Enamel Flashcards
What are features of enamel?
Hardest tissue in body
Resists abrasion
Brittle
Supported by dentine
Covers tooth crown
Varies in thickness
Translucent
Transparency increases with mineralisation
Where is enamel thicker?
Insical edge is thicker
Molar cusps are thicker
What are the enamel regional variations?
Surface enamel more mineralised and harder than deeper enamel
Hardness is more at cusp/incisal edge
What is the basic unit of enamel?
Enamel rod/prism
What are the qualities of the rods?
Rod is 5micrometres times 2.5 millimetres
Run from ADJ to surface
Contain >10^6 HA crystallites
Light microscopy appearance is due to the orientation of crystallites
Orientation varies along and within the rod
What are crystallites that run parallel to the rods called?
Rod regions
What are crystallites that run inclined to the rods called?
Inter-rod regions
Where is acid-etch more effective?
Within inter-rod regions because the etch works better on the sides of the crystallites
What are the cross-stations found in long parallel rods due to?
Due to daily incremental growth of enamel
What are the brown transverse striae due to?
Formed due to weekly growth
What is the shape of enamel rods, end on?
Keyhole
What is between the rods?
Inter-rod regions
In the keyhole shape, why is there a ‘head’ and a ‘tail’?
Both composed of the same hydroxyapatite crystals however the distinction is caused by variations of the crystallites in difference parts of the rod
What is the content of enamel?
Hydroxyapatite - 95% (weight), 90% (volume)
Water - 4% (weight), 5-10% (volume)
Organic matrix - 1% (weight), 1-2% (volume)
What is the organic matrix made of?
Proteins - amelogenins, enamelins, peptides, amino acids
What does the protein content of the rods regulate?
The nano mechanical properties of enamel (flexibility)
Why is tooth whitening harmful?
Removes protein component therefore making enamel more fragile
When is crystallite orientation determined?
During enamel formation
How are crystallites deposited?
At right angles to ameloblast membranes
What process is responsible for the organisation?
Tomes process (landmark within ameloblast)
Describe the process of crystallite formation
Proteins secreted by ameloblasts form pellets which concentrate calcium and phosphate in an organised way
Protein is then removed for crystallite to grow on it’s own
What are the qualities of hydroxyapatite crystallites?
Made of hydroxide, phosphate, calcium
Hexagonal shape
In enamel, larger than in dentine, cementum or bone
What can you substitute for hydroxide?
Mg2+, CO3, F-
What is important to note when looking at histological samples of enamel?
Hard tissues are difficult to cut
-ground sections have the mineral present (however no soft tissues)
-decalcified sections have no mineral present (only soft tissue)
What course do enamel rods run?
A sinusoidal course
What are some enamel optical features, and properties of them?
Hunter-Schreger bands - changes in direction between adjacent groups of rods, absent in outer enamel
Gnarled enamel -found in cusps, concentrated rods that look intertwined
Brown striae of retzius- (incremental lines), weekly enamel growth
Perikymata -once tooth erupts, surface, lines wear off
Neonatal line - seperates enamel formed after birth/before birth
What are features found in the ADJ and what are their properties?
Enamel tufts -hypomineralised regions due to residual matrix protein at prism boundaries (incomplete maturation)
Enamel lamella/fault line -incomplete maturation of groups of immature prisms extending through enamel thickness
Enamel spindles -odontoblast processes extending into enamel
Where can caries occur?
Fissures
