2. Teeth development –interaction between the
epithelium and underlying ectomesenchymal
tissue.
Molecules and signaling pathways are responsible
fo intiation , differentiation and morphogenesis.
Interaction may be short, mid, long term cell to
cell or cell to tissue interactions.
•
2
3. Ectoderm:Enamel
NEURAL CREST CELLS: constitute much
mesenchyme of head and neck
Derived from ectodermal germ layer-
ectomesenchyme or neuroectoderm
CT of face, dental structures
Molecule involved: wnt has been implicated in neural tube
formation and neural crest migration
3
4. •
•
Buccopharngygeal membrane ruptures at
about 27th day of gestation and the primitive
oral cavity establishes a connection with the
foregut
Most of the connective tissue cells underlying
the oral epithelium are of neural crest or
ectomesenchyme in origin
These cells instruct the overlying ectoderm to
start the tooth development, which begins in
the anterior portion of the future maxilla &
mandible and proceeds posteriorly
4
5. After rupture of Buccopharnygeal
membrane ,about 37 days of development,
the continuous band of thickened
epithelium forms around the mouth
Horse shoe shaped and correspond to the
ectoderm of future dental arches [U/L
jaws]
Rapid proliferation of basal cells of oral
ectoderm or may due change in the
orientation of mitotic activity.
5
6. At about 7th week the
primary epithelial band
divides into a lingual process
called dental lamina & a
buccal process called
vestibular lamina.
All deciduous teeth arises
from dental lamina, later the
permanent successors arise
from its lingual extension &
permanent molars from its
distal extension
6
7. Dental lamina appear
as thickening of oral
epithelium into the
ectomesenchyme.
At this early stage,
tooth bud
determined- crown
morphology
Functions From 6th week
of intrauterine to till
3rd molar development
7
8. MORPHOLOGICAL
1. Dental lamina
2. Bud stage
3. Cap stage
4. Early bell stage
5. Advanced bell stage
6. Formation of enamel and dentin matrix
PHYSIOLOGICAL
Initiation
Proliferation
Histodifferentiation
Morphodifferentiation
Apposition
Stages Teeth development
9. BUD STAGE
• This is the initial stage of tooth formation where
enamel organ resembles a small bud
• During the bud stage, the enamel organ consists
of peripherally located low columnar cells &
centrally located polygonal cells
• The surrounding mesenchymal cells proliferate,
which results in their condensation in two areas
Intiation of tooth
bud:
FGF2 from the
epithelium
Msx,Blx,barl-
Prepatterning of
tooth type-
Mesenchyme
Pax9-intiates tooth
bud.
9
10. CAP STAGE
• As the tooth bud continues to proliferate, tooth bud leads to the
cap stage which is characterized by a shallow invagination on the
deep surface of the bud
•Dental mesenchyme that is partially surrounded the enamel organ
called dental papilla or embroynic dental pulp
•Cells that adjacent to dental papilla are called dental follicle or
dental sac
H&E stained section
Induction of enamel knot: bmp4
10
11. OUTER & INNER ENAMEL EPITHELIUM
• The peripheral cells of the cap
stage are cuboidal , cover the
convexity of the cap & are called
the outer enamel epithelium
• The cells in the concavity of the
cap become tall columnar cells &
represent the inner enamel
epithelium
11
12. STELLATE RETICULUM
•Polygonal cells located between the outer and the inner enamel
epithelium, begin to separate due to water being drawn into the enamel
organ from the surrounding dental papilla
• As a result the polygonal cells become star shaped but maintain contact
with each other by their cytoplasmic process
• As the star shaped cells form a cellular network, they are called the
stellate reticulum
12
13. • The cells in the center of the enamel organ are densely packed
and form the enamel knot
• This knot projects toward the underlying dental papilla
MOLECULES INVOLVED:
•Induction of enamel knot-bmp4
Primary enamel knot act signaling
center for crown pattern
determination through the
production of signaling molecules
like SHH,Bmp-2 ,bmp-7,FGF-4
•Shape of tooth was determined by
mesenchyme
13
TRANSTIANT STAGE OF TOOTH DEVELOPMENT
At the same time a vertical extension of the enamel knot, called
the enamel cord occurs
14. 14
ENAMEL SEPTUM: When enamel cord
extends to meet the
outer enmal epithelium it is termed
as Enamel septum
ENAMEL NAVEL: The outer enamel
epithelium at the point shows a
small depression and this is termed
as enamel navel.
Enamel Niche: when tooth germ
appears to double attachment to
dental lamina . These strands
enclose the enamel niche, which
appears funnel shaped depression
containing connective tissue.
15. • The function of enamel knot
& cord may act as a reservoir
of the dividing cells for the
growing enamel organ
• The enamel knot act as a
signaling centers as many
important growth factors are
expressed by the cells of the
enamel knot & thus play an
important role in determining
the shape of the tooth
• The ectomesenchymal
condensation i.e the dental
papilla & the dental sac are
pronounced during this stage
of dental development
15
16. EARLY BELL STAGE:
Enamel Organ: 4 different of cells
INNER ENAMEL EPITHELIUM -Concave of EO
STRATUM INTERMEDIUM-adjacent to IEE
STELLATE RECTICULAM
OUTER ENAMEL EPITHELIUM -Convex of EO
16
17. NUTRITION SUPPLY FOR
ENAMEL FORMATION
Smooth enamel organ
to folds
To this fold capillaries
are drawn into from
dental sac into enamel
organ
17
18. H & E stained section
CELLS secrete
Glycosaminoglycons
which attracts water
CUSHING EFFECT to
enamel oral
18
19. H & E stained section
High alkaline
phosphatase activity
assists enamel to form
19
20. Short columanar to tall columnar
Differentiated into pre-ameloblast
Pre-ameloblast cells provide
signal to adjacent dental papilla to
differentiate into odontoblast
20
21. H & E stained section
Before inner enamel epithelium begins
to produce enamel,
The peripheral cells of
ectomesenchymal dental papilla
differentiate into odontblast
1st cuboidal shape –columnar to
produce dentin
The basement membrane at this stage-
membrana preformativa
Cell free zone: 1-2 µm wide
21
22. Area where the IEE and OEE meet
This gives rise to the epithelium for root
formation
Zone of reflexion
22
23. ADVANCED BELL STAGE/MORPHODIFFERENTIATION
Characterized by the commencement of
mineralization & root formation
For dentinogenesis and amelogenesis to
takes place normally differentiating
odontoblast and ameloblast will receive
signals from each other called Reciprocal
Induction
The boundary between the inner
enamel epithelium & odontoblasts outline
the future dentinoenamel junction
Formation of dentin occurs first after
received signals from preameloblast.
After the first layer of dentin is formed,
the ameloblasts lay down enamel over the
dentin in the future incisal & cuspal areas
23
24. The enamel formation then
proceeds coronally & cervically in
all the regions from the
dentinoenamel junction toward
the surface
The cervical portion of enamel
organ gives rise to Hertwig
Epithelial Root Sheath (HERS)
This HERS outlines the future
root & thus responsible for the
size, shape , length & number of
roots
24
25. FORMATION OF ENAMEL & DENTIN MATIX
( APPOSITION)
• Apposition is the deposition of the matrix of the hard enamel
structures
• Appositional growth is characterised by regular & rhythmic
deposition of the extracellular matrix, which is of itself incapable of
further growth
4 stages:
Elongation of IEE
Differentiation of odontoblast
Formation of dentin
Formation of enamel
25
26. • The development of roots begin after
enamel & dentin formation has reached the
future cementoenamel junction
• The enamel organ plays an important role
in root development by forming HERS,
which models the shape of the root
• HERS consists of outer & inner enamel
epithelium only
• As the first layer of the dentin has been
laid down, the epithelial root sheath loses
its structural continuity and is close relation
to the surface of the root
ROOT FORMATION
26
27. •Its remnants persists as an
epithelial network of strands
or clumps near the external
surface of the root
• These epithelial remnants
are found in the periodontal
ligament of erupted teeth
and are called as rests of
mallasez
27
28. • Prior to the beginning of root
formation, the root sheath forms the
epithelial diaphragm
• The outer & the inner enamel
epithelium bend at the future
cementoenamel junction into a
horizontal plane, narrowing the wide
cervical opening
• The proliferation of the cells of the
epithelial diaphragm is accompanied
by the proliferation of the cells of the
connective tissues of the pulp,
adjacent to the diaphragm
•
28
29. • Connective tissue of the dental
sac surrounding the root sheath
proliferates & invades the
continuous double epithelial layer
dividing it into network of epithelial
strands.
•The plane of the diaphragm
remains relatively fixed during the
development and growth of the
root
• In the last stages of the root
development, the proliferation of
the epithelium in the diaphragm
lags behind that of the pulpal
connective tissue
• The wide apical foramen is
reduced first to the width of the
diaphragmatic opening itself & later
is further narrowed by opposition
of dentin & cementum to the apex
of the root 29
