B. Microscopic features
3. Development of the dentogingival junction:
a. Early stages
In order to understand how the dentogingival junction comes into existence, it is necessary to review some aspects of tooth development and eruption.
Fig. 37 (From unknown source): During the bell stage of tooth development, the developing tooth consists of an ectodermal component, the enamel organ, derived from the oral ectoderm, that surrounds an ectomesenchymal component, the dental papilla (DP). (Source of image unknown). Within the bell-shaped ectodermal structure several distinct layers are visible. The innermost layer, or inner enamel epithelium (IEE) is in intimate contact with the dental papilla. Next to it is the stratum intermedium (SI) consisting of 2-4 layers of undifferentiated epithelial cells. The bulk of the cells are part of the stellate reticulum (SR), a network of star-shaped epithelial cells. The outermost layer consists of a single layer of cells, the outer enamel epithelium (OEE). The cells of the dental papilla in contact with the inner enamel epithelium differentiate into odontoblasts (OB) that proceed to form predentin (PD) and dentin (D). The inner enamel epithelium cells, in contact with the first-formed dentin, differentiate into pre-ameloblasts and then into ameloblasts that produce enamel on top of the already formed dentin. DL, dental lamina.
Fig. 38 represents a section taken from the bell-stage of tooth development. The dental papilla (DP) is on the left. Its outermost cell layer is composed of columnar odontoblasts (OB) that have already secreted some dentin (D) from which they are separated by a thin clear layer of predentin (PD). A thin layer of enamel (E) can be seen on the outer dentin surface. It is secreted by a layer of columnar ameloblasts (AB) in the secretory stage. Undifferentiated epithelial cells form the stratum intermedium (SI), directly adjacent to the ameloblasts. Shortly after the onset of amelogenesis, the stellate reticulum (SR) shrinks considerably so that the outer enamel epithelium (OEE) comes into close contact with the stratum intermedium cells (top of Fig. 38). The collapse of the enamel organ results in the formation of the reduced enamel epithelium. The ectomesenchymal tissue that surrounds the enamel organ forms the dental follicle (DF).\
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Created: May 8, 1999 Revised:
Max A. Listgarten: Comments to author: email@example.com
(Technical Support: Center for Dental Informatics: Heiko Spallek)