The cervical loop is the location on an

enamel organ 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 enam ...

in a developing

tooth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

where the

outer enamel epithelium The outer enamel epithelium, also known as the external enamel epithelium, is a layer of cuboidal cells located on the periphery of the enamel organ in a developing tooth. This layer is first seen during the bell stage. The rim of the enamel org ...

and the

inner enamel epithelium The inner enamel epithelium, also known as the internal enamel epithelium, is a layer of columnar cells located on the rim nearest the dental papilla of the enamel organ in a developing tooth. This layer is first seen during the cap stage, in wh ...

join. The cervical loop is a

histologic Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vis ...

term indicating a specific epithelial structure at the apical side of the tooth germ, consisting of loosely aggregated

stellate reticulum The stellate reticulum is a group of cells located in the center of the enamel organ of a developing tooth. These cells are star-shaped and synthesize glycosaminoglycans. As glycosaminoglycans are produced, water Water (chemical formula ...

in the center surrounded by

stratum intermedium The stratum intermedium in a developing tooth is a layer of two or three cells between the inner enamel epithelium and the newly forming cells of the stellate reticulum. It first appears during the early bell stage of tooth development, at aroun ...

. These tissues are enveloped by a basal layer of epithelium known on the outside of the tooth as

and on the inside as

. During root formation the inner layers of epithelium disappear and only the basal layers are left creating

Hertwig's epithelial root sheath 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 ...

(HERS). At this point it is usually referred to as HERS instead of the cervical loop to indicate the structural difference.

Cervical loop as epithelial stem cell niche

It is thought that the central epithelial tissue of the cervical loop, the

, acts as a

stem cell In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type o ...

reservoir. In continuously growing teeth such as the rodent incisor the original structure of the cervical loop is maintained and no HERS forms. The stem cells provide the epithelial progeny to sustain the continuous growth.

References

*Cate, A.R. Ten. Oral Histology: development, structure, and function. 5th ed. 1998. . *Ross, Michael H., Gordon I. Kaye, and Wojciech Pawlina. Histology: a text and atlas. 4th edition. 2003. . *Harada, H., Kettunen, P., Jung, H. S., Mustonen, T., Wang, Y. A., and Thesleff, I. (1999) Localization of putative stem cells in dental epithelium and their association with Notch and FGF signaling. J. Cell Biol. 147: 105-120 {{Tooth development Tooth development