Odontogenic Epithelium and its Residues
Roger M. Browne in Investigative Pathology of the Odontogenic Cysts, 2019
Progression from the bud to cap stage leads to differentiation of four regions in the enamel organ; (a) inner enamel epithelium: low columnar cells; (b) outer enamel epithelium: low cuboidal cells; (c) stratum intermedium: squamous shaped cells; (d) stellate reticulum: stellate shaped cells. The inner and outer enamel epithelium are continuous at the cervical loop and are derived from the basal cells of the tooth bud. This histogenesis appears to be controlled by epithelial-mesenchymal interactions since it has been shown that outer enamel epithelium can acquire the histogenic specificity of an inner enamel epithelium when cultured in heterotopic association with dental papilla.22 In such an association, a new stratum intermedium was observed in contact with the newly differentiated inner enamel epithelium reinforcing the concept of the interdependence of these two cell layers upon one another. It has been postulated that the epithelial-mesenchymal interactions involved in these histogenic modifications are matrix mediated through the dental basement membrane, which controls the cell kinetic changes and histogenesis.22,23 The extent to which tooth histogenic properties can be conserved by isolated cells is still in question.24,26
ExperimentaL Oral Medicine
Samuel Dreizen, Barnet M. Levy in Handbook of Experimental Stomatology, 2020
At doses of 1000 to 2000 R, the changes were localized to the labial part of the odontogenic zone consisting of transient edema and permanent injury to the zonal odontoblasts that caused dentinal hypoplasia and produced dentinal niches. After degeneration of the odontoblasts, osteodentin was formed in the adjacent area of the pulp. Slight inhibition of pulpal growth led to waviness of the dentinoenamel junction. Slight injury to the ameloblasts caused shallow enamel hypoplasia. At doses of 3000 to 4000 R, destructive changes were followed by regeneration. Destruction was manifested by severe pulpal and periodontal edema, which led to formation of cystic cavities that destroyed the odontoblasts and prevented formation of new ameloblasts. Great masses of osteodentin formed in the pulp. With stoppage of pulpal growth and eruption, there was progressive maturation of the entire enamel matrix and reversion of the enamel organ into reduced epithelium. Regeneration was dependent on the amount of enamel destruction caused by the expanding cyst cavities. Only if viable remnants of odontogenic epithelium persisted to the time of organization of the cysts did epithelial proliferation initiate formation of a new incisor.
The Cell Biology of Amelogenesis
Colin Robinson, Jennifer Kirkham, Roger Shore in Dental Enamel, 2017
The maturation-stage enamel organ is characterized by three major structural features: the vasculature, papillary cells, and maturation-stage ameloblasts (Figure 15). The vasculature can be further subdivided into fenestrated and nonfenestrated capillaries having one of two vascular patterns. Papillary cells have been classified into two groups: those abutting ameloblasts and distal cells surrounded by other papillary cells.154 Maturation-stage ameloblast modulate between two apical membrane configurations and several lateral membrane modifications.
Dental stem cells in tooth regeneration and repair in the future
Published in Expert Opinion on Biological Therapy, 2018
Christian Morsczeck, Torsten E. Reichert
These tissues have specific functions for tooth development [11,14]. The human enamel organ, for example, contains dental epithelial stem cells [17]. These epithelial stem cells are precursor cells for ameloblasts which produce the enamel of the tooth crown. Unfortunately, the human enamel organ with all dental epithelial stem cells is lost after tooth eruption. So, unfortunately, the genuine progenitor cells for ameloblasts are not available, for example, for the (re-)generation of the dental enamel and for whole tooth engineering. Whole tooth engineering has been already achieved in mice with early tooth germ cells from the dental epithelium and the dental mesoderm [5]. Interestingly, recently, Xu et al. isolated undifferentiated dental epithelial cells from the human dental follicle of impacted third molar tooth, but in very small amounts [18]. However, further investigations are required to characterize human dental epithelial stem cells from the dental follicle or from the Hertwig’s epithelial rest of Malassez, which are epithelial cells of the mature periodontal ligament (PDL) [19].
Preclinical characterization of bemarituzumab, an anti-FGFR2b antibody for the treatment of cancer
Published in mAbs, 2021
Hong Xiang, Abigael G. Chan, Ago Ahene, David I. Bellovin, Rong Deng, Amy W. Hsu, Ursula Jeffry, Servando Palencia, Janine Powers, James Zanghi, Helen Collins
Bemarituzumab administered to rats resulted in treatment-related findings at all dose levels with a clear dose relationship: most of the effects were more pronounced for animals given doses of 5 mg/kg and 100 mg/kg. The most prominent findings were incisor abnormalities (missing incisors, malocclusion, and discolored white teeth) that were accompanied by body weight loss and lack of weight gain caused by the decreased food intake due to the incisor deformation. Histopathologically, dysgenesis of the incisor was observed and the oral tissue demonstrated increases of ulceration and inflammatory cell infiltrates, most likely caused by the teeth malformation. Dysgenesis of the upper incisor teeth were characterized by primary and secondary changes. Primary changes included the complete loss of the enamel organ (replacement of the enamel organ by a thick zone of dense connective tissue resembling periodontal membrane) and disorganization of the pulp cavity and associated odontoblast and dentin layers. Primary changes were regularly accompanied by changes interpreted to be secondary to incisor malformation. These included remodeling of the tooth alveolus, increased thickness of the periosteum, scalloping of bone at the alveolar margin, formation of new woven bone at the alveolar margin, and the extension of new bone into the alveolar space and/or malformed tooth. The changes in teeth were consistent with the observation that FGFR2b signaling controls regeneration of rodent incisors, which is a rodent-specific phenomenon.18–20
Dental stem cells for tooth regeneration: how far have we come and where next?
Published in Expert Opinion on Biological Therapy, 2023
At the beginning of tooth development in the first (mandibular) arch of an embryo the tooth germ consists of two tissues: the dental mesoderm, which originates from neural crest cells, and the dental ectoderm, which is part of the surface ectoderm [3,4]. These two types of cells are the origin of the tooth germ and make up the entire tooth [5]. However, during development these two dental cell types become three tissues, one derived from the ectoderm – enamel organ – and two from the mesoderm – dental papilla and dental follicle (dental sac) [6,7]. While the enamel organ is the source of ameloblasts and is heavily involved in tooth crown morphology, some dental epithelial cells become Hertwig’s epithelial root sheath cells involved in tooth root development [8]. The dental mesodermal tissues deliver stem cells for the development of the tooth root and the dental pulp/dentin complex [9]. Interestingly, both dental mesodermal tissues can be harvested from impacted wisdom teeth and their stem cells isolated and used for different applications [10]. In contrast, the enamel organ and most dental ectodermal cells are lost beforehand. Only epithelial rests of Malassez can be obtained for example from impacted wisdom teeth, but a significant number of dental ectodermal progenitor cells cannot be isolated from this source [11,12]. Moreover, these cells are not the genuine progenitors for ameloblasts and it remains nuclear whether they can be used as ectodermal tooth germ cells in whole tooth regeneration approaches, which is the most advanced goal in regenerative dentistry. This article first summarizes the state of the art in tooth engineering.
Related Knowledge Centers
- Dental Lamina
- Dental Papilla
- Dentin
- Tooth Development
- Crown
- Inner Enamel Epithelium
- Outer Enamel Epithelium
- Stratum Intermedium
- Stellate Reticulum
- Pulp