enamel basic properties and structure

1. ENAMEL
Contents:
Physical properties .
Chemical properties.
Amelogenesis.
Life cycle of ameloblasts.

2. What is enamel?
 Enamel is the hardest calcified matrix in the body.
 The ameloblasts are lost as the tooth erupts into the oral
cavity,& hence the enamel cannot renew itself. To
compensate this enamel has acquired:
- complex structural organization
- high degree of mineralization.
 This reflect the unusual life cycle of ameloblasts and the
unique physicochemical properties of matrix proteins.

3. PHYSICAL CHARACTERISTICS OF ENAMEL:
Translucent ; color varies from light yellow to gray-white.
Thickness: 2.5mm at incisal & occlusal region
feather edged cervically.
Knoop’s hardness no.345
Modulus of elasticity: 80.5 Gpa

4. CHEMICAL CHARACTERISTICS OF
ENAMEL:
96% inorganic content, 4% organic content and water.
Inorganic content:
Crystalline calcium phosphate (hydroxyapatite)
Organic content:
Enamel proteins.
Enamel is built by carbanoappatite crystals which are 60-70 nm in width and
25-30 nm in thickness

5. Structure of enamel:
 Because of its highly mineralized nature, enamel is always
seen as an empty space in demineralized sections. Hence
electron microscope studies were done to reveal the
structure of enamel.
Fundamental
organizational
units
Enamel rods
(prisms)
Interrod enamel
(interprismatic
substance)

6. • Because of the high mineralized structure, enamel has high
brittleness which is compensated by the underlying dentine
which is comparatively less mineralized and has better
elastic modulus .
Enamel
organic
component
amelogenins
Non-
amelogenins
Inorganic
component
Hydroxyapatite
crystals

7. Organic matrix:
90%
10%
Sales
amelogenins non-amelogenins

8. Organic matrix:
• Amelogenins:
• -Heterogeneous group of
low molecular weight
proteins.
• -Amelogenin
• - hydrophobic, rich in
proline, histidine,
glutamine and leucine.
• Non-amelogenins
- High molecular weight
proteins.
-Enamelin, ameloblastin,
tuftelin.
-Hydrophillic rich in glycine,
aspartic acid and serine.

9. Inorganic matrix
 It contains hydroxyapatite crystals.
 Incorporated with strontium, fluoride, lead and
magnesium if present during mineralization.
 Central portion of matrix is rich in carbonate and
magnesium and hence has an increased solubility
when compared to surface enamel.

10. 
 RODS --shape like a cylinder
-made up of crystals parallel to the long axis of the rod.
 INTERROD – surrounds each rod.
- the crystals are oriented in a direction different from those
making the rods.
 ROD SHEATH – the narrow space containing organic material
delimiting the rod and interrod.
 No of rods
Lower lateral incisors- 5 million
Upper 1 molar - 12 million
Dimension
Breadth – 5 microns
Length - 9 microns
Diameter – 4 microns

11. Enamel rods
and
interrods

13. Length of the Rods:
 From the DEJ, the rods run a wavy and tortuous course
outwards to the surface of the tooth.
 Length of the rod > thickness of the
enamel.
 Length of the rod > Length of Rods at the
In the cusp cervical area.

14. Direction of rods:
Generally, the rods are oriented at right angles to the dentin
surface.
Deciduous teeth
Cervical and central part of the crown- approximately
horizontal.
Incisal edge- change gradually to an increasingly oblique
direction until they are almost vertical in the region of the cusp
tip.
Permanent teeth
The rods are oriented nearly horizontal in the occlusal 2/3.
Cervical region – the rods deviate from a horizontal to a
apical orientation.

16. Reciprocal induction:
Preameloblasts
secrete sialoproteins
Preodontoblasts
differentiation.
Deposition of
predentine
Stimulation of
ameloblasts and
enamel formation
Disintegration of
basal lamina
between ameloblasts
and odontoblasts.

17. Life cycle of ameloblasts:
Morphogenic
phase
Organizing
phase
Formative phase
Maturative phase
Protective phase
Desmolytic
stage

19. Amelogenesis:
 Amelogenesis is the formation of enamel and it’s basically
consists of 3 main stages.
 Presecretory stage. - secretory stage/ -maturation stage.
formative stage.
 Formation of enamel begins as soon as the IEE & OEE
differentiate.
 Once the predentine is formed the ameloblasts gets cut off
from the blood supply henceforth the stellate reticulum
disintegrates to reassure the blood supply to the
ameloblasts.

20. Light microscopy of
amelogenesis:
Protective stage
Stellate reticulum +OEE+IEE= papillary layer
which regresses to form REE
Ameloblasts become flattened and any fluoride
available will be utilized during this stage.
Reciprocal induction
Predentine stimulates ameloblasts to lay primary
layer of enamel.
Formation of tome’s process (picket fence or saw
tooth appearance)
Late bell stage
OEE & IEE differentiates and formation of cervical
loop
The IEE when traced coronally, the cells become
tall and nuclei are positioned towards
st.intermedium.

22. Electron microscopy of amelogenesis:
Presecretory
stage
• Morphogenic
phase.
• Differentiation
phase.
Secretory
stage
Maturation
stage
• Transitional
phase.
• Maturation
proper.

23. Presecretory stage:
 Morphogenic phase:
-Shape of crown is determined.
- Low columnar cells with centrally located nucleus &
poorly developed golgi bodies; mitochondria are scattered
throughout the cell.
- First junctional complex develop.
 Differentiation phase:
- Cells of IEE become tall columnar and the nucleus shifts
towards the St.Intermedium part of cell.
-Increase in RER and golgi bodies shift distally.
- Second junctional complex develop.
- Development of Tome’s process.

24. Junctional
complexes
First junctional
complex
Between
ameloblasts near
the st.intermedium.
Second junctional
complex
Between the
Tome’s process
(towards enamel)
The ameloblasts were considered nonsecretory cells till
the differentiation phase but later it was found that
ameloblasts start their secretion as early as the
beginning of disintegration of the basal lamina.

26. Formation of Tome’s process:
Cellular extension
of cytoplasm after
2nd junctional
complex
Initially only
proximal portion is
formed.
After initial layer of
enamel deposition,
distal portion is
formed.

28. Secretory stage:
Formation
of secretory
globules
Golgi
apparatus
surrounded
by cisternae
of RER.
Messenger
RNA for
enamel are
translated
into
ribosomes of
RER
RNA enters
RER and
enamel
proteins are
secreted.
Enamel
proteins trans
located into
golgi bodies.
Proteins are
bound to
membrane
bound
secretory
granules
Secretory
granules are
migrated into
Tome’s
process.

29. Enamel formation:
Ameloblasts deposit
secretory globules via
Tome’s
Interdigitation with
dentine. Enamel
without rods
Distal portion of
Tomes formed by
elongation of
ameloblasts
Proximal part starts to
secrete enamel proteins
for interrod
Distal part lays down
enamel
Enamel and interrod
made of same material
but differ in direction
of deposition
As the ameloblasts lay
down enamel at the
end they lose their
distal part and there is
no more interrod
Sandwiched prismatic
enamel between non-
prismatic enamel.

31. Maturation stage:
 Before the tooth erupts into the oral cavity ,the enamel
hardens by the process of maturation.
 This is by the following:
-growth of the preexisting crystals
 It takes place at the expense of enamel fluid and matrix
proteins .
 During this stage the ameloblasts are called post-secretory
cells( but they secrete min amt. of ameloblastin and
amelogenin).

32. Transitional
phase
Transformation of
ameloblasts into post
secretory cells.
Decrease in cell
organelles, cell size,
apoptosis
Maturation
proper
Bulk removal of
water and organic
material
Introduction of ruffle
ended and smooth
ended ameloblasts
for incorporation of
inorganic content

33. RUFFLED BORDER
-Prepares an acidic environment
for enamel production
-calcium binding protein,
lysosomes, calcium adenosine
triphosphates present.
- Constitute 80% of cell life.
SMOOTH BORDER
-causes balancing of pH.
-proximal junctions tight and
leaking distal junctions.
-no membrane calciumATP,
contains only small proteins.
-constitute 20% of cell life.

34. Mineral pathway and mineralization
 The process of mineralization begins as soon as full
thickness of enamel is laid.
 Already 30% of mineralization occurs as soon as the enamel
formation occurs. The remaining mineralization occurs by:
-trans cellular routes
-high capacity stores from RER.
 The surface of the enamel is more mineralized compared to
that of the inner surface .

36. Regulation of pH control:
 pH values are maintained neutral during secretory stage
then to acidic during maturation and shifting to near
neutral values. In the end pH rises to more alkaline levels
in more mature enamel.
• Local chloride
& bicarbonate
generation
Carbonic
anhydrase
•Bicarbonate and
chloride exchange
•Resembles that of
striated duct cells
Ruffle ended
ameloblasts •Neutral pH converted
into acidic.
•Acidic pH converted
into alkaline by smooth
ended ameloblasts.
Enamel
matrix

38. Secretory proteins:
Amelogenin
Ameloblastin
Enamelin
Enamelysin Kallikrin4
Amelin
Amelotin Tuftelin

39. Next seminar:
 Structural and organizational features of
enamel.
 Clinical implications of enamel.