Enamel Morphology Flashcards
which area of the tooth has the greatest mineralised enamel content
surface enamel
which area of the tooth has the hardest enamel?
cups/incisal edge
what is the basic unit of enamel?
enamel rod or prism
what direction do enamel rods run?
from ADJ to the surface
how many hydroxyapatite crystallites do enamel rods contain?
> 10^6
what is the appearance of enamel under light microscopy due to?
the orientation of crystallites
where do crystallites run in the rod regions in relation to the rods?
parallel
where do crystallites run in the inter-rod regions in relation to the rods?
on an incline
what region is etch more effective in?
inter-rod regions as it works better on the sides of crystallites compared to the tips
what are the cross striations in the rod due to?
daily growth
what are the transverse striae in the rods due to?
weekly growth
what does rod structure arise from?
variation in crystallite orientation
what makes up the content of enamel?
hydroxyapatite, water, organic matrix
what regulates the nanomechanical properties of enamel?
minor protein component
what happens if you remove the protein content from enamel?
you make the enamel more fragile
what makes the enamel flexible under biting forces?
minor protein component
when is crystallite orientation determined?
during enamel formation
where are crystallites deposited in relation to the ameloblast membrane
at right angles
describe the development of crystallites
ameloblasts secrete proteins which form palates which concentrate calcium and phosphate in an organised way. The calcium and phosphate can anucleate crystallites. Crystallites can only grow if they remove these proteins
in which tooth substance are hydroxyapatite crystals the largest?
enamel
what ions make up hydroxyapatite and where do they sit?
calcium on outskirts, hydroxyl at core, phosphate in between
what ions are used to substitute hydroxyapatite ions?
magnesium for calcium, carbonate for phosphate, fluoride for hydroxyl
what type of course do enamel rods run?
sinusoidal
what type of orientation causes banding patterns?
periodic orientation
where are hunter-schreger bands seen?
rod periodic orientation
where are hunter-schreger bands not seen?
outer enamel
what is gnarled enamel?
concentration of rods
where is gnarled enamel seen?
in cusps
what are the type of incremental lines?
brown striae of retzius and perikymata
why does brown striae of retzius appear?
as a consequence of growth on enamel
what does the brown striae of retzius share its origin with?
perikymata
what are enamel tufts?
hypomineralised regions due to residual matrix protein at prism boundaries
what is enamel lamella?
incomplete maturation of groups of prisms - fault line extending through enamel thickness
what are enamel spindles?
odontoblast processes extending into enamel
how can you tell enamel tufts and enamel spindles apart?
enamel spindles have a rounded end
