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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 .
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.
These tissues are enveloped by a basal layer of epithelium known on the outside of the tooth as outer enamel epithelium and on the inside as inner enamel epithelium. During root formation the inner layers of epithelium disappear and only the basal layers are left creating Hertwig's epithelial root sheath (HERS). At this point it is usually ...
Acellular cementum forms first. The cementoblasts differentiate from follicular cells, which can only reach the surface of the tooth's root once Hertwig's Epithelial Root Sheath (HERS) has begun to deteriorate. The cementoblasts secrete fine collagen fibrils along the root surface at right angles before migrating away from the tooth.
In dentistry, the epithelial cell rests of Malassez (ERM) or epithelial rests of Malassez (pax epithelialis pediodontii) are part of the periodontal ligament cells around a tooth. They are discrete clusters of residual cells from Hertwig's epithelial root sheath (HERS) that didn't completely disappear.
For cementogenesis to begin, Hertwig epithelial root sheath (HERS) must fragment. HERS is a collar of epithelial cells derived from the apical prolongation of the enamel organ. Once the root sheath disintegrates, the newly formed surface of root dentin comes into contact with the undifferentiated cells of the dental sac (dental follicle).
The most widely accepted theory suggests enamel pearls are formed from remnants of Hertwig’s epithelial root sheath (HERS), which adhere to the tooth surface after root development. [1] During normal tooth development, after dentin formation is initiated on the root surface, the root sheath disintegrates and moves away from the root allowing ...
The mechanism of differentiation of the cementoblasts is controversial but circumstantial evidence suggests that an epithelium or epithelial component may cause dental sac cells to differentiate into cementoblasts, characterised by an increase in length. [1] Other theories involve Hertwig epithelial root sheath (HERS) being involved. [2]