The document provides an extensive overview of tooth development, detailing stages such as the bud, cap, and bell stages, highlighting the roles of the dental lamina and Hertwig's epithelial root sheath in forming teeth. It elaborates on various developmental disorders, such as anodontia and dentinogenesis imperfecta, and includes clinical considerations for tooth anomalies like dens invaginatus and talon cusp. The text emphasizes the intricate biological processes involved in tooth formation from the 6th week of gestation through various stages of development until root formation.

1. DEVELOPMENT OF TOOTH
Piyush verma
MDS 1st year
Dept of Pedodontics & Preventive Dentistry

2. CONTENTS
1. Introduction
2. Dental Lamina
3. Vestibular Lamina
4. Tooth development
5. Developmental stages
• Bud stage
• Cap stage
• Bell stage
• Advanced bell stage
6. Hertwig’s epithelial root sheath and root formation
7. Conclusion
8. References

3. INTRODUCTION

4. 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

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. DENTAL LAMINA

8. • 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.

9. • At about 7th week the primary epithelial band divides into an inner (lingual)
process called Dental Lamina & an outer ( buccal) process called Vestibular
Lamina
• The dental lamina serves as the primordium for the ectodermal portion of
the deciduous teeth
• Later during the development of jaws, permanent molars arise directly from
the distal extension of the dental lamina

10. • The successors of the deciduous teeth develop from a lingual extension of the
free end of the dental lamina opposite to the enamel organ of each deciduous
teeth.

11. The lingual extension of the dental lamina is named the successional lamina &
develops from the 5th month in utero ( permanent central incisor) to the 10th
month of age (second premolar)

12. FATE OF DENTAL LAMINA
• It is evident that total activity of dental lamina exceeds over a period of atleast 5 yrs
• As the teeth continue to develop, they loose their connection with the dental lamina
•They later break up by mesenchymal invasion, which is at first incomplete and does not
perforate the total thickness of the lamina

13. • Fragmentation of the dental lamina progresses toward the developing enamel
organ
• Any particular portion of the dental lamina functions for a much briefer period
since only a relatively short time elapses after initiation of tooth development
before the dental lamina begins to degenerate
• However the dental lamina may still be active in the third molar region after it
has disappeared elsewhere, except for occasional epithelial remnants

14. CLINICAL CONSIDERATIONS

15. ANODONTIA
• Anodontia, also called anodontia vera, is
a rare genetic disorder characterized by
the congenital absence of
all primary or permanent teeth
• It is of following types
1. Complete anodontia/ total anodontia
2. Partial anodontia/ sub-Total anodontia
• Forms-
1. True anodontia
2. Psuedo anodontia
3. False anodontia
COMPLETE
PARTIAL

16. SUPERNUMERARY TEETH
Supernumerary teeth can be classified by
shape and by position. The shapes include:
• Supplemental(where the tooth has a
normal shape for the teeth in that series);
• Tuberculate (also called "barrel shaped");
• Conical (also called "peg shaped");
• Compound odontome (multiple small
tooth-like forms);
• Complex odontome (a disorganized mass of
dental tissue)
Hyperdontia is the condition of
having supernumerary teeth, or teeth which
appear in addition to the regular number of
teeth
When classified by position, a supernumerary tooth
may be referred to as a mesiodens, a paramolar, or a
distomolar.

17. VESTIBULAR LAMINA
• Labial and buccal to the dental lamina in each dental arch, another epithelial
thickening develops independently
• It is Vestibular Lamina also termed as lip furrow band
• Subsequently hollows and form the oral vestibule between the alveolar portion of
the jaws and the lips and cheeks.

18. TOOTH DEVELOPMENT

19. • At certain points along the dental lamina each representing the location of one of the
10 mandibular & 10 maxillary teeth, ectodermal cells multiply rapidly & little knobs
that grow into the underlying mesenchyme
• Each of these little down growths from the dental lamina represents the beginning of
the enamel organ of the tooth bud of a deciduous tooth
• First to appear are those of anterior mandibular region
• As the cell proliferation occurs each enamel organ takes a shape that resembles a cap

20. DENTAL PAPILLA
On the inside of the cap, the ectomesenchymal cells increase in number. The
tissue appears more dense than the surrounding mesenchyme and represents
the beginning of the dental papilla
B = Dental Papilla

21. DENTAL SAC/ DENTAL FOLLICLE
Surrounding the combined enamel organ or dental papilla, the third part of the tooth
bud forms. It is known as dental sac/follicle and it consists of ectomesenchymal cells and
fibres that surrounds the dental papilla and the enamel organ.
C= Dental sac

22. • Thus the tooth germ consists of ectodermal
component- the enamel organ, the
ectomesenchymal components- the dental papilla
& the dental follicle
• The enamel is formed from the enamel organ,
the dentin and the pulp from the dental papilla
and the supporting tissues namely the cementum,
periodontal ligament & the alveolar bone from the
dental follicle
• During & after these developments the shape of
the enamel organ continues to change
• The depression occupied by the dental papilla
deepens until the enamel organ assumes a shape
resembling a bell
• The dental lamina becomes longer, thinner &
finally loses its connection with the epithelium of
the primitive oral cavity

23. DEVELOPMENTAL STAGES

24. 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

25. BUD STAGE / PROLIFERATION
• 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
• 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

26. • 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

27. CAP STAGE / PROLIFERATION
• 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

28. 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

29. •The outer enamel epithelium is separated from the
dental sac, & the inner enamel epithelium from the
dental papilla, by a delicate basement membrane

30. 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

31. • 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

32. • At the same time a vertical extension of the enamel knot,
called the enamel cord occurs

33. • 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

34. BELL STAGE / HISTODIFFERENTIATION
• Due to continued uneven growth of the
enamel organ it acquires a bell shape
• In bell stage crown shape is determined
• It was thought that the shape of the crown
is due to pressure exerted by the growing
dental papilla cells on the inner enamel
epithelium
• This pressure however was shown to be
opposed equally by the pressure exerted by
fluid present in the stellate reticulum
• The folding of enamel organ to cause
different crown shapes is shown to be due to
different rates of mitosis & difference in cell
differentiation time

35. INNER ENAMEL EPITHELIUM
• The inner enamel epithelium consists of a single layer of cells that differentiate prior to
amelogenesis into tall columnar cells called ameloblasts
• These elongated cells are attached to one another by junctional complexes laterally &
to cells in the stratum intermedium by desmosomes
• The cells of the inner enamel epithelium exert a strong influence on the underlying
mesenchymal cells of the dental papilla, which later differentiate into odontoblasts

36. STRATUM INTERMEDIUM
• A few layers of squamous cells form the stratum intermedium , between the inner
enamel epithelium & the stellate reticulum
• These cells are closely attached by desmosomes & gap junctions
• This layer seems to be essential to enamel formation

37. STELLATE RETICULUM
• The stellate reticulum expands further due to continued accumulation of intra-cellular
fluid
• These star shaped cells, having a large processes anastomose with those of adjacent
cells
• As the enamel formation starts., the Stellate reticulum collapses to a narrow zone
thereby reducing the distance between the outer & inner enamel epithelium

38. OUTER ENAMEL EPITHELIUM
• The cells of the outer enamel epithelium flatten to form low cuboidal cells
• The outer enamel epithelium is thrown into folds which are rich in capillary network,
this provides a source of nutrition for the enamel organ
• Before the inner enamel epithelium begins to produce enamel. Peripheral cells of
the dental papilla differentiate into odontoblasts
• These cuboidal cells later assumes a columnar form & produce dentin

39. DENTAL LAMINA
• Dental lamina is seem to extend lingually and is termed successional dental lamina
as it gives rise to enamel organs of permanent successors of deciduous teeth
• The enamel organs of deciduous teeth in the bell stage show successional lamina &
their permanent successor teeth in the bud stage

40. DENTAL SAC
• The dental sac exhibits a circular
arrangement of fibres & resembles a
capsule around the enamel organ
• The fibres of the dental sac form
the periodontal ligament fibres that
span between the root & the bone
• The junction between the inner
enamel epithelium & odontoblasts
outlines the future dentino-enamel
junction

41. CLINICAL CONSIDERATIONS

42. DENTINOGENESIS IMPERFECTA
• Dentinogenesis imperfecta (hereditary
Opalescent Dentin) is a genetic
disorder of tooth development.
• This condition causes teeth to be
discolored (most often a blue-gray or
yellow-brown color) and translucent. Teeth
are also weaker than normal, making them
prone to rapid wear, breakage, and loss.
• These problems can affect both primary
(baby) teeth and permanent teeth.
• This condition is inherited in
an autosomal dominant pattern, which
means one copy of the altered gene in
each cell is sufficient to cause the disorder.

43. ADVANCED BELL STAGE / MORPHODIFFERENTIATION
 Characterized by the commencement
of mineralization & root formation
 The boundary between the inner
enamel epithelium & odontoblasts
outline the future dentinoenamel
junction
 Formation of dentin occurs first as a
layer along the future dentinoenamel
junction in the region of future cusps &
proceeds pulpally & apically
 After the first layer of dentin is formed,
the ameloblasts lay down enamel over
the dentin in the future incisal & cuspal
areas

44.  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

45. CLINICAL CONSIDERATIONS

46. HUTCHINSON’S INCISOR
MULBERRY MOLARS

47. FUSION
• The phenomenon of tooth
fusion arises through union of two
normally separated tooth germs, and
depending upon the stage of
development of the teeth at the time of
union, it may be either complete or
incomplete.
• However, fusion can also be the union
of a normal tooth bud to a
supernumerary tooth germ. In these
cases, the number of teeth is fewer if
the anomalous tooth is counted as one
tooth.

48. GEMINATION
Gemination arises when two
teeth develop from one tooth
bud and, as a result, the
patient has an extra tooth

49. FORMATION OF ENAMEL & DENTIN MATIX
( APPOSITION)
• Apposition is the deposition of the matrix of the hard enamel
structures
• Appositional growth of the enamel & dentin is a layer like
deposition of an extracellular matrix. This type of growth is
therefore additive
• Appositional growth is characterised by regular & rhythmic
deposition of the extracellular matrix, which is of itself incapable of
further growth

50. CLINICAL CONSIDERATIONS

51. ENAMEL HYPOPLASIA
Enamel hypoplasia is the
defect of the teeth in which
the tooth enamel is hard but
thin and deficient in amount
This is caused by defective
enamel matrix formation
with a deficiency in the
cementing substance

52. AMELOGENESIS IMPERFECTA
• Amelogenesis imperfecta presents with
abnormal formation of the enamel or
external layer of teeth. Enamel is composed
mostly of mineral, that is formed and
regulated by the proteins in it. Amelogenesis
imperfecta is due to the malfunction of the
proteins in the enamel:
ameloblastin, enamelin, tuftelin, amelogenin
• People afflicted with amelogenesis
imperfecta have teeth with abnormal color:
yellow, brown or grey. The teeth have a
higher risk for dental cavities and are
hypersensitive to temperature changes. This
disorder can afflict many number of teeth.

53. Dens- In- Dente ( DENS INVAGINATUS)
• Represents a defect of tooth in which a
focal area on the tooth surface is folded or
invaginated pulpally to a variable extent
• Defect in generally localized to a single
tooth & interestingly maxillary lateral
incisors are more commonly affected
• Bilateral involvement is often seen &
sometimes defect can involve multiple teeth
involving the supernumeraries
• In case of pulp involvement with or
without apical pathology, endodontic
treatment should be attempted. However in
more severe form extraction should be done

54. DENS EVAGINATUS
• Dens evaginatus is a condition found
in teeth where the outer surface appears
to form an extra bump or cusp.
• Premolars are more likely to be
affected than any other tooth. This may
be seen more frequently in Asians
• The pulp of the tooth may extend into
the dens evaginatus.
• There is a risk of the dens evaginatus
chipping off in normal function
• Hence this condition requires
monitoring as the tooth can lose its blood
and nerve supply as a result and may
need root canal treatment.

55. TALON CUSP
• A talon cusp, also known as an
"eagle's talon", is an extra cusp on an
anterior tooth.
• Of all cases, 55% occur on the
permanent maxillary lateral incisor,
and 33% occur on the
permanent maxillary central incisor.
They are found rarely in primary teeth
• Whenever the lingual pits are
present restorative treatments should
be done to prevent caries
• When talon cusp interferes with
normal occlusion preventive care
should be taken by performing
endodontic treatment

56. ROOT FORMATION

57. • 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

58. •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

59. • 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
• The free end of diaphragm does not grow
into the connective tissue but the
epithelium proliferates coronal to the
epithelial diaphragm

60. • 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 rapid sequence of proliferation &
destruction of Hertwig’s root sheath
explains the fact that it cannot be seen as
a continuous layer on the surface of
developing 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

61. • Differential growth of the epithelial
diaphragm in the multirooted teeth causes
the division of root trunk into 2 or 3 roots
• During the general growth of enamel
organ, expansion of its cervical opening
occurs in such a way that long tongue like
extensions of the horizontal diaphragm
develop
• Before division of the root trunk occurs,
free ends of the horizontal epithelial flaps
grow towards each other & fuse
• The single cervical opening is divided into
2 or 3 openings

62. • On the pulpal surface of
the dividing epithelial
bridges, dentin formation
starts
• On the periphery of each
opening, root development
follows in the same way as
described for single rooted
teeth

63. CLINICAL CONSIDERATIONS

64. DILACERATION
• Dilaceration refers to an angulation or a
sharp bend or curve anywhere along the
root portion of a tooth
• Condition probably occurs subsequent to
trauma or any other defect of development
which alters the angulation of the tooth
germ during root formation
• Can easily be detected by radiographs
• Care should be taken during extraction
since these teeth are more prone to fracture

65. CONCRESCENCE
Concrescence is a condition
of teeth where
the cementum overlying the roots
of at least two teeth join together.
The cause can sometimes be
attributed to trauma or crowding of
teeth.
Radiographic diagnosis is
mandatory before attempting tooth
extraction

66. CONCLUSION
Since development of tooth forms the base of
dentistry, a thorough understanding and a sound
knowledge is required by a dentist regarding the
development stages of tooth & the anomalies related
to it, so as to identify & treat them in a proper fashion.

67. REFERENCES
• Orban’s, Textbook of oral histology & embryology
• Ten cates, Textbook of oral histology
• Shaefer’s. Textbook of oral pathology
• Avery JK: Embryology of the tooth. J Dent Res 30:490,1951
• Avery JK: Primary induction of tooth formation. JDent Res
33:702,1954