tooth development pdf - dr.duran

ORAL HISTOLOGY and

EMBRYOLOGY COURSE

ORAL HISTOLOGY AND EMBRYOLOGY
COURSES

• Oral Histology and Embryology Practical lectures

will be every Monday at 01:30 in Biology and
Histology lab.

• Oral Histology and Embryology Theoretical Lectures

will be every Monday at 09:00 in Dentistry Hall.

• Lecturer: Dr. Duran Kala
• Lab assistant: Rojan Arif

Exams and Grades:

• In Histology and Embryology courses There will be:
• - Midterm practical exams = 10%
• - Lab Manuals = 10 %
• - Theoretical Midterm exams = 30%
• - Final Practical exam = 10%
• - Final Theoretical exam = 40%
• - Total = 100%

CHAPTERS

• 1-TOOTH DEVELOPMENT AND GROWTH
• 2-ENAMEL
• 3-DENTIN
• 4-CEMENTUM
• 5-PULP
• 6-PDL
• 7-EMBRYOLOGY
• 8-MANDIBLE
• 9-MAXILLA
• 10-BONE TISSUE TYPES
• 11-ALVEOLAR PROCESS
• 12-ORAL MUCOSA-SALIVARY GLANDS

•Histology is the study of anatomy

that deals with the minute
structure, composition, and
functions of tissues. Oral histology
describes in detail the tissues of the
teeth, periodontium, and the
surrounding oral mucosa.

TOOTH & RELATED TISSUES: Developmental goal

PULP

DENTINE

ENAMEL

CEMENTUM

PERIODONTAL
LIGAMENT/ PDL

ALVEOLAR BONE

GINGIVA

WABeresford

Tooth and Associated Structures

Tooth Development

A. Bud Stage
B. Cap Stage
C. Bell Stage
D and E. Dentinogenesis and

amelogenesis

Crown formation

G. Root Formation and

eruption

H. Function

Essentials of Oral Histology and Embryology,
Ed: James Avery, 2

edition. 2000.

Initiation of Tooth Development

The initiation of tooth development begins at 37 days of development
with formation of a continuous horseshoe-band of thickened epithelium
in the location of upper and lower jaws – Primary Epithelial Band

Each band of epithelium will give
rise to 2 sub divisions:
1. Dental lamina and
2. Vestibular lamina

Responsible for

the formation of the vestibule (the
space bordered by the junction of the
gingiva and the tissue of the inner
cheek)

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6

edition

At 5-6 w.i.u. Embryo

Head

Stomodeum

Heart

Front view

Lateral view

Stomodeum

Ectoderm

Dental
lamina

Future dental
papilla

Neural Crest Cells

Flat cells

Columnar cells

Basement
membrane

MESODERM
Connective
tissue

ECTODERM

( S.SQ.E. )

Stomodeum

Developing Tongue

Dental lamina

Maxillary Process

Mandibular process

http://www.usc.edu/hsc/dental/ohisto/

Dental Lamina

• Dental lamina appears as a thickening

of the oral epithelium adjacent to
condensation of ectomesenchyme

• 20 areas of enlargement or knobs

appear, which will form tooth buds
for the 20 primary teeth

• Not all will appear at the same time.

The first to develop are those of the

anterior mandible region

• At this early stage the tooth buds

have already determined their crown
morphology

• Successional lamina: lamina from

which permanent teeth develop

• The dental lamina begins to function

at 6

prenatal week and continues to

year of birth (3

molar)

Primary epithelial

band

Ectomesenchyme

Figures from: http://www.usc.edu/hsc/dental/ohisto/

Vestibular Lamina

Figure from Ten Cate’s Oral Histology, Ed., Antonio Nanci, 6

edition

Ectomesenchyme (ek´tōmez´ nkīm),
n a mass of tissue consisting of neurocrest cells present
in the early formation of an embryo. It eventually forms
the hard and soft tissues of the neck and cranium.

Tooth development is a continuous process, however
can be divided into 3 stages:

1. Bud Stage
2. Cap Stage
3. Bell Stage

1. Bud Stage

•

Bud stage is characterized by rounded, localized growth of

epithelium surrounded by proliferating(reproducing rapidly )
mesenchymal cells which are packed closely beneath and
around the epithelial buds

Meckel’s
cartilage

Intramembranous
ossification

1. Bud Stage

In the bud stage, the enamel organ consists of
peripherally located low columnar cells and centrally
located polygonal cells

http://www.usc.edu/hsc/dental/ohisto/

2. Cap Stage

Vestibular lamina

2. Cap Stage

Condensation of the ectomesenchyme immediately subjacent to the tooth
bud caused by lack of extracellular matrix secretion by the cells thus
preventing separation. Histodifferentiation begins at the end of cap
stage.
Epithelial outgrowth called Enamel Organ because it will eventually
form the enamel
Dental Papilla: Ball of condensed ectomesenchymal cells (it will form
dentin and pulp). The peripheral cells adjacent to the inner dental
epithelium will enlarge and later differentiate into odontoblasts

Enamel Organ

Dental Papilla

http://www.usc.edu/hsc/dental/ohisto/

2. Cap Stage

Enamel organ

Dental papilla

Dental follicle or sac

Dental follicle or dental sac is the condensed ectomesenchymal tissue
surrounding the enamel organ and dental papilla. This gives rise to
cementum and the periodontal ligament

(support structures for tooth)

Enamel knot

2. Cap Stage

Lateral Lamina: extension from the dental lamina that is connected
to the enamel organ

Enamel niche: It is an artifact produced during sectioning of the tissue.
It occurs because the enamel organ is a sheet of proliferating cells rather
than a single strand and contains a concavity filled with ectomesenchyme

Lateral lamina

Dental organ or tooth germ is a term used to constitute the structure that has
enamel organ, dental papilla and dental follicle

Enamel Knot: Densely packed accumulation of cells projecting from the inner
enamel epithelium into dental papilla. Exact role not known, but currently
believed to be the organizational center for cusp development (a pointed
structure on a cuspid, premolar, or molar ).

CA
P
S
TA
GE

Cell Free Zone

Inner Enamel Epithelium

Enamel cord

3. Bell Stage

• Continued growth leads to bell stage, where the enamel organ resembles a

bell with deepening of the epithelium over the dental papilla

• Continuation of histodifferentiation (ameloblasts and odontoblasts are defined)

and beginning of morphodifferentiation (tooth crown assumes its final shape)

Dental lamina

Outer dental
epithelium

Inner dental
epithelium

Dental papilla

Dental follicle
Cervical loop

http://www.usc.edu/hsc/dental/ohisto/

TOOTH PRIMORDIUM/GERM

DENTAL LAMINA

DENTAL PAPILLA

DENTAL SAC/FOLLICLE

DENTAL ORGAN

MESENCHYME

ALVEOLAR BONE

TOOTH TISSUES: Sources

DENTAL LAMINA

DENTAL PAPILLA

DENTAL SAC/FOLLICLE

DENTAL ORGAN

MESENCHYME

ALVEOLAR BONE

PULP

DENTINE

ENAMEL

CEMENTUM

PDL

A BONE

TOOTH TISSUES: Cell Sources

DENTAL LAMINA

DENTAL PAPILLA

DENTAL SAC/FOLLICLE

DENTAL ORGAN

ALVEOLAR BONE

PULP

DENTINE

ENAMEL

CEMENTUM

PDL

A BONE

TOOTH

Crest

Ameloblasts

Odontoblasts

CT cells

Cementoblasts

Fibroblasts

Osteoblasts & ‘clasts

3. Bell Stage (Early)

Inner dental epithelium: Short columnar cells bordering the dental papilla.
These will eventually become ameloblasts that will form the enamel of the
tooth crown by differentiating into tall columnar cells. The cells of inner dental
epithelium exert an organizing influence on the underlying mesenchymal cells
in the dental papilla, which later differentiate into odontoblasts.

Outer dental epithelium: Cuboidal cells that cover the enamel organ. Their function is
to organize a network of capillaries that will bring nutrition to the ameloblasts. In
preparation to formation of enamel, at the end of bell stage, the formerly smooth surface
of the outer dental epithelium is laid in folds.

Stellate reticulum

Inner dental epithelium

Stratum intermedium

Dental papilla

Outer dental epithelium

http://www.usc.edu/hsc/dental/ohisto/

3. Bell Stage (Early)

Stellate reticulum

Inner dental epithelium

Stratum intermedium

Dental papilla

Stellate reticulum: Star-shaped cells with processes, present between the outer
and the inner dental epithelium. These cells secrete glycosaminoglycans,
which attract water, thereby swelling the cells and pushing them apart.
However, they still maintain contact with each other, thus becoming star-shaped.
They have a cushion-like consistency that may support and protect the delicate
enamel organ. It is absent in the portion that outlines the root portions.

Stratum intermedium: Cell layer between the inner dental epithelium and
stellate reticulum which have high alkaline phosphatase activity. They assist
inner dental epithelium (ameloblasts) to form enamel.

Outer dental epithelium

http://www.usc.edu/hsc/dental/ohisto/

Stellate reticulum

Inner dental epithelium

Stratum intermedium

Dental papilla

Outer dental epithelium

Dental Papilla: Before the inner dental 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 shape and then a columnar form and acquire the specific potential to
produce dentin.

http://www.usc.edu/hsc/dental/ohisto/

3. Bell Stage

Higher power view

http://www.usc.edu/hsc/dental/ohisto/

Inner dental epithelium

Outer dental epithelium

Cervical loop

Cervical loop: Area where the inner and the outer dental epithelium meet at
the edge of the enamel organ. This point is where the cells will continue to
divide until the tooth crown attains its full size and which after crown
formation will give rise to the epithelium for root formation. Is also called
“Zone of Reflexion”.

3. Bell Stage

http://www.usc.edu/hsc/dental/ohisto/

Enamel cord

Enamel cord: Pattern of enamel knot that extends between the inner and
outer dental epithelium

Enamel knot

3. Bell Stage

http://www.usc.edu/hsc/dental/ohisto/

SUCCESSIONAL LAMINA:

lamina from which permanent teeth develop

Neural Crest Cells

Ectoderm

Dental
lamina

Future dental
papilla

Dental organ

Dental papilla

Ameloblasts

Differentiating
odontoblasts

Odontoblasts

New ameloblasts

New enamel

Denti
n

5-6 w.i.u.
embryo

Head

Stomodeu
m

3. Bell Stage

Dental lamina (and the lateral lamina) will disintegrate and loose contact
with oral epithelium. Sometimes, these epithelial cells will persist when
they are called “epithelial pearls” or “cell rests of Serre”

Clinical significance: Cysts will develop in these (eruption cysts) and prevent
eruption, or they may form odontomas (tumors) or may form supernumery
teeth

http://www.usc.edu/hsc/dental/ohisto/

Eruption Cyst

Future crown patterning also occurs in the bell stage, by folding of the
inner dental epithelium. Cessation(stopping) of mitotic activity within the inner
dental epithelium determines the shape of a tooth.

Crown Pattern Determination

Vascular and Nerve Supply during Tooth Development

Vascular Supply: Clusters of blood vessels in dental follicle and papilla

Clustering of vessels in papilla coincide with position
of root formation

Enamel organ is avascular, however vessels seen in

close association in the follicle

Nerve Supply: Initially noted in the dental follicle during bud to cap stage

However after start of dentinogenesis, seen in dental papilla

Nerve fibers do not enter enamel organ

Clinical Correlation. Several odontogenic cysts and tumors can arise
from developing tooth structures. Two such conditions are:

Ameloblastoma – which are tumors of odontogenic epithelium that
may arise from cell rests of enamel organ or from the developing
enamel organ among other things

Histology resembles enamel organ epithelium with peripheral columnar
ameloblast-like cells surrounding loosely arranged stellate-reticulum-like cells

Ameloblastoma

Enamel Organ

Odontogenic Myxoma:  Tumor of the jaw that arise from odontogenic
ectomesenchyme.  Histologically, looks similar to mesenchymal portion
of a developing tooth (dental papilla).

Odontogenic myxoma

Developing tooth

Formation of Permanent Dentition

Successional tooth bud

The tooth germs that give rise to permanent incisors, canines and premolars form
as a result of further proliferative activity within the dental lamina, lingual to the
deciduous tooth germ

The developing permanent molars have no deciduous predecessor and their tooth
germs originate from the dental lamina that extends posteriorly beneath the oral
epithelium after the jaws have grown

http://www.usc.edu/hsc/dental/ohisto/

Essentials of Oral Histology and Embryology,
Ed: James Avery, 2

edition. 2000.

Bell Stage

Essentials of Oral Histology and Embryology,
Ed: James Avery, 2

edition. 2000.

Hard Tissue Formation

Deposition of dental hard tissues is
called “apposition”

After the crown attains its final
shape during cap to early bell stage,
the inner dental epithelial cells stop
to proliferate, except the cells at the
cervical loop

First layer of dentin appears at the
cusp tips and progresses cervically,
and the columnar cells of the inner
dental epithelium become elongated
and show reverse polarization,
with the nuclei adjacent to stratum
intermediate (ameloblasts)

The boundary between the odontoblasts
and inner dental epithelium defines the
future dentino-enamel junction

http://www.usc.edu/hsc/dental/ohisto/

For dentinogenesis and amelogenesis to take place normally,
the differentiating odontoblasts and ameloblasts will receive
signals form each other – “reciprocal induction”

Stages of Apposition

1. Elongation of inner dental epithelium
2. Differentiation of odontoblasts
3. Formation of dentin
4. Formation of enamel

At the same time or soon after the first layer of dentin (mantle dentin) is formed,
the inner dental epithelial cells differentiate into ameloblasts and secrete enamel
proteins.  These proteins further will help in the terminal differentiation of
odontoblasts.  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.  The formation of
enamel is called amelogenesis.

Ameloblasts

First layer of enamel

Dentin

Odontoblasts

http://www.usc.edu/hsc/dental/ohisto/

Apposition

At the same time when the inner
dental epithelium is differentiating,
the undifferentiated ectomesenchymal
cells increase rapidly in size and
ultimately differentiate into odontoblasts

Differentiation of odontoblasts from
ectomesenchymal cells are induced by
influence from the inner dental epithelium

Experiments have shown that if there is
no inner dental epithelium, there is no
dentin formed

Odontoblasts Dentin

Enamel

Ameloblasts

http://www.usc.edu/hsc/dental/ohisto/

Structures at Appositional Stage

Dental follicle

Outer Dental Epith.

Stellate reticulum

Inner Dental Epith.

Pulp

Odontoblasts

Stratum intermedium

Essentials of Oral Histology and Embryology,
Ed: James Avery, 2

edition. 2000.

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

http://www.usc.edu/hsc/dental/ohisto/

Odontoblasts are highly polarized with the nuclei away from inner dental epith.

Following differentiation of odontoblasts, first layer of dentin is produced,
characterized by appearance of large-diameter type III collagen fibrils (0.1
to 0.2



m in dia) called von Korff’s fibers, followed by type I collagen fibers

– MANTLE DENTINE

At the same time as initial dentin deposition, the odontoblasts will develop stubby
Processes (short and thick extensions) at the side close to the inner dental
epithelium which extend into forming extracellular matrix

As the odontoblasts move pulpward, the odontoblast process (Tomes´ fiber) will
elongate and become active in dentine matrix formation

It is initially called predentin and following mineralization is called dentin

Dentinogenesis

Oral Histology, 5

edition, A R Ten Cate

The odontoblasts as they differentiate will start elaborating organic matrix
of dentin, which will mineralize. As the organic matrix of dentin is deposited,
the odontoblasts move towards the center of the dental papilla, leaving behind
cytoplasmic extensions which will soon be surrounded by dentin. Therefore,
a tubular structure of dentin is formed.

odontoblasts

dentin

ameloblasts

http://www.usc.edu/hsc/dental/ohisto/

Odontoblasts with cytoplasmic processes forming dentinal tubules

http://www.usc.edu/hsc/dental/ohisto/

2 steps of dentinogenesis:

1. Formation of collagen matrix
2. Deposition of calcium and phosphate

(hydroxyapatite) crystals in the matrix

Odontoblast

like squamous
epithelium

DENTIN:Composition

Collagen fibrils matriks, mineral
Crystalls,

glycoproteins & proteoglycans

Processes (fibers) of Odontoblast are lining
through the dentine tubules but cell bodies
are located in pulp region.

Odontoblasts and process

Odontoblast cells

Odontoblast extensions

Dentin

Pulp

Dentin

Cementum

Granular layer

of Tomes

Hyaline layer

Amelogenesis is also a two-step process:

First step produces a partially mineralized matrix (~ 30%)

Second step involves influx of additional mineral coincident
with removal of organic material and water to attain greater
than 96% mineral content

Amelogenesis

Essentials of Oral Histology and Embryology,
Ed: James Avery, 2

edition. 2000.

Amelogenesis

Amelogenesis begins after a few



m of dentin deposition at the

dentinoenamel junction

Ameloblasts goes through following functional stages:
1.

Morphogenetic. During this stage the shape of the crown is determined.

Histodifferentiation. The cells of the inner dental epithelium is

differentiating into ameloblasts.  The above two stages are the presecretory
stages, where the  cells differentiate, acquire phenotype,  change polarity,
develop an extensive protein synthesis machinery, and prepare to secrete  an
organic matrix of enamel.

3. Secretory stage: Ameloblasts elaborate and organize the entire enamel
thickness.  Short conical processes called Tomes´ processes develop at the
apical end of the ameloblasts.  The main protein that accumulates is
amelogenin.

Essentials of Oral Histology and Embryology,
Ed: James Avery, 2

edition. 2000.

4. Maturation stage: Ameloblasts modulate and transport specific ions

required for the concurrent accretion of mineral. At this stage,
ameloblast becomes more active in absorption of the organic matrix
and water, which allows mineralization to proceed. After the
ameloblasts have completed their contributions to the mineralization
phase, they secrete an organic cuticle on the surface of the enamel,
which is called developmental or primary cuticle

Protection: The ameloblast are shorter and contact the stratum
intermedium and outer dental epithelium and fuse to form the
reduced dental (enamel) epithelium. The reduced enamel epithelium
remains until the tooth erupts. As the tooth erupts and passes
through the oral epithelium, the incisal part of the reduced dental
epithelium is destroyed but the epithelium present cervically
interacts with oral epithelium to become the junctional epithelium

Amelogenesis

Amelogenesis Imperfecta

Hypomaturation

Hypoplastic

Hypocalcified

Summary of Tooth Development

(So Far)

The epithelium is separated from the
dental papilla by an acellular zone

Inner dental epithelial cells are elongated,
and the acellular zone is lost by
differentiation of odontoblasts

Odontoblasts retreat toward the center
of the pulp, leaving behind dentin

Ameloblasts begin to migrate outward and
leave behind formed enamel

Time Line of Human Tooth Development

(Table 5-2 in Text book)

Age

Developmental Characteristics

42 to 48 days

Dental lamina formation

55 to 56 days

Bud stage; deciduous incisors;
canines and molars

14 weeks

Bell stage for deciduous teeth; bud
stage for permanent teeth

18 weeks

Dentin and functional ameloblasts
in deciduous teeth

32 weeks

Dentin and functional ameloblasts
in permanent first molars

Incremental pattern of dentin
and enamel formation from
initiation to completion

Growth areas of developing crown.
Growth at cusp tip, intercuspal region,
and cervical region

Essentials of Oral Histology and Embryology,
Ed: James Avery, 2

edition. 2000.

Root Formation

Development of root begins after the enamel and dentin formation has
reached the future cementoenamel junction

Epithelial cells of the inner and outer dental epithelium proliferate from the
cervical loop of the enamel organ to form the Hertwig’s epithelial root sheath.
The root sheath determines if a tooth has single or multiple roots, is short or
long, or is curved ir straight

Hertwig’s epithelial
root sheath

http://www.usc.edu/hsc/dental/ohisto/

Hertwig’s epithelial
root sheath

Inner dental epithelium

Outer dental epithelium

Stratum intermedium

Eventually the root sheath will fragment to form several discrete clusters
of epithelial cells known as epithelial cell rests of malassez. These will persist in
adults within the periodontal ligament

http://www.usc.edu/hsc/dental/ohisto/

The epithelial rests appear as small clusters of epithelial cells which
are located in the periodontal ligament adjacent to the surface of
cementum. They are cellular residues of the embryonic structure
known as Hertwig's epithelial root sheath.

Epithelial Cell Rests of Malassez

http://www.usc.edu/hsc/dental/ohisto/

Primary apical formen

Epithelial diaphragm: the proliferating
end of the root sheath bends at a near
45-degree angle. The epithelial
diaphragm will encircle the apical
opening of the dental pulp during root
development

http://www.usc.edu/hsc/dental/ohisto/

Secondary apical foramen form as a result of two or three tongues of
epithelium growing inward toward each other resulting in multirooted teeth

Essentials of Oral Histology and Embryology,
Ed: James Avery, 2

edition. 2000

Direction of root growth versus eruptive movement of tooth

Essentials of Oral Histology and Embryology,
Ed: James Avery, 2

edition. 2000.

Soon after root formation begins, tooth begins to erupt until it reaches
its final position

While roots are forming, the supporting structures of tooth also
develop – periodontal ligament and cementum

As the root sheath fragments, the dental follicle cells will penetrate between
the epithelial cells and lie close to the newly formed root dentin

These cells will differentiate into cementoblasts, which will make cementum

Fibers of the periodontal ligament, which will also form from the cells of the
dental follicle will get anchored in the organic matrix of the cementum which
will later get mineralized

Tooth eruption and Development of

supporting structures

Figure :Average periods for emergence and exfoliation of primary teeth

Figure: Average periods of emergence of permanent teeth.