Hertwig's epithelial root sheath

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

WikiDoc Resources for Hertwig's epithelial root sheath
Articles
Most recent articles on Hertwig's epithelial root sheath Most cited articles on Hertwig's epithelial root sheath Review articles on Hertwig's epithelial root sheath Articles on Hertwig's epithelial root sheath in N Eng J Med, Lancet, BMJ
Media
Powerpoint slides on Hertwig's epithelial root sheath Images of Hertwig's epithelial root sheath Photos of Hertwig's epithelial root sheath Podcasts & MP3s on Hertwig's epithelial root sheath Videos on Hertwig's epithelial root sheath
Evidence Based Medicine
Cochrane Collaboration on Hertwig's epithelial root sheath Bandolier on Hertwig's epithelial root sheath TRIP on Hertwig's epithelial root sheath
Clinical Trials
Ongoing Trials on Hertwig's epithelial root sheath at Clinical Trials.gov Trial results on Hertwig's epithelial root sheath Clinical Trials on Hertwig's epithelial root sheath at Google
Guidelines / Policies / Govt
US National Guidelines Clearinghouse on Hertwig's epithelial root sheath NICE Guidance on Hertwig's epithelial root sheath NHS PRODIGY Guidance FDA on Hertwig's epithelial root sheath CDC on Hertwig's epithelial root sheath
Books
Books on Hertwig's epithelial root sheath
News
Hertwig's epithelial root sheath in the news Be alerted to news on Hertwig's epithelial root sheath News trends on Hertwig's epithelial root sheath
Commentary
Blogs on Hertwig's epithelial root sheath
Definitions
Definitions of Hertwig's epithelial root sheath
Patient Resources / Community
Patient resources on Hertwig's epithelial root sheath Discussion groups on Hertwig's epithelial root sheath Patient Handouts on Hertwig's epithelial root sheath Directions to Hospitals Treating Hertwig's epithelial root sheath Risk calculators and risk factors for Hertwig's epithelial root sheath
Healthcare Provider Resources
Symptoms of Hertwig's epithelial root sheath Causes & Risk Factors for Hertwig's epithelial root sheath Diagnostic studies for Hertwig's epithelial root sheath Treatment of Hertwig's epithelial root sheath
Continuing Medical Education (CME)
CME Programs on Hertwig's epithelial root sheath
International
Hertwig's epithelial root sheath en Espanol Hertwig's epithelial root sheath en Francais
Business
Hertwig's epithelial root sheath in the Marketplace Patents on Hertwig's epithelial root sheath
Experimental / Informatics
List of terms related to Hertwig's epithelial root sheath

(1) The HERS, (2) ERM, (3) Dental follicle, (4) cementoblasts, (5) periodontal ligament, (6) alveolar cells, (7) bone, (8) odontoblasts.

Overview

The Hertwig's epithelial root sheath (frequently abbreviated as "HERS") is a proliferation of epithelial cells located at the cervical loop of the enamel organ in a developing tooth. Hertwig's epithelial root sheath initates the formation of dentin in the root of a tooth by causing the differentiation of odontoblasts from the dental papilla. The root sheath eventually disintegrates, but residual pieces that do not completely disappear are seen as epithelial cell rests of Malassez (ERM).

Evolution of HERS

Hertwig's epithelial root sheath was not discovered in any mammalian species. Instead this epithelial structure was discovered by Oskar Hertwig in 1874 in an amphibian. While in mammalian the HERS is rather a transient structure in amphibians it is more or less a permanent one. Here the root epithelium does not fenestrate like in mammalians. Within vertebrates 3 distinct stages of HERS development can be observed.

1. In teleosts and chondrichthyans no HERS or root is really formed, and tooth development is restricted to crown development. An inflexible joint is formed between the tooth and the bone at the apical end of the tooth where the epithelium remains open.
2. In amphibians and non-crocodilian reptiles a continuous root sheath or HERS is formed without fragmentation of the epithelium. Once again a rather rigid connection between bone and tooth is formed at the apical end of the tooth where no epithelium is present.
3. In crocodilians and mammals the HERS is a transient structure and fragments to form the epithelial cell rests of Malassez. Through the gaps in the root epithelium elements of the periodontal ligament can migrate and form a flexible connection between bone and root.

References

• Ten Cate, A.R. Oral Histology: development, structure, and function. 5th ed. 1998. ISBN 0-8151-2952-1.
• Hertwig, O. (1847) Über das zahnsystem der amphibien und seine bedeutung für die genese des skelets der mundhöhle. Arch. Mikrosk. Anat. EntwMech. 11 (suppl): 55-56
• Luan, X., Ito, Y. and Diekwish, T.G.H. (2006) Evolution and development of Hertwig's Epithelial Root Sheath. Dev. Dyn. 235: 1167-1180.
• Thomas, H.F. (1995) Root formation. Int. J. Dev. Biol. 39: 231-237