development of tooth along with genes involved in tooth develoment, stages of tooth development and developmental disorders of tooth development

1. Development of tooth
Presented by
Amolika Choube
Oral Pathology and Microbiology
MDS Ist year

2. Contents
• Introduction
– Primitive stomatodeum
– Neural crest
– Primary epithelial band
• Stages of tooth development
– Physiological
• Initiation
– Genes involved in tooth
development
• Proliferation
• Histodifferentiation
• Morphodifferentiation
• Apposition
– Morphologic
• Dental lamina.
• Bud stage.
• Cap stage.
• Bell Stage.
Early
Advanced
• Transitory structures
• Timeline of tooth
development
• Hard tissue formation
• Root formation
• Clinical considerations
– Agenesis
– Developmental disorders

3. Primitive stomatodeum
• The foregut is bounded ventrally by the
pericardium and dorsally by developing brain,
cranially separated by the buccopharyngeal
membrane.
• The buccopharyngeal membrane ruptures at
27th day of gestation

5. The newly formed stomatodeum lined by 2 – 3
cell thick epithelium
migration of neural crest cells in embryonic
connective tissue.
ectomesenchyme

6. The Neural Crest
• During formation of neural tube, a group of cells
separate have high capacity to migrate
and differentiate extensively in the developing
embryo neural crest cells ( in mammals from
lateral aspect of neural plate )
• Neural crest cells induction epithelial –
mesenchymal transformation cell adhesive
properties and cytoskeletal organisation change
migration
• Bone morphogenic proteins, Wnt , fgf signaling
pathways are believed to be critical for neural cell
cascade induction

7. Neurons , Schwann
cells, pigment cells
and meninges

8. • At molecular level , neural crest cell competence
is indicated by the expression of members of the
Snail (Snail and Slug ) zinc finger transcription
factor family that repress the expression of the
cell adhesion molecule E cadherin.
• Proper neural crest cells is essential for
development of face and teeth.
• Treacher Collins syndrome : neural crest cells fail
to migrate to the facial region.
• All tissues of the tooth ( except enamel and some
cementum ) and its supporting apparatus derived
directly from the neural crest cells

9. Primary epithelial band
• After about 37 days of development , a
continuous band of thickened epithelium
forms ( change in the orientation of mitotic
spindle and cleavage plane of dividing cells) in
the presumptive upper and lower jaws. (
horse shoe shaped).
• Each band of epithelium
primary epithelial band ( at 7th week)
dental lamina vestibular lamina

11. Stages in tooth development
Physiological stages
• Initiation
• Proliferation
• Histodifferentiation
• Morphodifferentiation
• Apposition
Morphological stages
• Dental lamina.
• Bud stage.
• Cap stage.
• Bell Stage.
• Early
• Advanced

12. Dental lamina
• Localised proliferative activity leads to formation of a series
of epithelial outgrowths in the ectomesenchyme, at sites
corresponding to the future deciduous teeth.
• Ectomesenchymal cells accumulate around the outgrowths
bud cap bell
Permanent molar – distal extension of dental lamina
Lingual extension/ successional lamina : successors of
deciduous teeth

13. FATE OF DENTAL LAMINA :-
• It extends over a period of atleast 5 years.
• it may still be active in the molar region.
• Remnants of dental lamina persists as a
epithelial pearls or islands within the jaw as
well as in the gingiva, referred to as CELL OF
SERRES (sometimes it may proliferate and lead
to odontogenic cyst & tumours

14. Vestibular lamina
• The vestibule forms as a result of the proliferation
of vestibular lamina into the ectomesenchyme .
vestibular lamina cells
enlarge
degenerate
cleft that becomes the vestibule

16. Initiation of tooth
• After the 12 th day of development the 1 st
arch loses its odontogenic potential , which is
then assumed by ectomesenchyme .
• Day 11 – earliest histologic indication of tooth
development- thickening of epithelium on the
oral surface of 1st branchial arch

17. gene name Proposed function
Barx BarH1 homologue in
vertebrates (TF)
In odontogenic homeobox
code molars develop from
cells expressing Barx - 1
Bmp Bone morphogenic protein (SP) Expressed in bud to cap stage
transition (Bmp-4)
Dlx Distaless homologue in
vertebrates (TF)
Fgf Fibroblast growth factor (SP) 1. Induction of Lhx genes
2. Position and number of
tooth germs (Fgf 8),
proposed to act
antagonistically with Bmp -
4
3. Induction of Pax -9
Gli Glioma associated oncogenic
homologue (zinc finger protein
) ( TF)
Mediates Hedgehog signaling
Hgf Hepatic growth factor (SP)
Lef Lymphoid enhancer –binding
factor 1 (TF)
1st expressed in dental
epithelium
Lhx Lim – homeobox domain gene
(TF)
Earliest mesenchymal markers

18. Msx Msh –like genes in vertebrates
(TF)
Msx-1 expressed with Bmp-4
in mesenchymal cells that
condense around toth buds.
Patterning of incisors ,canines ,
premolars ( Msx-1 , Msx-2)
Otlx Otx –related homeobox gene
(TF)
Pax Paired box homeotic gene (TF) 1. Determines the location of
tooth germ (Pax- 9).
2. Expression of Pax- 9 and
Activin A in
ectomesenchyme marks
the site of tooth germ
initiation.
3. Expressed in bud stage
mesenchyme

19. Pitx Transcription factor named for
its expression in pituitary
gland
Ptc Patched cell- surface receptor
for sonic hedgehog (SHH)
Shh Sonic hedgehog (SP) Stimulates epithelial cell
proliferation( functions as a
mitogen) , signaling in tooth
development
Slit Homologous to Drosophila slit
protein (SP)
Smo Smoothed PTC coreceptor for
SHH
Wnt Wingless homologue in
vertebrates (SP)

20. Epithelial mesenchymal interactions
during tooth development
• Reciprocal interactions between the epithelium
of enamel organ and mesenchyme of the dental
papilla→ epithelial – mesenchymal interactions .
Q. Which of the two components is more important
for inducing morphogenesis and histogenesis –
the enamel organ or the dental papilla

21. Series of experiments had following inferences:
1. At cap stage , the principal organiser is the
dental papilla in terms of both
morphogenesis and histogenesis.
2. Dental papilla is the dominant tissue
determining the shape of the tooth at cap
stage.
3. The premigratory neural crest cells will form
teeth only when associated with the oral
epithelium

22. g

24. Bud stage
• First epithelial incursion into the
ectomesenchyme of the jaw
• Enamel organ – simple , spherical and ovoid ,
poorly morphodifferentiated and
histodifferentiated

25. • Cells of tooth bud:
1. higher RNA than epithelia
2. lower glycogen
3. increased oxidative
enzyme activity

26. Cap stage
• Morphodifferentiation progresses by 11 th week
– cap shape
• Condensation of ectomesenchyme
• As the tooth bud enlarges, it drags along with it a
part of dental lamina - developing tooth is
tethered to the dental lamina by an extension –
lateral lamina.
• Dental organ / enamel organ :
A. Dental papilla – pulp –dentin complex
B. Dental follicle /sac – supporting tissues

27. • Histodifferentiation , as transition occurs from
bud stage to cap stage :
1. outer enamel epithelium –cuboidal,
2. inner enamel epithelium- short columnar ,
high gycogen content
3. Stellate reticulum – rich in
glycosaminoglycans ( enamel pulp)
hydrophilic, star shaped
A - Enamel organ
B - Dental lamina
C - Vestibular lamina
D - Dental Papilla
E - Dental sac

28. 2
1
3
1) Inner enamel ep
2) Outer enamel ep
3) Cervical loop
4) Stellate reticulum
5) Enamel knot
6) Enamel cord
7) Enamel navel
4
5
6
7
transient structure
during cap stage
http://www.iob.uio.no/studier/undervisning/histologi/index.php

29. Transitory structures
• Enamel knot : Clusters of non dividing epithelial cells in
sections of molar cap stage tooth germs.
• It expresses genes for signaling molecules including Bmp-2,
Bmp – 4, Bmp- 7, Fgf-4, Fgf- 9, Wnt- 10b, Slit- 1 and Shh.
• Enamel cord : vertical extension of enamel knot .
• 3 dimensional nesting pattern of enamel knot between the
inner and outer enamel epithelia .
• Single primary enamel knot at cap stage, secondary enamel
knots at tips of future cusps in molars.
• Fgf – 4 and Slit -1 – best molecular markers for enamel knot
formation.
• Enamel knot represents organisational center which
orchestrates cuspal morphogenesis.
• Enamel knot and enamel cord may act as reservoir of
dividing cells for growing enamel organ.
• Both these structures are related anatomically to the site
where the lateral lamina attaches to the enamel organ cap

30. • Enamel septum : when the enamel cord
extends to meet the outer enamel epithelium
it is termed as enamel septum, divides stellate
reticulum into two parts.
• The outer enamel epithelium at the point of
meeting with enamel cord shows small
depression – enamel navel – resembles
umbilicus

31. Early bell stage
• During this stage the tooth crown assumes its final shape
(morphodifferentiation), and the cells that will be making the hard tissue
acquire their distinctive phenotype – histodifferentiation .
1. Outer enamel epithelium – peripheral , low cuboidal, high nuclear –
cytoplasmic ratio , free ribosomes , rER , mitochondria , few tonofilament
and junctional complexes joining adjacent cells
2. Inner enamel epithelium – short columnar , centrally placed nucleus , high
glycogen content , free ribosomes, rER, mitochondria , poorly developed
golgi complex
3. Stratum intermedium – epithelial cells between inner enamel epithelium and
stellate reticulum differentiate
- exceptionally high activity of enzyme alkaline phosphatase
- along with inner enamel epithelium act synergistically as a single functional
unit for formation of enamel

32. • Dental papilla is separated from enamel organ
by a basal lamina from which a mass of fibrils
extends into an acellular zone → corresponds
to lamina fibroreticularis → 1st secreted
enamel matrix proteins accumulate here.
• The dental papilla referred to as tooth pulp
when the calcified matrix appears at cuspal tip
of bell stage tooth germ.
• The dental lamina fragments , separating
developing tooth from oral epithelium.
• The inner enamel epithelium completes its
folding → shape of the future crown pattern

33. • Differential rates of mitotic division within the
inner enamel epithelium – cessation of mitotic
divisions within the cells of inner enamel
epithelium determines the shape of tooth.
• The point where the cells differentiate
represents the site of future cusp ,or growth
center.
• Eventually the differentiation of inner enamel
epithelium and papilla cells sweeps down
along the cusp slopes and is followed by
deposition of dentin and enamel defining the
dentinoenamel junction

34. To be continued….
• Late bell stage
• Hard tissue formation
• Root formation
• Clinical considerations

35. Advanced bell stage
• Commencement of
mineralisation and root
formation.
• Terminal differentiation
of ameloblasts and
odontoblasts →
histodifferentiation
Orbans 12 ed

36. • At the sites of future cusp tips where the
dentin will 1st appear at the cusp tips , the
cells of inner enamel epithelium cease to
divide, cells elongate and reverse polarity.
• As these changes appear in the inner enamel
epithelium →the undifferentiated
ectomesenchymal cells differentiate →
odontoblasts.
• Differentiation of odontoblasts is initiated by
organising influence of cells of IEE.
• IEE cells express several growth →TGF- ẞ1,
BMP-2 and insulin like growth factor

37. Cells of IEE (differentiating
ameloblasts)
Induce dental papilla
Odontoblasts.
Orbans 12th ed

38. Differentiating ameloblasts
Enamel matrix proteins
GF
epithelial – mesenchymal interaction
Terminally differentiated odontoblasts
Newly formed dentin
Enamel
matrix
formation
enamel
mineralise

39. Time line of human tooth
development
• 42 to 48 days – dental lamina formation
• 55 to 56 days – bud stage : deciduous incisors ,
canines and molars
• 14 weeks – bell stage for deciduous teeth ;
bud stage for permanent teeth
• 18 weeks – dentin and functional ameloblasts
in deciduous teeth
• 32 weeks – dentin and functional ameloblasts
in permanent 1st molars

40. Root formation
• At late bell stage when
amelogenesis and
dentinogenesis are well
advanced , the external
and internal enamel
epithelia at the cervical
loop of enamel organ
form a double layered
epithelial root sheath,
which proliferates
apically to map out the
shape of future roots
Orbans 12 ed

41. Epithelial root sheath
proliferates apically .
The primary apical foramina
at the growing end may
subdivide into a number of
secondary apical foramina by
ingrowth of epithelial shelves
from margin of root sheath .
Between 2 epithelial layers ,
there is no stellate reticulum
or stratum intermedium
which if present account for
the presence of localised
areas of enamel pearls

42. Above the root diaphragm ,
Cells of internal layer of root sheath
Peripheral cells of dental papilla
odontoblast
Root dentinogenesis
Epithelial root sheath loses continuity
Mesenchymal cells of dental follicle
differentiate to cementoblast
induce
diffrentiate
By contact with
root dentin
BERKOVITZ

43. Berkovitz
A - EPITHELIAL ROOT
SHEATH
B - DENTAL PAPILLA
C- DENTAL FOLLICLE
D – ODONTOBLASTS
E – EPITHELIAL RESTS
F – CEMENTOBLASTS
G – DEVELOPING
ALVEOLAR BONE
H – DEVELOPING
CEMENTUM
J – DEVELOPING
PERIODONTAL LIGAMENT
K- ROOT DENTIN

44. inner investing layer of dental follicle derived from
ectomesenchyme (neural crest).
Outer and intermediate layer mesodermal
• Inner layer
cementoblasts layer of
cuboidal cells on root
dentin cementogenesis.
• Cells of the remaining
dental follicle become
obliquely oriented along the
root surface, increased
content of intracellular
orgenelles
fibroblasts of PDL
collagen
BERKOVITZ

45. • Connective tissue
immediately below the
developing root apex
fibrous network with fluid filled
interstices , attachment on either
side to the alveolar wall
Cushion hammock ligament
Current view : no role in
eruption
Merges at side with
developing PDL
Pulp limiting membrane Berkovitz

46. CLINICAL CONSIDERATIONS
AGENESIS
DEVELOPMENTAL
DISTURABANCE
Disturbances in number
of teeth
Disturbances in size of
teeth
Disturbances in form of
teeth
Disturbance in structure of
teeth

47. Disturbances in number of teeth
Soames and
Southam

48. Disturbances in size of teeth
macrodontia microdontia
•size of teeth and the jaws are influenced
by genetic and environmental factors
•May be generalised or localised .
•True generalised macrodontia associated
with pituitary gigantism
•Microdontia may be associated with
Down syndrome and congenital heart
disease.

49. Disturbances in form of teeth
Dilaceration :
• Sharp bend or curve , in the root
or crown of formed tooth.
• most frequently involves the
maxillary incisors.
Talon cusp : projects from cingulum
area of maxillary or mandibular
permanent incisor.
Rubinstein – Taybi syndrome –
developmental retardition,
broad thumbs and great toes,
characteristic facial features ,
delayed or incomplete descent
of testes in males , and stature ,
head circumference , and bone
age below fiftienth percentile

50. • Taurodontism (bull –
like tooth)
- Pulp chamber has greater
apico- occlusal height
- No constriction at the
amelocemental junction
- Affects multirooted teeth,
caused by failure of
Hertwigs sheath to
invaginate at proper
horizontal level.
Syndromes associated :
Klienefelter, poly- X syndromes

51. Dens in dente
(dens invaginatus, dilated composite odontome)
• Invagination in surface of
tooth crown before
calcification .
• Due to
- Localised external
pressure
- Focal growth retardition
- Focal growth stimulation
- Permanent maxillary
lateral incisors most
commonly involved

52. Dens evaginatus
(occlusal tuberculated premolar, Leong’s premolar,
evaginated odontome, occlusal enamel pearl)
• Appears clinically as an
accessory cusp or a
globule of enamel on the
occlusal surface of
premolar .
• Due to proliferation or
evagination of the area of
IEE and subjacent
odontogenic
mesenchyme into dental
organ during tooth
development
Shafers

53. Double teeth
• Fusion : union between
dentin and/ or enamel of
two or more separate
developing teeth.
• Gemination : partial
development of two teeth
from a single tooth bud
following incomplete
division.
• Double teeth more common
in primary than in
permanent dentition .
• Anterior teeth mainly
involved
Soames and Southem

54. • Concrescence:
- acquired anomaly
- Union by cementum
alone following
hypercementosis
- More common in
permanent than
primary dentition

55. Disturbances in structure of teeth
Soames and Southem

56. Soames and Southem

57. Tooth agenesis
• The process of tooth development is under
strict genetic control heritable.
• Most common developmental anomaly in
humans, 2 % - 10% excluding molars( 25%
population).
• Tooth agenesis can be syndromic ,
nonsyndromic, or acquired.
Rena N. D’Souza

58. • Nonsyndromic
Genes implicated in epithelial – mesenchymal
interactions by studies in mouse are strong
candidates for human genetic conditions
involving teeth abnormalities
1. Reigers syndrome : mutations in the RIEG ,
autosomal dominant condition , manifests as
hypodontia , and anomalies in the eye and
umbilicus.
The mouse ortholog of RIEG is Pitx- 2 , otlx-2 and is
expressed in presumptive tooth epithelium
sporadic
familial Autosomal
dominant

59. 2. Msx- 1 was the first tooth signaling molecule
associated with nonsyndromic premolar agenesis
: Arg239Pro missense mutation within the DNA –
binding homeodomain of MSX- 1 associated with
congenital absence of 2nd premolars and third
molars.
Nonsense (SER104Stop) mutation in exon 1 of
MSX- 1 tooth agenesis with cleft lip , cleft
palate or both.
3. Witkops syndrome- nonsense mutation in the
homeodomain of MSX- 1 that resulted in
truncated MSX- 1 protein incisor and premolar
agenesis and nail hypoplsia

60. 4. Solitary Median Maxillary Central Incisor :
caused by premature fusion of enamel knots
in the midline and that is seen commonly in
holoprosencephaly. Missense mutation in
Shh.
5. AXIN 2 , a Wnt – signaling receptor was
identified as responsible for a nonsyndromic
form of tooth agenesis

61. References
• Nanci A. Tencate’s oral histology. 6th edition.
Mosby; 2003. P 79-110.
• Berkovitz B, Holland G, Moxham B. Oral
anatomy, Histology and Embryology. 4th ed.
Mosby; 2009.p 129-51.
• Avery J.Oral Development and Histology. 3rd
ed. Thieme New York; 2002. P172-89.
• Shafer,Hine ,Livy.Textbook of oral pathology.5th
ed.