The enamel organ, also known as the dental organ, is a cellular aggregation seen in a developing tooth and it lies above the dental papilla. The enamel organ which is differentiated from the primitive oral epithelium lining the stomodeum. The enamel organ is responsible for the formation of enamel, initiation of dentine formation, establishment of the shape of a tooth's crown, and establishment of the dentoenamel junction.
The enamel organ has four layers; the inner enamel epithelium, outer enamel epithelium, stratum intermedium, and the stellate reticulum.
The dental papilla, the differentiated ectomesenchyme deep to the enamel organ, will produce dentin and the dental pulp. The surrounding ectomesenchyme tissue, the dental follicle, is the primitive cementum, periodontal ligament and alveolar bone beneath the tooth root. The site where the internal enamel epithelium and external enamel epithelium coalesce is the cervical root, important in proliferation of the dental root.
Tooth development
Tooth development begins at week 6 in utero, in the oral epithelium. The process is divided into three stages:
Initiation
Morphogenesis and
Histogenesis
At the end of week 7 i.u., localised proliferations of cells in the dental laminae form round and oval swellings known as tooth buds, which will eventually develop into mesenchymal cells and surround the enamel organ. Each epithelial swelling and the surrounding mesenchymal cells form a tooth germ.
Tooth germs are the primitive structure of teeth; their formation is in three distinct stages: bud stage, cap stage, bell stage.
The stages are based on the degree of development of enamel organ. Oral epithelium forms the tooth enamel while the ectomesenchyme forms the pulp and dentine of the tooth. The ectomesenchyme lies deep to the oral epithelium.
Bud Stage
This is the initial stage of tooth development, which occurs at week 8 i.u.. Proliferation of dental lamina occurs, forming small tooth buds which are spherical or ovoid condensations of epithelial cells, now known as the enamel organ. The enamel organ consists of peripherally located, low columnar cells and centrally located polygonal cells. The enamel organ is also surrounded by proliferating mesenchymal cells, which results in the condensation of two distinct areas:
The dental papilla: below the enamel organ
The tooth sac: ectomesenchymal condensation of the area surrounding the tooth bud and dental papilla.
Both the dental papilla and the tooth sac are not structurally defined in the bud stage, and will become more defined in subsequent stages (Cap and Bell stages). The interaction and signalling between the enamel organ and the surrounding mesenchymal cells play an important role in the later stages of tooth development. Each dental arch will have 10 tooth buds, accounting for 20 primary teeth.
Cap Stage
The cap stage occurs in week 9-10 i.u. Unequal proliferation of cells during this stage, invaginating into the ectomesenchyme tissue, leads to the formation of the cap-shaped enamel organ. The ectomesenchyme tissue also invaginates superficially to shape the primitive dental pulp. Differentiation of cells occurs at this stage to make different tissue layers; external enamel epithelium, stratum intermedium, stellate reticulum, internal enamel epithelium, dental papilla, and dental follicle. The external enamel epithelium, a layer of simple cuboidal epithelium, has a protective role during tooth development. The stellate reticulum, the innermost layer of the enamel organ, gathers GAGs between cells. The internal enamel epithelium will form enamel during the Bell Stage
Early Bell stage
There is uneven growth of enamel organ in this phase, and the epithelial cap deepens. The cap shape of the enamel organ assumes a bell shape as the undersurface of the cap deepens. Foldings of the internal enamel epithelium (done by the growing papilla cells) maps out the occlusal pattern of the tooth crown. The process is known as morphodifferentiation. The pressure exerted by the dental papilla cells has been shown to be opposed equally by the pressure from the fluid in the stellate reticulum (present in the enamel organ).
The folding of the enamel organ is caused by different rates of mitosis and difference in cell differentiation times, causing different crown shapes in each tooth.