🪴 GoDeep
Search
← University Challenge
Portrait of Enamel

Anatomy · Head, neck & teeth

Enamel

The hardest tissue in the body

Tooth · outer covering of the crown

The glassy, semi-translucent outer layer of the crown of a tooth, and the hardest and most highly mineralised substance in the human body. About 96 per cent of it is mineral, mainly hydroxyapatite, laid down as tightly packed rods. It is formed by cells that disappear when the tooth erupts, so once lost it can never be regrown.

How to spot them

  • ▸The white, shiny covering of the visible crown, thickest at the biting surface and thinning to nothing at the neck
  • ▸About 96 per cent mineral by weight, mainly hydroxyapatite
  • ▸Contains no living cells, blood vessels or nerves
  • ▸Sits on the dentine, at a boundary called the enamel-dentine junction

What to know

The hardest substance in the human body, about 96 per cent mineral

Tooth enamel — carbonated hydroxyapatite

Made by cells called ameloblasts that are lost when the tooth breaks through the gum, so it cannot repair itself

Enamel is acellular and cannot regenerate once formed

Densely packed rods about five micrometres wide that run out from the underlying layer to the surface

Enamel rods (prisms)

Growth lines in its cross-section named after a Swedish anatomist, as it is laid down in daily increments

The striae of Retzius (Anders Retzius)

Attacked by acid produced by plaque bacteria once the surrounding pH falls below about 5.5, and strengthened by a halogen in toothpaste

Enamel demineralisation; fluoride forms the more acid-resistant fluorapatite

Mottled white or brown stains from excess fluoride while the tooth was forming in childhood

Dental fluorosis of the enamel

Derived from the surface ectoderm of the mouth rather than from the mesenchyme, unlike the layer beneath it

Enamel is of epithelial (ectodermal) origin; dentine and cementum are from neural crest mesenchyme

Key ideas

  • Being 96 per cent mineral makes it extremely hard but brittle: it relies on the tougher, more flexible dentine beneath it, like a glass coating on a spring.
  • Because it contains no cells, the body cannot mend it. Fluoride and the minerals in saliva can remineralise early damage but cannot replace lost enamel.

Quick-fire facts

  • •About 96 per cent mineral, 3–4 per cent water and organic matter; hardness roughly 5 on the Mohs scale
  • •Up to about 2.5 mm thick over the cusps, tapering to almost nothing at the cervical margin
  • •Ameloblasts are lost when the tooth erupts, so the tissue cannot regenerate
  • •The colour of a tooth comes largely from the yellower dentine shining through translucent enamel; whitening agents act on the enamel and dentine stains
  • •Amelogenesis imperfecta is a group of inherited conditions in which enamel forms poorly
  • •Fluorosis is caused by excess fluoride during tooth development; topical fluoride after eruption strengthens enamel
  • •Hunter–Schreger bands and the striae of Retzius are visible in sections of enamel; the neonatal line marks the stress of birth
  • •Erosion (acid from diet or reflux) and attrition (grinding) wear it away without bacteria being involved

Drill it — 7 cards

1 / 7new card

Sources