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The dentinoenamel junction or dentin-enamel junction (DEJ) [1] is the boundary between the enamel and the underlying dentin that form the solid architecture of a tooth. It is also known as the amelo - dentinal junction, [ 2 ] or ADJ.
Tooth development begins at week 6 in utero, in the oral epithelium. The process is divided into three stages: Initiation; Morphogenesis and; Histogenesis [2]; 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.
The Hertwig epithelial root sheath (HERS) or epithelial root sheath is a proliferation of epithelial cells located at the cervical loop of the enamel organ in a developing tooth. Hertwig epithelial root sheath initiates the formation of dentin in the root of a tooth by causing the differentiation of odontoblasts from the dental papilla.
Dentin has microscopic channels, called dentinal tubules, which radiate outward through the dentin from the pulp cavity to the exterior cementum or enamel border. [17] The diameter of these tubules range from 2.5 μm near the pulp, to 1.2 μm in the midportion, and 900 nm near the dentino-enamel junction. [ 18 ]
Cross-section of a tooth. B is dentin. Dentin (/ ˈ d ɛ n t ɪ n / DEN-tin) (American English) or dentine (/ ˈ d ɛ n ˌ t iː n / DEN-teen or / ˌ d ɛ n ˈ t iː n / DEN-TEEN) (British English) (Latin: substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth.
Dentin, less mineralized and less brittle, 3–4 in hardness, compensates for enamel and is necessary as a support. [7] On radiographs, the differences in the mineralization of different portions of the tooth and surrounding periodontium can be noted; enamel appears lighter than dentin or pulp since it is denser than both and more radiopaque. [8]
Enamel tufts do not normally lead to enamel failure, due to these defects stabilizing potential fractures. The processes involved include the creation of stress shielding by increasing the compliance of enamel next to the dentin. [8] Decussation is another factor by which cracks form wavy stepwise extensions that arrest their further development.
Coronal cementum - where the enamel overlaps the cement. Abutment - It is also known as vis a vis relation, where the cement and enamel meet at the butt joint, occurring in 30% of sections, and the least common, occurring in 10% of sections. Gap between cementum and enamel exposing the dentin. [5]