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oral biology
enamel
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Created by
Charlotte Summers
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Cards (69)
What is the hardest biological tissue?
Enamel
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What is the composition of enamel?
96%
mineral
, 2%
organic
, 2%
water
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What property of enamel allows it to withstand shearing and impact forces?
High
abrasion
resistance
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Why is enamel considered brittle?
It has low
tensile
strength and
fractures
without support from
dentin
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Can enamel repair or undergo replacement?
No
, it cannot repair or undergo replacement
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What is the vascular and nerve supply status of enamel?
Enamel is
avascular
and has no nerve supply
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What cells are responsible for the formation of enamel?
Ameloblasts
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Where is enamel thickest on the tooth?
Over
cusps
and
incisal
edges
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What is the thickness of enamel over the cusps of permanent teeth?
1.5 mm
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What is the thickness of enamel over the cusps of deciduous teeth?
1.3 mm
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How does the surface enamel compare to subsurface enamel?
Surface enamel is
harder
,
denser
, and less
porous
than subsurface enamel
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What is the mineral component of enamel?
Hydroxyapatite
crystals
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What lies between the hydroxyapatite crystals in enamel?
Water
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What is the organic component of enamel?
Matrix
proteins
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What are the two types of organic matrix proteins in enamel?
Amelogenins
and
non-amelogenins
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What role do amelogenins and non-amelogenins play in enamel?
They control the
growth
and
organization
of enamel
crystals
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What is the shape of enamel crystallites in cross-section?
Hexagonal
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What is the basic structural unit of enamel?
Enamel rods
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How are enamel rods arranged?
Millions
of
crystallites
arranged into rods and
interrod
enamel
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What is the diameter and length of each enamel rod?
1.6 micrometres in diameter and 2.5 mm long
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How do interrod crystals differ from rod crystals?
Interrod crystals
deviate
40-60
degrees compared to rods
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How does the orientation and size of enamel rods contribute to enamel properties?
They contribute to the level of
hardness
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What is the key hole pattern of enamel rods?
Clear
head
and
tail
regions
Arranged in
staggered
rows
Tail
of rod lies between two
heads
in the row
below
Heads
parallel
with rod, tails
diverge
to the long
axis
of the rod
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What are the bands of Hunter and Schreger?
10-13 layers
of
rods
follow the same direction
Blocks of rods above and below follow
different
paths
Strengthen
enamel and prevent
cracks
from
spreading
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What do incremental lines in enamel demonstrate?
They demonstrate the
growth
of
enamel
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What are short period increments in enamel growth called?
Cross striations
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What are long period increments in enamel growth called?
Enamel striae
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What are cross striations in enamel?
Lines that cross
enamel rods
at
right
angles
to long axes
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What is the common interval for cross striations?
1.6 micrometres
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What do striae of Retzius represent?
Successive
positions of the
enamel-forming
front
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How do striae of Retzius appear over cusps and incisal edges?
They don’t reach the
surface
unless
enamel
is
lost
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How many cross striations are typically found between adjacent striae?
7 to 11
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What happens to striae if there is a metabolic disturbance during amelogenesis or mineralization?
Attenuated
striae occur
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What are neonatal incremental lines in enamel?
Marked
striae formed at
birth
reflecting
metabolic
changes
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How do rods change during neonatal incremental lines?
Rods change
direction
and
thickness
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What happens to rods after neonatal incremental lines?
Rods eventually
turn
back
again and regain
previous
orientation
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What are perikymata incremental lines?
Striae
that
extend
to reach the surface of
lateral
enamel
End as fine
grooves
running
circumferentially
around the
crown
Lost through
wear
unless well
protected
Mainly seen on
labial
surfaces
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What are the stages of amelogenesis?
Pre-secretory
Secretory
Maturation
Post-maturation
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What occurs during the pre-secretory phase of amelogenesis?
Cells differentiate into
ameloblasts
at the future
enamel-dentin
junction
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What characterizes the secretory phase of amelogenesis?
Ameloblasts
form
matrix
enamel without
rod
formation
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See all 69 cards
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