Development ang growth of teeth

DEVELOPMENT ANG GROWTH
OF TEETH
Dr.bhavna tyagi

Introduction
The primitive oral cavity is lined by stratified
squamous epithelium called oral ectoderm or
primitive oral epithelium.
The oral ectoderm contacts the endoderm of foregut
to form the buccopharyngeal membrane.
At the 27th day of gestation this membrane ruptures
and the primitive oral cavity establish a connection
with the Foregut.
Connective tissue cells underlying the oral ectoderm
instruct or induce the ectoderm to start tooth
development.
2

Diagram showing Buccopharyngeal
membrane
3

Primary epithelial band
2 or 3 week after the rupture of buccopharyngeal
membrane.
Certain area of basal cells of oral ectoderm
proliferate more rapidly.
Leads to formation of Primary epithelial band .
(These band of epithelium are roughly horseshoe
shaped structure. These correspond in position to
the future dental arches)
4

The position of the maxillary and
mandibular primary epithelium band
shown by shaded areas
5
Maxillary primary epithelial
band
Mandibular primary
epithelial band

Dental lamina
At about 7th week of the primary epithelium
band divides into
Dental lamina Vestibular lamina
(inner/lingual process) (outer/buccal process)
 The dental lamina serves as the primordium
for the ectodermal portion of the deciduous
teeth .
 Permanent molars arise directly from the
distal extension of the dental lamina.
6

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.
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).
7
Diagram showing Dental
lamina and vestibular
lamina

Fate of dental lamina
 It is evident that total activity of dental lamina
exceeds over a period of at least 5 yrs.
 The dental lamina may still be active in the third
molar region .
 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.
Remnant of dental lamina persist as Epithelial pearls
or islands with in the jaw as well as in gingiva called
as cell rest of serres.
8

Vestibular lamina
Labial and buccal to the dental lamina in each
dental arch, another epithelial thickening
develops independently called as 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.
11

Initiation of Tooth
How dental development initiated?
Mouse 1st arch epithelium + caudal or cranial neural
crest in the anterior chamber of eye =tooth
formation.
Epithelium from any other source like 2nd arch ,does
not elicit the response.
After 12th day of development, 1starch epithelium
loses this odontogenic potential, assumed by
Ectomesechyme.
Eg.late 1st arch ectomesenchyme +embryonic
plantar epithelium =enamel organ.
Epithelial dental organ + skin mesenchyme =organ
loses dental characteristics.
12

What these experiments indicate?
Odontogeneis is initiated first by factor
resident in the 1st arch epithelium influencing
ectomesenchyme but that with time this
potential is assumed by ectomesenchyme.
13
Intraocular recombination of
neural crest and dental
epithelium. A, Tooth formed from
the combination of cranial neural
crest and mandibular epithelium.
B, Tooth formed from the
combination of trunk neural crest
and mandibular epithelium.
(Courtesy A.G.S. Lumsden.)

What are the signals mediating the initial steps in
tooth development?
The earliest mesenchymal markers for tooth
formation are the Lim- homeobox domain
genes (transcription factors),Lhx-6 and Lhx-7.
Experimental data demonstrate that the
expression of Lhx-6 and Lhx-7 results from a
signaling molecule originating from the oral
epithelium of the 1st branchial arch.
2nd arch mesenchyme recombinant with the 1st
branchial arch of oral epithelium=Lhx-6,7
induced.
14

If 1st branchial arch mesenchyme (which
expresses Lhx-6 and Lhx-7) + 2nd branchial
arch epithelium = expression of both genes
down regulated.
A prime candidate for the induction of Lhx
genes is Fgf-8(fibroblast growth factor).
15

What controls the position and number of tooth
germs along the oral surface?
The Pax-9(paired box homeotic gene) gene is
one of the earliest mesenchymal gene that
define the localization of tooth germ.
Pax -9 gene co - localizes with the exact sites
where tooth germs appear.
16

Tooth Type Determination
 The determination of specific tooth type at
their correct positions in the jaw is referred as
patterning of the dentition.
Two hypothetical models have been proposed
17
Field theory Clone theory

Field model
Proposes that the factors responsible for tooth
shape reside with in the ectomesenchyme.
The fact that each of the fields expresses
differing combinations of patterning homeobox
genes supports this theory.
18

19
The homeobox genes Msx-1, Msx-2, Dlx-2, and Barx-1 expressed in mandibular
mouse ectomesenchyme associated with differing tooth families. Because the
mouse does not develop a canine, the code given is speculative, but the overlap is
present in the presumptive canine region. (Information derived from Thomas BL,
Sharpe PT: Patterning of the murine dentition by homeobox genes, Eur J Oral Sci
106[suppl 1]:48, 1998.)

Oodontogenic homeobox code model of dental patterning. A, Domains of Barx-1 and Dlx-
1/-2 expression overlap in the mesenchyme of the presumptive molar region, whereas
domains of Msx-1, Msx-2, and Alx-3 overlap in presumptive incisor mesenchyme. B,
Mouse dental pattern. Incisors deriving from Msx-1/Alx-3 expressing cells; molars
deriving from Barx-1/Dlx-1/-2 expressing cells. C, Human dental pattern. Premolars and
canines can be derived from the same odontogenic code as that observed in mice by
virtue of the overlapping domains of gene expression. Thus canines and premolars may
be derived from cells expressing DLX-1/-2 and MSX-1, for example. (From McCollum MA,
Sharpe PT: Developmental genetics and early hominid craniodental evolution, Bioessays
23:481, 2001.) 20

Clone model
Proposes that each tooth class is derived from a
clone of ectomesenchymal cell programmed by
epithelium to produce teeth of a given pattern.
21
Clone theory. A, The molar clone has induced the dental lamina to begin tooth
development. At its posterior border the clone and dental lamina grow posteriorly by
means of the progress zone. B, When a clone reaches the critical size, a tooth bud is
initiated at its center. A zone of inhibition surrounds the tooth bud, and the next tooth bud,
C, is not initiated until the progress zone of the clone has escaped its influence. (From
Osborn JW,Ten Cate AR: Advanced dental histology, ed 3, Oxford, UK, 1983. Reprinted by
permission of Elsevier Ltd.)

Tooth development
Introduction
Tooth formation is a continuous process.
Characterized by series of stages.
 Each tooth develops through successive bud,
cap and bell stages.
During these stages, the tooth germs grow
and develop into specialized cell which form
enamel, dentin, cementum.
22

 Ectodermal cells multiply rapidly & little knobs
grow into the underlying mesenchyme.
Representing the location of one of the 10
mandibular and 10 maxillary deciduous teeth.
 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.
NOTE: Not all of these enamel organs start to
develop at the same time, First to appear are
those of anterior mandibular region.
23

Developmental stages
Bud stage
Cap stage
Bell stage
Root formation
24

Bud stage / Proliferation stage
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.
26

Bud stage
27
a
b
c
d
e
f
g
a.Oral ectoderm
b.Dental lamina
c.Enamel organ
d.central polyhedral
cell
e.Peripheral columnar
cell
f.Condensation of
ectomesenchyme
g.Developing bone

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.
The cells of the dental papilla form the dentin
and pulp while the dental sac forms cementum
& periodontal ligament.
28

Bud to Cap Transition
The transition from bud to cap marks the onset of
morphologic differences between tooth germs
that give rise to different type of teeth.
Msx-1 expressed with Bmp-4 in mesenchymal cell
that condense around tooth buds.
Pax-9 is also expressed in bud stage
mesenchyme.
Msx-1-/- and Pax-9 -/- embryos have tooth
development arrested at the bud stage.
29

Cap stage / proliferation
30
a
b
c
d
e
f
g
a.Oral ectoderm
b.Dental lamina
c.Outer enamel
epithelium
d.Dental follicle
e.Stellate reticulum
f.Inner enamel
epethelium
g.Dental papilla

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
31

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.
The outer enamel epithelium is separated from
the dental sac, & the inner enamel epithelium
from the dental papilla, by a delicate basement
membrane
Hemidesmosomes anchor the cells to the basal
lamina
32

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 of osmotic force exerted by
glycosaminoglycan contained in the ground
substance
As a result the polygonal cells become star
shaped but maintain contact with each other
by their cytoplasmic process
33

As the star shaped cells form a cellular
network, they are called the stellate reticulum
This gives the stellate reticulum a cushion like
consistency
 Acts as a shock absorber that may support
and protect the delicate enamel forming cells
34

Dental Papilla
Under the influence of proliferating epithelium of
enamel organ, the ectomesenchyme that is
partially enclosed by the invaginated portion of
inner enamel epithelium proliferates.it condense
to form Dental Papilla.
It is the formative organ of the dentin and the
primordium of the pulp.
The dental papilla shows active budding of
capillaries and mitotic figures.
Peripheral cells adjacent to IEE enlarge and later
differentiate into the odontoblasts.
35

Dental Sac
Marginal condensation in the ectomesenchyme
surrounding the enamel organ and the dental
papilla called as Dental sac.
36
Diagram showing:
Dental follicle
Dental papilla
Enamel organ

Temporary structures
Enamel knot
Enamel cord
Enamel septum
Enamel niche
37

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.
When the enamel cord extends to meet the OEE
called as enamel septum.
Fgf-4 and slit-1 may be the best molecular
markers for enamel knot formation
38

Diagram showing enamel knot
39

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.
41

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
43

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
45

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.
The well developed cytoplasmic organelles, acid
mucopolysaccharides ,and glcogen deposites indicate
high degree of metabolic activity.
 This layer seems to be essential to enamel
formation.
The cells of this layer soon are characterised by an
exceptionally high activity of the enzyme alkaline
phosphatase.
Absent in part of tooth germ that outlines root
portion. 46

STELLATE RETICULUM
47
The stellate reticulum expands further due to
continued accumulation of intra-cellular fluid.
The 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 centrally placed
ameloblast and the nutrient capillaries near the
outer enamel epithelium

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 intense
metabolical active of the avascular enamel
organ
48

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
49

Diagram showing Permanent tooth
bud
50

DENTAL PAPILLA
Dental papilla is enclosed in the invaginated
portion of 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
The basement membrane that separates the
enamel organ ant the dental papilla just prior to
dentin formation is called the MEMBRANA
PERFORMATIVA
51

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.
52

Two Important Events Occur During
BELL STAGE
The dental lamina joining the tooth germ to
the oral epithelium breaks up into discrete
islands of epithelial cells , thus separating the
developing tooth from the oral epithelium.
The IEE completes its folding ,making it
possible to recognize the shape of the future
crown pattern of the tooth.
53

Advanced Bell stage /
MORPHODIFFERENTIATION
54
Characterized by the commencement of
mineralization & root formation.
The boundary between the inner enamel
epithelium & odontoblasts outline the future
dentino enamel junction
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 over the dentin in
the future incisal & cuspal areas

The enamel formation then proceeds coronally
& cervically in all the regions from the dentino
enamel 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
56

57
Collapsed stellate reticulum
Ameloblast
Enamel
Dentin
OEE
Dental sac
odontoblast
Developing pulp
Advanced bell stage

FORMATION OF ENAMEL & DENTIN
MATRIX ( 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
58

ROOT FORMATION
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 (cervical loop /zone of reflexion)
The cell of the IEE remains short and normally do
not produce enamel.
59

Hertwig’s root epithelium
60

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 malasez
61

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
62

 The differentiation of odontoblast and the
formation of dentin follow the lengthening of
root sheath.
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 epithelium is moved away from the surface
of the dentin so the connective tissue come in
contact with the outer surface of the dentin
and differntiate into cementoblast that deposit
layer of cememtum over dentin.
63

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
65

Fragmentation of the root sheath and the initial formation
of cementum. Follicular cells migrate through a break in
the epithelium (arrow) to lie against the surface of newly
formed dentin.
66

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
into2 or 3 openings.
67

Root formation as seen on the undersurfaces of
developing tooth germs: A, two-rooted tooth, and
B, three-rooted tooth. C, Section of a tooth with
developing root. The roots have not finished
forming, and the division into two roots is clearly
visible. (Redrawn from Oöe T: Human tooth and
dental arch development, Tokyo, 1981, Ishiyaka.)
68

 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.
69

Clinical considerations
A lack of initiation results in the absence of
either a single tooth or multiple teeth (partial
anodontia),most frequently the permanent
upper lateral incisors , 3rd molars and lower 2nd
premolar.
May be a complete lack of teeth
Abnormal initiation may result in the
development of single/multiple supernumerary
teeth
70

In vit A deficiency the ameloblast fails to differentiate
properly , so osteodentin is formed.
Hypopituitarism and Hypothyroidism results in a
small clinical crown.
 Disturbances in morphodifferentiation may affect
the form and size of the tooth without impairing the
function of the ameloblasts or odontoblast.
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.
 GEMINATION arises when two teeth develop from
one tooth bud and, as a result, the patient has an
extra tooth
71

Congenital syphilis : peg shapes teeth with the
permanent central incisor showing a notched
incisal edge condition is known as Hutchinson’s
incisor.
Genetic and environmental factors may disturb
the normal synthesis and secretion of the
organic matrix of enamel leading to a condition
called Enamel hypoplasia
Organic matrix is normal but its mineralization
is defective, then the dentin or enamel is said
to be hypocalcified or hypomineralized.
72

References
• Orban’s, Textbook of oral histology &
embryology.
• Ten cates, Textbook of oral histology.
• James k. avery,oral development and
histology.
• Mazi jose, Mannual of oral histology and oral
pathology
73

Development ang growth of teeth

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (20)

Andere mochten auch

Andere mochten auch (20)

Ähnlich wie Development ang growth of teeth

Ähnlich wie Development ang growth of teeth (20)

Mehr von Sharda university

Mehr von Sharda university (13)

Kürzlich hochgeladen

Kürzlich hochgeladen (20)

Development ang growth of teeth