1st yr BDS

2.  Amelogenesis is under genetic control
 Amelogenesis & Dentinogenesis occurs
almost simultaneously, but as distinctly
different process
 They both begin @ DEJ

4.  Odontoblasts initiate Dentine matrix
formation prior to the beginning of
amelogenesis.
 They produce collagen, that is formed into
bundles that point towards the cells of the
internal enamel epithelium (Pre-
ameloblasts)

5. Proximal
end
Distal
end
IEE
cell
Pre-
ameloblasts
This stage has 2 principal features
1. Differentiation of the pre-
ameloblasts
2. Formation & subsequent resorption
of the basal lamina
During bell stage ,
Cells of IEE ceased to divide
committed enamel forming cell  pre-
ameloblasts
resorption
of the
basal
lamina
Dentine

6.  Ameloblasts differentiate from,
cuboidal  columnar
 The cell become polarized
 These columnar cells  pre-
ameloblasts
Pre-
ameloblasts

7.  A basal lamina separates the preameloblasts
from the dental papilla
 This lamina marks the position of future DEJ
 Differentiation of the odontoblasts 
controlled by cells of IEE  by release of
growth factors (TGF-β)

8.  Once the odontoblasts
have differentiated
basal lamina disappears
as the first layer of the
dentine matrix is laid
down
 IEE enzymes 
degradation
resorption
of the
basal
lamina
Dentine

9.  For a brief period  future ameloblasts &
odontoblasts are in intimate contact 
 first cells to lay down matrix
 provide signal for to begin
secretion

10.  Odontoblasts non-collagenous protein &
DSPP (also by pre-ameloblasts) this initial
matrix defines DEJ
 Before any mineralization begins, pre-
ameloblasts secrete enamel protein on the top
of the dentinal matrix some of which diffuse &
taken up by odontoblasts

11. form in the enamel matrix within these irregularities in
contact with the ameloblasts
Cell processes extend into irregularities on the adjacent predentine
surface
of the pre-ameloblasts
Immediately after this, is laid down

12.  Initial enamel absence of Tomes process

 Pre-ameloblast
› Length= 40 μm
› Diameter = 2-4 μm

13.  Ameloblasts become long, cells 
length =60 μm & width= 2-4 μm
 Following deposition of aprismatic enamel 
a forms at the distal
secretory end of the ameloblasts

14. Ameloblasts
Enamel
matrix
Dentine
St.
intermedium
Tomes process

15. of tomes process  responsible for
of enamel
 Relationship between ameloblasts size &
prism pattern
› Large ameloblasts = type 3 pattern
› Smallest ameloblasts = type 2 pattern

16. Ameloblasts
Developing
enamel
Tomes
process
Interpit
prongs

17. “picket fence” arrangement
front changes
Tomes process
Tomes
process

18.  As the ameloblasts shifts from
Presecretory phase  secretory
phase , there is marked
aggregation of
 The material contained within the
vesicle represents the
Secretory
granules

19.  The contents of the vesicles are
discharged into the extracellular
space
› at the distal end of the cell
› between the cell membrane of the
adjacent ameloblasts

20.  As the enamel matrix
is secreted  the
ameloblasts are
pushed away from the
dentinal surface
Ameloblasts
Developing
enamel
Developing
dentine
Odontoblasts

21. so a distinct like
predentine is seen in enamel
appear almost
Within this organic matrix before matrix
is thick
Secreted
matrix
between
ameloblasts
Secretory
vesicle
Early
enamel
dentine
Ameloblasts

22.  1st formed crystals  ,
10-15 nm wide & 1-2 nm thick
 During development  enamel crystals form
 aligned to the surface
of the ameloblasts

23.  Enamel crystals  elongate around the of
tomes process  prism
 Crystallites extending from where ameloblasts
are joined  prism
 As a part of ameloblast is non-secretory  clear
border between core & boundary

24.  Full thickness of enamel matrix  Secretory
phase
 Tomes process  retracts  distal end
becomes flat  , thin layer of
enamel is formed at surface

25.  4 ameloblasts  single prism
 Each ameloblasts  development of 4
prims
 Enamel prism elongate incrementally
 Daily increment – cross striations
 Weekly increment– enamel striae

26.  Period in which ameloblasts change from
secretory  maturation form
 Initially deposited enamel 
› High content of water & protein
› Low content of mineral
 Enamel maturation  by ameloblasts  but
in a very changed form

27.  Enamel secretion stops
 Much of matrix is removed
 Reduction in height of ameloblasts  signals
onset of transition
 No. of ameloblasts reduced by 50%
(apoptosis)

28.  In remaining ameloblasts  organelles
associated with protein synthesis (RER)
reduced by autophagocytosis
 Enamel organ invaginated by blood vessels
 Blood vessels  lie close (but not in contact)
with the proximal end (base) of the ameloblasts

29.  Proteins & peptides  25-30 % by weight
(mature enamel  1 %)
 Developing enamel matrix during the early
secretory phase 
 Enamel protein Unique protein different from
any other protein found in body

30. 1 % of weight
Proteins (mainly non-amelogenenins )
Mature enamel
The majority of enamel protein are degraded
Following the process of maturation
90-95 %5-10 %

31.  Amelogenins hydrophobic , tends to clump or
aggregate
 They spread throughout the whole developing
enamel thickness
 Resultant matrix  , through which
molecules & ions can spread readily
significant in production of large crystals

32.  Folding of molecule  self assembly
formation of minute
(20nm)
 1st crystals are formed between these
spheres

33.  It is broken down by proteolytic cleavage with
increasing depth of enamel
 Absent from inner layer of enamel
 25 kDa  20 kDa  5 kDa (TRAP)tyrosine-rich
amelogenin peptide
 occurs after secretion of enamel
matrix  continues throughout secretory stage

34.  Location prism cores
 Control growth of crystals by an inhibitory
action
 Largest enamel protein

35.  Initially located  prism near secretory
ameloblasts
 Smaller breakdown products prism
 Function  generation of
 Also produced by HERS during root formation

36.  Signaling molecule during epithelial
mesenchymal interaction
 Location DEJ nucleator at the
commencement of initial enamel
mineralization
 Enamel tufts tuft protein

37.  Produced by ameloblasts @ maturtion stage
 Expressed later than other enamel protein
 Associated with basal lamina role in cell
adhesion

39.  Proteinases & metalloproteinases
 Enamelysin  whose cleavage product
accumulate as the hydroxyapatite crystals
lengthen
 Kallikrein 4 enamel matrix serine proteinase
 Activity of these enzymes  peak @ maturation
stage  when most of enamel protein is lost

40.  The process by which enamel changes into
final form
 Once the entire thickness of the enamel has
formed  it is structurally complete
 Newly formed enamel  , 20
% organic & 15 % inorganic

41.  Enamel crystals  increase in width &
thickness
 Consequent reduction in intercrystallite
space
 Ameloblasts move Ca, phosphate &
carbonate ion into the matrix

42.  Ameloblasts remove water & degrade
enamel matrix protein from it.
content of the enamel reduced
from 30 % 
 Crystallites expand from 1.5 nm thick  25
nm removal of matrix

43.  Enamel organ  serine proteinase 
degradation of enamel protein  mineral
gain
 At this initial stage  space created is
occupied by water  enamel become
porous

44.  Tomes process is lost
 Organelle content reduced
 Remaining organelle congregate at the
distal end of the ameloblasts ruffled border
 ‘Ruffle- ended’ ameloblasts alternates with
‘smooth-ended’ ameloblasts

45. Ruffled
border
Resorptive
vesicle
Enamel

46.  Modulation  indicate alternation between
resorptive & secretory phase of activity
 Movement of Ca2+ ions
› Ruffle- ended : actively controlled
› Smooth- ended : diffusion (hence few would
enter the enamel)

47.  Local pH changes
› Ruffle- ended normal pH favors mineralization
› Smooth – ended  mildly acidic pH  resist
mineralization
 Ameloblasts may induce pH changes
modulating bicarbonate level

48.  Lowering of molecular weight of enamel
protein  by a group of proteinases in
enamel matrix
 The of the mineralization
process  after virtually all protein has been
removed

49. The increase in
mineral density
begins over the
cusp tips &
progresses
cervically
Initial
enamel
deposition
Increased
mineralization
follows during
maturation

50.  Once maturation is complete  ameloblasts
become
 A thin amorphous layer of protein (
) separates the cells
from the enamel
 Ultrastructure level this has appearance of
basal lamina

51. Enamel space
Dental follicle
Oral epithelium
Reduced enamel
epi.

52.  Basal lamina
› Material extruded from the enamel during
maturation
› Last secretory product of ameloblasts
 The remnants of the enamel organ merges
with flattened ameloblasts RER

53.  Ca  reaches the matrix principally via the
enamel organ
 It travels via extracellular route
 The ameloblasts layer has a limited &
variable but controlled permeability
 This property  proximal cell junctional
complex

54. Ameloblasts
Enamel
Calcium

55.  First formed enamel at the DEJ  less well
organized than the bulk of the enamel in terms
of crystallite size & morphology  Aprismatic
 Tuftelin – crystallite growth & nucleation
 Amelogenins capable of self-assembling into
minute spheres between which the 1st
crystallite of enamel are formed

56.  The form as a from the
matrix that is supersaturated with
hydroxyapatite
 Initially crystals grow by fusion of nucleation
sites
 Once prismatic structure is established
crystallites enlarge in rather than width

57. The matrix can control the crystallite growth
pattern by two mechanisms
 By breaking down protein in a controlled pattern
to provide the space for new crystallite
deposition same dimension microchannels
 By modulating the effect of inhibitory molecule

58.  After maturation phase the role of the
matrix proteins is largely ended
 Virtually all proteins has been lost & what
remains is replaced by tissue fluid
 The matrix proteins  actually removed long
before crystallite growth ends

59.  The degraded matrix proteins accumulate in
the extracellular space around the
ameloblasts and by inhibiting further activity,
could control & limit the thickness of enamel
deposited.

60.  The increase in mineral during maturation
follows a different pattern from the initial
deposition
 The initial crystallites form as a precipitate
within the matrix that is supersaturated with
hydroxypapatite.

61.  Crystallites form and grow while close to the cell
membrane of the tomes process.
 They grow by the deposition of ions on the
crystallites faces.
 As the ameloblasts retreat, they form pyramidal
tomes processes at their distal ends  the
enamel formed thereafter is  prismatic

62. Tomes
process

64.  Morphogenic
 Organizing
 Formative
 Maturative
 Protective
 Desmolytic