genesis good ppt
TRANSCRIPT
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Amelogenesis
Professor Dr Maha M F Mounir
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Dentinogenesis occurs prior to
amelogenesis
Soon after the deposition of
the first layer of dentin (mantle
dentin), odontoblasts express
MMPs to digest the basementmembrane to allow E & D
matrices & their respectivemineral phases to come onto direct contact
a strong mechanical bond is
formed between E & D
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Stages of ameloblastic diffrentiation
& formation of enamel
1. Morphogenic stage
2.Organization & differentiation stage
3. Formation stage
4. Apposition stage 5. Secretory stage
6. Early & late maturation stage 7. Protection stage
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Matrix formation
Cells of IEE begin todifferentiate into
ameloblasts, theyelongate & their nuclei
shift Distally (away
from DP), & thecytoplasm becomes filled
with organelles neededfor synthesis &
secretion of enamel
proteins
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First formed enamel- rodless enamel
The proximal end of the newly
formed ameloblast (near the DP)Is still flat. The ameloblast start
to synthesize & secrete enamelproteins (matrix) against the
newly mineralized mantle dentin
Fine hydroxyapatite crystalsbecomes packed perpendicular to
ameloblastss flat proximal end rodlessE
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Secretory Phase of ameloblast
ameloblast cell
lengthen,
proliferation ofRER+ redistribun
of cellularOrganelles i.e;
basal migration of
nucleus & apical
migration of Golgi
(Polarization )
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Secretory Phase of ameloblast
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After this first rodless E layer is formed, the
ameloblasts migrate away from dentin surface
which permits the
formation of conicalprojections called Tomes
Processes( separatedFrom the cell body by
Junctional complex).
Saw-toothed appearance.
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Enamel formation & maturation The formation of enamel & dentin matrices
occurs nearly simultaneously. Following the deposition of a layer of
aprismatic (rodless) enamel, ameloblastsdeposit enamel in the form of rods or
prisms that become highly mineralized.
This is followed by enamel maturation
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TP divided into 2 parts
1.Proximal part; contactsadjacent amelobls A, takes
Place earlier & results in theformation of E matrix wall.
These walls enclose a pit
into which the slopping--2.Distal interdigitating
part fills(the pit)with matrix;surrounded by or
interdigitates with enamel
B
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Tomes processes The Tomes process
fits in the pit forming the
enamel rod growth zone,
while the edges of theTomes process corres-
ponds to rod sheath &inter-rod enamel
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Enamel maturation Ameloblasts function to resorb much of the
water & organic matrix from enamel inorder to provide space for the growing
enamel crystals.
Hydroxyapatite crystals in enamel
increase in size, which results in enamel
being formed of 96%mineral, & 4%organic material + water.
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The arrangement of ameloblasts with their
Tomes process results in the formation of
enamel rods.
A 4 fold increase in the size of crowns
occurs from the start of initiation until
completion of hard tissue deposition. Thisincrease is accomplished by cell division,
then incremental deposition i.e. ameloblast
first forms an increment of organic matrix,that later mineralizes. As daily increments of
organic matrix form, the adjacent earlier-
formed increment mineralizes. Enamel & dentinal matrices form by
incremental deposition of about 4$m of
matrix daily
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incremental deposition of
enamel
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Life cycle of ameloblast The process of amelogenesis is a series of
successive stages of proliferation,differentiation, secretion & maturation.
The formation of enamel & dentin matrices
occurs nearly simultaneously
The tooth follicle develops around the
tooth & eventually gives rise to thesupporting structures.
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Enamel rod & rodless enamel
(prismless)
When enamel secretion
occurs along a flat secretory
front, during the initial & final
secretion of enamel, there areno orisms in the enamel
When enamel secretion occursby fully developed secretory
ameloblast with Tomes process,
enamel rods are formed.
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Enamel cuticle
Completed crownsin crypts have a
cuticle formed on
the surface of
enamel for
protection
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Thank you