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1. MOLECULAR BIOLOGY OF
ODONTOGENESIS
SUKESH KUMAR.V
PG 1ST YEAR
DEPT. OF ORAL PATHOLOGY

2. CONTENTS
Introduction
-Dental Lamina
-Tooth development
-Developmental stages
-Bud stage
-Cap stage
-Bell stage
-Hard tissue formation
-Root formation
MOLECULAR EVENTS
-Ectomesenchymal interactions (EMI)
-Growth Factors
-Transcription Factors & Homeobox Genes.
-Tooth Initiation, Position & Gene interactions in various steps of
development
-Gene Mutations & Tooth abnormailities
-Conclusion.

3. Tooth formation occurs in the 6th week of intrauterine
life with the formation of primary epithelial band. 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
INTRODUCTION

4. Tooth Development
A. Bud Stage
B. Cap Stage
C. Bell Stage
D and E. Dentinogenesis and
amelogenesis
F. Crown formation
G. Root Formation and
eruption
H. Function

5. • The primitive oral cavity, or stomodeum, is lined by stratified squamous
epithelium called the oral ectoderm
• The oral ectoderm contacts the endoderm of the foregut to form the
buccopharyngeal membrane

6. • 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 ectoderm 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
3= Connective tissue cells

7. Initiation of Tooth Development
Each band of epithelium will give
rise to 2 sub divisions:
1. Dental lamina and
2. Vestibular lamina
• 2- 3 weeks after the rupture of buccopharyngeal membrane,
certain areas of basal cells of oral ectoderm proliferate rapidly,
leading to the formation of primary epithelial band
• The band invades the underlying ectomesenchyme along each of
the horse-shoe shaped future dental arches.

8. The vestibular lamina cells rapidly enlarge and then degenerate – forms a cleft
that becomes the vestibule of the oral cavity.
The initiation of tooth formation starts around the 37th day of gestation.

9. Stomodeum
Developing Tongue
Dental lamina
Maxillary Process
Mandibular process

10. Dental Lamina
• Dental lamina appears as a thickening
of the oral epithelium adjacent to
condensation of ectomesenchyme
• 20 areas of enlargement or knobs
appear, which will form tooth buds
for the 20 primary teeth
• Not all will appear at the same time.
The first to develop are those of the
anterior mandible region
• At this early stage the tooth buds
have already determined their crown
morphology
Successional lamina:
•Lingual extension of Dental lamina
•lamina from
which permanent teeth develop
• The dental lamina begins to function
at 6th prenatal week and continues to
15th year of birth (3rd molar)
Primary epithelial
band
Ectomesenchyme

11. Tooth development is a continuous process, however can be
divided into 3 stages:
1. Bud Stage
2. Cap Stage
3. Bell Stage
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

12. 1. Bud Stage
• Bud stage is characterized by rounded, localized growth of
epithelium surrounded by proliferating mesenchymal cells,
which are packed closely beneath and around the epithelial buds
 In the bud stage, the enamel organ consists of peripherally located
low columnar cells and centrally located polygonal cells
•The area of condensation immediately below the enamel organ is the dental papilla
• The ectomesenchymal condensation that surrounds the tooth bud & the dental papilla
is the tooth sac

13. • The dental papilla as well as the dental sac are not well defined
during the bud stage, they become more defined during the
subsequent cap & bell stages
• The cells of the dental papilla form the dentin and pulp while the
dental sac forms cementum & periodontal ligament

14. CAP STAGE
• As the tooth bud continues to proliferate, it does not expand
uniformly into a large sphere
• Instead unequal growth in different parts of the tooth bud leads to
the cap stage which is characterized by a shallow invagination on
the deep surface of the bud

15. 2. Cap Stage
Condensation of the ectomesenchyme immediately subjacent to the tooth bud
caused by lack of extracellular matrix secretion by the cells thus preventing
separation. Histodifferentiation begins at the end of cap stage.
Epithelial outgrowth is called Enamel Organ because it will eventually form the
enamel
Dental Papilla: Ball of condensed ectomesenchymal cells (it will form dentin
and pulp). The peripheral cells adjacent to the inner dental epithelium will
enlarge and later differentiate into odontoblasts
Enamel Organ Dental Papilla

16. 2. Cap Stage
Enamel organ
Dental papilla
Dental follicle or sac
Dental follicle or dental sac is the condensed ectomesenchymal tissue
surrounding the enamel organ and dental papilla. This gives rise to
cementum and the periodontal ligament (support structures for tooth)
Enamel knot

17. 2. Cap Stage
Lateral Lamina: extension from the dental lamina that is connected
to the enamel organ
Enamel niche: It is an artifact produced during sectioning of the tissue.
It occurs because the enamel organ is a sheet of proliferating cells rather
than a single strand and contains a concavity filled with ectomesenchyme.
Because enamel organ sits over dental papilla like a cap, this stage is known as the CAP STAGE.
We can also see that the inner and the outer dental epithelium are being organized
Lateral lamina

18. Dental organ or tooth germ is a term used to constitute the structure that has
enamel organ, dental papilla and dental follicle
Enamel Knot: Densely packed accumulation of cells projecting from the inner
enamel epithelium into enamel organ. Exact role not known, but currently
believed to be the organizational center for cusp development.

19. Enamel knots are clusters of nondividing epithelial cells visible
in sections of molar cap stage
Enamel knot precursor cells are first noted by expression of
p21 gene expression
Enamel knot and enamel cord are temporary structures that
disappear before enamel formation begins. It has been speculated
that the function of the enamel knot and cord may be to act as a
reservoir of dividing cells for the growing enamel organ

20. 3. Bell Stage
• Continued growth leads to bell stage, where the enamel organ resembles a
bell with deepening of the epithelium over the dental papilla
• Continuation of histodifferentiation (ameloblasts and odontoblasts are defined)
and beginning of morphodifferentiation (tooth crown assumes its final shape)
Dental lamina
Outer dental
epithelium
Inner dental
epithelium
Dental papilla
Dental follicle
Cervical loop

21. 3. Bell Stage (Early)
Inner dental epithelium: Short columnar cells bordering the dental papilla.
These will eventually become ameloblasts that will form the enamel of the
tooth crown by differentiating into tall columnar cells. The cells of inner dental
epithelium exert an organizing influence on the underlying mesenchymal cells
in the dental papilla, which later differentiate into odontoblasts.
Outer dental epithelium: Cuboidal cells that cover the enamel organ. Their function is
to organize a network of capillaries that will bring nutrition to the ameloblasts. In
preparation to formation of enamel, at the end of bell stage, the formerly smooth surface
of the outer dental epithelium is laid in folds. Between the folds, adjacent mesenchyme
of the dental sac forms papillae that contain capillary loops and thus provide nutritional
supply for the intense metabolic activity of the avascular enamel organ
Stellate reticulum
Inner dental epithelium
Stratum intermedium
Dental papilla
Outer dental epithelium

22. 3. Bell Stage (Early)
Stellate reticulum
Inner dental epithelium
Stratum intermedium
Dental papilla
Stellate reticulum: Star-shaped cells with processes, present between the outer
and the inner dental epithelium. These cells secrete glycosaminoglycans,
which attract water, thereby swelling the cells and pushing them apart.
However, they still maintain contact with each other, thus becoming star-shaped.
They have a cushion-like consistency that may support and protect the delicate
enamel organ. It is absent in the portion that outlines the root portions.
Stratum intermedium: Cell layer between the inner dental epithelium and
stellate reticulum which have high alkaline phosphatase activity( basal medium). They assist
inner dental epithelium (ameloblasts) to form enamel.
Outer dental epithelium

23. Stellate reticulum
Inner dental epithelium
Stratum intermedium
Membrana preformativa
Outer dental epithelium
Dental Papilla: Before the inner dental epithelium begins to produce enamel,
the peripheral cells of the mesenchymal dental papilla differentiate into
odontoblasts under the organizing influence of the epithelium. First, they assume
a cuboidal shape and then a columnar form and acquire the specific potential to
produce dentin. The basement membrane that separates the enamel organ and
the dental papilla just prior to dentin formation is called the “membrana
preformativa”
Dental papilla

24. Inner dental epithelium
Outer dental epithelium
Cervical loop
Cervical loop: Area where the inner and the outer dental epithelium meet at
the rim of the enamel organ. This point is where the cells will continue to
divide until the tooth crown attains its full size and which after crown
formation will give rise to the epithelium for root formation. Is also called
“Zone of Reflexion”.
3. Bell Stage

25. Enamel cord
 Enamel cord: Pattern of enamel knot that extends between the inner and
outer dental epithelium
Enamel knot
3. Bell Stage
•Dental lamina (and the lateral lamina) will disintegrate and loose contact
with oral epithelium. Sometimes, these epithelial cells will persist when
they are called “epithelial pearls” or “cell rests of Serre”
•Clinical significance of epithelial pearls :
Cysts will develop in these (eruption cysts) and prevent
eruption, or they may form odontomas (tumors) or may form supernumery
teeth

26. Advanced Bell Stage
Essentials of Oral Histology and Embryology,
Ed: James Avery, 2nd edition. 2000.

27. Future crown patterning also occurs in the bell stage, by folding of the
inner dental epithelium. Cessation of mitotic activity within the inner
dental epithelium determines the shape of a tooth.
Crown Pattern Determination

28. Hard Tissue Formation
Deposition of dental hard tissues is
called “apposition”
After the crown attains its final
shape during cap to advanced bell stage,
the inner dental epithelial cells stop
to proliferate, except the cells at the
cervical loop
First layer of dentin appears at the
cusp tips and progresses cervically,
and the columnar cells of the inner
dental epithelium become elongated
and show reverse polarization,
with the nuclei adjacent to stratum
intermediate (ameloblasts)
The boundary between the odontoblasts
and inner dental epithelium defines the
future dentino-enamel junction

29. For dentinogenesis and amelogenesis to take place normally,
the differentiating odontoblasts and ameloblasts will receive
signals form each other – “reciprocal induction”
Stages of Apposition
1. Elongation of inner dental epithelium
2. Differentiation of odontoblasts
3. Formation of dentin
4. Formation of enamel

30. At the same time or soon after the first layer of dentin (mantle dentin) is formed,
the inner dental epithelial cells differentiate into ameloblasts and secrete enamel
proteins. These proteins further will help in the terminal differentiation of
odontoblasts. The ameloblasts will then start laying down organic matrix of
enamel against the newly formed dentinal surface. The enamel matrix will
mineralize immediately and form the first layer of enamel. The formation of
enamel is called amelogenesis.
Ameloblasts
First layer of enamel
Dentin
Odontoblasts

31. Root Formation
Development of root begins after the enamel and dentin formation has
reached the future cementoenamel junction
Epithelial cells of the inner and outer dental epithelium proliferate from the
cervical loop of the enamel organ to form the Hertwig’s epithelial root sheath.
The root sheath determines if a tooth has single or multiple roots, is short or
long, or is curved ir straight
Hertwig’s epithelial
root sheath

32. Hertwig’s epithelial
root sheath
Inner dental epithelium
Outer dental epithelium
Stratum intermedium
Eventually the root sheath will fragment to form several discrete clusters
of epithelial cells known as epithelial cell rests of malassez. These will persist in
adults within the periodontal ligament

33. The epithelial rests appear as small clusters of epithelial cells which are located in
the periodontal ligament adjacent to the surface of cementum. They are cellular
residues of the embryonic structure known as Hertwig's epithelial root sheath.
Epithelial Cell Rests of Malassez

34. Primary apical formen
Epithelial diaphragm: the proliferating
end of the root sheath bends at a near
45-degree angle. The epithelial
diaphragm will encircle the apical
opening of the dental pulp during root
development

35. Secondary apical foramen form as a result of two or three tongues of
epithelium growing inward toward each other resulting in multirooted teeth

36. Soon after root formation begins, tooth begins to erupt until it reaches
its final position
While roots are forming, the supporting structures of tooth also
develop – periodontal ligament and cementum
As the root sheath fragments, the dental follicle cells will penetrate between
the epithelial cells and lie close to the newly formed root dentin
These cells will differentiate into cementoblasts, which will make cementum
Fibers of the periodontal ligament, which will also form from the cells of the
dental follicle will get anchored in the organic matrix of the cementum which
will later get mineralized
TOOTH ERUPTION AND DEVELOPMENT OF
SUPPORTING STRUCTURES

37. MOLECULAR EVENTS
• Odontogenesis is a complex & also co-ordinated process
involving ectomesenchymal (EMI) interactions.
• Molecular interactions between epithelium & mesenchyme
leads to generation of tooth components viz; Enamel Dentine
& Cementum.
• Signalling between epithelium & mesenchymal components is
regulated by a set of genes termed as “Homeobox” genes.{1}

38. • More than 300 genes are involved in this intricate process.{2}.
• Major molecular signals during tooth formation include,
several multifactorial growth factors such as
-Transforming Growth factor(TGF)
-Fibroblast growth factor (FGF)
-Epidermal Growth factor (EGF)
-Hedgehog (HH)
-Wnt Families.{2}
-Several Transcription factors of Homeobox, paired box, & high
mobility group(HMG) box gene families are expressed at sites
of tooth formation & have been implicated in the
determination of tooth shape and identity.{2}

39. Growth factors / Homeobox genes Abbrevation Factor/
Protein
Growth
factors
Fibroblast growth factor Fgf
Secreted
protein
Bone morphogenetic protein Bmp
Sonic hedgehog Shh
Wingless homologue in vertebrates Wnt
Homologous to drosophila slit proetin Slit
Homeobox
Genes
BarH1 homologue in vertebrates Barx
Transcription
Factor
Receptor
Distaless homologue in vertebrates Dlx
Muscle segment homeobox like gene Msx
Glioma associated oncogene homolouge Gli
Lymphoid enhancer binding factor 1 Lef
Lim homeobox domain gene Lhx
Paired box homeotic gene Pax
TF expression in the pituitary gland Pitx
Otx related homeobox gene Otlx
Veretbrate homologue of the Drosophila runt gene Runx
Patched cell surface receptor for hh Ptc
Smoothed Ptc coreceptor for Shh Smo

40. ROLE OF EMI IN TOOTH DEV.
• Before an insight into role of EMI in tooth dev, it is important
to know about 2 terms viz;
• ODONTOGENIC POTENTIAL: represents an instructive
induction capability of a tissue to induce gene expression in an
adjacent tissue & to intiate tooth development.
• ODONTOGENIC COMPETENCE: represents the capability
of a tissue to respond to odontogenic signals & to support
tooth formation.
• Tissue recombination experiments between dental epithelial &
mesenchymal tissue have demonstrated that odontogenic
potential resides in dental epithelium and then shifts to
mesenchyme.{3}

41. ROLE OF EMI IN TOOTH DEV.
• Removal of epithelium from mandibular arches at E10 or
before, results in a total & rapid loss of almost all
ectomesenchymal homeobox gene expression, indicating that
ectomesenchymal gene expression is dependent on epithelial
signaling.
• Removal of epithelium at E11,doesnot affect EM gene
expression indicating that gene expressions are established &
maintained at this stage.
• These results indicate that the inducing signals arise from the
epithelium, however, the EM dependency over the epithelium
ceases with in 24 hours, i.e, from E10 to E11.{1}

42. ROLE OF EMI IN TOOTH DEV
• Therefore, at the pre-bud stages of tooth development by
E11.5, both epithelial and mesenchymal gene expression
domains are independently fixed & interact with eachother
controlling the morphogenic pathways, which is termed as
“epithelial-mesenchymal interactions”{1}.
• Tissue recombinant experiments have shown that, the
presumptive dental epithelium posses the odontogenic
potential, capable of inducing tooth formation when
confronted with non-dental mesenchyme; however only
cranial neural crest cell (NCC) derived mesenchyme is
Odontogenic competent.{3}.
• Teeth failed to form when dental epithelium was recombined
non neural crest derived mesenchyme such as skin or limb
mesenchyme.{3}

43. Jaw
mesenchyme
Oral ectoderm
Nonoral ectoderm
Nondental
mesechyme
Nondental
mesechyme
Oral ectoderm
Jaw
mesenchyme
Nonoral ectoderm
Tissue recombination experiments reveal sources of secreted factors that control
tooth development at early stages
Ectodermal signals are required for the initiation of
tooth development

44. ROLE OF EMI IN TOOTH DEV
• In contrast, at Early bud stage (E12.5), the odontogenic
potential has switched to the mesenchyme ,which becomes
able to instruct non-dental epithelium to form tooth specific
structures. (Reciprocal signaling){3}
Tissue recombination experiments have shown that at induction
of tooth primordia at a later stages is by Mesenchyme

46. Signal are transferred from cell to cell 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.

47. ROLE OF GROWTH FACTORS
• Classic studies demonstrated the importance of Cross talk
between dental epithelium and mesenchyme during tooth
development.
• These cross talk between two layers are mediated by diffusible
signaling molecules.
• These diffusible molecules are GROWTH FACTORS.{3}
• Growth factors mediate inductive interactions during
odontogenesis

48. Fgf- Fibroblast growth factor
• Several members of FGF family are expressed in early
developing tooth germs
• They function at distinct steps of development from intiation
to the formation of the last tooth cusp.
• binds to cell surface receptors which are single
transmembrane proteins with intercellular tyrosine kinase
domains.
• expression of different patterns of Fgf in epithelium and
mesenchyme as regulatory signaling cascade during tooth
development, such as
Growth factors

49. • Fgf-4,8,9: have been implicated as epithelial signals regulating
mesenchymal gene expression & cell proliferation during
tooth inititation & later during epithelial folding
morphogenesis & the establishment of tooth shape.
• Fgf-10:expression observed in presumptive dental epithelium
& mesenchyme during tooth inititation, & also in dental
papilla mesenchymal cells of cap & bell stages, both in
incisors and molars.
• Fgf-3: expression observed in dental mesenchyme at later bud
stage, also in dental papilla mesenchymal cells of cap & bell
stages,both in incisors and molars
• Also participates in signaling functions of primary enamel
knot.
• The dynamic expression patterns of different FGFs in
epithelium(E)and mesenchyme(M) & their interaction suggest
existence of regulatory siganling cascades b/w E&M.{2}

50. Growth factors
Bmp- Bone morphogenetic protein :
• Bmps have been shown to participate in epithelial
mesenchymal siganaling regulating tooth morphogenesis.
• The expression of several Bmps has been localized to the
developing tooth at several stages such as,

51. • Bmp 4 – associated with shift of odontogenic potential from
epithelium to mesenchyme.
• Bmp 2, 4, 7 – are restricted to epithelial cell population,
Enamel knot together with other signaling molecules
suggesting functions such as signals regulating the shape of
teeth.
• Bmp 5 – expressed in epithelial ameloblasts, may be involved
in the induction & formation of Dentine & Enamel.
• Bmp 3 – expression is confined mesenchymal cells, in
particular Dental Follicle cells that give rise to cementoblasts
{2}.

52. Growth factors
Hedgehog superfamily
• Discovered in Drosophila – as a signal regulating
segmental & imaginal disc patterning
• In Mammals – Sonic hh, Indian hh, Desert hh.
• Encode secreted proteins involved in signaling between
cells.{2}

53. Growth factors
Wnt- wingless homolouge in vertebrates
• contains 20 secreted glycoproteins.
• involve in cell proliferation, migration, differentiation, and
ectomesencymal interaction.
• Also involved in skeletal development and bone
remodelling{2}

54. ROLE OF TRANSCRIPTION FACTORS
• Experiments have revealed the expression of numerous
transcription factors in the developing tooth where the
expression patterns of these factors often overlap with those of
growth factors suggesting a potential relationship between the
two class of gene products.{3}
• Homeobox genes(HOX) are group that encodes for
transcription factors.{2}.
• HOX gene network appears to be active in human tooth germs
between 18-24 weeks of development, which explains pivotal
importance of these genes in development{2}.

55. HOMEOBOX GENES
• 180 base pair sequence code for homeodomain of a 60
amino acid DNA binding motif.
• Originally discovered in fruit fly “Drosophila
melanogaster”- responsible for specifying segment
identity.
• Colinearity property(spatial arrangement of genes along
chromosome is in the same order of expression along
antero-posterior axis)
Genes located 3` end- expressed anteriorly
5` end- expressed posteriorly

56. HOMEOBOX GENES
Msx homeobox gene family
• Msx 1, Msx 2 - related to Drosophil gene muscle segment
homeobox.
• Msx 1 – on chromosome
• Msx 2 protein , a transcriptional repressor play a role in
craniofacial development.
• Msx 1, 2 – expressed in several embryonic structures
including premigratory & migratory neural crest, neural crest
derived mesenchyme of pharyngeal arches and median nasal
process. {2}

57. HOMEOBOX GENES
Dlx family
• dista less family of homeobox gene, contains 6 members.
• Dlx 1, 2 – Ch 2q32 expressed in epithelium- mesenchyme of
maxillary and mandibular divisions of 1st brachial arch.
• Dlx 5, 6 – Ch 7q22.
• Dlx 7 – Ch 7
• Dlx 3 – Ch 3
• These are involved in the patterning of ectomesenchyme of the
first brachial arch with respect to tooth development.
• Loss of function mutation of these genes-failure of dev. Of upper
molars{2}

58. HOMEOBOX GENES
Barx homeobox genes
• Bar class genes expressed in craniofacial structures.
• Brax 1 – maxillary and mandibular processes and in tooth
primordia.
• Barx 2 – located on human Ch 11q25 - oral epithelium prior to
tooth development.{2}.

59. HOMEOBOX GENES
Pax homeobox genes
• loacted on Ch 14, play a role in early development.
• Pax 9 proteins possess 128 AA DNA-binding domain, a paired-
domain , which make sequence specific contact with DNA.
• Expressed in Pharyngeal pouches, developing vertebral column,
neural crest derived mesenchyme of maxillary and mandibular
arches, contributing to palate and tooth formation.{2}.
• Activates transcription of Msx1 at bud stage.{1}

60. HOMEOBOX GENES
Lim homeobox genes:
Lhx is member of the LIM homeobox gene family expressed in
mesenchyme of palate
• Lhx 1, 2 – differential regulation during orofacial
ontogenesis.{2}
Runx 2
• key regulator of osteoblast differentiation and bone formation.
• Dental epithelium regulates mesenchymal Runx2 Expression
during bud & cap stage.{2}

61. LIM homeobox genes (Lhx 6 and 7) constitue to that
group of gene clusters which are dispersed outside the
homeobox gene clusters and they are transcriptional
regulators controlling pattern formation.
Lhx 6/7 expressed (oral portion of mesenchyme).
Marks the region where tooth buds form
Goosecoid (Gsc) expression.
Marks the aboral portion of the mesenchyme
•FGF8 activates LIM homeobox genes (Lhx 6 and
7),
which is unaffected by BMP4 .
•Therefore the jaw is divided into a
tooth-forming LHX-positive domain and
non-tooth-forming GSC-positive domain. {1}
Overall called Odontogenic Homeobox Code
ESTABLISHMENT OF ORO-ABORAL AXIS

62. TOOTH TYPE DETERMINATION
The determination of specific tooth types at their correct positions in
the jaws is referred to as patterning of the dentition.
-Incisiform, caniniform, molariform Are Three Families Of Teeth
Determination of teeth shape of different families:
2 Hypothetical models:
1. Field model 2. Clone model
1.Field model
Proposes that, Factors responsible for tooth shape reside within the
ectomesenchyme in distinct but graded fields for each tooth family.
Support:
Each fields express differing combination of Homeobox genes.

63. TOOTH TYPE DETERMINATION
2.Clone model
Proposes that, A clone of ectomesenchymal cells which are
programmed by epithelium to produce teeth of a given pattern.
Support:
Isolated presumptive first molar tissues continue to develop 3
molar teeth in their positional sequence.
Both models can be combined

64. TOOTH TYPE DETERMINATION
BARX-1,DLX-1
MOLARIFORM
TEETH
MSX-1,DLX-1
CANINIFORM
TEETH
MSX-1,MSX-2,ALX-3
INSISIFORM TEETH

65. TOOTH INITIATION AND POSITION
• It appear to originate from oral epithelium
• The Pax-9(paired box homeotic gene) is the earliest
mesenchymal gene that define localization of the tooth
germ
• Inducing factor: Fgf-8(secreted fibroblast growth factor)
• Repressing factor: BMP-2 and BMP-4 (bone
morphogenetic protein)

66. • The expression of several genes in ectomesenchyme
(Pax-9 and Activin-A) marks the site for tooth germ
initiation.
• The antagonistic interaction between Fgf 8 and Bmp4
regulates the expression of Pax 9 but not of Activin-A
this proves that they do not have a direct role in tooth in
initiation

67. TOOTH INITIATION AND POSITION
oral epithelium
Nondental
epithelium
Jaw mesenchyme
Pax-9
Msx-1
Pax-9
Msx-1
-FGF8 is an epithelial signal required for initiation of tooth
development
-FGF8 is expressed throughout entire dental epithelium
FGF 8 FGF 8

68. Positioning the sites of tooth formation :
Antagonistic signaling by BMP4
Dental epithelium
Nondental
epithelium
FGF8 Pax9 BMP4
Jaw mesenchyme
(neural crest)
Pax-9
Msx-1
Pax-9
Msx-1
Sites of co-
expression of
FGF8 and BMP4
Pax9 induces expression of BMP4 in the condensing mesenchyme
BMP4 produced in the dental mesenchyme induces LEF1 expression in
the epithelium

69. • Other genes being involved are
-Otlx-2(Otx related homeobox genes)
-Dlx-2(distaless homologue in vertebrates)
-Msx-1 & Msx-2(Msh-like genes in vertebrates).
-Hox-7, Hox-8 play an important role in tooth initiation & later in
morphogenesis.{1}
-Hox-8-uniform expression in cuspless incisors , which lack an
enamel knot, navel and septum.

70. BUD STAGE
• It is the first epithelial incursion into the ectomesenchyme of
the jaw.
• Epithelium is separated from the underlying ectomesenchyme
by a basement membrane.
• Round ovoid swellings rise from the basement membrane at
10 different points corresponding to the future deciduous teeth
positions

72. • Lef-1(Lymphoid enhancing factor) is seen in the epithelium of
tooth bud and it later shifts to the ectomesenchyme. Any
mutation in this gene will result in arrest at bud stage.{1}
• Dlx-2 expression at the bud stage resides downstream of Msx-
1
• Bmp-4 and Fgf-3 are required for maintaining Dlx-2
expression

73. • The ectomesenchyme surrounding the tooth bud and
dental papilla is the dental sac.
• Both become more well-defined in the cap and bell stage.
• Cells of the dental papilla will form the tooth pulp and
dentin
• cells in the dental sac/ dental follicle will form cementum,
alveolar bone and pdl

74. BUD TO CAP TRANSITION
• Marks the onset of morphologic difference between tooth
germs that give rise to different types of teeth.
• Msx-1 is expressed with Bmp-4 in the mesenchymal cells that
condense around tooth buds.
• Absence of Msx-1 embryos, tooth development is arrested at
bud stage indicating that Msx-1 is required for expression of
Bmp-4
• Bmp-4 maintains Msx-1 expression in tooth bud mesenchyme
indicating that bmp-4 induces its own expression via msx-1.
• BMP-4 in bud mesenchyme maintains – BMP-2 & SHH
expression in epithelium, which are in same pathway.

75. • Blocking shh signaling shows that at E11-E12 , shh is required
for dental epithelium proliferation to form tooth buds, where
as blocking E13 affects tooth bud morphology but still can
form teeth.
• Another Homeobox gene with a role in bud to cap transition is
Pax-9.
• Pax-9 is expressed in bud stage mesenchyme & also in
domains similar to activin-betaA & Msx-1 in patches of
mesenchyme that masks the sites of tooth formation.

76. CAP STAGE
• This stage appear like the enamel organ is present over the
dental papilla like a cap.
• As the tooth bud continues to proliferate from the bud stage it
does not expand uniformly.

77. ENAMEL KNOT
• Cluster of non dividing epithelial cells visible in sections of
molar cap stage tooth germs.
• Enamel knot precursor cells first detected at the tip of tooth
bud by expression gene p21 followed by shh.
• Histologically it is detected in cap stage by the expression of
gene Bmp-2, Bmp-4, Bmp-7, Fgf-4, Fgf-9, Wnt-10 , Slit-1 &
shh.
• Receptors for enamel knot signals are localised in the
epithelial cells surrounding enamel knot.

78. ENAMEL KNOT
• Controls growth & patterning of tooth cusps.
• Each tooth germ has single enamel knot at cap stage & as
these disappear secondary enamel knots appear at the tips of
future cusps of molars.
• Fgf-4 & slit1 are best molecular markers for enamel knot
because these are only two genes expressed in primary and
secondary enamel knots.

79. BELLSTAGE
• Bell stage so called because the continuous growth of tooth
germ leads to deepening of the undersurface of the epithelial
cap that resembles the shape of a bell
• Tooth assumes it’s morphodifferentiation and
histodifferentiation at this stage

80. ROOT INITIATION AND MORPHOGENESIS
• Root formation is initiated by enamel organ epithelial
invagination between the dental papilla.
• Following fenestration of HERS, the epithelial cells persist as
epithelial cell rests of malassez & probably are involved in
cementum maintainence.
• HERS cells undergo E-M transition under influence of TGFβ1.
• Dlx-2 in present in odontogenic cells from tooth initiation and
morphogenesis to root formation.
• Dlx-2 with Msx-2, Dlx-5 : role in HERS cell differentiation and
osteocalcin gene expression.{1}

81. ROOT INITIATION AND MORPHOGENESIS
• Bmps have been found to get expressed sequentially at various
stages of root odontoblastic differentiation.
• Bmp-4 is expressed in mesenchyme lining the root sheath
epithelium, which inturn expresses Msx-2.
• Bmp-4 : early pre-odontoblasts lining HERS epithelium.
• Bmp-2, Bmp-7 : pre-odontoblst and odontoblast , absent from
mature odontoblasts.
• Bmp-3 : expressed intensly in dental follicle cells, particularly in
cementoblasts.{1}

83. GENE MUTATIONS- TOOTH ABNORMALITIES
Msx, Dlx Tooth agenesis, Craniosynostosis,
Tricho- dento-osseous syndrome
Msx Autosomal dominant oligodontia
Pax-9 mutations cause selective tooth agenesis predominantly molars and
premolars.
Runx-2 Cleidocranial dysplasia.
Supernumarary teeth (arrested at bud stage)
Lhx-8 Cleft palate
Alx-4 Foramina parietalia permagna –
c/f: mild dysmorphism , dental abnormalities, &thumb broadening{2}

84. GENE MUTATIONS- TOOTH ABNORMALITIES
Barx-1 Axenfeld Reiger syndrome
Iridogoniodysgenesis syndrome
Pitx-2 -Maxillary teeth development arrested at
placodal stage
-Mandibular teeth development arrested at
budstage
-Rieger syndrome(characterized by oligodontia)
Pitx-2 + Lef-1 abnormalities in late stages of tooth
development
Pitx-2+ a-catenin mutations in early stages of tooth development.

85. CONCLUSION
• The considerable understanding profile of gene expression ,
unveiling the molecular basis involved in tooth morphogenesis
will provide important insight for studying genetically related
dental abnormalities & tooth regeneration in humans.
• The knowledge of developmental & molecular biology along
with experimental embryology, stem cell biology makes tooth
regenration a realistic possibility in the near future, which
would greatly improve the quality of human life.

86. REFERENCES
• Antonio Nanci. Ten Cate`s. Oral histology development, structure, and
fuction
• Essentials of Oral Histology and Embryology,Ed: James Avery, 3rd edition.
• orban`s oral histology and embryology 13th edition.
• {1} Chatterjee S, Boaz K. Molecular biology of odontogenesis,jofs
• {2} Sivakumar G, vijayashree priyadharsini, Saraswathi TR. Gene network
in odontogenesis and associated disorders. Jofs.
• {3}Making a tooth : Growth factors , transcription factors , & stem cells.
• Epithelial-mesenchymal signalling regulating tooth morphogenesis.