The document outlines the process of odontogenesis, detailing the stages of tooth development, including the bud, cap, and bell stages, as well as the roles of dental and vestibular laminae. It emphasizes the importance of understanding these developmental stages for diagnosing dental anomalies and describes the histophysiological changes that occur during tooth formation. Additionally, it provides a timeline of human tooth development and references key literature on the subject.

2. Jishnu Kinkor Goswami

3. Contents
 Introduction
 Dental Lamina
 Vestibular lamina
 Development of tooth bud
 Stages of tooth development
 Histophysiological Stages
 Bud stage
 Cap stage
 Bell stage
 Root formation
 References

4. Introduction
 The Process of tooth development is known as Odontogenesis
 Understanding the process of tooth development is of particular
importance for the dentist; as developmental disturbances may
occur at any stage of this process resulting in different types of
tooth anomalies.

5.  Primitive oral cavity is lined by Stratified
Squamous Epithelium also called Oral
Epithelium.
 After about 37 days of Intra uterine life a
continuous band of horse shoe shaped
thickened epithelium forms in the area of
the future arches around the mouth, known
as the Primary Epithelial Band.

6.  After 7 weeks, the primary
epithelial band quickly gives
rise to two processes which
grows into the underlying
connective tissue. These are the
dental lamina, which forms first
lingually, and the vestibular
lamina, which forms later
buccally.
Nasal
Septum
Palatal
Shelf
Tongue
Dental Lamina(DL) and Vestibular lamina(VL)
marked with Arrowhead and arrow respectively
D L
V L

7.  The cells of the connective tissue
are derived from neural crest cells
hence they are of
ectomesenchymal origin, and these
cells signal the overlying ectoderm
to start tooth development.
The Vestibular and dental lamina at
higher magnification
Vestibular lamina Dental Lamina

8. Dental Lamina
 The epithelial cells of Dental
lamina continues to
proliferate further, leading to
epithelial outgrowths into the
underlying mesenchyme at
sites corresponding to the
positions of the future
deciduous teeth.
 Ectomesenchymal cells
accumulate around these
epithelial outgrowths.

9.  Dental lamina serves as
primordium for the ectodermal
portion of deciduous teeth, hence
all Deciduous teeth arise from
Dental Lamina
 Later during development of jaws,
permanent molars arise directly
from distal extension of dental
lamina.

10.  The other permanent teeth develop from a lingual extension of the free end
of dental lamina( also called successional lamina) opposite to enamel organ
of each deciduous teeth.

11. Fate of Dental Lamina
 Total activity of dental lamina exceeds for over 5 years, after which it
begins to degenerate.
 As teeth develops, they lose their connections with dental lamina.
 Remnants of dental lamina persists as epithelial islands/pearls within the
jaws, known as epithelial rests of serres.

12. Vestibular Lamina
 The vestibule forms as a
result of the proliferation of
the vestibular lamina into the
ectomesenchyme soon after
formation of the dental
lamina.
 The cells of the vestibular
lamina rapidly enlarge and
then degenerate to form a
cleft that becomes the
vestibule between the cheek
and the tooth-bearing area. Vestibular
lamina
Enamel
Organ

13. Development of Tooth bud
 At certain point along dental lamina, each representing the
location of 10 mandibular and 10 maxillary teeth, ectodermal
cells multiply still more rapidly to form knob like structures
that grow into underlying mesenchyme called Enamel organ.

14. As proliferation continues, each enamel organ changes shape and
increase in size.

15.  As proliferation advances, each enamel organ takes a
shape that resembles a cap.
 On the inside of the cap, the ectomesenchymal cells
increase in number. The tissue appears more dense than
the sorrounding mesenchyme, and represents Dental
papilla.

16.  Sorrounding the combined Enamel organ and Dental
papilla, the third part of tooth bud develops, called as
Dental sac/follicle.
 The ectomesenchymal cells and fibres of dental sac
covers the enamel organ and dental papilla.

17.  Hence the tooth bud consists of Ectodermal
component, the Enamel organ; the ectomesenchymal
component, Dental Papilla and Dental sac/ follicle.
 The enamel is formed from the Enamel organ; the
dentin and pulp from Dental papilla; and the
supporting tissues namely the cementum, periodontal
ligaments and alveolar bones from Dental sac.

18.  Depression occupied by dental papilla deepens as
development continues, until enamel organ starts
resembling a bell.
 The dental lamina becomes longer and thinner till it
finally loses connection with the epithelium of primitive
oral cavity.

19. Stages of tooth development
Morphological stages:
 Bud stage
 Cap stage
 Bell stage:
* Early
* Advanced
Physiological stages:
 Initiation
 Proliferation
 Histodifferentiation
 Morphodifferentiation
 Apposition

20. Histophysiology of tooth
development
1- Initiation:
 The dental lamina and associated tooth buds represent those parts of
the oral epithelium that have the potential for tooth formation.
 Different teeth are initiated at definite times.
 Initiation induction requires ectomesenchymal–epithelial interaction.

21. 2- Proliferation:
 Enhanced proliferative activity ensues at the points of initiation and
results successively in the bud, cap, and bell stages of the
odontogenic organ.
 Proliferative growth causes regular changes in the size and
proportions of then growing tooth germ.

22. 3- Histodifferentiation: The formative cells of the tooth germs developing
during the proliferative stage undergo definite morphologic as well as
functional changes and acquire their functional assignment (the appositional
growth potential).
4- Morphodifferentiation: The morphologic pattern, or basic form and relative
size of the future tooth, is established by morphodifferentiation, that is, by
differential growth.

23.  Morphodifferentiation therefore is impossible without proliferation.
 The advanced bell stage marks not only active histodifferentiation but also
an important stage of morphodifferentiation in the crown, outlining the
future dentinoenamel junction.
5- Apposition: is the deposition of the matrix of the hard dental structures.

24. Bud Stage
 Enamel Organ develops
into round or ovoid
swelling called tooth bud.
 Enamel organ at this stage
consists of:
* Peripherally located low
columnar cells
* Centrally located
polygonal cells.
Dental
lamina
Tooth
Bud

25. The sorrounding mesenchymal
cells proliferates leading to
their condensation in 2 areas:
 Ectomesenchymal
condensation just below
enamel organ is dental
papilla
 Ectomesenchymal
condensation sorrounding
enamel organ and dental
papilla is dental follicle.

26.  Dental sac and follicle are not well-defined at this stage.

27. Cap Stage
 As the tooth continues to
proliferate, it does not
expand uniformly into
large sphere.
 Instead unequal growth
in different parts of the
enamel organ leads to
the cap stage.

28. At this stage, tooth germ consists
of:
 Outer enamel epithelium
 Inner enamel epithelium
 Stellate reticulum
 Dental papilla
 Dental sac

29.  Outer enamel epithelium consists
of cuboidal cells and covers the
convexity of the enamel organ.
 Inner enamel epithelium covers the
concavity of the cap and are tall
columnar in shape.

30.  Outer enamel epithelium is separated from dental sac and inner enamel
epithelium from dental papilla by a delicate basement membrane.
 Stellate reticulum contains polygonal cells located between inner and outer
enamel epithelium, they separate from one another and becomes star shaped
due to accumulation of intracellular fluid, but remains in contact through
cytoplasmic process.
 They protect and support the delicate enamel forming cells by cushioning
effect.

31.  The cells in the centre of
enamel organ are densely
packed and are called enamel
knot.
 Enamel knot may function as a
signaling centre as many
growth factors are expressed by
the cells, hence determining the
shape of the tooth.
 The Ectomesenchymal
condensation i.e. dental papilla
and dental sac becomes more
prominent during this stage.

32. Bell Stage
 Due to continued uneven growth of the enamel organ and
the deepened invagination of epithelium, it acquires a bell
shape.
 The crown shape is determined at this stage
 Subdivided into:
* Early bell stage
* Late bell stage

33. Early bell stage
 Inner enamel epithelium
 Outer enamel epithelium
 Stratum intermedium
 Stellate reticulum
 Cervical loop
 Dental papilla
 Dental sac

34.  Inner enamel epithelium
contains tall columnar
cells that later
differentiates into
ameloblasts.
 These cells contain
nucleus away from
basement membrane and
nuclear cytoplasmic ratio
is high.

35.  A few layer of squamous cells
form the stratum intermedium,
between the inner enamel
epithelium and the stellate
reticulum.
 These cells are closely attached
by desmosomes.
 This layer is essential for
enamel formation.

36.  Stellate reticulum expands further due to an increase in
intracellular fluid.
 These star shaped cells, having a large processes
anastomose with adjacent cells.
 When enamel formation starts, this zone starts collapsing
to reduce distance between inner and outer enamel
epithelium.

37.  The cells of outer enamel epithelium flattens to low
cuboidal form.
 Since the outer enamel epithelium is rich in capillary
network, it provides nutrition to the cells of enamel organ.

38.  The peipheral cells of dental papilla differentiates into
odontoblasts before the inner enamel epithelium starts
producing enamel.
 The dental sac exhibits a circular arrangement of fibres &
resembles a capsule around enamel organ.

40.  Dental lamina extends
lingually and is termed
successional lamina as it
gives rise to permanent
successors of deciduous
teeth.
 The Cervical loop contains
only inner and outer enamel
epithelium.
 The cells continue to divide
until tooth attains full size
and gives rise to epithelial
component of root formation
after crown formation.

41. Advanced bell stage
 The dental lamina separates
from tooth germ, and breaks
into discrete epithelial
islands.
 Mineralization and root
formation starts at this stage.
 The boundary between inner
enamel epithelium and
odontoblasts represents the
Dentino-enamel junction.

42.  Formation of dentin occurs
first as a layer along the
future Dentino enamel
junction in the region of
future cusps and proceeds
pulpally and apically.
 After the first layer of dentin
is formed, the ameloblasts
lay down enamel over the
dentin in future incisal and
cuspal areas.

43.  The enamel formation starts by differentiation of cells of inner enamel
epithelium first at the cusp tips then proceeds coronally and cervically in all
the regions from the Dentino-enamel junction towards the surface.
 Root formation begins after enamel and dentin formation have reached the
cemento-enamel junction.

44. Root formation
 The cervical portion of the enamel
organ, gives rise to the Hertwig’s
Epithelial Root Sheath(HERS),
formed due to proliferation of
cervical loop cells.
 Consists of only inner and outer
enamel epithelium.
 The HERS determines the shape,
size, length & Number of roots.

45.  When dentin is formed it loses its
structural integrity due to invasion
by sorrounding connective tissue of
dental sac.
 The epithelium is moved away from
surface of dentin so that connective
tissue cells come into contact with
outer surface dentin & differentiate
into cementoblasts that deposit a
layer of cementum onto surface of
dentin.
Dentin
Odontoblasts
Predentin
Pulp

46.  Remnants of Hertwig’s Epithelial Root Sheath are found in Periodontal
ligament and are known as cell rests of Malassez.
 Prior to the beginning of root formation, epithelial root sheath forms
epithelial diaphragm by bending at future Cemento-Enamel junction into a
horizontal plane, narrowing the wide cervical margin.

48.  Proliferation of cells of epithelial diaphragm is
accompanied by ectomesenchymal cell proliferation
adjacent to diaphragm.
 In the last stages of root development, the proliferation of
epithelium in diaphragm lags behind that of pulpal
connective tissue
 Thus wide apical foramen is reduced to width of
diaphragmatic opening itself, later by apposition of dentin
and cementum at the apex of root.

49.  In case of multirooted teeth, there is differential
growth of epithelial diaphragm in the form of tongue
like extensions which grow towards each other and
fuse causing division of trunk into two or three roots.
 Before division of the root trunk occurs, free ends of
the horizontal epithelial flaps grow towards each other
and fuse.

50. Timeline of Human tooth development
Age Developmental Characteristics
42 to 48 days Dental Lamina Formation
55 to 56 days Bud stage for Deciduous teeth
14 weeks Bell stage for Deciduous teeth;
Bud stage for Permanent teeth
18 weeks Dentin & Functional Ameloblasts in
deciduous teeth
32 weeks Dentin & Functional ameloblasts in
permanent teeth

51. References
o Antonio Nanci. Development of the Tooth and its Supporting Tissues.
Ten Cate’s Oral Histology Development Structure and Function. 8th Edition;
2012, 70-94.
o GS Kumar. Development and Growth of Teeth. Orban’s Oral
histology and Embryology. Elsevier, 13th Edition; 2013, Page no. 24-47.