Enamel Flashcards
What is the hardest tissue in the body?
- Enamel
What are the regional variations of enamel? (2 points)
- Surface enamel is more mineralised and harder than deeper enamel
- Hardness decreases from cusp tip/incisal edge to cervical region
What is enamel maturation?
- The process of changing from about 30% inorganic mineral in enamel matrix of the teeth to the 96% inorganic content in mature enamel.
- The maturation is accomplished by the ameloblast cells over a long period, with a decrease in water and organic content, and an increase in mineral content and size or density of hydroxyapatite crystals.
- The final stages of enamel maturation occur after the tooth has erupted into the oral cavity
What is the basic unit of enamel?
- Rod/prism
What are the dimensions of enamel rods?
- 5micrometers x 2.5mm
Where do enamel rods run from?
- ADJ to the surface
How many HA crystallites do enamel rods contain?
10^6
Where are enamel rods perpendicular?
- When they are closest to the ADJ
Where are enamel rods parallel?
- When nearest to the surface of the tooth, which helps keep the enamel from splitting and ensures that the surface of the tooth is smooth
Why do long, parallel enamel rods have cross striations?
- Consequence of the growth of the rod -> daily growth is approx. 4 micrometres
How far apart are brown transverse striae?
- 25-35 micrometres apart
When are brown transverse striae formed?
- At weekly intervals
How does enamel rod structure arise?
- From variations in orientation of crystallites
Are ‘head’ and ‘tail’ regions of enamel rods composed of the same HA crystals?
- Yes
What is the HA content in enamel?
- 95% weight
- 90% volume
What is the water content in enamel?
- 4% weight
- 5-10% volume
What is the organic matrix content in enamel?
- 1% weight
- 1-2% volume
What is contained within the organic matrix of enamel? (5 points)
- Proteins
- Amelogenins
- Enamelins
- Peptides
- AA’s
After a restoration has ben placed, what will happen to the composition of enamel? (2 points)
- Will loose water
- Will loose organic matrix
What part of enamel gives it the ability to withstand forces?
- The organic matrix
- ‘minor protein component regulates the nanomechanical properties of enamel’
Where are crystallites deposited in relation to the ameloblast membrane?
- At right angles
What is the tomes process?
- A histological landmark identified on an ameloblast, cells involved in the production of tooth enamel.
- During the synthesis of enamel, the ameloblast moves away from the enamel, forming a projection surrounded by the developing enamel.
- Tomes processes are those projections
- They are located on the secretory basal end of the ameloblast
What shape are crystallites?
- Hexagonal
In which area are crystallites the largest: enamel, dentine, cementum or bone?
- Enamel
How much of the enamel rod do HA crystallites go through?
- A small portion
Will you see enamel in ground sections histologically?
- Yes, mineral present (no soft tissues)
Will you see enamel in decalcifies sections histologically?
- No, (will only see soft tissues)
Enamel rods run in a sinusoidal course: what does this mean?
- Have an s-shape arrangement
Do adjacent groups of enamel rods have the same or different arrangements?
- Different
What are Hunter-Schreger bands found in enamel?
- The periodic orientation of enamel rods causes periodic orietation
- Alternating light and dark lines seen in enamel of the tooth that begin at the ADJ and end before they reach the enamel surface, they may represent areas of enamel rods cut in cross-sections dispersed between areas of rods cut longitudinally
Where are Hunter-Schreger bands absent from in enamel?
- In the outer enamel
What is gnarled enamel?
- Enamel under the cusp of a tooth characterised by twisting. Intertwining groups of enamel rods, thought to resist shearing forces
What are ‘brown striae of Retzius’?
- Prominent lines that run obliquely across the prisms to the surface
- They represent the successive positions of enamel forming front
What is the neonatal line?
- A particularly marked striae that is formed at birth
- It reflects the metabolic changes at birth
- Prisms change both direction and thickness at this event
What is the name of the junction between enamel and dentine?
- The amelo-dentinal junction
What are enamel tufts?
- Less mineralised areas of enamel in the inner third of enamel adjacent to the ADJ. They resemble tufts of grass
What are enamel lamella?
- Incomplete maturation of groups of prisms - ‘fault’ line extending through enamel thickness
What are enamel spindles?
- Odontoblast processes extending into enamel
