DEVELOPMENT
OF
TEETH
dr shabeel pn
DEVELOPMENT OF TEETH
INTRODUCTION
The
morphogenesis
of
teeth
and
development of dentition involve a number of
closely related processes. It begins with local
changes and there is growth of corresponding
parts of jaw. Appearance of teeth in the mouth at
appropriate time can have very profound effect
on the feeding behavior and mastication skills.
dr shabeel pn
HOW TOOTH DEVELOPMENT INITIATES
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During development of embryo, there is formation of 3
germ layers
a)
Ectoderm
b)
Endoderm
c)
Mesoderm
The primitive oral cavity or stomodeum is lined by
stratified
squamous
epithelium
called
ORAL
ECTODERM.
Ectoderm contacts with endoderm of foregut to form the
bucco pharyngeal membrane.
At about 27th day of gestation the membrane ruptures
and
primitive oral cavity establishes a connection
with foregut.
Connective tissue cells underlying the oral ectoderm
induce overlying ectoderm to start tooth development.
These ectomesenchymal cells consist of few spindle
shaped cells
separated
by
gelatinous
ground
substance. This indication
begins mainly in the
ant portion.
dr shabeel pn
PRIMARY EPITHELIAL BAND
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It is a continuous band of thickened epithelium
formed in both upper & lower jaw.
Formed by fusion of separate plates of
thickened epithelium after 37 days of
development.
It is a horseshoe shaped structure, which
corresponds in position to the
future dental
arches.
It results due to change in orientation of the
plane of cleavage of dividing cells.
It gives rise to 2 subdivisions.
a) Vestibular Lamina
b) Dental Lamina
dr shabeel pn
DENTAL LAMINA
Dental lamina is a band of epithelium that has
been invaded by underlying mesenchyme and dental
arches.
Formed when certain areas of the basal cell
proliferate at more rapid rate than the cells of adjacent
areas.
FUNCTIONS :
1)
2)
3)
First PhaseAct as primordium for the
ectodermal portion of deciduous teeth - 8th
week.
Second Phase-Initiation of successor of
deciduous teeth by successional dental
lamina.
Third PhaseInitiation of permanent molar.
dr shabeel pn
FATE OF DENTAL LAMINA
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Total activity of dental lamina extends over a period of
min of 5 years.
As dentine and enamel start to develop dental lamina
begins to degenerate separating into clumps but whose
thickness of lamina is not perforated.
Give whorled appearance over developing deciduous
teeth.
Persist as epithelial rests but sometimes they proliferate
to form cystu cavities known as eruption cyst recognized
as blush swelling over erupting teeth and they delay
eruption.
Breaking upon of dental lamina determine crown pattern.
Degeneration of lamina separates developing tooth from
oral epithelium as a result of degeneration tooth
continues its development within tissues of jaw.
Penetration of lingual epithelium by tooth is unique
example of natural break in the epithelium of the body.
dr shabeel pn
dr shabeel pn
VESTIBULAR LAMINA
•Also called up furrow band or vestibular band.
•Horseshoe shaped in growth of epithelium, which
develops buccal to dental lamina.
•Vestibular band grows deeply into mesenchyme of
premature jaws separating lips and cheeks from tooth
forming region. It subsequently thickens & clears at
vestibular growth form oral vestibular lamina.
TOOTH DEVELOPMENT
Development history is divided into several
morphologic stages. They do not properly describe the
functional changes that occur during development.
Different stages are named according to shape of
epithelial part of tooth germ.
dr shabeel pn
dr shabeel pn
TIME SCALE OF HUMAN TOOTH
DEVELOPMENT
AGE
42-48 days
55-56 days
14 weeks
18 weeks
32 weeks
Development characteristics
Dental lamina formation
Bud stage, deciduous incisor canine
& molar.
Bell stage for deciduous teeth, bud
stage for permanent teeth
Dentin and functional ameloblastes
in deciduous teeth.
Dentine & functional ameloblast in
permanent teeth.
dr shabeel pn
STAGES
BUD STAGE
• Differentiation of dental lamina leads to formation of
round, ovoid swelling at 10 different points
corresponding to future position of deciduous teeth.
These are the primordia of enamel organ.
• Enamel organ consists of peripherally located low
columnar cells and centrally located polygonal cells.
• Dental papilla : It is the area of ectomesenchymal
condensation subjacent to enamel organ. Cells of dental
papilla will form tooth pulp & dentine.
* Dental sac: It is area of ectomesenchymal
condensation surrounding the tooth bud & dental
papilla. Cells of dental sac will form cementum &
periodontal ligament.
dr shabeel pn
dr shabeel pn
CAP STAGE :
* Characterized by a shallow invagination of deep surface of a
bud.
* Outer & inner enamel epithelium.
* Cuboidal cells cover the convexity of the cap.
* Columnar cells cover the concavity of the cap.
* Stellate Reticulum:
Polygonal cells begin to separate as more intercellular
fluid is produced and forms cellular network called
stellate reticulum.
•Enamel Knot:
Cells in center of the enamel organ are densly packed.
This knot projects towards underlying dental papilla.
Vertical extension of enamel knot forms enamel cord.
Both the structures disappear before enamel formation
begins.
*Dental papilla & dental sac :
Dental papilla is for mature organ of dentine & shows
active budding of capillaries & mitotic figures.
• Dental sac are important for formations of cementum &
periodontal ligament.
dr shabeel pn
dr shabeel pn
BELL STAGE :
 Stage of Histodifferentiation and Morph differentiation.
 During histodifferentiation some cells of dental organ
diffentiates into specific form and shape. This is seen in early Bell
stage.
 During morph differentiation Dental organ assumes characteristic
shape of the tooth. This is seen in late Bell stage.
 The invagination of the epithelium deepens and its margins
continue to grow and enamel organ assumes a bell shape.
 During histodifferentiation cells acquire their functional
assignment. Odontoblasts are differentiated from mesenchymal
cells with formation of dentin the cells of inner dental epithelium
transform into ameloblasts and enamel matrix is lead down
opposite the dentin. Presence of dentin is absolutely essential for
laying down of enamel.
 Differentiation of epithelial cells are essential for differentiation of
epithelial Odontoblasts and initiation of dentin formation. Future
dentino enamel junction is outlined and the form of crown is
established.
 Tooth germ shows the following structures:
dr shabeel pn
I. Dental organ :
a)
b)
c)
d)
Outer dental epithelium:
A single rows of cuboidal
cells is thrown into folds and contain blood vessels at late
bell stage.
Stellate reticulum: There is increase in intercellular fluid
and layer expands. The cells assume star shape with long
processes that anastomose with adjacent cells.
Stratum intermedium: Several layers of squamsus cells
appear between stellate reticulum and inner dental
epithelium and are called stratum intermedium. This layer
is essential for enamel formation. It helps in calcification of
enamel and is a reserve source for new ameloblasts.
Inner dental epithelium: This consists of single layer of
cells that differentiates into tall columnar cells, the
ameloblasts. They have a hexagonal shape on cross
section and are 4u in diameter and 40u in height. These
cells influence the underlying mesenchymal cells, which
differentiates into Odontoblasts.
dr shabeel pn
II. Dental Papilla :
It is the mesenchyme enclosed portion of the Dental
organ. The peripheral cells under the influence of inner dental
epithelium assume an cuboidal shape first & columnar later
and are called Odon oblast, which produce dentin. The
basement membrane separating the epithelial dental organ
and dental papilla is called membrana performativa which
forms future dentino enamel junction.
III. Dental sac:
Before formation of dental tissues begins, the dental sac
shows a circular arrangement of its fibres and resembles a
capsular structure. With the development of the root the
fibers of dental sac differentiates into the periodontal fibres
that become embedded in the developing cementum and
alveolar bone.
dr shabeel pn
dr shabeel pn
Apposition
The tooth germ forms calcified tissues of the tooth,
the enamel, the dentin and the cementum. There is a layer
like deposition of an extra cellular matrix resulting in
additive growth. There is regular and rhythmic deposition,
which is incapable of further growth.
dr shabeel pn
FORMATION OF ROOT
Root start forming after dentin formation has reached
future cementoenamel junction. Both dental organ and dental
papilla play part in formation of root.
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Hertwig's epithelial root sheath :
The outer and inner dental epithelium meets one
another at future cervical area and is called cervical
loop.
This cervical loop forms epithelial sheath of
Hertwig, which moulds the shape of the root and
initiates dentin formation.
dr shabeel pn
 The root sheath consists of only outer and inner dental
epithelium.
 The inner layer of cells remains short and do not produce
enamel. These cells induce the differentiation of cell of dental
papilla into Odontoblasts, which lay a layer of dentin. At the
same time the continuity of Hertwig's sheath is destroyed due
to infiltration of connective tissue and the root sheath breaks
up into small strands of epithelium called epithelial rests of
Molassez.
 While the coronal part of the sheath degenerates, the apical
part continues to grow in length and aid in lengthening of root.
 The cells of dental sac differentiate into cementoblasts,
which lay cementum over the outer surface of the dentin in
root portion. At the same time precollagenous fibers appear
between cementoblasts and become continuous with outer
surface of dentin. They become collagenous and are
transformed into cementoid tissue, which calcifies to form
cementum.
dr shabeel pn
 The sheath is folded first at future cemento enamel junction
into a horizontal plane. This is called epithelial diaphragm.
 Differential growth of the epithelial diaphragm in multirooted
teeth causes the division of the root trunk into two or three roots.
During the general growth of the enamel organ the 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 the free ends of these
horizontal epithelial flaps grow toward each other and fuse. The
single cervical opening of the coronal enamel organ is then
divided into two or three openings.
Enamel pearls:
If the cells of epithelial root sheath remain adherent to the
dentin surface, they may differentiates into fully functioning
ameloblasts and produce enamel. Such droplets of enamel called
enamel pearls.
dr shabeel pn
dr shabeel pn
Clinical Considerations :
1. Ectodermal dysplasia : Tooth bud may be absent.
2. Anodontia:
Complete absence of teeth.
3. Accessory teeth:
There
may
be
extra
or
supernumerary teeth buds resulting in accessory teeth.
4. Predeciduous or neonatal tooth: Teeth are seen to erupt
immediately after birth.
5. Gemination: 2 teeth may be fused to each other.
6. Malocclusion: The alignment of upper and lower teeth
maybe incorrect.
dr shabeel pn
7. Teeth may form in abnormal situations e.g. in the ovary or in the
hypo physis cerebrae.
8. In vitamin A deficiency ameloblasts fail to differentiate properly.
Consequently, their organizing influence on the adjacent
mesenchymal cells is disturbed and a typical dentin known as
osteodentin is formed.
9. Endocrine disturbances affect the size or form of the crown of teeth
clinical examinations shows that retarded eruption that occurs in
persons with hypo pituitarism and hypothyroidism results in a
small clinical crown that is often mistaken for a small anatomic
crown.
10. The upper central incisors may become notched at the edge or
screwdriver shaped in individuals born with congenital syphilis.
This condition is known as Hutchinson's incisor.
11. Genetic and environmental factors may disturb the normal
synthesis and secretion of the organic matrix of enamel leading to a
condition called enamel hypoplasia.
12. If organic matrix is normal but its mineralization is defective then
enamel or dentin is said to be hypo calcified or hypo mineralized.
dr shabeel pn