Development of teeth (amelogenesis)

1. Dr.Shrimahalakshmi
II yr PG
Department of Pediatric & Preventive dentistry

2. • INTRODUCTION
• DEVELOPMENT OF TEETH
• CLASSIFICAION OF TOOTH DEVELOPMENT
• MORPHOLOICAL STAGES
• BUD STAGE
• CAP STAGE
• BELL STAGE
• AMELOGENESIS
• REFERENCES

3. Human teeth is diphodont,
Aids in mastication, speech, esthetics.
Tooth development (ODONTOGENESIS) is the complex process by which teeth form from
the embryonic cells, grow, and erupt into the oral cavity.
Primary
dentition
6th and 7th
week
Permanent
dentition
20th week IUL
and 10th month
after the birth
3rdmolar
5th year of life.

4. • At 21st day IUL, when the head fold occurs,
the primitive mouth is temporarily closed by
a buccopharyngeal membrane.
• Sooner, this membrane ruptures, facilitating
the communication between oral and
pharyngeal part.

5. ORAL / ABORAL AXIS
• Controlled by the signaling molecule FGF-8, which is expressed in the
oral epithelium from embryonic day 8.
• This induces the expression of genes necessary for tooth development
such as homeobox genes Lhx-6, Lhx-8 in the oral mesenchyme.

6. TOOTH ORIGIN
• The tooth originates
from ectoderm of 1st
pharyngeal arch and
ectomesenchyme of the
neural crest.

7. EPITHELIAL MESENCHYMAL INTERACTION
• It is a series of programmed, sequential and
reciprocal (complex and multiphasic)
communications between the epithelium and
mesenchyme (two heterotypic cell populations)
resulting in the differentiation of one or both the
cell populations involved.

8. MECHANISM OF EPITHELIAL-MESENCHYMAL INTERACTION
Cell
signal to
each
other
through
signaling
molecule
s
Transmit
information
to adjacent
cells
Activation of
transcription
factors
Enter
nucleus
Regulate
s gene
expressio
n
New
proteins
are
produce
d
Change
in target
cell

9. 2nd arch
mesenchyme +
1st arch
epithelium
Lhx-6 &
Lhx-7
induced
1st arch
mesenchyme +
2nd arch
epithelium
Lhx-6 &
Lhx-7 down
regulated

10. Inductive odontogenic potential- ability of a tissue to induce tooth
formation, even when recombined with the non-dental tissue, and it is
most often represented as signaling molecule

11. PRIMITIVE ORAL CAVITIY
Basal - columnar cells
Superficial - two to three
layers of flat cells

12. Ectomesenchyme cells
The neural crest cells originating from the neural tube at the time of
closure, subsequently migrates into the jaws.

13. PRIMARY EPITHELIAL BAND AT 6TH WEEK IUL
Thickening of oral
epithelium.
Earliest histological
indication of tooth
development.

14. • These epithelial thickenings occur on the
• Infero-lateral borders of fronto-nasal process
• Infero-lateral borders of the maxillary processes
• Superolateral borders of mandibular processes

15. Primary
epithelial band
Dental lamina
(lingually)
Deciduous teeth
Permanent teeth
Vestibular lamina
(labially)
Oral vestibule
6th week – Primary epithelial band
7th week – dental lamina

16. DENTAL LAMINA
Aka odontogenic band, tooth
band.
It determines the location of
tooth bud to develop

17. TOOTH GERM POSITIONING
• FGF-8 has been proposed to act antagonistically with BMP-4 to specify the sites of
tooth initiation.
- regulated by PITx-2
• Wnt – maintains boundaries between tooth forming areas and non-tooth forming
areas
Lef-1 > expressed in dental epithelium thickenings.
>also the ectopic expression of Lef-1 in the oral epithelium also results
in ectopic tooth formation.

18. - 5 months IUL – 10 months after birth
- 4th month, 1st year & 4th year
DENTAL LAMINA

19. EPITHELIAL CELL REST
OF SERRE
• Dental lamina functions – 5 years
• Remnants of dental lamina persists as
epithelial islands within gingiva called
epithelial cell rest of serre.

20. VESTIBULAR LAMINA
LIP FURROW BAND/ VESTIBULAR
RIDGE/ LABIO-GINGIVAL LAMINA.
The vestibular lamina is formed as ectodermal
proliferation in the underlying
ectomesenchyme.

21. • At first, it is a broad cellular band.
• Epithelial degeneration occurs inside
the vestibular lamina to form the oral
vestibule separating the cheek & lip
from the teeth bearing area.

22. • BUD STAGE
• CAP STAGE
• EARLY BELL STAGE
• ADVANCED BELL
STAGE

23. HISTOPHYSIOLOGICAL CLASSIFICATION OF TOOTH
DEVELOPMENT
• Dental lamina Initiation
• Bud stage Proliferation
• Cap stage Histodifferentiation
• Bell stage (early) Morphodifferentiation
• Bell stage (advanced) Apposition
• Formation of enamel & dentin matrix

24. INITIATION
Initiation of tooth development implies determination
of dental mesenchyme and the formation of dental
lamina

25. PROLIFERATION

26. HISTODIFFERENTIATION &
MORPHODIFFERENTIATIONThe formative cells of
tooth germs developing
during the proliferative
stage undergo definite
morphologic as well as
functional changes to
acquire their functional
characteristics.

27. BUD STAGE
• Due to extensive proliferation and
growth of dental lamina into
mesenchyme, it assumes bud shape.
• Mandibular anteriors – 7th week
• Peripheral – Low cuboidal
• Central – Polyhedral
• Cells have higher RNA content than
those of the overlying epithelium.
• Lower glycogen

28. BUD STAGE
The ectomesenchymal
condensation that surrounds
the tooth bud forms dental
papilla and dental sac in
future.

29. • Four major signaling pathways and their inhibitors control tooth
formation:
• BMP
• FGF
• SHH
• WNT
• Overexpression of BMP or functional inactivation of FGF or SHH –
arrest at bud stage.

30. Lef-1 > first expressed in dental epithelium thickenings.
> during bud formation it shifts its location to express in
condensing mesenchyme.
>in Lef-1 knock-out mice, all the dental development is
arrested at the bud stage.

31. genes

32. CAP STAGE
• As the tooth bud continues to proliferate, the rate of mitosis is
increased in peripheral areas.
• A shallow deep invagination on the deeper surface of the bud
occurs, resulting in formation of cap.
• Outer enamel epithelium
• Inner enamel epithelium
• Stellate reticulum

33. Outer enamel epithelium:
• Basement membrane – 1-2mu mm
• Relatively small amount of intracellular
organelles.
• Desmosomes and gap junctions
• Cervical loop – increased mitotic activity.

34. glycosaminoglycan
Water pulled
apart
Desmosomal
contacts
Star shaped
Stellate Reticulum:
• Fully developed at bell stage.
• Few ER & mitochondria.
• Well developed golgi apparatus.
• Protection of underlying dental tissues
against the physical disturbances and
to the maintenance of tooth structure.

35. DENTAL PAPILLA
Organizing influence of proliferative
epithelium of enamel organ
Ectomesenchymal cells proliferate
Budding of capillaries and mitotic
activity
dental papilla – odontoblasts,
primordial of pulp
Fibroblast (primary) and mesenchymal
cells with communicating cytoplasmic
process.
Basement membrane – reticulate fibres,
ground substance of mesenchymal
origin.

36. Marginal condensation in the
ectomesenchyme surrounding the
enamel organ and dental papilla.
In this zone a denser and
more fibrous layer develops
primitive dental sac
formation of cementum and the
periodontal ligament
DENTAL SAC

37. • The ENAMEL KNOT projects in part towards the underlying dental papilla, so
that the centre of the epithelial invagination shows a slightly knob like
enlargement that is bordered by the labial and lingual enamel grooves.
ENAMEL KNOT Hans Ahrens, 1913

38. • Vertical extension of the enamel knot -
ENAMEL CORD.
• When the enamel cord extends to meet the
outer enamel epithelium it is termed as
ENAMEL SEPTUM, as it divide the
stellate reticulum into two parts.

39. • The outer enamel epithelium at the point of meeting shows a small
depression and this is termed ENAMEL NOVEL, as it resembles
the umbilicus.
Enamel knot - Passive
aggregation of existing cells

40. • The function of the enamel knot and cord may act
as a reservoir of dividing cells for the growing
enamel organ.
• Recent studies have shown that enamel knot acts
as a signaling center as many important growth
factors are expressed by the cells of the enamel
knot
• Thus, they play an important part in determining
the shape of the tooth.

42. • These enamel knot cells express high levels of Shh, Fgf4, Fgf9, but low levels of
Fgf receptors.
• Thus, the knot remains in non proliferative state, while the epithelial cells
surrounding the knot have high proliferation.

43. Bud to cap transition

45. • As the undersurface of cap deepens, the enamel
organ assumes a bell shape.
• IEE interacts with the adjacent mesenchymal cells
and determines the shape of the crown.
• During the late bell stage the morphology of the
crown is determined.
EARLY BELL STAGE

46. • It was thought that the shape of crown is due to pressure exerted by the
growing dental papilla cells on the IEE. Though, this pressure however
was shown to be opposed equally by the pressure exerted by the fluid
present in stellate reticulum.
• At present, the concept of folding of enamel organ to cause different
crown shapes is shown to be due to intrinsic growth caused by
differential rates of mitotic division within the IEE.

47. • The IEE cells which lie in the future cusp tip or incisor region stop dividing
earlier and begin to differentiate first.
• Pressure exerted by the continuous cell division on these cells from other enamel organ
cause these cells to be pushed out into the enamel organ in the form of a cusp tip.
• The cells in another future cusp area begin to differentiate & by a similar way results in a
cusp tip form. The area between two cusp tips (i.e) the cuspal slope extends and
therefore the cusp tips to the depth of the sulcus.
Inner enamel epithelium

48. - layers of cells between IEE and SR.
- high mitotic activity (cytoplasmic
organelles, acid muco, glycogen
deposits).
- Important for tooth formation esp
enamel since its not seen in root
formation.
Stratum intermedium

49. • SI function: not understood, but its believed to plat a role in enamel
production either itself though control of fluid diffusion into and out
of ameloblasts or by actual contribution of necessary formative
elements or enzymes

50. • DENTAL LAMINA;
The dental lamina joining the tooth germ to oral
epithelial fragments, eventually separating the
developing tooth from oral epithelium.
It extends lingually and termed successional
dental lamina as it gives rise to enamel organ of
permanent successors of deciduous teeth.
The enamel organ of deciduous teeth in bell
stage show successional lamina and their permanent
successor teeth in bud stage.

51. CERVICAL LOOP
• OEE & IEE are continuous; the region
where the IEE & OEE meet is known as
zone of reflexion or cervical loop.
• This point is where the IEE continue to
divide until the tooth crown attains its full
size and which, after crown formation, gives
rise to epithelial component of root
formation.

53. ADVANCED BELL STAGE
• This stage is characterized by
the commencement of
mineralization and root
formation

54. LIFE CYCLE OF AMELOBLAST &
ODONTOBLASTS

55. Life cycle of
ameloblasts
According to their function, can be divided into six stages:
1. Morphogenic stage
2. Organizing stage.
3. Formative stage.
4. Transitional stage
5. Maturative stage.
6. Protective stage.
7. Desmolytic stage.
Pre secretory
stage
Post
maturative
stage

56. o IEE - still undergo mitosis at the cervical region.
o Cuboidal or low columnar.
o Cell free zone – 1-2mu mm wide.
o Nucleus – large; round or oval; filling the cytoplasm.
o Golgi apparatus - undeveloped
o Centrioles - located in the proximal end of the cell
o Rich in RNA.
o Mitochondria - evenly scattered throughout the cytoplasm.
o Cell attachment - Proximal junctional complex.
I. Morphogenic
Stage.

57. • This stage has 2 principal features:
• Resorption of basal lamina
• Differentiation to ameloblast
II. Differentiation
“organization” Stage.

58. • Pre-ameloblast – produces some enamel
proteins, even before the basal lamina is lost
- expresses dentin sialoprotein,
an odontoblast product transiently.
- phagocytosed by developing
odontoblasts.
- suggesting that they
participate in epithelial mesenchymal
interaction.
II. Differentiation
“organization” Stage.

59. Ameloblast
Intimate
contact (pre-
ameloblast &
odontoblast)
Endocytosis
Preameloblast-
Degradation of
basal lamina
First layer of
dentine
Resorption of Basal lamina

60. Elongated up to 40 microns.
Nucleus – round; shifts to proximal end
Golgi complex - increases in volume; migrates
distally;
Mitochondria – clusters in infra-nuclear
cytoplasm
RER – significantly increased
Second junctional complex develops at distal
extremity of the cell.
Ameloblasts

61. Ameloblasts
• Polarized
• Height – 60 mu mm
• Width – 2-4 mu mm
• Vesicles and vacuoles appear in
cytoplasm.

62. • With the formation of first layer of dentin the nutrition to ameloblasts from
the dental papillary cells is blocked.
• To compensate, the stellate reticulum collapses and the invagination of
OEE by blood vessels lying outside.

63. • Golgi complex – extensive & well developed;
- forms cylindrical tubules around
the RER; occupies major supra nuclear
compartment.
• mitochondria clustered in the proximal region.
• RER increased in number.
III. Secretory “Formative” Stage.

64. Rough
Endoplasmic
reticulum
Golgi
apparatus
Packed into
secretory
granules
Secreted
against mantle
dentin
• The hydroxyapatite crystals are
randomly packed in this first
layer of enamel at the inner rod-
less Enamel.
• Some authors consider that the
dentine crystals form the
nucleation sites for enamel
crystals.
III. Secretory
“Formative” Stage.

65. • The initial matrix defines enamel-dentine junction.
• 1st layer of enamel > diffuses into dentin matrix > taken up by odontoblast
• The sections of DEJ, appears like a shallow depression of dentin fits round
projections of enamel.
• 50 mu mm thickness.
• Thin & needle like

66. • An important event in the production of enamel is
the development of a cytoplasmic extension of
ameloblasts called tomes process.
• As the first layer of enamel is formed, ameloblast
migrate away from dentine surface which permits the
formation of Tomes’ process.
• The distinction between Tome’s and ameloblast is
clearly marked by distal junctional complex.

67. The mineralizing surface
presents a honeycomb
appearance, the pits in the
surface being occupied by
Tome’s process
• With the
development of
the Tomes
process, the
shape of the
mineralizing front
changes to a

68. Tome’s process
Distal and proximal extremities
of tomes process
Proximal – inter rod substance;
Distal - rod
Crystals has a perpendicular
direction on the membrane of
Tome’s process

69. Composition of immature or
mineralized enamel matrix
• Proteins – 25-30% early developing enamel.
• Amelogenin (90%) & non-amelogenin (10%)
• Amelogenins – hydrophobic, protein rich in proline, histidine, glutamine.
• Non-amelogenin – enamelin, ameloblastin, enamelysin, amelotin, odontoblast
ameloblast associated.

71. IV. Transitional Stage.
Partial mineralization
25-30% occur before
full thickness of
enamel is formed
Full maturation
occurs after full
thickness of enamel is
formed

72. Tomes’ processes – become shorter.
Loses its distal portion of Tome’s process.
Decrease in its volume and organelle content.
The cells now appear almost similar to IEE.
During this period the outer rodless enamel is
formed.

73. • The number of ameloblasts reduced.
• 50% ameloblast – apoptosis
• RER, golgi complex reduced - autophagocytosis

74. Ameloblasts are
slightly reduced in length
closely attached to enamel matrix.
25% of the cells die during this phase.
cytoplasmic vacuoles containing material
resembling enamel matrix.
These structures indicate an absorptive function of
these cells.
V. Maturative Stage.

75. Ameloblasts develop cycles of modulation of alternating ruffled
and smooth bordered end which is expressed like a wave.
Associated with
introduction of inorganic
materials.
Distal tight proximal
junctions.
Associated with
removal of protein and
water.
Distal leaky proimal
junction.
V. Maturative Stage.

76. Maturation seems to begin at the dentinal end of the rod
• Each rod mature from the depth to the surface
• The sequence of maturing rod is from cusps or incisal edge
toward the cervical line
• Ameloblasts undergo a transition that not only reduces their secretion of enamel
proteins, but also initiates the secretion of kallikrein 4 (KLK4), a serine protease
that degrades the organic matrix, facilitating its removal from the extracellular
compartment

78. • Ameloblast ceased to be arranged in a well-defined
layer.
• No longer distinguished from the cells of stratum
intermedium and OEE.
• These cells are called as Reduced Enamel
Epithelium.
VI. Protective Stage.

79. • If the connective tissue comes in contact with
the enamel, enamel may be either resorbed or
covered by a layer of cementum.
• REE – secrets some material – establish the
dentino gingival junction.

80. VII. Desmolytic Stage.• The REE proliferates and seems to induce
atrophy of the connective tissue, separating it
from the oral epithelium.
• The fusion of two epithelium occurs as
pathway for tooth eruption
• Premature degeneration of the reduced
enamel epithelium may prevent the eruption
of a tooth.

81. • Initial layer, once mineralized it is
covered by a thin layer of enamel into
which some odontoblast process
extends, forming enamel spindles.
• Darker spindle like structures
extending from DEJ to 100mu mm
into enamel surface.
• Best seen in longitudinal surface of
cuspal areas
ENAMEL SPINDLE

82. ENAMEL LAMELLAE
• They consist of organic material with
little inorganic mineral.
• They develop in the areas of tension.
• When the rod crosses such planes, a
short segment of rod remains
uncalcified.

83. ENAMEL TUFTS• Enamel tuft starts at DEJ and reaches into
enamel to about 1/5th to 1/3rd of thickness.
• Tuft consists of hypocalcified enamel rods
and interprismatic substance.
• They extend into long axis of the crown,
so that they are abundantly seen in
longitudinal and horizontal sections.

84. Incremental Lines of Retzius:
It represents the successive apposition of
different layers of enamel during crown
formation.
Brownish bands in ground sections.
This line represents:
1. Periodic bending of E. rods.
2. Variation in organic structure.
3. Physiologic calcification rhythm.

85. • At the middle and cervical parts,
they run obliquely and deviate
occlusally;
• At cusp tis & incisal edges these
line forms semi-circle as they do
not reach the surface

86. Perikymata
• They are transverse, wave like
grooves, continuous around tooth.
• Usually lies parallel to each other
and to CEJ.

87. Neonatal line
• Particularly marked striae
• It reflects the metabolic changes at birth

88. REFERENCES
• Tencates Oral histology, 3rd edition
• Orbans Oral histology and Embryology, 13th edition
• Essentials of Oral histology & Embryology, James K Avery, 3rd edition
• Oral anatomy, histology and embryology, B.K.B. Berkovitz,
G.R.Holland, B.J.Moxham, 4th edition