This presentation includes the development of tooth along with genes responsible for initiation, localaization and patterning of teeth.

1. DEVELOPMENT OF
TEETH AND
SUPPORTING
STRUCTURES
-Dr. VASAVI REDDY

2. CONTENTS:
 Introduction
 Primary Epithelial Band: Dental Lamina ,Vestibular Lamina.
 Initiation of the Tooth.
 Tooth Type Determination.
 Regionalization of Oral and Dental Ectoderm.
 Developmental stages: Bud stage, cap stage, bell stage, advanced bell stage
 Amelogenisis.
 Dentinogenesis.
 Root Formation.
 Histophysiological stages.
 Evolution of periodontium
 Tooth Supporting structures development.
 Developmental Anomalies.
 Conclusion.

3. Introduction:
The actual development of teeth
starts at approximately 6 to 7
weeks after conception.
It occurs by the interaction of the
oral epithelial cells and the
underlying mesenchymal cells.

4. Development:
 The epithelium of the primitive oral cavity is
called Oral Ectoderm. This oral ectoderm contacts
the endoderm of the foregut to form the
buccopharyngeal membrane.
 At about 27th day, this membrane ruptures and a
primitive oral cavity establishes connection with
foregut.
 The most connective tissue cells underlying the
oral ectoderm are ectomesenchyme in origin.
 After 2 to 3 weeks of the rupture, the cells of oral
ectoderm proliferate and forms a continuous band
of thickened epithelium around the mouth in
upper and lower jaws.
 This band is horse shoe shape. Each band is known
as primary epithelial band.
 At about 7th week, this band divides into an inner
process called dental Lamina and outer process
called the vestibular lamina.

5. Epithelium mesenchymal interaction:
 The neural crust migrate into the Ist brachial
arch,which gets deposited and forms a band of
ectomesenchyme beneath the epithelium of the
primitive oral cavity (Stomatodeum).
 Then the epithelium of the stomatodeum releases
factors which initiates epithelial mesenchymal
interaction.
 These interactions are a series of programed,
sequential and reciprocal communication between
the epithelium and mesenchyme by signaling
molecule are in the form off growth factors,
genetic factors and extra cellular matrix.

6. -Present Labial or buccal to
dental lamina
-Proliferation of vestibular
lamina into mesenchyme
-Rapidly enlarges and then
degenerate to form cleft
vestibule
-Shows continuous and
localized proliferative
activity
-Forms series of epithelial
outgrowth
-Determines future
deciduous tooth position
PRIMARY EPITHELIAL BAND (roughly horseshoe shaped)
(forms at 6th week of embryogenesis)
DENTAL LAMINA VESTIBULAR LAMINA

7. FATE OF DENTAL LAMINA:
 It is evident that the total activity of the dental lamina
extends over a period of at least 5 years.
 As the teeth continue to develop, they lose 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.
 Remnants of the dental lamina persist as epithelial pearls
or islands within the jaw as well as in the gingiva. These
are referred to as cell rest of Serres.

8. INITIATION OF TOOTH:
 Murine experiments indicate is that odontogenesis is
initiated first by factors resident in the first arch
epithelium influencing ectomesenchyme but that with
time this potential is assumed by the ectomesenchyme.
 These experimental findings are mirrored by the
expression pattern of transcription and growth factors in
these tissues.
 The earliest histologic indication of tooth development is
at day 11 of gestation, which is marked by a thickening of
the epithelium where tooth formation will occur on the
oral surface of the first branchial arch

9. SIGNALS MEDIATING INITIAL STEPS OF TOOTH DEVELOPMENT??
 To date, the earliest mesenchymal markers for tooth formation are the LIM-
homeobox (Lhx) domain genes (transcription factors), Lhx-6 and Lhx-7 which
are expressed in the neural crest–derived ectomesenchyme of the oral portion
of the first branchial arch.
 Experimental data demonstrate that the expression of Lhx-6 and Lhx-7 results
from a signaling molecule originating from the oral epithelium of the first
branchial arch.
 A prime candidate for the induction of Lhx genes is secreted fibroblast growth
factor-8; this growth factor is expressed at the proper place and time in the
first branchial arch and is able to induce Lhx-6 and Lhx-7 expression in in
vitro experiments.
 FGF-8 is known to establish oro aboral axis and position of tooth germ.

10. WHAT CONTROLS THE POSITION AND THE
NUMBER OF TOOTH GERMS ALONG THE
ORAL SURFACE?
 The Pax-9 gene is one of the earliest mesenchymal genes
that define the localization of the tooth germs.
 Shh gene have a role in stimulating epithelial cell
proliferation and its local expression at the sites of tooth
development
 Lef-1 is first expressed in dental epithelial thickenings
and during bud formation shifts to being expressed in the
condensing mesenchyme
 Ectopic expression of Lef-1 in the oral epithelium also
results in ectopic tooth formation

11. TOOTH TYPE DETERMINATION
 PATTERNING – determination of specific tooth types at
their correct positions in the jaws
 The determination of crown pattern is a remarkably
consistent process. Although in some animal teeth are all
the same shape (homodont), in most mammals they are
different (heterodont), falling into three families:
incisiform, caniniform, and molariform.
 Two hypothetical models have been proposed to explain
how these different shapes are determined, and evidence
exists to support both

12. FIELD MODEL:
 It proposes that the
factors responsible for
tooth shape reside
within the
ectomesenchyme in
distinct graded and
overlapping fields for
each tooth family.
 The fact that each of
the fields expresses
differing combinations
of patterning
homeobox genes
supports this theory

13. The homeobox code (field) model for
dental patterning

14. CLONE MODEL:
 It proposes that each tooth class is derived from a clone
of ectomesenchymal cells programmed by epithelium to
produce teeth of a given pattern.
 In support of this contention, isolated presumptive first
molar tissues have been shown to continue development
to form three molar teeth in their normal positional
sequence.

15. INSTRUCTIVE SIGNALS
FOR PATTERNING
 Signaling molecules often
regulate the expression of
transcription factors that
turn out to regulate the
expression of those same
signaling molecules.
 At least 12 transcription
factors are expressed in
odontogenic mesenchyme,
and some have redundant
roles.

16. REGIONALIZATION OF ORAL AND DENTAL
ECTODERM
 Because regionally restricted expression of signaling protein
genes in oral ectoderm controls dental initiation and
patterning, it follows that the mechanisms that control the
regional restriction of ectodermal signals need to be
understood.
 Misexpression of Wnt-7b in presumptive dental ectoderm results
in loss of Shh expression and failure of tooth bud formation.
 This shows that the Wnt-7B gene represses Shh expression in
oral ectoderm and thus the boundaries between oral and dental
ectoderm are maintained by an interaction between Wnt and
Shh signaling.

17. DEVELOPMENTAL STAGES
 Although tooth development is a continuous process, the developmental
history of a tooth is divided into several morphologic “stages” for descriptive
purposes.
 While the size and shape of individual teeth are different, they pass through
similar stages of development. They are named after the shape of the enamel
organ (epithelial part of the tooth germ), and are called the: bud,cap, and
bell stages

18. BUD STAGE
 The epithelium of the dental laminae is separated
from the underlying ectomesenchyme by a
basement membrane.
 Simultaneous with the differentiation of each
dental lamina, round or ovoid swellings arise from
the basement membrane. These are the primordia
of the enamel organs, the tooth buds.
 In the bud stage, the enamel organ consists of
peripherally located low columnar cells and
centrally located polygonal cells.
 Many cells of the tooth bud and the surrounding
mesenchyme undergo mitosis.

19. CAP STAGE
 increased mitotic activity and the
migration of neural crest cells into
the area the ectomesenchymal
 condense cells surrounding the
tooth bud.
 The area of ectomesenchymal
condensation immediately
subjacent to the enamel organ
 epithelial outgrowth, which
superficially resembles a cap
sitting on a ball of condensed
ectomesenchyme dental papilla.

20.  The enamel niche is an apparent
structure in histologic sections,
created because the dental lamina
is a sheet rather than a single
strand and often contains a
concavity filled with connective
tissue.
 Dental follicle is the condensed
ectomesenchyme limiting the
dental papilla and encapsulating
the enamel. It forms cementum,
periodontal ligament, alveolar
bone issue.

21.  The cells in the center of the
enamel organ synthesize and
secrete glycosaminoglycans into
the extracellular compartment
between the epithelial cells
 Glycosaminoglycans are hydrophilic
and so pull water into the enamel
organ.
 fluid increases the volume of the
extracellular compartment of the
enamel organ, and the central
cells are forced apart.
 Because they retain connections
with each other through their
desmosome contacts, they become
star-shaped.
stellate reticulum

22. Enamel knots
 Each tooth germ has a single primary enamel
knot and secondary enamel knots at the tips
of the future cusps in molars at the cap
stage.
 The enamel knot precursor cells can be
detected first at the tip of the tooth buds by
expression of the p21 gene, followed shortly
after by Shh.
 By the cap stage, when the enamel knot is
visible histologically, it expresses genes for
many signaling molecules, including Bmp-2,
Bmp-4, Bmp-7, Fgf-4, Fgf-9, Wnt-10b, Slit-1,
and Shh
 Fgf-4 and Slit-1 may be the best molecular
markers for enamel knot formation because
these are the only two genes that have been
observed in both primary and secondary
knots.

23.  a vertical extension of the enamel knot, called the enamel cord
 When the enamel cord extends to meet the outer enamel epithelium it is
termed as enamel septum, for it would divide the stellate reticulum into two
parts.
 The outer enamel epithelium at the point of meeting shows a small
depression and this is termed enamel navel as it resembles the umbilicus.
 These are temporary structures (transitory structures) that disappear before
enamel formation begins
 Outer and inner enamel epithelium
 -The peripheral cells of the cap stage are cuboidal, cover the convexity of the
“cap,” and are called the outer enamel (dental) epithelium. The cells in the
concavity of the “cap” become tall, columnar cells and represent the inner
enamel (dental) epithelium.
 -The outer enamel epithelium is separated from the dental sac, and the inner
enamel epithelium from the dental papilla, by a delicate basement
membrane. Hemidesmosomes anchor the cells to the basal lamina

24. BELL STAGE
 Four different types of epithelial
cells can be distinguished on light
microscopic examination of the
bell stage of the enamel organ.
The cells form the inner enamel
epithelium, the stratum
intermedium, the stellate
reticulum, and the outer enamel
epithelium.
 The junction between inner and
outer enamel epithelium is called
cervical loop and it is an area of
intense mitotic activity.

25. 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 cells are 4 to 5 micrometers (μm)
in diameter and about 40 μm high. These
elongated cells are attached to one
another by junctional complexes laterally
and to cells in the stratum intermedium
by desmosomes.
 The cells of the inner enamel epithelium
exert an organizing influence on the
underlying mesenchymal cells in the
dental papilla, which later differentiate
into odontoblasts.

26. Stratum intermedium
 A few layers of squamous cells form the
stratum intermedium, between the inner
enamel epithelium and the stellate
reticulum.These cells are closely attached
by desmosomes and gap junctions.
 The well-developed cytoplasmic
organelles, acid mucopolysaccharides, and
glycogen deposits indicate a high degree
of metabolic activity.
 This layer seems to be essential to enamel
formation. It is absent in the part of the
tooth germ that outlines the root portions
of the tooth which does not form enamel.

27. Stellate reticulum
 The stellate reticulum expands
further, mainly by an increase in the
amount of intercellular fluid.
Desmosome junctions are observed.
 Before enamel formation begins, the
stellate reticulum collapses, reducing
the distance between the centrally
situated ameloblasts and the nutrient
capillaries near the outer enamel
epithelium.
 Its cells then are hardly
distinguishable from those of the
stratum intermedium. This change
begins at the height of the cusp or
the incisal edge and progresses
cervically.

28. Outer enamel epithelium
 The cells of the outer enamel epithelium
flatten to a low cuboidal form.
 At the end of the bell stage, preparatory to
and during the formation of enamel, the
formerly smooth surface of the outer enamel
epithelium is laid in folds.
 Between the folds the adjacent mesenchyme
of the dental sac forms papillae that contain
capillary loops and thus provide a rich
nutritional supply for the intense metabolic
activity of the avascular enamel organ.
 This would adequately compensate the loss of
nutritional supply from dental papilla owing
to the formation of mineralized dentin.

29. Dental papilla
 The dental papilla is enclosed in the
invaginated portion of the enamel
organ.
 Before the inner enamel 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 form;
later they assume 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 lamina
 The dental lamina is seen 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 and their
permanent successor teeth in the
bud stage

30. ADVANCED BELL STAGE  During this stage the boundary between inner
enamel epithelium and odontoblasts outlines the
future dentino enamel junction.
 Here, histologically enamel and dental formation can
be appreciated.
 As the hard tissue formation continue, the
nutritional supply to the ameloblasts from dental
papilla is cut off and they derive alternate source
from dental sac.
 The outer enamel epithelium becomes more
irregular and stellate reticulum collapses further to
bring the blood vessels of dental sac closer.
 Deposition of enamel proceeds coronally and
cervically in all regions from the dentino enamel
junction.
 Once the enamel and dentine formation reach the
cervical region of tooth, root formation begins.
 The cervical region of enamel organ gives rise to
epithelial root sheath of Hertwig’s

31. Molecular insights of tooth development

32. ROOT FORMATION
 Once crown formation is completed, epithelial cells of
the inner and outer enamel epithelium proliferate from
the cervical loop of the enamel organ to form a double
layer of cells known as Hertwig’s epithelial root sheath
 As the inner epithelial cells of the root sheath
progressively enclose more and more of the expanding
dental pulp, they initiate the differentiation of
odontoblasts from ectomesenchymal cells at the
periphery of the pulp, facing the root sheath. These cells
eventually form the dentin of the root.
 Once a layer of radicular dentine is formed, in that
region HERS undergoes degeneration allowing the dental
follicle cells to come in contact with newly formed
dentine.
 These dental follicle cells that come in contact with
newly formed dentine differentiate into cementoblasts
and deposit cementum on the outer surface of dentine.
 Radicular dentine formation continues apically and
inward while cementum formation continues apically
and outward till the entire length of root is formed.

33. Hertwig’s epithelial root sheath.
 The rim of this root sheath, the epithelial
diaphragm, encloses the primary apical foramen.
 Once the desired length of root is formed, the
lengthening of HERS stops.
 The Hertwig’s Epithelial Root sheath do not
undergo complete degeneration instead remnants
may persist which move away from the root
surface and remain in the pdl and are called
‘cell rests of Malassez’.
 To picture multiple root formation, one must
imagine the root sheath as a skirt hanging from
the enamel organ.
 Aberrations in this splitting of the primary apical
foramen can lead to the formation of
pulpoperiodontal canals at the sites of fusion of
the epithelial tongues

34. HISTOPHYSIOLOGY
INITIATION:
 Initiation induction needs ectomesenchymal-epithelial interaction. It is Dental papilla
mesenchyme can induce or instruct the tooth epithelium and non tooth epithelium
PROLIFERATION:
 Enhanced proliferation activity ensues at the points of initiation and results successively in
the bud, cap, bell stages. These changes causes regular changes in size and proportions of
growing tooth germ.
HISTODIFFERENTIATION:
 It succeeds the proliferation stage. The formative cells of tooth development undergo
definitive morphological and functional changes and acquire their functional assignment. This
phase reaches its highest development in bell stage
MORPHODIFFERENTIATION:
 Basic size and relative size of future tooth is established by differential growth. Advance bell
stage shows morphodifferentiation.
APPOSITION:
 Appositional growth is characterized by regular and rhythmic deposition of extracellular
matrix. Period of activity and rest alternate at definite intervals.

35. AMELOGENESIS:
 It is formation of enamel by ameloblasts of
epithelial origin facing the odontoblast layer.
 Differentiation of ameloblasts is initiated by
odontoblasts and the cells of stratum
intermedium via molecular signals, such as
BMP and FGF.
 The major proteins of the enamel matrix are
amelogenins, enamelins, ameloblastins, and
tuftelins.
 At the same time or soon after the first
layer of dentine( mantle dentine) is formed,
the inner dental epithelial cells differentiate
into ameloblasts and secrete enamel
proteins.
 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.

36. DENTINOGENESIS:  Dentin is formed by odontoblasts that
differentiate from ectomesenchymal cells of
dental papilla with influence from the inner
dental epithelium.
 Differentiation of odontoblasts is mediated by
expression of signaling molecules and growth
factors in the inner dental epithelial cells.(
fibronectin;laminin;chondroitin sulfate;
TGF;BMP)
 Following differentiation of odontoblasts, first
layer of dentin is produced, MANTLE DENTINE.
 As the odontoblasts move inward pulpually,
the odontoblast process (Tomes´ fiber) will
elongate and become active in dentine matrix
formation.
 It is initially called predentin .
 Mineralization is initiated in matrix vesicles
where the first apatite crystals are formed.

37. Evolution of periodontium
 The introduction of the socketed attachment of teeth is believed to have arisen 200 million
years ago when the earliest mammals were evolving from their reptilian predecessors
 Three basic types of tooth attachment are observed in extant reptiles (Osborn 1984;
Gaengler 2000):
1. Acrodont type: characteristic of the Tuatara (Sphenodon punctatus) as well as agamid
lizards and chameleons, is characterized by ankylosis of the tooth to the crest of the tooth-
bearing element.
2. Pleurodont: the tooth being ankylosed to the pleura (lingually sloping inner surface) of the
tooth-bearing element.
3. Thecodont: where the teeth are set in sockets but do not ankylose to the tooth-bearing
elements. Instead, crocodile teeth show a fibrous attachment to the wall of the alveolus by
means of the periodontal ligament.

38. Based on sets of teeth:
 Monophyodont: means "having one set of teeth". Animals like the beluga
whale ,dolphin, the porpoise and the narwhal.
 Diphyodont: means "having two sets of teeth". Mammals usually have two
dentitions and these are termed the primary and secondary dentition.
 Polyphyodont: refers to dentitions that have an endless succession of teeth.
Teeth are exfoliated or lost and are soon followed by replacement tooth.
Examples: shark, frog, mud puppy and iguana.

39.  Osborn (1984) believed that the
appearance of a periodontal ligament
around the apices of teeth in mammal-
like reptiles was the most critical stage
in the evolution of a gomphosis.
 Using anti-keratin antibodies as a
marker for epithelial cells, it is
demonstrated that Hertwig’s epithelial
root sheath in the gomphosis type,
facilitating periodontal ligament fiber
insertion and cementum deposition,
while in the ankylosis HERS was
continuous and cementoid-ankylosis
occurred apical of HERS.
Evolution of gomphosis:

40.  The evolutionary steps leading to the development of a gomphosis
may include the reduction of mineralized tissue in the periodontal
ligament space and may represent a functional response to axial
loads.
 To conclude, during the transition, two events appeared to emerge:
1) the establishment of root size and shape by HERS, and
2) the disintegration of HERS to allow mesenchymal cells from the
dental follicle to secrete cementum and establish a periodontal
ligament.
 It thus appears that the primary role of HERS during root
morphogenesis was to establish a long mammalian and crocodilian
root with periodontal ligament and then to become fragmented and
reduced to allow for connective tissue attachment

41. Development of gingiva
 Gingiva, comprising of gingival epithelium and connective tissue, is a portion of
oral mucosa that covers tooth bearing part of the alveolar bone and cervical
neck of tooth.
 Gingiva evolves as crown enters the oral cavity by breaking through the oral
epithelium.

42. Development of junctional epithelium:
 The ameloblasts shorten after the primary enamel cuticle
has been formed, and the epithelial enamel organ is
reduced to a few layers of flat cuboidal cells, which are
then called reduced enamel epithelium.
 During eruption, the tip of the crown approaches the oral
mucosa and the reduced enamel epithelium and oral
mucosa meet and fuse.
 The reduced enamel epithelium remains organically
attached to part of enamel that has not yet erupted.
 During transition from ameloblast to junctional epithelium
the changes in keratin expression occur as a form of
differentiation.
 As the tooth erupts the reduced enamel epithelium grows
gradually shorter. A shallow groove, gingival sulcus
develops between gingiva and surface of tooth. It deepens
as a result of separation of reduced dental epithelium from
the actively erupting tooth.

43. Development of gingival connective tissue
 Gingival connective tissue fibroblasts originate from
perifollicular mesenchyme, a derivative of the
stomodeal mesoderm
 During normal development of the periodontium,
gingival fibroblasts do not come into contact with
the tooth surface.
 New fibroblasts are derived from the proliferation
of undifferentiated perivascular cells.
 The collagen matrix of gingival connective tissue is
well organized into fiber bundles, which constitute
the gingival supra-alveolar fiber apparatus. It is
made up of the transseptal, circular, semicircular,
transgingival, and intergingival fibers, which
connect and link the adjacent teeth of one arch.

44. DEVELOPMENT OF PERIODONTAL LIGAMENT:
 The development of the periodontal ligament begins
with root formation prior to tooth eruption.
 The dental follicle cells, located between the alveolar
bone and the epithelial root sheath, are composed of
two subpopulations :mesenchymal cells of the dental
follicle proper and the perifollicular mesenchyme
perifollicular mesenchyme.
 As the root formation continues, cells in the
perifollicular area gain their polarity, increased cellular
volume and synthetic activity.
 These cells become elongated and they actively
synthesize and deposit collagen fibrils and glycoproteins
in the developing periodontal ligament.
 Experimental studies suggest that stem cells occupy
perivascular sites in the periodontal ligament and in
adjacent endosteal spaces.

45. Development of the principal
fibers
 Fiber bundles originate at the surface of the newly
formed root dentin in close relation to elongated
and highly polarized fibroblasts. These nascent
fiber bundles (fringe fibers) are tightly packed
(bundled) by the action of cementoblasts during
the initial development of acellular extrinsic fiber
cementum.
 active fibroblasts adjacent to cementum of coronal
third of root, appear to become aligned in an
oblique direction to long axis of teeth.
 Cemental and alveolar fibers continue to elongate
toward each other, ultimately to meet intervene
and fuse as covalent bonding and crosslinking of
individual collagen molecular units occur.
 During the development of the fibers, fibroblasts
exhibit cytoplasmic polarity toward the root and
alveolar bone surfaces respectively.

46. Cellular components:
 The periodontal ligament is known to
have heterogeneous population of
fibroblasts.
 With the onset of root formation, the
organelles in the cell increases,
collagen and ground substance
formation begin and fills the
extracellular spaces.
 The developing periodontal ligament,
as well as the mature periodontal
ligament, contains undifferentiated
stem cells.
 Experimental studies suggest that stem
cells occupy perivascular sites in the
periodontal ligament and in adjacent
endosteal spaces

47. Development of cementum
The development of cementum has
been subdivided into a
 prefunctional stage: which occurs
throughout root formation
 functional stage:which starts
when the tooth is in occlusion and
continues throughout life.

48.  Although cementum formation takes place along
the entire root, its initiation is limited to the root
edge.
 HERS becomes interrupted, and ectomesenchymal
cells from the inner portion of the dental follicle
then can come in contact with the predentin.
 Infiltrating dental follicle cells receive a reciprocal
inductive signal from the dentin and/or the
surrounding HERS cells and differentiate into
cementoblasts.
 During these processes, some cells from the
fragmented root sheath form discrete masses
surrounded by a basal lamina, known as epithelial
cell rests of Malassez, which persist in the mature
PDL .
 Precursor cells for cementoblasts in the dental
follicle and that factors within the local
environment regulate their ability to function as
cementoblasts that form root cementum or as
fibroblasts of the PDL.
Cementogenesis

50. ALVEOLAR BONE DEVELOPMENT
 Alveolar bone is formed during fetal
growth by intramembranous ossification.
 The 2 parts of alveolar process can be
distinguished as alveolar bone proper and
the supporting alveolar bone.
 Alveolar bone proper:- it appears as thin
radio opaque line adjacent to socket,
termed as lamina dura.
 The alveolar bone proper forms the
alveolar wall that lines the
tooth sockets, and the
supporting alveolar bone consists of inner
and outer cortical plates.
 Its formation is initiated with the eruption
of the developing tooth.

51.  At the late bell stage, bony septa and bony bridge start to form, and
separate the individual tooth germs from another, keeping individual
tooth germs in clearly outlined bony compartment.
 At this stage, the dental follicle surrounds each tooth germ, which is
located between a tooth germ and its bony compartment.
 The major changes in the alveolar processes begin to occur with the
development of the roots of teeth and tooth eruption.
 As the roots of teeth develop, the alveolar processes increase in
height. Also, cells in the dental follicle start to differentiate into
periodontal ligament fibroblasts and cementoblasts responsible for the
formation of the periodontal ligament and cementum, respectively.
 At the same time, some cells in the dental follicle also differentiate
into osteoblasts and form the alveolar bone proper.
 The formation of the alveolar bone proper is closely related to the
formation of the periodontal ligament and cementum during root
formation and tooth eruption.

52. DEVELOPMENTAL ANOMALIES AT DIFFERENT STAGES
OF TOOTH DEVELOPMENT
INITIATION
 Anodontia.
HISTODIFFERENTIATION
 Regional odontodysplasia.
INITIATION AND PROLIFERATION
 Oligodontia.
 Supernumerary teeth.
 Gemination or fusion.

53. Morphodifferentiation:
Microdontia. Macrodontia. Concrescence. Dilaceration.
Taurodontism. Dens evaginatus.
Dens
invaginatus.

54. Apposition:
Amelogenesis
imperfecta
Dentinogenesis
imperfecta.
Enamel hypoplasia.
Dentin dysplasia:

55. Summary

56. Conclusion
 Since the development of tooth forms the base of
dentistry a thorough understanding and sound knowledge
is necessary for a dentist to provide an appropriate
treatment

57. References
 ORBANS’s Oral HISTOLOGY AND AND EMBRYOLOGY
 TEN CATE’S ORAL HISTOLOGY
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