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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.
The cervical loop is the location on an enamel organ in a developing tooth where the outer enamel epithelium and the inner enamel epithelium join. The cervical loop is a histologic term indicating a specific epithelial structure at the apical side of the tooth germ, consisting of loosely aggregated stellate reticulum in the center surrounded by ...
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.
The growth of cervical loop cells into the deeper tissues forms Hertwig's Epithelial Root Sheath, which determines a tooth's root shape. The dental papilla contains cells that develop into odontoblasts, which are dentin-forming cells. [27]
In the tooth bud, regions where enamel formation is completed, the enamel organ gives rise to Hertwig's epithelial root sheath, composed of two epithelial layers derived from the external and internal epithelia. The sheath is irregularly fragmented in time and space as it promotes cementum deposition on the newly formed dentin.
The bell stage is the fourth stage of tooth development which occurs between the eleventh and twelfth week of prenatal development.During this stage of odontogenesis, the epithelial tooth germ forms a bell-shaped structure in the labio-lingual section and is characterised by the formation of the dental sac.
Other theories involve Hertwig epithelial root sheath (HERS) being involved. [2] Martha Somerman and her laboratory played a key role in identifying and characterizing cementoblasts, the cells responsible for forming cementum, a vital mineralized tissue covering tooth roots. [3] [4]