PPT of development of teeth for 1st BDS students

1. DEVELOPMENT OF TOOTH
(ODONTOGENESIS)
By: Dr.Smitha Rao

2. Introduction:
Tooth development is the complex process by
which teeth form from embryonic cells, grow,
and erupt into the mouth
Although many diverse species have teeth,
non-human tooth development is largely the
same as in humans
For human teeth to have a healthy oral
environment, enamel, dentin, cementum, and
the periodontium must all develop during
appropriate stages of fetal development

3. Introduction:
Primary teeth start to form between the sixth and
eighth weeks in utero, and permanent teeth begin to
form in the twentieth week in utero
If teeth do not start to develop at or near these
times, they will not develop at all
A significant amount of research has focused on
determining the processes that initiate tooth
development. It is widely accepted that there is a
factor within the tissues of the first branchial arch that
is necessary for the development of teeth

4. Primary epithelial band:
After about 37 days of development a
continuous band of thickened epithelium forms
around the mouth in the presumptive upper
&lower jaws
These are roughly horseshoe shaped bands
& correspond in position to the future dental
arches
Formation of these bands is the result not
so much of a increase proliferative activity
within the epithelium as of a change in
orientation of the mitotic spindle & cleavage

5. Primary epithelial band:

6. Primary epithelial band
Vestibular lamina Dental lamina
Separates future lip
from future
alveolar process
Tooth germs

7. During the seventh week, each primary epithelial
band begins to divide on is deeper aspect into 2
processes
The outer or more buccal of this is known as the
vestibular band or vestibular lamina or lip
furrow band
Vestibule forms as a result of the proliferation of
the vestibular lamina into the ectomesenchyme
Vestibular lamina:

8. By 8th week IUL, the dental lamina shows 10 areas of
thickening → TOOTH BUDS → primordial of dec. teeth
Developing tooth bud:
4
5
3
6
7
8
9
1
2
10
dental lamina
Tooth bud

9. Developing tooth bud:
Dental lamina
Permanent tooth buds
Deciduous
tooth bud
Succession
al lamina

10. Within the dental lamina continued & localized
proliferative activity leads to the formation of a
series of epithelial outgrowths into the
ectomesenchyme at sites corresponding to the
positions of the future deciduous teeth
At this point mitotic index, the labeling index
&the growth of epithelial cells are significantly
lower than corresponding indexes in the
underlying ectomesenchyme & ectomesenchymal
cells accumulate around the outgrowths
Dental lamina:

11. Dental lamina:

12.  After initiation of tooth development, dental
lamina degenerates
 Total functional activity period of DL is around
5 yrs
 After functional activity, the remnants of the
dental lamina may persist in the jaw or gingiva
Fate of Dental lamina:

13. Epithelial pearls of Serres
• Remnants of the dental lamina persists
as
epithelial pearls or islands within the
jaws as well as in the gingiva called as
Cell Rests of SERRE.

14. Developing
Tongue
Meckel's cartilage
Developing
tooth bud
Developing
lip
Developing tooth bud:

15. Stages of development of tooth:

16. Stages of tooth development:
Morphologic stages Histogenetic/physiologic phases
Dental lamina Initiation
Bud stage Proliferation
Cap stage-early
-advanced
Histodiffrentiation
Bell stage-early
-advanced
Morphodifferentiation
Formation of enamel & dentin
matrix
Apposition

17. Stages of tooth development:
Classified according to the shape
of the epithelial component of
the tooth into:
bud stage
cap stage
Early bell stage
Advanced Bell stage

18. BUD STAGE
 Arises as a discrete areas of thickening along the dental
lamina
 The bud stage is characterized by the appearance of a
tooth bud without a clear arrangement of cells
 The stage technically begins once epithelial cells
proliferate into the ectomesenchyme of the jaw
 The tooth bud itself is the group of cells at the end of the
dental lamina Oral epithelium
Dental
mesenchyme
Dental epithelium
Basement
membrane

19. BUD STAGE

20. BUD STAGE
 Enamel organ of bud stage contains 2 types of cells:
1. Polygonal cells - centrally situated
2. Low columnar cells -peripherally situated
Polygonal cells
Low columnar cells
Mesenchymal
condensation

21. CAP STAGE

22. CAP STAGE
Tooth germ continues to proliferate at
different rates in different parts of the
tooth bud
The epithelial portion assumes a cap
stage
There is a shallow mesenchymal
invagination on the deep surface of the
bud

23. DENTAL PAPILLA & FOLLICLE
 On the inside of the cap, the ectomesenchymal
cells increase in number. Thetissue appears more
dense than the surrounding mesenchyme and
representsthe beginning of the dental papilla .
 FOLLICLES -it consists of ectomesenchymal cells
and fibres that surrounds the dental papilla and the
enamel organ.
 The enamel is formed from the enamel organ,the
dentin and the pulp from the dental papillaand the
supporting tissues namely the
cementum,periodontal ligament & the alveolar bone
from thedental follicle

24. CAP STAGE
Dental organ
Outer Enamel
Epithelium
Inner Enamel
Epithelium
Stellate
Reticulum

25.  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 .
 The outer enamel epithelium is separated from the
dental sac, & the inner enamel epithelium from
thedental papilla, by a delicate basement
membrane

26. CAP STAGE
 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 eachother by their
cytoplasmic process•
 As the star shaped cells form a cellular network,
they are called the stellate reticulum

27. STELLATE RETICULUM
Role of stellate reticulum
mechanical nutritive
Protects tissue
Maintains tooth
shape

28. TRANSIENT STRUCTURES OF ENAMEL ORGAN
1. Enamel Niche
2. Enamel Cord
3. Enamel Knot
4. Enamel Navel
5. Enamel Septum

29. TRANSIENT STRUCTURES OF ENAMEL ORGAN

30. ENAMEL NICHE
 The enamel niche is a apparent structure created by
the plane of histologic sections cutting through a curved
dental lamina so that mesenchyme appaers surrounded
by the dental epithelium.
 The enamel organ looks to be connected to the oral
epithelium by two or more strands of dental lamina.
 The enamel niche is the name of the mesenchymal
cells which look to be surrounded by the strands of the
dental lamina.
 In actuality, there is no mesenchyme completely
surrounded by dental lamina.
 These cases are a result from the dental lamina being a
curved structure while the slide contains tissue taken in
one plane

32. ENAMEL KNOT AND CORD
 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
 • At the same time a vertical extension of the
enamel knot,called the enamel cord occurs
 The function of enamel knot & cord may act as a
reservoir of the dividing cells for the growing
enamel organ•

33. ENAMEL KNOT AND CORD
 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 pronouncedduring cap
stage of dental development

34. ENAMEL SEPTUM AND ENAMEL NAVEL
 When the enamel cord completely divides the
stellate reticulum into two parts reaching the outer
enamel epithelium,it is termed ENAMEL SEPTUM.
 When the enamel cord meets the outer enamel
epithelium,a small invagination is termed ENAMEL
NAVEL.

36. CAP STAGE

37. BELL STAGE

38. BELL STAGE / HISTODIFFERENTIATION
 • Due to continued uneven growth of the enamel
organ it acquires a bell shape•
 In bell stage crown shape is determined
 Characteristic feature of bell stage:
1. The shape of the future tooth crown is defined
2. Inner enamel epithelial cells elongate &
differentiate into ameloblasts

39. BELL STAGE
Dental papilla
Dental sac
Stellate reticulum
OEE
IEE
Dental lamina

40. BELL STAGE
Enamel organ
Outer enamel
epithelium Inner enamel
epithelium
Stratum
intermedium
Stellate
reticulum

41. BELL STAGE
Inner enamel epithelium :
 Consists of single layer of cells that differentiate
prior to amelogenesis into tall columnar cells
called ameloblasts
 Elongated cells are attached to one another by
junctional complexes & to cells in the stratum
intermedium by desmosomes
 Cells exert an organizing influence on the
underlying mesenchymal cells in the dental
papilla

42. BELL STAGE
Stratum intermedium
 Few layers of squamous cells between IEE &
Stellate reticulum
 Closely attached by desmosomes & gap junctions
 Well defined cytoplasmic organelles, acid
muco-polysaccharides & glycogen deposits →
↑ degree of mitotic activity
 Layer seems to be essential for Enamel formation

43. BELL STAGE
Stellate reticulum:
 There is ↑ in intercellular fluid & the layer
expands
 Cells assume star shape with long processes that
anastomose with adjacent cells
 It collapses before enamel formation begins
 This reduces the distance between centrally
situated ameloblasts & nutrient capillaries near
the OEE

44. BELL STAGE
Outer enamel epithelium :
 Consists of single layered cuboidal cells
 Before enamel formation begins, OEE is folded
 Capillary network develops in between the folds
from dental sac & provides a rich supply to the
avascular enamel organ

45. BELL STAGE
Dental papilla:
 Mesenchyme enclosed in invaginated portion
of dental organ
 The peripheral cells under the influence of
IEE assumes a cuboidal shape first &
columnar cells later → Odontoblast →dentin
 The basement membrane separating Enamel
organ & dental papilla → membrana
preformativa

46. BELL STAGE
Dental sac:
 Forms cementum, alveolar bone,
periodontal ligament
 Condensation of mesenchymal cells around
dental organ

47. ADVANCED BELL STAGE
 2 more features of tooth development
seen:
1. Future DEJ: forms from the boundary
present between IEE & Odontoblasts
2. Her twig's epithelial root sheath:
develops from cervical portion of the
enamel organ

48. ADVANCED BELL STAGE
 Formation of dentin occurs first as a layer along the
future dentino enamel junction in the region of
future cusps &proceeds pulpally & apically.
 After the first layer of dentin is formed,the
ameloblasts lay down enamel overthe dentin in the
future incisal & cuspal areas

49.  Root start forming after dentin formation
has reached future CEJ
 Dental organ & Dental papilla play part in
formation of root
 OEE & IEE meet one another at future
cervical area → cervical loop

50. Cervical loop
Epithelial sheath of
Hertwig
Moulds the
Shape of roots
Initiates dentin
formation

51.  This HERS outlines the future root &thus responsible
for the size, shape ,length & number of roots .
 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 .
 •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

52. H
e
r
t
w
i
g’
s
s
h
e
a
t
h
Epithelial rests of Malassez

54.  Hertwig’s root sheath consists of the outer &
inner enamel epithelia only
 The inner layer of cells remain short & do not
produce enamel
 These cells induce the differentiation of cells of
dental papilla into Odontoblasts →Dentin layer

55.  Cells of dental sac → cementoblasts → cementum
 The Hertwig’s epithelial root sheath folds at future CEJ into a
horizontal plane → epithelial diaphragm
 The plane of diaphragm remains relatively fixed during
development & growth of root
 The proliferation of cells of epithelial diaphragm is
accompanied by proliferation of cells of connective tissue of
the pulp, which occurs in the area adjacent to the diaphragm
 The differentiation of odontoblasts & the formation of dentin
follow the lengthening of root sheath

57.  Differential growth of the epithelial
diaphragm in the multirooted teeth causes
the division of root trunk into 2 or 3 roots•

59. Teeth may develop in abnormal locations
Partial anodontia
Supernumerary teeth - mesiodens
Osteodentin formation
Delayed eruption of tooth
Hutchinson's incisor
Enamel hypoplasia

60. Histophysiologic Phases
Initiation :
 Feature of bud stage of odontogenesis
 Epithelial ectomesenchymal interaction is
essential for initiation induction
 Lack of initiation-absence of either a single
tooth or many teeth.
 Abnormal initiation-single or supernumerary
teeth

61. Histophysiologic Phases
Proliferation :
oCharacterized by regular changes
in the size & shape of the tooth
germ
oTooth germ has a strong affinity to
develop into various structures

62. Histophysiologic Phases
Histodifferentiation :
Shows maximum development in the
early bell stage of tooth development
The formative cells of the tooth germ
undergo definite morphologic as well as
functional changes
Cells differentiate & give up their
capacity to multiply.
Peripheral cells of the dental papilla
differentiate into odontoblasts

63. Histophysiologic Phases
Morphodifferentiation :
 Proliferation is essential for
morphodifferentiation
 Dentinoenamel &the cementoenamel
junctions are developed by the continuous
deposition of enamel, dentin & cementum
 Complete morphologic pattern, size &
shape of a tooth are established

64. Histophysiologic Phases
Apposition :
 Rhythmic ,layer-like deposition of an
extracellular matrix of enamel &dentin
 Pattern of deposition of enamel & dentin is
different
 Regular &rhythmic deposition of the
extracellular matrix
 Periods of activity & rest are present
during tooth development

65. Teeth may develop in abnormal locations
Partial anodontia
Supernumerary teeth - mesiodens
Delayed eruption of tooth
Hutchinson's incisor
Enamel hypoplasia
Clinical considerations