4014407
Enamel composition and structure
- Physical properties
- Hardest substance in the human body
- Brittle - underlying dentine
supports the enamel
- Regional variations - surface enamel is
the hardest and thickest. Vertical
orientation of enamel near surface
therefore more resistant to masticatory
forces.
- Age variations - enamel
translucency increases with
age, shows underlying dentin
- Hardest substance in the human body
- Chemical properties
- 96% by weight inorganic matrix -
Hap crystals; long crystallites. F-
substitution increases stability
against acid dissolution.
- Remaining weight is organic
matrix, consisting of...
- Amelogenins - 90% of
the organic content,
facilitates crystal growth
during maturation
- Non-amelogenins
- Ameloblastin
- Enamelin
- Also involved in crystal growth
- Ameloblastin
- In immature
enamel, nearly 30%
wt is organic content
- Amelogenins - 90% of
the organic content,
facilitates crystal growth
during maturation
- 96% by weight inorganic matrix -
Hap crystals; long crystallites. F-
substitution increases stability
against acid dissolution.
- Structure and structural features
- Basic unit - prism
- Reflects path of
ameloblast from ADJ to
surface - 1:1 ratio
- T/F - are prisms present in
enamel close to ADJ and surface?
F because aprismatic enamel
found here due to lack of PTP +
DTP when it was secreted
therefore aprismatic (reflects
start and end of secretory stage)
- Reflects path of
ameloblast from ADJ to
surface - 1:1 ratio
- Apperance in microscopy
- LM - fish scales,
key hole, etc
- SEM - interrod / rod
orientations apparent
- LM - fish scales,
key hole, etc
- Hunter-Schreger bands - cause by changes
in direction of adjacent groups of rods =
light reflects differentially as dark+light
bands
- Enamel lamellae - linear
structure going into various
depths of enamel - filled with
organic material
- Enamel spindles - odontoblast
process embedded in enamel
after enamel matrix is
mineralised
- Enamel tufts - branches structures
going into enamel at ADJ
- ADJ appearance - scalloped = increase SA for
- Striae of Retzius - incremental growth
lines, successive aposition of layers of
enamel. Appears at surface of enamel
as perikymata.
- Gnarled enamel - rod "twisting"
due to difference in orientation of
groups of rods/prisms -
undulations near cusp region
- Basic unit - prism
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