Enamel is formed through the process of amelogenesis, which involves the life cycle of ameloblasts. Ameloblasts undergo morphological and physiological changes during the secretory, transitional, and maturative stages of amelogenesis. During the secretory stage, ameloblasts develop Tomes' processes which extend into the enamel matrix and help establish the rod and interrod structure of enamel. As enamel matures, ameloblasts transition to having microvilli and modulate between ruffled and smooth shapes to both remove organic material from the enamel and introduce inorganic minerals to fully mineralize the enamel.

1. Enamel & Amelogenesis
By
Amira Mohsen Elsherbini

3. Every one has a unique figure print…
•Do you Know that you
have a dental print that is
as unique as your finger
print?11
•It is your ENAMEL

4. Whatdoyouthinktheproblem
is?

5. Itmightbe
•Developmental 
(Amelogenesis and
life cycle of ameloblast)
•External factor 
Properties (Chemical or Physical)
•Surface structure 
Structure of enamel , surface structure and
hypocalcified structures.

6. So…..
By definition
What is Enamel ???
The hardest calcified structure in the body
Ectodermal in origin
non-collagenous tissue
covering the anatomical crown of teeth
 forming a protective converging against
masticatory forces.

7. Enamel
 Acellular,
 inert,
non vital and insensitive tissue,
when destroyed by any means usually
wear or caries it can not be
replaced or regenerated.

8. PropertiesofEnamel
Physical
1- COLOR
2-THICKNESS
3-HARDNESS
4- BRITTLENESS
5-solubility
6- PERMEABILITY
chemical
1- Inorganic
2 - organic

9. Chemical composition
Organic 4%
• 1-2% non-collagenous
proteins “ Enamel proteins“
• 2-3% water.
Amelogenin (90%)
Non amelogenins (10%)
Fine lacy network, forms an
envelop surrounding each crystal.
Non organic (mineral) 96%
• Calcium and phosphate in the
form of hydroxyapatite crystals.
Ca 10(PO4)6 (OH)2
• Traces of strontium,magnesium,
lead and fluoride

10. PhysicalProperties
• 1-COLOR
YELLOWISH WHITE
Translucent enamel
GRAYISH WHITE
Opaque enamel
Depending on degree of translucency which
depends on
a. Degree of calcification.
b. Homogenisity of enamel

11. PhysicalProperties
•2-Thickness
• Variable
• Maximum thickness (2.5 mm) at the
cusp tip or incisal edge
• Thinnest at cervix where it ends at a feather
edge.
• As a functional adaptation, thickness of
enamel
is more in lingual aspect of maxillary molars and
buccal aspect of mandibular teeth, in relation to
functional
cusps.

12. PhysicalProperties
•3-Hardness
•Is the hardest calcified tissue in the body due to
 high mineral content &
 crystallite arrangement
•Enamel of the permanent teeth is harder than that of the
deciduous one.
•Micro-hardness is grater at surface and cusp tip than ADJ
and cervical line
•Hardness increase with flouride application.

13. PhysicalProperties
•4-Brittleness:
• Enamel is brittle (like glass)
• especially when it looses its foundation of elastic
dentin
• Brittleness increase with
• age
• Undermining
• Non vital
•5-Solubility:
• Enamel is soluble in acids.
• Solubility depends on the presence of certain ions like fluoride.
• Surface enamel is less soluble.

14. PhysicalProperties
•5-Permeability
It acts as a semi permeable membrane for some ions and dyestuffs
of small molecular size through pores between the crystals.
Permeability is mainly from saliva to the outer layer of enamel, but
less from the pulp to the inner enamel layer across the dentin

15. Objectives
•Developmental 
(Amelogenesis and
life cycle of ameloblast)
•External factor 
Properties (Chemical or Physical)
•Surface structure 
Structure of enamel , surface structure and
hypocalcified structures.

17. Amelogenesis
•It can be divided into 3 main stages
• Presecretory stage.
•Secretory stage.
•Maturation stage.

18. Pre requesites of Amelogenesis

19. Story of Enamel formation
Amelogenesis and life cycle of ameloblast)
My old friend told me precious data

20. life cycle of ameloblast
I. Morphogenic.
II. Differentiation.
III. Secretory.
IV. Transitional.
V. Maturative.
VI. Protective.
VII.Desmolytic

22. Before we start
• What is Enamel?
• Every hard structure is formed by mineral deposition on collagen except Enamel
• At every stage
• stage of tooth dev
• Light microscope
• Electron microscope
• Nucleus
• Golgi and centriole
• Mitochondria
• attachment
• Basement membrane
• hard structure (if present)
• special ch.ch
• Nutrition

23. • The dentinal end of the ameloblast, at which enamel is formed, is
called distal (former basal)
• The (apical) end facing the stratum intermedium is called basal or
proximal.

24. • Ameloblasts during their life time
undergo morphological and physiological
changes that are directly related to their
function.
• These changes can be described as
life cycle of ameloblasts

25. Morphogenic stage
stage of tooth dev 

26. Morphogenic stage
Electron microscope 
short columnar cells
Nucleus  oval and
central & fills the cell body
Golgi and centriole
proximal end
Mitochondria 
dispersed
Basement membrane 
separate the IEE from cell
free zone and dp
cell free zone  acellular
cell free zone  Acellular
It has argyrophil fibers and
the cytoplasmic processes of
the superficial cells of the

27. Morphogenic stage
• Electron microscope 
• attachment  proximal junctional complex
• hard structure (if present)  ---
• special ch.ch  IEE interact with the adjacent
mesenchymal cells,
determining the shape of D.E.J
and the crown.
• Nutrition - from dental papilla
Cell free
zone
Cell rich
zone

28. Differentiation (Organization / pre-secretory) stage

29. Differentiation ( Organization) stage
• stage of tooth dev  early bell stage
• Light microscope  Tall columnar cells (twice the size)
• Electron microscope 
• Nucleus  migrate to proximal end
• Golgi and centriole distal end
• Mitochondria  migrate proximally and Increase in no
• Attachment  with migration of mitochondria
• Basement membrane  separate the IEE from and dp
• Special ch.ch  epithelial mesenchymal interaction

30. Induction and polarization
Inner dental epithelium
Proximal end
Distal end
Odontoblasts
Cell free
zone
Cell rich
zone
CentrioleNucleus Golgi apparatus Mitochondria

32. hard structure (if present)  predentin formation.
Nutrition  from dental follicle.

33. secretory stage
Two forms of
Amelobalsts
With two
different
arrangements
of Enamel
flat basal region Tomes process

34. secretory stage
The secretory ameloblasts are structurally suited
for synthesis and secretion of enamel proteins.
The cells have
o many mitochondria,
o Well developed golgi complex
o and extensive cisterns of rough endoplasmic reticulum.
Cytoplasm also shows many secretory granules,
vacuoles, free ribosome, various types of
Vesicles.

35. Messenger RNA carries the message from nucleus to cytoplasm
(aminoacid sequence)
↓
Ribosomes translate the message (enamel protein)
↓
Protein is synthesized in rough endoplasmic reticulum (Amelogenin &
Non-amelogenin)
↓
Protein undergoes post translation modification in golgi complex
↓
Packing of protein into secretory granules (stippled enamel) against first layer of
dentin (nucleation site)
Structure-less (rodless) enamel
Ameloblasts synthesize enamel
protein (1st form)

36. Reciprocal Induction
Odontoblast
Dentin matrix
Ameloblast
Enamel matrix
(stippledstruc
ture-less E)
Dentin

37. • Starts at the cusp tip or the incisal edge and proceed cervically

38. Ameloblasts synthesize enamel protein
(2nd form) : Tome’s process
As the first layer (little thickness) of enamel is deposited,
the ameloblast migrate away from dentine surface,
ameloblasts develop a conical process at the
base, which is called Tomes’ process.
 The distinction between process and cell body
is clearly marked by distal junctional complex.
This Tomes’ process contains primarily secretory
granules and small vesicles while cell body contains
abundant synthetic organelles.
Tome’s process jut into newly formed E matrix giving
it saw tooth appearance

39. Secretion of enamel is confined to
two sites
 Adjacent to proximal part of the process
close to junctional complex; resulting in formation
of inter rod, this wall encloses a pit in which Tomes’ process fits.
one surface of Tomes’ process (later on fill these pits with
matrix).
 So, the crystal orientation and direction in the wall of pit
differ from that in the pits giving the inter rod enamel and the
filling area become the enamel rods.
Inter rod is one step a head before the rod….
The Tomes' process that create the unique structure of enamel persist
until final few increments in the surface are secreted
(outer structureless enamel)

42. The organic matrix of enamel consists of enamel protein, 90%of
enamel protein is amelogenins and remaining of enamel protein
10% consist of enamelilin, tuftelin and amelin.
The role of enamel protein is to provide an environment to accept
mineral.
Stratum intermedium with ameloblasts form a functional cellular unite
responsible for E formation.
 SI plays a role in the formation of enamel itself; either through
I. The control of fluid diffusion into and out of ameloblasts.
II. The actual contribution of necessary formative elements or enzymes “Alk.
Phosphatase”.

44. 4-Transitional stage
 Withdrawal of Tomes’ processes
reduction in the height of the ameloblasts
decrease in its volume and organelle content.
During this period most probably the outer
structureless or prismless enamel is formed.
Outer structure less
Inner structure less
ADJ

45. Maturative stage
•Enamel maturation (full mineralization) occurs after
most of the thickness of the enamel matrix has
been formed in the occlusal or incisal area.
•In the cervical parts of the crown, enamel
matrix formation is still progressing at this time.

46. Maturative stage
In this stage ameloblasts have to introduce the inorganic material
necessary for maturation and also reabsorb
proteins and water to provide space for the
minerals.
• In order to perform these dual
functions -
Ameloblasts show
Morphological alterations.

47. Changes in
Ameloblasts
Slight reduction in length.
Cs are closely attached to
enamel matrix.
Cs contain cytoplasmic vacuoles
containing material resembling
enamel matrix.
Display microvilli at their distal
extremities forming a striated
border “increasing surface area”
 These structures indicate an
absorptive function of these
cells.

48. Cell modulation…
The cell alternate between ruffled and smooth ended
shape (every 8 hr, ie 3 cycles/ day) expressed like a wave.
Smooth
Associated with
removal of
protein and
water.
 Distal leaky
junction and
proximal tight
junctions
Ruffled
Associated with
introduction of
inorganic
materials.
Distal tight and
leaky proximal
junctions.

49. Newly formed
crystals
Mature crystals
The crystals thicken rapidly and the intervening protein is
squeezed out.

51. Protective stage

52. Protective ameloblast
• After complete enamel formation and full mineralization, ameloblast
 lose the ruffled border and become smooth.
 Secrete a protein between distal ends of cells and the enamel surface
similar to basal lamina (hemidesmosomes)which give firm
attachment of ameloblast to the enamel.
The columnar ameloblasts shorten to cuboidal
 and along with other collapsed layers of
enamel organs (the stratum intermedium,
stellate reticulum & outer enamel epithelium)
form a 2–3 layered stratified epithelium which
is termed as reduced enamel epithelium (REE).

53. Function of reduced enamel epithelium (REE).
 Protect the mature enamel by separating it
from the C.T until the tooth erupt.
 Path way for eruption of the tooth by
Contact with the oral epithelium.
• Form the primary epithelial attachment as
an important role in establishing the
dentogingival junction.
• enamel may be resorbed or cementum
deposition may occur on enamel surface.

54. • enamel may
be resorbed
or cementum
deposition
may occur on
enamel
surface

55. Desmolytic Stage
reduced enamel epithelium proliferates and seems to
induce atrophy of the connective tissue separating it
from the oral epithelium as pathway for tooth eruption.
•It is probable that the epithelial cells elaborate
enzymes that are able to destroy connective tissue fibers
by desmolysis.
• Premature degeneration of the reduced enamel
epithelium may prevent the eruption of a tooth

56. Enamel dysplasia
• Interference with the secretion  reduction in the amount &/or
composition of the enamel matrix.

57. Defects of Amelogensis
• by febrile disease
disturb the all teeth forming in this time characterized by
distinctive bands of malformed surface enamel. On recovery,
normal enamel resumed.
•by tetracycline
induced disturbances in teeth, which incorporated in
mineralizing tissues result in band of brown pigmentation or
even total pigmentation.
•Fluoride ion
chronic ingestion of F concentration in excess of 5 parts per
million , result in mottled enamel as patches of hypomineralized
and altered enamel.

58. Characteristic Features of Enamel are:
1. Ameloblasts, the enamel forming cells are ectodermal in origin
2. Enamel formation occurs only for a limited period of time till the desired
thickness is
formed
3. In an erupted tooth enamel is not lined by formative cells
4. Enamel does not have the capacity to repair or regenerate
5. Enamel is a nonliving tissue not containing cells or cellular components
6. Enamel is avascular and insensitive
7. Organic matrix of enamel is unique composed of enamel protein and is
non-collagenous.