Embryological basis of dental tissue genesis
Lined by stratified
i.e. Oral ectoderm or
primitive oral epithelium
Connective tissue cells underlying oral
ectoderm are neural crest or
ectomesenchymal in origin , which
induce tooth development Ruptures at 27th day (4th week) of
Primary epithelial band /6th week (2-3
weeks after rupture of BF membrane)
Continuous band of
Roughly horse shoe shaped
Thickening first seen in anterior midline
Certain areas of basal cells of oral ectoderm
proliferate more rapidly than do cells of
Initiation of tooth development
• The initiation of tooth development begins at 37th day with
formation continuous horse shoe shaped band of thickened
epithelium in the location of upper and lower jaws– Primary
Each band of epithelium
gives rise to 2 subdivisions
Vestibular lamina (Lip furrow
Vestibular lamina – labial and
buccal to the dental lamina in
each dental arch, another
thickening develops apparently
and some what latter called
Continued thickening of dental lamina in 10 areas of upper and
Thickenings corresponds to the position of future primary
• Development of 1st molar – 4th month in utero
• 2nd molar – 1st year after birth.
• 3rd molar – 4th or 5th years
• Succesional lamina – 5th month in utero
(permanent central inciosor) & (10th month –
Formation of vestibule in oral cavity
Cells of vestibular lamina
Degeneration of central
Sulcus of vestibule
Is a band of epithelium
Serves as a primordium for
the ectodermal portion of the
• Within dental lamina localized and continuous proliferative
activity leads to formation of series of epithelial outgrowths
into the ectomesenchyme at the sites corresponding to the
future deciduous teeth which represents the beginning of
• Successors of deciduous teeth arises from the lingual
extension of free end of dental lamina opposite to enamel
organ of each deciduous tooth, these lingual extensions are
referred to as “Successional lamina" and develops from 5th
month in utero to 10th month of age.
Functions of dental lamina
• Phase –I :- initiation of entire deciduous dentition (8th week).
• Phase – II :- Initiation successors of deciduous dentition (5th
to 10th month).
• Phase – III :- Initiation of permanent molars.
Fate of dental lamina
• The total activity of dental lamina extends over a period of at
least 5 years.
• Any particular portion of dental lamina functions for much
briefer period, since only a relatively short time elapses after
initiation of tooth development before dental lamina begins
to degenerate at particular location i.e. it might be still active
in 3rd molar area when it has disappeared elsewhere.
• Dental lamina looses its connection from enamel organ at the
start of bell stage.
• Remnants of dental lamina persists as epithelial pearls or
islands within jaw termed as “cell rests of Serre’s”
Rests of serre’s or epithelial cells
• Also called as “Epithelial Pearls or islands”.
• These are remnants of dental lamina.
• These are identified in jaws and gingival soft tissues.
• They results from early break up of dental lamina during bell
- Gingival cyst of adult
- Gingival cyst of new
Rests of Malassez
• The break up of heartwig’s root sheath during root
formation i.e. these are remnants of Heartwig’s
epithelial root sheath.
• These are identified in periodontal ligament and are
responsible for the development of radicular cyst.
How development tooth begins??
1st arch and ectomesenchymal cells
derived from the neural crest cells
Up to 1st 12 days 1st arch epithelium retains the
ability to form tooth like structure when
combined with neural crest cells of regions
This potential is lost and transformed to neural crest
cells to produce tooth like structure
Interaction of epithelium derived
Stages of tooth development
Early bell stage
Advanced bell stage
STAGES IN TOOTH GROWTH
Morphologic changes physiologic processes
• Dental lamina Initiation
• Bud stage Proliferation
• Cap stage
• Early bell stage Histodiffrentiation
• Advanced bell Marphodiffrentiation
6th to 7th weeks
stomodeum gives rise to
oral epithelium and dental
All the enamel organ
don’t start at same time,
first to start are those of
Bud stage or proliferative stage
8th week of prenatal development
Growth of dental lamina into bud that penetrates
• Initial proliferation of oral epithelial cells and
adjacent mesenchymal cells is occurring and
the cells proliferate faster than the adjacent
cells giving rise to bud shaped enamel organ.
Enamel organ – spherical to
ovoid epithelial condensation
Cells of tooth bud have --
Increase RNA content,
Decrease Glycogen content
and increase oxidative
Cells undergo mitosis and
get condensed. Enamel organ surrounded
Histologically enamel organ at bud stage consists of,
• Peripherally located low columnar cells.
• Centrally located polygonal cells.
• Many cells of tooth bud and surrounding mesenchyme
undergoes mitosis, i.e. increased mitotic activity.
• Ectomesenchymal cells or neural crest cells migrates in the
area surrounding tooth bud.
• Ectomesenchymal condensation occurs surrounding the bud.
9th to 10th week
Unequal growth in
different parts of tooth bud
leads to concave surface
forming cap like structure.
Enamel organ forms into
There is a formation of
Early cap stage – 11 week
cuboidal cells – Outer
Tall columnar cells in the
concavity – Inner enamel
Polygonal cells in between
OEE and IEE called –
• Outer enamel epithelium
Cuboidal cells covering convexity.
Separated from dental sac by basal
• Inner enamel epithelium
Tall columnar cells lining concavity of
Separated from the dental papilla by
• Cells in the center of the enamel organ.
• These cells are star shaped which secrete GAG.
• Stellate reticulum cells synthesize and secrete GAG’s into
extracellular compartment between epithelial cells –>
hydrophilic -- > pull water into the enamel organ and central
cells are forced apart.
• They are so named because they retain connection with each
other through desmosomal contacts, they become star
shaped, the center of the enamel organ thus termed Stellate
What is tooth germ??
The enamel organ, the
dental papilla and the
dental sac together
Enamel organ – enamel
Dental papilla –Dentin
Dental sac – PDL,
Cementum and bone
Strand of cells extending from stratum intermedium
into Stellate reticulum
These are vertical extensions of enamel knot.
These acts as reservoir of dividing cells for the
growing enamel organ
- Double attachment of
enamel organ to overlying
- Funnel shaped area
between lateral and medial
strands of dental lamina
A. Lateral enamel strand
B. Medial enamel strand
C. Enamel niche
• When the enamel cord extends to meet the outer enamel
epithelium is termed as enamel septum.
• The outer enamel epithelium at the point of meeting shows a
small depression and is termed as enamel navel as it
What is enamel organ??
• The developing tooth as it progresses from
bud stage to advanced bell stage is called the
“enamel organ” or “dental organ”
• 11th to 12th weeks
• Differentiation of
enamel organ into bell
with four cell types and
dental papilla into 2 cell
Early bell stage (14th week)
Dental lamina break downs and degenerates
Shows 4 distinct layer
Outer enamel epithelium
Inner enamel epithelium
Outer enamel epithelium
• A single layer of very low cuboidal cells.
• At the end of this stage just before enamel formation, the
smooth surface of outer enamel epithelium get thrown into
• 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.
Outer enamel epithelium
Role of OEE
• Maintenance of the shape
of the enamel organ
• Exchange of substance
between enamel organ and
• Holds the contents of
• As a constituent of
epithelial root sheath plays
a role in root formation.
• Expands mainly by an increase in the amount of intracellular
• The star shaped cells with long processes anastomose with
those of adjacent cells.
• Before enamel formation begins, the Stellate reticulum
collapses, reducing the distance between centrally situated
ameloblasts and the nutrient capillaries near the outer
• Changes begins at the height of the cusp or the incisal edge
and progresses cervically.
• These are 3-4 layers of squamous cells between inner enamel
epithelium and Stellate reticulum.
• These cells are attached by desmosomes and gap junctions.
• There are abundant cell organelles, acid mucopolysaccharides
and glycogen deposits in these cells, which indicate high
• This layer is essential for enamel formation.
• Are absent in the part of the tooth germ that outlines the root
portion of the tooth which doesn’t form enamel.
Inner enamel epithelium
Its cells become ameloblasts
which form enamel.
It induces adjacent cells of
dental papilla to form
odontoblasts which in turn
Following amelogenesis, the
cells contribute to form the
REE together with OEE and
Important role in crown
formation due to intrinsic
The cells of the inner enamel epithelium exert an
organizing influence on
mesenchymal cells in the dental papilla
later differentiate into odontoblasts.
• Are about 40 um high and 4-5 um in diameter.
• These cells attach to each other laterally by
junctional complexes and cells of stratum
intermedium by desmosomes.
• Under the inductive influence of inner enamel epithelium, the
peripheral cells of the dental papilla differentiate into
• These cells initially become cuboidal and later assume
• These cells now acquire the potential to produce dentine.
• The basement membrane that separates enamel organ and
the dental papilla just prior to dentin formation is called
• Just before the formation of dental tissues begins, the
collagen fibers of the dental sac are arranged in a circular
• The dental sac look like a capsule around the enamel organ
and dental papilla.
Changes before enamel formation
• The Stellate reticulum collapses and the
distance between inner enamel epithelium
and blood capillaries of the dental sac is
reduced, so that more nutrient reach the
ameloblasts during the period of high
• The formerly smooth surface of outer enamel
epithelium thrown into folds.
• Between the folds the mesenchyme of dental
sac form projections or dental papillae that
carry capillary loops closer to the ameloblast
IEE become taller –
Peripheral cells of the
dental papilla –
substance and collagen
fibers – Dentin matrix
There is change in cell
With change in polarity
the cell called an
ameloblasts that begins
secretion of enamel matrix.
Boundary between inner
enamel epithelium and
odontoblasts outline the
• The ameloblasts have fully differentiated from
the cells of inner enamel epithelium.
• The odontoblasts have fully differentiated
from dental papillae cells.
• The boundary between the ameloblasts and
odontoblasts define the future dentino-
Histological difference from early bell stage
• Hard tissue (Enamel and Dentin) formation.
• Collapsed Stellate reticulum and folding of outer enamel
epithelium bringing capillaries of the dental follicle nearer to
• Dental papilla shows differentiated odontoblasts at periphery
• Dental follicle is distinct enclosing enamel organ and dental
• The inner enamel epithelium induces peripheral
cells of dental papilla to differentiate into
• The odontoblasts start secreting the organic
matrix of dentin.
• Only dentin matrix is formed, do the ameloblasts
in the area differentiate fully and start secreting
• This independence of tissue is an example of
INITIATION Lack of initiation may result in absence of single tooth or multiple
teeth (anodontia). The upper lateral incisor followed by 3rd molars
and lower 2nd premolar commonly involved.
Abnormal initiation result in development of supernumerary tooth.
E.g. – Mesiodens followed by 4th molar
Sometimes fused or geminated teeth are formed.
This stage reaches its highest level in bell stage of enamel organ.
E.g. -- Dentinogenesis imperfecta or formation of atypical dentin
The advanced bell stage is important stage. This stage establishes the
morphologic pattern, or basic form and relative size of future tooth.
Supernumerary (talon’s) cusp, twinning, loss of cusps or roots, or
malformed or peg shaped tooth (Hutchinson’s incisor), dens in dente
APPOSITION Both enamel hypoplasia and hypo calcification can occur as a result
of an insult to the cells responsible for the apposition stage.
Intrinsic staining and concrescence.