| Epithelial root sheath | |
|---|---|
 (1) The HERS, (2) ERM, (3) Dental follicle, (4) cementoblasts, (5) periodontal ligament, (6) alveolar cells, (7) bone, (8) odontoblasts. | |
| Details | |
| Identifiers | |
| Latin | vagina epithelialis radicis |
| TE | root sheath_by_E5.4.1.1.2.3.26 E5.4.1.1.2.3.26 |
| Anatomical terminology | |
TheHertwig epithelial root sheath (HERS) orepithelial root sheath is a proliferation ofepithelialcells located at thecervical loop of theenamel organ in adeveloping tooth. Hertwig epithelial root sheath initiates the formation ofdentin in the root of atooth by causing thedifferentiation ofodontoblasts from thedental papilla. The root sheath eventually disintegrates with the periodontal ligament, but residual pieces that do not completely disappear are seen asepithelial cell rests of Malassez (ERM).[1] These rests can become cystic, presenting future periodontal infections.[2]
Hertwig epithelial root sheath is derived from the inner and outer enamel epithelium of the enamel organ.[2]
The sheath is also responsible for multiple or accessory roots (medial growth) and lateral or accessory canals in the root (break in epithelium).[3] It is controversial, but HERS may be involved incementogenesis and the secreting of cementum, or that HERS-derived products might be related to enamel-related molecules, and that these proteins might initiate acellularcementum formation.[4]
While in mammals the HERS is rather a transient structure, in amphibians it is more or less a permanent one. Here the root epithelium does notfenestrate like in mammalians. Within vertebrates 3 distinct stages of HERS development can be observed.
Hertwig epithelial root sheath was not discovered in any mammalian species. Instead this epithelial structure was discovered byOskar Hertwig in 1874 in an amphibian (see notes below for further discussion in other animals).[4]