enamel Flashcards
describe enamel
hardest tissue in body resists abrasion brittle supported by dentine covers tooth crown translucent transparency increases with mineralisation
where is enamel thickest in molars?
cusps
where is enamel thickest in incisors?
incisal edge
what teeth is enamel thinnest?
deciduous
-teeth present for shorter time
where is enamel more mineralised and harder?
surface enamel
what is an
enamel rod?
basic unit
where do enamel rods run?
surface to ADJ
what size in an enamel rod?
5microm x 2.5 mm
how many HA crystallites do rods contain?
> 10^6
what causes the appearance of rods/rod structure?
orientation of crystallites
what is a rod region?
crystallites run parallel to rods
what is an interrod region?
crystallites run incline to rods
what are long parallel rods?
cross striations in rods
due to daily growth
what are brown transverse striae?
formed at weekly intervals
consequence of growing enamel
what are the components of enamel?
HA -95% weight water -4% weight organic matrix -1% weight
what are the components of the organic matrix?
proteins: amelogenins, enamelins, peptides, amino acids
what regulates the nanomechanical properties of enamel?
the minor protein component
when is crystallite orientation determined?
during enamel formation
how are crystallites deposited?
at right angles to ameloblast membrane
what shape are HA crystallites?
hexagonal
what size are HA crystallites?
70nm x 25 nm x 1 microm
where are HA crystallites smaller than in enamel?
dentine, cementum and bone
what shape do enamel rods run?
sinusoidal
what are hunter-schreger bands?
rod periodic orientation
absent in outer enamel
