overlapping distribution in mouse incisors. [ABSTRACT FROM AUTHOR]

Nonmammalian vertebrates have the capacity of lifelong tooth replacement. In all vertebrates, tooth formation requires contact and interaction between the oral or pharyngeal epithelium and the underlying mesenchyme. To secure lifelong replacement, the presence of odontogenic stem cells has been postulated, particularly in the epithelial compartment. This study uses an advanced teleost fish species, the marine medaka Oryzias melastigma, a close relative to Oryzias latipes, to examine the expression and distribution of telomerase reverse transcriptase (Tert), the catalytic unit of telomerase, in developing pharyngeal teeth and to relate these data to the proliferative activity of the cells. The data are complemented by expression analysis of the pluripotency marker oct4 and bona fide stem cell marker lgr5. Tert distribution and tert expression in developing tooth germs show a dynamic spatiotemporal pattern. Tert is present first in the mesenchyme but is downregulated as the odontoblasts differentiate. In contrast, in the epithelial enamel organ, Tert is absent during early stages of tooth formation and upregulated first in ameloblasts. Later, Tert is expressed and immunolocalized throughout the entire inner enamel epithelium. The pattern of Tert distribution is largely mutually exclusive with that of proliferating cell nuclear antigen (PCNA) immunoreactivity: highly proliferative cells, as revealed by PCNA staining, are negative for Tert; conversely, PCNA-negative cells are Tert-positive. Only the early condensed mesenchyme is both Tert- and PCNA-positive. The absence of tert-positive cells in the epithelial compartment of early tooth germs is underscored by the absence of oct4- and lgr5-positive cells, suggesting ways other than stem cell involvement to secure continuous renewal. [ABSTRACT FROM AUTHOR]

PURPOSE: Previous studies have evaluated the presence of serotonin in the dental epithelia and mesenchyme during odontogenesis, suggesting its participation in tooth development. MATERIALS AND METHODS: Here, we used fluoxetine, a selective serotonin re-uptake inhibitor, at a dose of 10 mg/kg, administered for 20 days during pregnancy in 12 Wistar rats to examine the influence of this drug on the development of the enamel organ of the upper first molars of rat fetuses at 17 days of intra-uterine life (i.u.l.), and at one, five and ten days postpartum. The pregnant rats were anesthetized with xylazine at 10 mg/kg and ketamine at 25 mg/kg. The fetuses were removed and beheaded; their jaws were removed, and the upper jaws were exposed. The tissues were fixed in Bouin's fixative, decalcified in 5% nitric acid for 4 - 12 h, conventionally processed for microscopy, and embedded in paraffin. Serial sections of approximately 5 mm were obtained and stained with hematoxylin and eosin, as well as periodic acid-Schiff. RESULTS AND CONCLUSION: Morphological analysis showed no structural changes in the experimental group compared to the controls, suggesting that, at the dose used, fluoxetine does not interfere with serotonin-mediated development of the enamel organ or the process of amelogenesis.