Enamel
Enamelum
Enamel is the hardest substance in the body. It is an acellular, about 96% mineral coat of hydroxyapatite covering the crown of each tooth.
Overview
Enamel is about 96% inorganic by weight, as hydroxyapatite crystals. The rest is a little organic matrix (enamelins and residual amelogenins) and water. The crystals are packed into enamel rods (prisms) that run from the dentinoenamel junction to the surface. Enamel is thickest over the cusps, about 2–2.5 mm, and thins to a knife edge at the cemento-enamel junction. Incremental growth lines (striae of Retzius) record its rhythmic formation.
Ameloblasts of ectodermal origin secrete enamel and are lost when the tooth erupts. Mature enamel therefore has no cells, vessels or nerves and cannot regenerate. It can only demineralise and remineralise at its surface. Fluoride replaces hydroxyl groups to form fluorapatite, which is more resistant to acid.
- Location
Outer covering of the anatomical crown.
Anatomy
- Histology
Rod (prismatic) and inter-rod enamel. Ground sections are needed to study it, because enamel dissolves in routine decalcified sections.
Function
- Wear-resistant cutting and grinding surface.
- Protects the underlying dentin and pulp from thermal, chemical and mechanical injury.
Clinical significance
Caries, erosion and fluorosis
Acid demineralisation from plaque produces caries. Acid erosion comes from GERD, bulimia and acidic drinks. Excess fluoride during development causes mottled fluorosis. Amelogenesis imperfecta is an inherited defect of enamel formation.
Compiled from standard anatomy and physiology references — see the Digestive System sources. For education only; not medical advice.