Griffith University Oral Biology 2 1009 DOH

Tooth Development

Dr. Mahmoud Bakr

Lecturer in General Dental Practice

B.D.S, M.D.S (Cairo University), ADC (Australia)

Member of the Australian Dental Association (ADA),

the Australian Biology Institute Inc. (ABI) and the

Egyptian Dental Union (EDU)

Learning objectives:

After completing this lecture you should be able to:

1- Describe stages of tooth development in writing

and by drawing a diagram and demonstrate

understanding of the process of tooth eruption.

2- By observing the histological details of cells and

tissues, you should be able to use a microscope to

identify different morphological stages of tooth

development and understand the histological

processes involved in preparing slides.

• All Microscopic images are taken from the

Digital Library of the Oral Biology

Department (Cairo University).

TOOTH DEVELOPMENT

AND GROWTH

At 5-6 w.i.u. Embryo

Head

Stomodeum

Heart

Front view Lateral view

The embryo at 5-6 w.i.u is formed of

three germ layers:

• Ectoderm which forms the external

lining of the body and oral cavity later

on

• Mesoderm from which intermediate

tissues such as Blood, Cartilage and

Bone are derived

• Endoderm which lines internal organs

(Guts)

The primitive Oral Cavity is called

Stomodeum

and is lined by Ectoderm

Which is formed of two layers of :

1- Basal Columnar cells

2- Superficial flat cells

From both of these layers + Mesenchyme

all teeth and oral structures are formed

Stomodeum

Stomodeum

Ectoderm

Dental lamina

Future dental papilla

Neural Crest Cells

A

Flat cells Columnar cells

Basement

membrane MESODERM

Connective

tissue

ECTODERM

( S.SQ.E. )

• During CNS development a new type of cells appear called

NEURAL CREST CELLS

They are Ectodermal in origin.

These cells have the ability to:

1- Migrate to other tissues

2- Differentiate into other types of cells

3- Send signals to neighboring tissues

So they migrate from the dorsal surface of the embryo to the Stomodeum where they reside in the mesenchyme changing it into Ectomesenchyme.

WHY?????

• It is called now Ectomesenchyme because when of Neural Crest Cells which are Ectodermal in origin migrates to the Mesenchyme of the stomodeum it turns it into Ectomesenchyme.

i.e: Mesenchymal tissue that contains Ectodermal cells

BRANCHIAL ARCHES

DEVELOPMENT

3 weeks IUL. embryo

The Embyo is flattened dorso-

ventrally, so six pairs of finger-like

projections extend from the

Endoderm of the foregut to the

outer Ectodermal lining.

These are called the Branchial arches

and they are lined by Ectodrem

from the outside, Endoderm from

the inside with Mesoderm

inbetween.

Note: The 1st Branchial arch is

lined by Ectoderm from outside

and inside.

T.S in Branchial arches

• T.S in

Branchial

Arches

• Branchial arch

• Branchial cleft

• Pharyngeal pouch

• Ectoderm

• Mesoderm

• Endoderm

Derivatives of the first branchial

arch (Mandibular Arch):

• 1-The mandible and maxilla

• 2-The lower lip, part of the upper lip and

cheek

• 3-All the teeth

• 4-All salivary glands

• 5-All muscles of mastication

• 6-The anterior two thirds of the tongue

Remnants of Meckel’s cartilage:

• -incus and malleus

• -lingula of the mandible

• -mental ossicles

• -sphenomandibular

ligament

Nerve supply of Branchial Arches

1st Branchial arch (Mandibular Arch)

Mandibular Nerve

2nd Branchial arch (Hyoid Arch)

Facial Nerve

Note: Nerve supply of different structures

correlates with their developmental origin.

i.e: All structures derived from the 1st

branchial arch are supplied by the same

nerve that supplies the arch

(Mandibular Nerve).

STAGES OF TOOTH DEVELOPMENT MAY BE DESCRIBED ACCORDING TO:

1- Changes in the morphology of the developing tooth (MORPHOLOGICAL STAGES)

2- Its physiological changes (HISTOPHYSIOLOGICAL STAGES).

Note: both the morphological and the histophysiological changes are shearing in the different tooth development stages.

STAGES OF TOOTH

DEVELOPMENT AND GROWTH

MORPHOLOGICAL STAGES

1- DENTAL LAMINA.

2- BUD-STAGE.

3- CAP-STAGE.

4- BELL-STAGE

(EARLY AND LATE).

Early Late

HISTOPHYSIOLOGICAL

STAGES

1- INITIATION.

2- PROLIFERATION.

3- HISTO-DIFFERENTIATION.

4- MORPHO-DIFFERENTIATION.

5- APPOSITION.

1- Dental Lamina

• Under the influence of Neural Crest Cells

proliferation of Ectoderm occurs to form

two band like structures or two Dental

Laminae.

• One carries the upper teeth and the other is

for lower teeth

1-DENTAL LAMINA

MESODERM

(Connective

tissue)

ECTODERM

( S.SQ.E. )

Flat cells

Columnar cells

Basement

membrane

DENTAL LAMINA

MESENCHYMAL

CONDENSATION

1

EPITHELIAL

PROLIFRATION

2

Dental

lamina

2- Bud stage

• Again under the influence of Neural Crest cells 10 rounded projections (ENAMEL ORGANS) appear on the labial surface of the dental lamina, corresponding to the ten Deciduous teeth.

• Each Bud (Enamel Organ) is surrounded by Mesenchymal condensation which is the Dental papilla + Dental Sac

• In this stage the changes are Morphological only

2-BUD STAGE

EPITHELIAL

PROLIFRATION

MESENCHYMAL

CONDENSATION

A simple equation

Tooth Germ=

Enamel Organ + Dental Papilla + Dental Sac

Enamel organ gives Enamel

Dental Papilla gives Dentin and Pulp

Dental Sac gives Cementum, Periodontal

ligament (PDL) and Alveolar Bone

QUESTION

• What is the difference between Enamel

organ and Tooth germ??????????

• ANSWER: Enamel organ is a part of three

parts forming a tooth germ

ANOTHER QUESTION

• Which tissue of the tooth is Ectodermal in origin????????

• ANSWER: ENAMEL which is derived from ENAMEL ORGAN which is Ectodermal in origin

• Note the E E E

3- Cap Stage • Under the effect of Neural crest cells the enamel

organ of bud stage undergoes unequal or

differential growth to change in shape from bud

to cap.

• The enamel organ of cap stage has an inner

surface lined by columnar cells called Inner

enamel epithelium or Inner dental epithelium.

• It has an outer surface lined by cubiodal cells

called Outer enamel epithelium or Outer dental

epithelium.

• The inner and outer enamel epithelium meet at the

cervical loop.

3-CAP STAGE Histological structure of the tooth germ

3-Dental sac

1-Dental organ

Enamel knot

Cell free zone

Inner D. E.

Outer D. E.

Stellate R.

2-Dental papilla

Enamel

cord

• The polyhedral cells in the middle of the

enamel organ change into star shaped cells

called Stellate Reticulum due to secretion

of a hydrophilic substance called

Glucosaminoglycans (GAG's).

• The enamel organ is surrounded by dental

papilla and dental sac as in bud stage.

CAP STAGE

1-DENTAL

ORGAN

2- DENTAL

PAPILLA

3-

DENTAL

SAC

TOOTH

GERM

CAP STAGE

1-DENTAL

ORGAN

2- DENTAL

PAPILLA 3-

DENTAL

SAC

TOOTH

GERM

There are transient structures in the cap stage:

1-Enamel knot and enamel cord: rounded

cells that connect I.E.E and O.E.E and

a- is thought to determine the future site of the

cusp or incisal edge.

b- may give rise to another type of cells called

stratum intermedium.

2-Cell free zone: separates the dental papilla

from the inner surface of the enamel organ.

• So the changes in Cap stage are

MORPHOLIGICAL as well as

HISTOPHYSIOLOGICAL

C

A

P

S

T

A

G

E Cell Free Zone

Inner Enamel Epithelium

Enamel cord

Inner Enamel Epithelium

Odontoblasts

Dental Sac

4-EARLY BELL STAGE Histological structure of the tooth germ

4- Early bell stage

• Under the effect of neural crest cells:

• The Inner enamel epithelium align

themselves on the future dentino-enamel

junction, so the shape & type of the tooth

• Can be determined in this stage.

• Lingual to the enamel organ of the

deciduous tooth a downward proliferation

from main dental lamina appears and called

Successional dental lamina which carries

the permanent successor.

• Histological changes take place in the cells of the enamel organ:

• Inner enamel epithelium (I.E.E): become longer and rearrangement of the organelles take place (REPOLARIZATION) and now it is called Preameloblasts.

• I.E.E elongate towards cell free zone leading to its disappearance, so Preameloblasts become in contact with the peripheral layer of dental papilla leading to INDUCTION of ODONTOBLASTS.

• Stratum intermedium: 2 or 3 rows of flat cells above the Preameloblasts rich in (alkaline phosphatase), these cells arise from the enamel knot and cord.

• Outer enamel epithelium (O.E.E):

cuboidal cells as in cap stage but shorter.

• Stellate reticulum: same as cap stage but

the processes are longer & cell body is

smaller.

• The dental papilla: same as cap stage but

cell free zone disappears after elongation of

I.E.E.

• The dental sac: same as in cap stage.

EARLY BELL STAGE Histological structure of the tooth germ

SR

SI

IDE

OB

DP

ODE

EARLY BELL STAGE Histological structure of the tooth germ

Cervical

loop

LDL

DENTAL LAMINA

PROPER

SUCCESSIONAL LAMINA

DENTAL LAMINA

PROPER

LATERAL

DENTAL

LAMINA

SUCCESSIONAL

LAMINA

DO

SUCCESSOR

PRIMORDIUM

5-LATE BELL STAG Histological structure of the tooth germ

5-LATE BELL STAGE Histological structure of the tooth germ

STRATUM

INTER.

STELLATE RETICULUM

INNER

DENT.

EPITH. PREDENTIN

ODONTOBLASTS

• The difference between early bell stage and late bell stage is the deposition of the 1st layer of hard dental structure (DENTIN).

• The enamel organ loses its connection to the dental lamina and the remnants of dental lamina is called EPITH RESTS OF SERRES or SERRES PEARLS.

• Inner enamel epithelium: Preameloblasts elongate more to form AMELOBLASTS.

• Stratum intermedium: same as in early bell stage.

• Outer enamel epithelium: become flat and its plasma membrane becomes folded to increase the surface area available for obtaining nutrition from dental sac as nutririon from dental papilla cannot be obtained after deposition of hard dental structures (ENAMEL & DENTIN).

• Stellate reticulum: cell body is smaller and processes are longer.

• Dental papilla & Dental sac: same as in early bell stage.

SERRES’ PEARLS

LATE BELL SATGE Histological structure of the tooth germ

ENAMEL

DENTIN

PREDENTIN

OUTER DENTAL

EPITHELIUM

CAPILLARY LOOP

SR

AB

SI

ADVANCED BELL STAGE Histological structure of the tooth germ

DS

E

ODE

SR

SI

AB

OB

PD

D

DP

PULP

ADVANCED BELL STAGE Histological structure of the tooth germ

ASG

PULP

OB

PD

D

E

SR

SI

AB

NOTE

EARLY ADVANCED

ASG

FUNCTIONS

OF THE ENAMEL ORGAN

1- OUTER ENAMEL EPITHELIUM.

Active transport of materials specially, after hard dental tissues formation.

2- STELLATE RETICULUM:

a- Act as a buffer against physical forces that may distort the configurations of the developing amelodentinal junction giving rise to gross morphological changes.

b- It permit a limited flow of nutritional elements from the outlying blood vessels to the formative cells, so it acts as a store house for the nutritive materials.

c- It keeps room for the developing enamel.

3- STRATUM INTERMEDIUM. The function of this layer is

not understood:

a- It is believed to control fluid diffusion into and out of the

ameloblasts.

b- It provides the enamel organ with alkaline phosphatase

enzyme needed for mineralization.

c- These cells plus the inner dental epithelium are considered as

a single functional unit responsible for enamel formation.

4- INNER ENAMEL EPITHELIUM.

a- It exerts an organizing influence on the undifferentiated cells

of the dental papilla to differentiate into odontoblasts.

b- Transport of the nutritive materials from the dental papilla

to the enamel organ before dental hard tissues formation.

c- Arranged in a pattern to determine the future morphology of the amelodentinal junction and the crown.

d- It lays down enamel matrix and helps in its mineralization.

e- It shares in the root formation.

f- It secretes primary enamel cuticle, after the full thickness of enamel is deposited, to protect the enamel of the unerupted tooth against resorption and preventing deposition of Cementum.

g- It shares in the formation of the reduced enamel epithelium.

4- INNER ENAMEL EPITHELIUM.

FUNCTIONS OF THE ENAMEL ORGAN (cont.)

Organizing Nutritive

Morphology

Enamel matrix Root formation.

Primary

enamel cuticle

Reduced enamel

epithelium.

FUNCTIONS OF THE DENTAL

PAPILLA AND DENTAL SAC

• The Dental Papilla Gives Rise To

Dentin And Dental Pulp.

• The Dental Sac Gives Rise The

Cementum, Periodontal Ligament And

Alveolar Bone Proper.

FUNCTIONS OF THE DENTAL

PAPILLA AND DENTAL SAC

The Dental Papilla Dentin

PULP

The Dental Sac Cementum,

Periodontal Ligament

Alveolar Bone Proper

FUNCTIONS OF THE DENTAL

LAMINA

1- Initiation Of The Entire Deciduous Dentition ( 2 MIU).

2- Initiation Of The Permanent Successors

( 5 MIU. For Central Incisors, 10 M. Of Age For Second

Premolars).

3- Initiation Of The Permanent Molars

( First Molar 4 MIU., Second Molar 1 Year, Third Molar

4 Years)

It is thus evident that the activity of the dental lamina

extends over a period of about five years and disintegrates

completely or remains as epithelial rests of Serres.

Root formation • After complete formation of the crown, i.e when

Enamel & Dentin formation reaches the future CEJ root formation starts.

• Root formation starts at the cervical loop.

• Epithelial Diaphragm: is a horizontal proliferation formed of I.E.E and O.E.E leading to primary closure of the apex.

• Secondary closure takes place through deposition of Dentin and Cementum at the apex.

• Epithelial root sheath of Hertwig (ERSH): is vertical proliferation formed of I.E.E and O.E.E that forms the shape of the root.

• A proliferating zone of dental papilla occurs with epithelial diaphragm and ERSH.

EPITHELIAL DIAPHRAGM

ASG

EPITHELIAL

DIAPHRAGM Histological structure

OB

PD

D

DP

DF

ODE

SR

SI

AB

E

• The peripheral layer of dental papilla is differentiated into odontoblasts.

• Odontoblasts start formation of Dentin and when complete formation of Dentin occurs ERSH is degenerated.

• Remnants of ERSH are called EPITHELIAL RESTS OF MALASSEZ.

• After degeneration of ERSH dentin is exposed to Dental sac, so UMC's (Undifferentiated mesenchymal cells) become differentiated into:

• CEMENTOBLASTS: which lay down cementum matrix and FIBROBLASTS: which form periodontal ligaments, and OSTEOBLASTS: which form alveolar bone matrix.

SINGLE ROOT FORMATION

SINGLE ROOT

FORMATION

image image

ASG

Hertwig’s

root sheath Epithelial

diaphragm

SINGLE ROOT

FORMATION

NEWLY FORMED ROOT

ASG

MULTI-ROOTED TOOTH

• In case of Bi-rooted teeth two tongue-like

projections develop at the level of

Bifurcation.

• In case of Tri-rooted teeth three tongue-like

projections develop at the level of

Trifurcation.

Tongue Like

Extensions

Epithelial

diaphragm

Epithelial

diaphragm

Tongue Like

Extensions

Epithelial

diaphragm

MULTI-ROOTED TOOTH

ASG

CLINICAL

CONSIDERATIONS

All clinical considerations are

related to the Epithelial Root

Sheath of Hertwig (ERSH):

Early degeneration of ERSH

before Odontoblasts

differentiation leads to

Accessory root canal

ACCESSORY ROOT CANAL

Accessory root canals can form as

well as result to:

Blood vessels interrupting the

course of ERSH

Failure of fusion of tongue-like

projections in multirooted teeth

ENAMEL PEARL

On the opposite hand late

degeneration of ERSH after

complete formation of the whole

thickness of Dentin leads to

formation of Enamel on the root

(Enamel Pearl)

INTERMEDIATE CEMENTUM

DENTIN

CEMENTUM

Intermediate Cementum is a

tissue that has intermediate

properties between Dentin and

Cementum.

It occurs due to degeneration of

Odontoblasts AFTERERSH

BEFOREdifferentiation but

complete thickness of Dentin is

formed.

It is the severe curvature of the root.

It occurs due to trauma of a deciduous

tooth pushing the developing tooth germ

and bending ERSH.

These teeth with dilacerated roots may fail

to erupt, difficult to extract and

impossible to perform Endodontic

treatment on these teeth.

DILACERATION

Dilaceration

Important note:

Epithelial rests of serres (serres

pearls) are found in the crown as

a remaining parts of Dental

Lamina and may proliferate to

form Eruption Cyst.

Epithelial rest of Malassez are

found in the root as a remaining

part of ERSH and may proliferate

to form Periodontal Cyst.

GUESS THE STAGE !

ODE

SR

CL

EK

DS