Amelogenesis is a process of enamel formation. Enamel is the hardest calcified matrix of the body .it is translucent &varies in colour from light yellow to grey white, it also varies in thickness from max. of approx. 2.5mm.The cells responsible for formation of enamel is ameloblast , are lost as the tooth erupts into oral cavity &hence enamel cannot renew itself .The development of tooth is divided into bud ,cap ,early bell stage & late bell stage. Enamel formation begins in the bell stage. The fully formed enamel consist of approx.. 96% of mineral & 4% organic material and water.
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Amelogenesis by dr.suriya visithiriyan
1.
2. 2
1. Introduction
2. Ameloblast
3. Amelogenesis
4. Ameloblast secretory products
5. Mineral pathway and mineralization
6. Regulation of PH
7. Age changes
8. Clinical consideration
3. 3
AMELOGENESIS is a process of enamel formation
Enamel is the hardest calcified matrix of the body
It is translucent and varies in color from light yellow to grey white.
It also varies in thickness, from a maximum of approximately 2.5 mm
Enamel consists of approximately 96% mineral and 4% organic
material and water
Enamel formation begins in the bell stage
The cells responsible for formation of enamel is Ameloblast
Introduction
4. 4
AMELOBLAST
Cells that are present only during tooth development that deposit tooth enamel
Derived from inner enamel epithelium of enamel organ, an ectodermal component
According to the functions performed, the life cycle of ameloblasts can be divided into
1. Pre-secretory stage
Morphogenic stage
Organizing/differentiating
stage
2. Secretory stage
Formative stage
3. Post-secretory stages
Maturative stage
Protective stage
Desmolytic stage
5. “
5
Morphogenic stage
This stage determines the shape of tooth
Cells are low columnar with central nucleus
Cytoplasmic organelles not abundant
Centrioles and golgi complex located at
apical part
Mitochondria evenly distributed
6. “
6
Organizing/differentiation stage
Inner enamel epithelium cells undergo differentition
to ameloblast
Ameloblast exert organinzing influence on dental
papilla and differntiate to odontoblast
Cells increase in length to 40 microns and abundant
cytoplasmic organelles
Reversal polarity
Interdependance between ameloblast and
odontoblast referred as reciprocal induction
7. 7
Formative stage
Formation of secretion of enamel matrix and partial
mineralization
Function only after layer of dentin is deposited
Have many mitochondria,well developed golgi complex,
extensive cisterna of RER and cytoplasm have secretory
granules,vacuoles,free ribosome,microtubules
Systhesis of enamel protein
Exocytosis
Development of Tome’s process
Enamel Rods formation
8. 8
Maturative stage
Mineralization and
maturation of enamel
Ameloblast modulation
Slight reduction in height &
decrease organelles content
excess synthetic organelle
are removed & remaining are
shifted to distal ends
Protective stage
Ameloblast with enamel organ
perform protective function
Secrete protein on newly
formed enamel
Reduced enamel epithelum(REE)
REE protects enamel till tooth
erupts
Desmolytic stage
REE secretes collagenous
enzyme
Solid plug of epithelial
cells
Tooth eruption
10. 10
•Secretion of enamel
protein
•Produces a partially
mineralized (30%) enamel
•Deposition of hydroxyapatite
Crystal
•Organic mineral and water are
lost and mineral is added to
attain >96% mineral content
•Two step process
11. 11
Amelogenesis has been described in as many as six phases but generally is subdivided
into three main functional stages
Pre-secretory secretory Maturative
Morphogenetic Differentiation Transitional
Maturation
proper
12. 12
Differentiating ameloblast require their
phenotype
Change polarity
Develope an extensive protein synthetic
apparatus
Prepare to secrete the organic matrix of enamel
13. 13
Shape of crown is determined is bell stage
Inner enamel epithelium still undergo mitotic division
limited to cervical portion
Cells are cuboidal or low columnar with large central
nucleus, poor golgi elements in proximal position
Mitochondria & cytoplasmic components scattered
throughout the cell
14. 14
Cells of inner enamel epithelim differentiate into ameloblast
Basal lamina is fragmented by cytoplasmic projections and
disintegrates during mantle predentin formation
Cells elongate and nuclei shift proximally
Golgi increases and migrates distally
Rough endoplasmic recticulum increases
Second junctional complex is developed at distal proximity
dividing the ameloblast into body and and distal extension
called tomes process ,against enamel
15. 15
Fine actin containing filaments radiate from junctional
complexes forming proximal and distal terminal webs
16. 16
Cells acquire intense synthetic and secretory activity
Enamel proteins are translated by REE modified by golgi
apparatus packed into secretory granules
These granules migrate to distal extremity of the cell ,into tomes
process
When enamel formation beings ,tomes process comprises of only
a proximal portion
Contents of secretory granules is released against newly formed
dentin the along the surface of tomes process
Initial layer of enamel does not contain rods
17. 17
Ameloblast migrate away from the dentin surface and develop distal portion of
tomes process as an outgrowth of proximal portion
Secretion of enamel protein becomes unstable and confined to two sites
Secretion from 1st site (proximal portion) results in formation of interrod enamel
that delimits a pit in which distal portion of tomes process resides
Secretion from 2nd site (distal part) provides matrix that result in formation of rod
enamel which fills the pit
Proximal
part
distal part
18. 18
Tome’s process decrease in size as rod grows in diameter
Narrow space is formed along the circumference between rods and interrods
which is filled by organic material ,forming rod sheath
Rods and interod enamel differ only in the orientation of crystallites
Enamel layer composed of rod/interrod-prismatic layer sandwitched between
thin and rodless aprismatic layer initial &final layer
Interrod (IR) enamel surrounds the forming rod (R) and the distal portion of Tomes' process (dpTP)
(A) first (initial) and (B) last (final) enamel layers are aprismatic; that
is, they do not contain rods
19. 19
Before eruption of teeth into the oral cavity ,enamel
hardens
This change results from growth in width and
thickness of pre-existing crystal
Amelogenesis is a slow process that it take as long as 5
years to complete ,upto 2/3rd time is take by maturation
stage
20. 20
Ameloblast undergo significant morphological changes
Height of the cell reduces
Cell volume and organelles decreases
Ameloblast undergo programmed cell death
25% cells die during transitional stage another 25% as
enamel maturation proceeds
22. 22
Removal of water and organic material from enamel and
introduction of inorganic material
Dramatic activity of ameloblast is modulation , cyclic creation,
loss and recreation of highly invaginated ruffle-ended apical surface
(alternate between ruffle and smooth ended)
Modulation occur rapidly once in every 8 hrs
23. 23
Proximal junction is leaky and distal is tight
Acidification associated with outgoing mineral accretion during
maturation causes ruffle end ameloblast to produce bicarbonate ions,
this process alkalines the enamel fluid to prevent demineralization of
growing crystal & maintain ph conditions optimized for functioning of
matrix degrading enzymes
These cells shows considerable endocytic activity and contain
1.Numerous lysosomes
2.Calcium binding protein
3.Calcium ATPase
That appear to promote the pumping of calcium ions into maturing
enamel
Ruffle ended ameloblast
24. 24
Proximal junction is tight and distal is leaky
Bulky-degrading enzyme act extracellularly to digest various
matrix proteins into fragments small enough to leave enamel
Polypeptide fragments leave the enamel through distal
junctions of smooth ended ameloblast & diffuse laterally amoung
the ameloblast to be taken up along their basolateral surface
Smooth ended ameloblast
25. 25
Ameloblast complete transitional phase &begins the cycle they
deposit an atypical basal lamina at their flattend apex
This layer adheres to enamel surface and ameloblast by the
means of hemidesmosomes
It contains LAMININ 332 , heterotrimer molecule essential for
formation of hemidesmosomes
Its deficiency leads to focal enamel hypoplasia
26. 26
Amelogenins
90% of enamel proteins are hetergenous group
of low molecular weight
These are hydrophobic proteins rich in
prolins,histidine & glutamine
Molecular weight ranges 5-45kDA
These accumulate during secretory stage
Undego minor short term & major longterm
extracellular processing by proteolytic enzyme
into low molecular fragments
Loss of function causes deposition of thin
hypoplastic enamel layer which lack rods &
interrods
Non-amelogenins
Consist of remaining 10% of enamel
proteins of amelogenesis such as
enamelin ,ameloblastin, tuftlin
27. 27
Calcium moves from the blood vessels through the enamel organ to
reach enamel likely implicates intercellular and transcellular routes
The stratum intermedium may also participate in the translocation
of calcium, since calcium-ATPase activity has been localized at the
cell membrane of the stratum intermedium.
No matrix vesicles are associated with the mineralization of enamel
Mineral pathway and mineralization
28. 28
Regulation of ph during enamel formation
pH values of forming enamel are maintained near neutral
during secretion
Considerable variation during maturation, shifting from
acidic to near-neutral values and then rising to higher pH
levels in more mature enamel
Carbonic anhydrases (mainly CA2 and CA6) to generate
local bicarbonate; chloride ion exchangers,bicarbonate co
transporters,NA+/H+ exchangers
29. 29
Age changes
Enamel is non vital organ , incapable of regeneration
Masticatory attrition
Discolouration
Reduced permiability
Modification in surface layer
Increase incidence of caries