i tied to explain with the germ layers

1. GGOOOODD MMOORRNNIINNGG

2. TTHHEE DDEEVVEELLOOPPMMEENNTT OOFF
TTOOOOTTHH && IITT’’SS
IINNNNEERRVVAATTIIOONN

Dr.Sharanprakash R Shetgar
1st yr MDS public health dentistry
Narsinhbhai Patel Dental college and

3. Content
 Introduction
 Embryological basis of dental tissue genesis
 Stages in tooth development Histophysiology
 Transitory structures
 Genes signaling
 Development of Root
 Conclusion
 RReeffeerreenncceess

4. Introduction
 Development of tooth is a complex
process, in which reciprocal and
sequential interaction between the oral
epithelium and mesenchymal cells,
regulate cell activities like
proliferation, condensation, adhesion,
migration, differentiation and
secretion, which leads to the formation
of a functional tooth organ

5. How tooth development initiates
During the embryo ,there is formation of
3 layers
1)Ectoderm
2)Endoderm
3)Mesoderm

6.  The primitive oral cavity or stomodaeum is lined
by stratified squamous epithelium called ORAL
ECTODERM
 ECTODERM contacts with ENDODERM of
foregut to form the buccopharyngeal membrane
 27th day of gestation this membrane rapture and primitive
oral cavity established
 Connective tissue cells of underlying the ORAL
ECTODERM are of neural crest or ectomesenchyme in
origin, which induces the overlying ectoderm to start of
tooth development.

7. Embryological basis of dental tissue genesis
 4th week of intra uterine life
Lined by str. squ epi
i.e oral ectoderm
CT cells overlying ectoderm are
ectomesenchyme in origin,
induce tooth devp
Ruptures at 27th
day of gestation

8. Primary Epithelial band/ 6th week
Oral ectoderm proliferates more
rapidly then adjacent cell.
This leads to formation of the
Primary epithelial band
Continuous band of
thickened epithelium
 Roughly horse shoe shaped
 Thickening first seen in ant
midline

9. Formation of vestibule of oral cavity
Cells of vestibular
lamina proliferate
Degeneration of
central epi cells
Sulcus of the vestibule

10. 7th week
Buccally located
Vestibular lamina
Lingually dental lamina

11. Dental lamina
 Cont. proliferative activity
leads to the forming of a
series of epi ingrowths into
the ectomesenchyme
 Dental laminae serves as
ectodermal portion of
Deciduous teeth
 Later, during the devpt of jaw,
the permanent molars arises
from distal extension of dental
lamina
1st molar > 4th mt in utero
2nd molar > 1st yr
3rd molar >4th/5th year

12. 8th week
Contd thickening of DL in 10 areas of upper/ lower arch
Thickenings correspond to position of future primary dentn

13. Function of dental lamina
 Phase 1: Initiation of entire deciduous
dentition (8th wk).
 Phase 2:Initiation successors of
deciduous dentition. (5thmt to 10th mt)
 Phase 3:Initiation of permanent molars
 Phase 4 :Disintegrations (up to 5 yrs ), Remnants
of dental lamina epithelial pearls in jaw/ gingiva
refers to Cell rest of Serres

14. Stages In Tooth Development Histophysiology
PHYSIOLOGICAL
STAGES
 Initiation.
 Proliferation.
 Histodifferentiation.
 Morphodifferentiation.
 Apposition
MORPHOLOGICAL
STAGES
•Dental lamina.
•Bud stage.
•Cap stage:
•Bell Stage:
early.
advanced.

15. A) Bud stage
B )Bell stage
C )Bell stage
D )
Dentinogenises
E )Amelogenises
F )Apposition of
dentin and
enamel
G )Eruption
H )Functional

16. Bud stage (8th week)
Basement
membrane
Tooth bud

17. BUD STAGE
 Enamel org a n
spherical to ovoid epi
condensation
 Cells undergo mitosis &
condense
 Dental papilla > cell
subjacent to enamel
organ
 Dental sac >surrounds
tooth bud and dental
papilla
Enamel organ ,
surrounded by mesenchyme

18. EARLY CAP STAGE:
11th week
 Peripheral cuboidal cells---
OEE
 Tall columnar cells in the
concavity--- IEE
 Polygonal cells b/w outer &
IEE form a cellular
network--- SR
(12th week)

19. Cap Stage
Dental papilla dentin & pulp
Dental sac cementum & PL

20. 13 th week

21. Early bell stage (14th week)
 Dental lamina breaks down & degenerates
 Shows 4 distinct layers: OEE
Stellate reticulum (SR)
Stratum intermedium (SI)
IEE
OEE
IEE

22. Outer enamel epithelium
Role of OEE:
OEE folds and forms the
shape the enamel
organ. B/w folds the
adjacent mesenchyme
of dental sac forms
papillae that contains
the blood capillary
loops which provides
the nutritional supply
to avascular enamel
organ
Early bell stage

23. Stellate reticulum
Role of stellate reticulum
mechanical
nutritive
Protects tissue Maintains tooth
shape
Early bell stage

24. Stratum intermedium Early bell stage
Possess attachments
Absents on root portion
Desmosomal
attachment
Gap junction
B/w
Stellate reticulam &
Staturm intermedium
B/w
Staturam
intermedium & IEE
Nutritional supply for IEE
Which is essential for Enamel formation

25. Inner enamel epithelium
FUNCTION:
 Cells exert an
organizing influence on
the underlying
mesenchymal cells in
the DP that later diff
into odontoblasts
Early bell stage

26. 17th week
17 Week
DL begin
to degenerate
Degeneration of
dental lamina

27. Late bell stage (18th week)

28. Commencment of
mineralization & root
formation starts
Peripheral cells of dental
papilla--- odontoblasts
>DENTIN
 Ameloblast differentiated
by IEE > ENAMEL over
dentin
Establishment of
Dentinoenamel junction
(reciprocal induction )
Late bell stage

29. Enamel oragan
IEE
Ameloblast
Enamel
Dental papilla
Odontoblast
Dentin
Dental sac
Cementum,PDL &
Aleveror Bone

30. TRANSITORY STRUCTURES
 Enamel knot
 Enamel cord
 Enamel niche

31. The Enamel knot
 Localized mass of cells in
IEE
 Signaling centre during
tooth development.
 Produce molecules
associated with signaling
BMP-2 & 7, FGF, P21,
SHH & MSX-1

32. The Enamel cord
 Strand of cells seen at
bell stage extending
from SI into SR.
 ROLE:
Involved in the
process by which cap
stage is transformed
into bell stage

33. Enamel niche
 Seen where tooth germ appear to have a double
attachment to dental lamina
 Functional significance: unknown

34. Successional dental lamina
In dvpng primary tooth, DL
devps an extn to lingual
side
Successional lamina
Forms the perm incisors,
canines & premolars

35. Epithelial-mesenchymal interactions during
tooth development
Cells signal to each other through signaling molecules.
Transmit information to adjacent cells.
Molecules get attached to receptors of target cells.
Cell molecular cascade is activated in the cytoplasm.
Activation of transcription factors.
Enter the nucleus and regulate gene expression.
New proteins are produced.
Change in behavior of target cell.
Continues signaling process.

36. Questions to be answered
1. Which of the two components is more
important for inducing morphogenesis
and histogenesis?
Enamel organ & dental papila
2. What determines the shape of the
tooth?

37. GENE SIGNALING

38. Genes expressed during tooth development
 Lef – lymphoid enhancer- binding factor (TF)
 Pax – paired box homeotic gene( TF)
 Fgf – fibroblast growth factor (SP)
 Msx – msh like genes in vertebates( TF)
 Dlx-- distalless homologue
 Wnt –wingless homologue
 Lhx -- lim homeobox domain gene
 Bmp – bone morphogenetic proteins
 Shh -- sonic hedge hog
 Hgf- hepatic growth factor
 Barx – BarH1 homologue

39. Lim homeobox domain genes
 Lhx-6 & 7–earliest mesenchymal markers for tooth formn
exp in nueral crest ectomesenchyme of first
branchial arch at day 9
 Fgf 8 & pax 9– earliest mesenchymal genes that det
positions of tooth germs
 Shh – implicates tooth initiation

40. Role in determining tooth shape and position
( homeobox code model)
Primary epithelial band
ectomesenchyme
Incisors
Msx 1 & 2
Canine
Msx 1 & 2, Dlx2
Molars
Barx1, Dlx2

41. BMPs & FGF
Role of Bone morphogenetic
protein 4 is activating Msx gene
expression and cascade of
differentiation with
underlying ectomesncyne
On activation it inductive potential
transfer to dental
ectomesenchyme
This reciprocal interaction
involves genetic signaling
Signaling centers are present in
Enamel knot prior cusp formation

42. Enamel knot a signaling center
Expresses
locally
•BMP-2,-4,-7
•FGF-4
•Shh
•p21
Represents a
organizational center
which governs cuspal
morphogenesis

43. Development of Root
Initiated through the contributions of the
cells:
Enamel organ
Dental papilla
Root pulp
Dental sac
Cementum
PDL

44. Root sheath development
 Proliferating zone cervical
loop
hertwig’s root sheath
 Root sheath--- the architect of
root
 Bent portion of root sheath ---
epi diaphragm apical
foramen

45. SINGLE ROOT FORMATION
 Occurs by growth of root
sheath, like a cuff around the
cells of pulp
 Followed by devp of root
dentin
 As dentin matrix mineralizes,
sheath cells form a thin
deposit of cementum on root
surface
Development of root

46. Formation of multirooted teeth
 In devp of tooth with two /
three roots
 Horizontal epithelial flap
sheath expands
eccentrically
 Later flap proliferates and
unites each other

47. Rests of Malassez >
HERES, remnants in
peridonta ligaments
Enamel pearls >
Epithilial root sheath
differentiate to enamel

50. Applied aspect
 Will be continued later …

52. Conclusion ……………….
Being a public health dentist it’s our duty, not
only to understand accurately the mechanism
of tooth development but also to understand
the developmental defects for correct
diagnosis and to develop certain curative and
preventive measures to diminish the disease
burden on the community

53. RREEFFEERREENNCCEESS
 ORAL CELLS AND TISSUES PP..RR.. GGAARRAANNTT.
 ORAL ANATOMY, HISTOLOGY AND EMBRYOLOGY 3RD ed BBEERRKKOOVVIITTZZ
 ORAL HISTOLOGY, DEVELOPMENT, STRUCTURE AND FUNCTION 6TH ed .
TTEENNKKAATTEE.. AA.. RR..
 ORBAN’S ORAL HISTOLOGY AND EMBROLOGY 11TH ed.
BBHHAASSKKAARR..SS..NN..
 ESSENTIALS OF ORAL HISTOLOGY AND EMBRYOLOGY 2ND ed
JJAAMMEESS..KK..AAVVEERRYY..
 DENTISTRY FOR CHILD AND ADOLOSCENTS 8TH ed MMcc DDOONNAALLDD..
 COLOUR ATLAS OF ORAL HISTOLOGY AND EMBRYOLOGY.
BBEERRKKOOVVIITTZZ..