genesis Good Ppt

8/6/2019 genesis Good Ppt

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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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