what is the function of enamel
resists abrasion
what are features of enamel
brittle
varies in thickness
translucent
transparency
what does enamel cover
tooth crown
what is enamel supported by
dentine
what happens if enamel is unsupported
will fail
what does translucency of enamel mean
it reflects colors and where the colour is a different place in the dentine due to the shape of the dentinal tubules
what does transparency of enamel increase with
mineralization
what is enamels thickness based upon
its function
why is the enamel on deciduous teeth thinner
they spend less time in the mouth
which is more mineralized - surface or deeper enamel
surface
when does surface and deeper enamel have the same level of mineralization
when it erupts
what is the purpose of a fissure sealant
protect the surface while it is still maturing
Where does the hardness of enamel decrease
cervical regions
what is hardness of enamel associated with
fragility of enamel
receiving attack from caries
what part of the tooth is more prone to recurrent caries
cervical
what is the basic unit of enamel
enamel rod/prism
what is the dimensions of the enamel rod
5 micrometres x 2.5mm (length of enamel)
where does the rod run from
ADJ to the surface
what does the rod contain
a high concentration of hydroxyapatite crystallites (more than 106)
what is the arrangement of rods
key holes
what are cross striations
consequence of daily growth of the rod when it was created
what is the daily growth of rods
4 micrometers
what is brown transverse striae
consequence of the weekly growth of the rods
what surface is more prone to etching
side surface of crystallites
what is the distinction between head and tail regions caused by
ariations in the orientations of the crystallites in different parts of the rod – there is no real space between the rods, this space is just a difference in orientation of the crystallites
what is the weight and volume of hydroxyapatite in enamel
weight - 95%
volume - 90%
what is the weight and volume of water in enamel
weight - 4%
volume - 5-10%
what is the weight and volume of organic matrix in enamel
weight - 1%
volume - 1-2%
what does the organic matrix consist of
proteins
what are the proteins in the organic matrix
amelogenins
enamelins
petptides
amino acids
what is there an absence of in the organic matrix of enamel
collagen
what does the minor protein component regulate in enamel
nanomechanical properties of enamel
ts ability to withstand forces is linked to the presence of the organic component and if you remove the organic component you lose the little amount of flexibility that is present
when is crystallite orientation determined
during enamel formation
how are crystallites deposited in regards to the ameloblast membrane
at right angles
what will the arrangement of the tomes process determine
orientation of the crystallites
what happens in the development of crystallites
Ameloblasts will create a globular structure in which the inner portion can be hyperconcentrated in terms of calcium-phosphate, this is called supersaturation
There is a cocoon protecting the calcium phosphate that needs to be removed for the crystal to form
We require the breakdown of amelogenins - this is the maturation stage of amelogenesis
If we don’t have the breakdown of amelogins then we get amelogenesis imperfecta
The crystal then grows to its full potential
what is the formula for hydroxyapatite crystals
Ca10(PO4)6(OH)2
what is the shape of hydroxyapatite crystals
hexagonal
how do the crystallites in enamel compare to those elsewhere
they are larger
what can we have ionic substitution by
magnesium
carboante
fluoride
what does magnesium substitute
calcium
what does carbonate substitute
phosphate
what does fluoride substitute
hydroxyl
what do we require for substitution
remineralization/demineralization process
what are ground sections
mineral present but no soft tissues
what are decalcified sections
no mineral but only soft tissues
how do enamel rods run
sinusoidal course
what does periodic orientation cause
banding pattern
hunter-schreger bands
where are hunter schrager bands absent
in outer enamel
where do we see gnarled enamel
cusps
what is gnarled enamel due to
greater concentration of rods
why do we have gnarled enamel in cusps
the greater number of rods means that the distribution of force will be better if we have more rods
what are the incremental lines
Brown striae of retzius
perikymata
neonatal line
what is perkymata
exposed on the outside of enamel, disappear and wear off as we
what is neonatal line associated with
associated with diet change that happens at birth
what are enamel tufts due to
hypomineralised regions due to the residual matrix protein at prism boundaries. The tufts penetrate the prisms but do not go all the way through
what is enamel lamella
incomplete maturation of groups of prisms – ‘fault’ line extending through enamel thickness – it goes all the way through the rod
what is enamel spindle
odontoblast processes extending into enamel. Very early stage of formation of the ADJ, the odontoblast left its projection and created a spindle.
