DEVELOPMENT OF

TOOTH
The primitive cavity (STOMODEUM) is lined by STRATIFIED
SQUAMOUS EPITHELIUM , called ORAL ECTODERM

This contacts with the endoderm of the FOREGUT to form

the BUCCOPHARYNGEAL MEMBRANE

27th day of gestation

membrane ruptures &
establishes the
connection with the
foregut.

(4th week of development)

Most cells underlying oral ectoderm are NEURAL CREST/
ECTOMESENCHYMAL in origin & INDUCE overlying
ectoderm to START TOOTH DEVELOPMENT.

6th WEEK OF DEVELOPMENT

Oral epithelium thickens

and INVAGINATES into the
ectomesenchyme to
form a PRIMARY
EPITHELIAL BAND
 7th WEEK OF DEVELOPMENT
Primary epithelial band divides into VESTIBULAR LAMINA (
buccally situated) & DENTAL LAMINA ( lingually
situated)
vestibular lamina (lip furrow band) develops the vestibule of
mouth and separates the lips and cheek from the tooth
bearing regions
Dental lamina contributes to the development of tooth

8th WEEK OF DEVELOPMENT

A series of swellings develop on the deep surface of dental

lamina, which indicates EARLY DEVELOPING TOOTH GERMS
Dental lamina appears as an ARCH SHAPED BAND OF TISSUES
which follows the line of vestibular fold
Each epithelial swelling is almost completely surrounded
by a mesenchymal condensation

A) MECKEL’S CARTILAGE

B) DENTAL LAMINA

C) DEVELOPING TONGUE

D) NEUROVASCULAR
BUNDLE
dental lamina serves as a PRIMORDIUM for the
ectodermal portion of decicuous teeth

Permanent molars arise directly from the DISTAL

EXTENTION OF DENTAL LAMINA

DISTAL PROLIFERATION of dental lamina is responsible for

location of germs of permanent molars in RAMUS OF
MANDIBLE and TUBEROSITY OF MAXILLA

ALL SUCCESSORS OF DEC. TEETH DEVELOP from a LINGUAL

EXTENTION of free end of dental lamina OPPOSITE TO
ENAMEL ORGAN OF EACH DECIDUOUS TOOTH
Arrow marks showing series of swelling
representing developing tooth germs on deep
surface of dental lamina.
A = vestibular fold
FATE OF DENTAL LAMINA

Total activity extends for a period of at least 5 yrs

May still be active in the region of 3rd molar or occassional
epithelial remnanats
As teeth develop. Continues, they loose connection with
dental lamina
Remnants of dental lamina persist as EPITHELIAL PEARLS
OR ISLANDS within jaw as well as gingiva
Also called as CELL RESTS OF SERRES
FATE OF DENTAL LAMINA

Epithelial pearls of Serres

 At certain points along dental lamina, ectodermal cells multiply
more rapidly & form little knobs that grow into underlying
mesenchyme, each refers to as a bud or ENAMEL ORGAN OF
TOOTH BUD OF DECIDUOUS TOOTH
The enamel organ shows spherical to ovoid EPITHELIAL
CONDENSATION
All do not start to dev. at same time, first to appear are those of
ANTERIOR MANDIBULAR REGION

Enamel organ surrounded by the

ectomesenchyme
• The tooth buds along with underlying
ectomesenchyme form the TOOTH GERM of
10 different deciduous teeth in each dental
arch.
• The tooth germ is an aggregate of different
types of cells, derived from the ectoderm of
the 1st branchial arch and the
ectomesenchyme containing the neural crest
cells.
• This tooth germ is the primordia for
developing tooth and eventually contribute to
formation of different tissues of a tooth.
• These cells of tooth germ are organised into
three distinct parts,i.e, the enamel organ, the
dental papilla and the dental sac or follicle.
• Thus, the components of tooth germ are:
ENAMEL ORGAN- this develops from the dental
lamina and hence is ectodermal in origin and
is involved in formation of enamel
DENTAL PAPILLA- ectomesenchymal in origin
and give rise to dentin and pulp
DENTAL SAC OR FOLLICLE- ectomesenchymal in
origin and responsible for formation of PDL
and cementum
• As the cell proliferation continues, each
enamel organ increases in size, sinks deeper
into the into ectomesenchyme and due to
differential growth changes its shape
• Based on the shape of the enamel organ, the
developmental stages of the tooth can be
divided into various morphological stages
• As the development proceeds through various
morphological stages, many physiological
changes also take place in different
component of the tooth germ which are
named as physiological processes
MORPHOLOGIC STAGES PHYSIOLOGIC PROCESSES

Dental Lamina Initiation

Bud stage Proliferation

Cap stage Histodifferentiation

Bell stage (early) Morphodifferentiation

Bell stage (advanced)

Form. Of E & D matrix Apposition

MORPHOLOGICAL STAGES OF
TOOTH DEVELOPMENT
 BUD STAGE
Represented by enamel organ.
Consist of
peripheral low columnar cells
central polygonal cells
Supporting ectomesenchymal cells are closely
packed beneath & around epithelial bud.
The enamel organ consists of PERIPHERALLY LOCATED LOW
COLUMNAR CELLS & CENTRALLY LOCATED POLYGONAL CELLS.

Increased MITOTIC ACTIVITY & MIGRATION OF NEURAL CREST CELLS

results in CONDENSATION of ECTOMESENCHYMAL CELLS
surrounding tooth bud.

Area of condensation imbed adjacent to enamel organ is DENTAL

PAPILLA ( forms DENTIN & PULP)
Condensation surrounding tooth bud & dental papilla is the
DENTAL SAC ( forms CEMENTUM & PDL )

Both dental papilla and dental sac become more well defined
as enamel organ grows into CAP & BELL SHAPES
A = ENAMEL ORGAN
B = ECTOMESENCHYMAL CONDENSATION
 CAP STAGE
Shallow invagination on deep surface of the
bud.

Outer Enamel Epithelium- Peripheral Cuboidal

cells-cover convexity of cap

Inner Enamel Epithelium- tall columnar cells in

concavity
A. Stellate Reticulum
B. OEE
C. IEE
D. Dental papilla
E. Dental Follicle
 Stellate Reticulum
 Polygonal cells begin to separate as more
intercellular fluid is produced & form Stellate
reticulum.

 Cells appear as Branched network.

 Reticular network fluid filled with mucoid rich in

albumin-gives cushion like effect to S.R.

 Function-support & protect delicate enamel

forming cells.
 Enamel Cord & Enamel Knot
 In the center of E.O. cells are densely packed-
known as Enamel Knot

 Vertical extension of enamel knot- Enamel Cord

 Temporary structures, disappear after enamel

formation

 Function- act as a reservoir of dividing cells for

growing E.O.
1) Dental lamina
2) Dental sac
3) OEE
4) Stellate reticulum
5) IEE
6) Dental papilla
7) Enamel cord
8) Enamel navel
9) Blood vessel
10) Enamel niche
11) Successional Dental
Lamina
 DENTAL PAPILLA
 Ball of condensed ectomesenchymal cells
 Form Dentin & Pulp.
 Peripheral cells adjacent to IEE enlarge &
differentiate into odontoblasts.
 Also show active budding of capillaries & Mitotic
figures.
DENTAL SAC
 Marginal condensation of ectomesenchymal cells
surround the E.O. & dental papilla.
 Function- form. of Cementum & PDL
 BELL STAGE
Epithelial cells – 4 types:
 Inner Enamel epithelium
(F)
 Stratum Intermedium (E)
 Stellate reticulum (C)
 Outer Enamel epithelium
(A)
 Early bell stage (14th week)

Enamel organ Shows 4 distinct layers:

OEE
Stellate reticulum
Stratum intermedium
IEE
A = Inner investing layer of dental follicle
B = Outer layer of dental follicle
 Outer enamel epithelium
Outer layer of cuboidal cells
Cells contain large, centrally
placed nuclei
Cells contain small amts of
intra cellular organelles assoc
with protein synth.
OEE is continuous with IEE at
CERVICAL LOOP (point of inc
mitotic activity)
Seperated from surr
mesenchymal tiss by a
basement memb 2um thick
Role of Outer Enamel Epithelium

Maintains shape of enamel organ

Exchange of substance b/w enamel organ & environment

Protective layer for entire enamel organ

Attachment of gingiva to the tooth

 Stellate Reticulum
most fully developed tissue at bell
stage
Expands further bec of inc in amt of
GLYCOSAMINOGLYCAN.
Star shaped cells with long process &
conspicuous nuclei
Collapses before enamel formation
begins. This reduces distance b/w
ameloblast and nutrient capillaries.
This change begins at height of cusp
or incisal edge & progresses
cervically.
 Role of Stellate Reticulum

protection of underlying dental tissue against physical

disturbance

Maintenance of tooth shape

Helps in crown morphogenesis

 Stratum intermedium
First appearance at bell stage

Consists of 2 to 3 layers of
flattened cells lying b/w I.E.E. &
S.R

Resemble the cells of S.R.,

though the inter cellular spaces
are smaller & alkaline
phosphatase levels are higher
 Role of Stratum Intermedium

Synthesis of proteins

Transport of materials to and from ameloblast in I.E.E

 Early bell stage

Inner enamel epithelium

 Cells are mainly
COLUMNAR but in the
region of FUTURE CUSP
TIPS they become
ELONGATED
 4-5 um diameter and 40 um
height
 Rich in RNA but lack
ALKALINE PHOSPHATASE
 Separated from peripheral
cells of dental papilla by a
BASEMENT MEMBRANE &
CELL FREE ZONE 1-2 um
wide
17th week

DL begin
to degenerate

developing
Permament
teeth
Late bell stage (18th week)
Associated with the FORMATION OF DENTAL HARD TISSUES

DENTIN FORMATION ALWAYS PRECEEDS ENAMEL

FORMATION

PRE AMELOBLASTS provide INDUCTIVE INFLUENCE on

adjacent MESENCHYMAL CELLS OF DENTAL PAPILLA so that
they become COLUMNAR & differentiate into
ODONTOBLASTS.
ODONTOBLASTS then become involved in the formation of
PRE DENTIN & DENTIN.The presence of DENTIN INDUCES
AMELOBLASTS TO SECRETE ENAMEL
DENTIN MATRIX IS SHOWN BY BLUE COLOUR
ENAMEL MATRIX IS SHOWN BY RED COLOUR
A = PERMANENT TOOTH
Lingual downgrowths of O.E.E. appear from enamel organ &
give rise to tooth germs of permanent successors. These
appear alongside the incisors at 5 months in utero

The downgrowths disappear in enamel organ of permanent

teeth

Dental lamina grows backward behind dec 2nd molar to bud off
perm molar teeth

1st perm molar appears at about 4 months i.u

Tooth bud for 2nd perm molar appears about 6 months after
birth, while 3rd molar about 4-5 years after birth

Enamel and dentin formation start at tips of future cusps and

incisal edges

Boundary b/w IEE & odontoblasts marks future DEJ

Cervical portion of EO gives rise to H.E.R.S

DENTIN MATRIX IS SHOWN IN
GREEN COLOUR

ENAMEL MATRIX IS SHOWN IN

RED COLOUR

A = ODONTOBLASTS
B = AMELOBLASTS
C = STRATUM INTERMEDIUM
D = STELLATE RETICULUM
E = OUTER ENAMEL
EPITHELIUM
1. Inner Enamel epithelium
single layer of columnar cells c/a Ameloblasts.
attached to each other by junctional complexes laterally
& to cells in Stratum intermedium by desmosomes.
Cells direct cells of dental papilla to differentiate into
Odontoblasts.
Basement memb. separating E.O. & dental papilla
before dentin form.- c/a Membrane preformation
2. Stratum intermedium
few layers of sq.cells b/w IEE & Stratum Reticulum
closely attached by-desmosomes & gap junc.
High degree of metabolic activity
Essential for enamel formation.
3. Stellate Reticulum

Star shaped with long processes

Collapses before enamel form. begins;

reducing the dist from centrally situated
ameloblasts & nutrient capillaries near OEE

Change begins at height of cusp or incisal edge

& progresses cervically.
4. Outer Enamel Epithelium

Flattened to low cuboidal form

At end of bell stage, OEE is laid in folds b/w

folds adj. mesenchyme of dental sac forms
papillae  contain capillary loops provide
nutrition for avascular enamel organ
 ADVANCED BELL STAGE
Boundary b/w IEE & odontoblasts outlines the future
DEJ
Cervical portion of E.O. Hertwig’s Root Sheath
HERTWIG’S ROOT SHEATH & ROOT FORM.
Dev. Of root begins after enamel & dentin form. Has
reached future CEJ
Molds the shape of root & initiates radicular dentin
form.
Consist of- OEE & IEE
Loses continuity after first dentin layer form.
Epi remnants in PDL c/a Rests of Malassez
LATE BELL STAGE

Enamel matrix

Dentin matrix
ROOT FORM.
 Root sheath bends at future CEJ in horizontal plane-
Epithelial Diaphragm
 Only the coronal portion of epi. Diaphragm
proliferates & lengthening of root sheath takes place
 Differentiation of odontoblasts & radicular dentin
form.
 Connective tissue of dental sac proliferate & invade
HEE dividing into epi. Strands
 Conn. Tissue cells in contact with outer layer of
dentin cementoblasts that deposit layer of
cementum onto dentin
 LAST STAGE –proliferation of epi.diaphram lags
behind that of the pulpal connective tissue
 Wide apical foramen reduces 1st to the width of
diaphragmatic opening &then by the deposition of
D&C, to the apex of the root
A. Odontoblasts
B. Ameloblasts
C. Stratum intermedium
D. Stellate reticulum
E. OEE
Enamel matrix
Dentin matrix

LATE BELL STAGE

Differential
growth of
diaphragm in
multirooted
teeth causes div.
of root trunk.
STAGES OF DEVELOPMENT IN
MULTIROOTED TEETH
Histophysiology & Clinical
Considerations
INITIATION
 Initiation induction require ectomesenhymal-epi.
Interaction
 D.P can induce even non tooth epi to form E. e.g.– in
the ovary – dermoid cyst or tumor.
 Lack of initiation-partial anodontia(ULI,3rd M,2nd L Pre
M)
-anodontia
 Abnormal initiation – single/multiple supernumerary
teeth
PROLIFERATION
 Cause regular change in size & proportion of growing
tooth germ
 HISTODIFFRENTIATION
 Formative cells undergo definite morphologic changes &
acquire their func. Assignment
 Highest development –bell stage
 Vit A deficiency – ameloblasts fail to differentiate
properly- organizing influence on adjacent mesenchymal
cells is disturbed - form atypical D ( osteodentin)

MORPHODIFFERENTIATION
 Basic form & relative size-by differential growth
 Morphodifferentiation is impossible without
proliferation
 Disturbance in morph. – affect form & size
(supernumerary cusp/roots , twinning- peg/normal
tooth
 Ectodermal
Dysplasia

Mesiodens
 APPOSITION
Deposition of matrix of the hard dental struc.
Characterized by regular & rhythmic deposition of
extra cellular matrix-incapable of further growth.
Genetic & environmental factors may disturb N
synthesis & secretion of organic matrix- E
hypoplasia
Hypo calcification/ Hypo mineralization- normal
organic matrix but defective mineralization.