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اآلية ) (53فصلت

The development of the tooth involves many complex biological processes.

The fundamental developmental processes is similar for all teeth.

Dr Hesham Dameer

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.

By hesham Dameer

Stages of teeth development

1. Dental lamina2. Bud stage3. Cap stage4. Bell stage ( early & advanced )5. Root Stage

MORPHOLOGICAL STAGES

HISTOPHYSIOLOGICAL STAGES

1 -INITIATION.

2 -PROLIFERATION.

3 -HISTO-DIFFERENTIATION.

4 -MORPHO-DIFFERENTIATION.

5 -APPOSITION.Dr Hesham Dameer

Initiation of Tooth DevelopmentInitiation of Tooth DevelopmentThe initiation of tooth development begins at 37 days of developmentwith formation of a continuous horseshoe-band of thickened epitheliumin the location of upper and lower jaws – Primary Epithelial Band

Each band of epithelium will give rise to 2 sub divisions:1. Dental lamina and2. Vestibular lamina

Dr Hesham Dameer

Early Dental Lamina

Tongue Dental lamina Vestibular lamina

Primary epithelial band

Ectomesenchyme

Vestibular lamina:- It is a wedge of epithelial cells facial to dental lamina. It proliferates into ectomesenchyme. Then degenerates at the center to form cleft which becomes the oral vestibules.

Dr Hesham Dameer

Dr Hesham Dameer

The dental lamina

MESODERM

(Connective tissue)

ECTODERM

Flat cells

Columnar cells

Basement membrane

Also

No teeth without dental lamina

No fruits without a tree

Dr Hesham Dameer

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 which replace the primary teeth except for the permanent molars.

Dr Hesham Dameer

Dental lamina formation and development of tooth buds

mesenchymal proliferation

Dental lamina

• MMax. bone development

Mand. bone dev.

TongueDental lamina &Tooth bud

Meckel's cartilage

B• F. Developing

mandibular bone • G. Meckel's cartilage • A. Dental lamina • B. Tooth bud• C. Mesenchymal

cells condensation

A

B C

F

Dr Hesham Dameer

Function of the dental lamina 1. Initiation of deciduous dentition ( 2 MIU ) .2. Initiation of successors of deciduous dentition . This is preceded

by the growth of the terminal end of the dental lamina lingual to the deciduous enamel organ . ( 5 MIU. For central incisors, 10 M. of age for second premolars ) .

3. Initiation of permanent molars . This is preceded by the extension of dental lamina distal to the

enamel organ of the second deciduous molar to form the permanent molar tooth buds

( first molar 4MIU. , second molar 1 year , third molar 4-5 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 Serresepithelial rests of Serres.

Fate of the dental lamina1) The broad connection of the dental lamina with the

dental organ seen in the cap stage is broken in the bell stage by mesenchymal invasion .

2) The mesenchymal invasion at first divides the general dental lamina into lateral dental lamina and dental lamina proper. The dental lamina proper, growths at its terminal end ( successional lamina ) which form the primordium of the permanent tooth germ . The lateral dental lamina which connected to the deciduous tooth germ degenerates .

Sometimes , the remnants of the dental lamina persists as epithelial rests and known epithelial rests of serres .

GENERAL DENTAL LAMINA

LATERAL DENTAL LAMINA

SUCCESSIONAL LAMINA ( DENTAL LAMIA PROPER )

Epithelial rests of serres

mesenchymal invasion

Epithelial rests

Epithelial rests of Serres

Dr Hesham Dameer

Tooth bud stage :• At certain regions along the

dental lamina , 10 rounded or ovoid localized growth of epithelium ( Tooth bud ) in each arch correspond to the primordia of the enamel organs of the decidous teeth . These buds were surrounded by proliferating mesenchymal cells, which are packed closely beneath and around the epithelial buds

Dr Hesham Dameer

The mesoderm exerts a pressure at the base of tooth bud . The pressure of the mesoderm leads to invagination of the undersurface of the tooth bud , while the lower margin of the concavity proliferates downward to surround the actively growing mesoderm .

Pressure of the mesoderm

Dr Hesham Dameer

• As a result of this topographic alteration , the round shaped tooth bud is transformed to a cap shaped structure .

Later on , the cap shape structure can be distinguished into different cell layers , as follows:

Dr Hesham Dameer

Dr Hesham Dameer

Early cap stage:-

The inner cell become low columnar called inner epithelium or inner dental epithelium. The outer cells become flat and called outer dental epithelium or outer enamel epithelium. The ectomesenchymal tissue becomes condensed in the concave surface and called dental papilla (much cells, low fibers). Some ectomesenchymal fibers surround the cap called dental follicle (sac) (low cells, much fibers). Enamel knot may be formed due to localized thickening at the inner dental epithelium at center.Strands of epithelial cells also may be formed and called enamel cord .

Dr Hesham Dameer

Cell Free Zone

Inner Enamel Epithelium

Enamel cord

3- DENTAL SAC (follicle )

Dr Hesham Dameer

Cap stage

Late cap stage:- A fourth layer of epithelial cells is formed between the inner dental epithelium and stellate reticulum called stratum intermedium. It is formed of two layers of rounded cells which have high activity of alkaline phosphatase enzyme that responsible for enamel formation.

Cervical loop:- It is the most peripheral areas in both sides of cap (the proliferation zone) the outer and inner enamel epithelial cells come together with minimal inclusion of the stratum intermedium and stellate reticulum. After crown formation cervical loop cells proliferate to form bilayer of cells (outer and inner enamel epithelium) called root sheath of Hertwig's

Dr Hesham Dameer

1- Cap-shaped stage2- Tooth bell stage

Dr Hesham Dameer

A. Early bell stage

B. Advanced bell stage

bell stage

By hesham Dameer

This stage is reached when the invagination of the dental organ is deepened and also the margin of the dental organ ( cervical loop )grows deeper into the underlying mesenchyme .

1. Enamel organ tissues begin to differentiate.2. Enamel organ begins to fold into shape of finishedcrown.3. Dental papilla tissues begin to differentiate.Associated with these changes , other changes occur in the dental

organ as : 1. Outer enamel epithelium become cells transformed into folded

layer instead of the previous smooth layer . The adjacent ectomesenchyme invade these folds.

The ectomesenchyme contain a rich capillary buds to provide nutrition for the highly and metabolically active dental organ .

A . Early bell stage:

2. Inner enamel epithelium become tall columnar and measure 4 to 5 micrometer in diameter and about 40 micrometer in length . These cells exert an inductive effect on the underlying ectomesenchymal cells found in the dental papilla resulting in there differentiation into odontoblasts .

3. Stellate reticulum The mucoid fluids in the intercellular spaces increases , thus the cells of the stellate reticulum appear star shaped . As amelogenesis starts , the reticulum will collapse and reduce in size . Thus the capillaries of the invading ectomesenchyme found in the folds of the outer enamel epithelium will come in close relation to the inner enamel epithelium .

Dr Hesham Dameer

3. Stratum intermedium Several squamous cells develop between the stellate reticulum and the inner enamel epithelium . These cells have a high degree of metabolic activity and appear to be essential for enamel formation .

3. Dental papilla Before amelogenesis, the inductive effect exerted by the organized inner enamel epithelium ( tall columnar cells ), causes transformation of the peripheral ectomesenchymal cells of the dental papilla into odontoblasts and become potentially capable to form dentin .

4. Dental sac The fibrillar components of the dental sac arrangethemselves in a circular pattern . As the root start to develop and cementum is being is being deposited on dentin surface, the fibers of the dental sac differentiate into periodontal fibers and become embedded into the developing cementum and alveolar bone .

Dr Hesham Dameer

Functions of the enamel organ

1- Outer enamel epithelium : Active transport of nutrient materials specially, after hard tissues

formation .

2- Stellate reticulum : a. Act as a buffer against physical forces that may distort the

configurations of the developing tooth . b. It permit a limited flow of nutritional elements from the

capillaries of the invading ectomesenchyme found in the folds to the formative cells .

c. It keep a room for the developing enamel .

Dr Hesham Dameer

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 phosphate enzyme needed for mineralization .

c. These cells plus the inner dental epithelium are considered as a single unite responsible for enamel formation .

4. Inner enamel epithelium :

a. It exerts an inductive effect 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. It arranged in a pattern to determine the morphology of the crown .d. It lays down enamel matrix and helps in its mineralization .e. It shares in the root formation.g. It secretes primary enamel cuticle and share in the

formation of the reduced enamel epithelium which help in protection of the newly formed enamel against resorption and preventing precipitation of cementum .

5- Dental papilla :

Gives rise to dentin and dental pulp .6- Dental sac : Give rise to cementum, periodontal ligament and alveolar

bone.

Early bell stage

• A= cervical loop• B= stellate

reticulum• C= enamel cord• D= inner enamel

epithelium• E= stratum

intermedium• F= dental lamina• G= outer enamel

epithelium• H= dental papilla

• A= dental papilla (a very condensed group of cells)

• B= ameloblast cell layer of the inner enamel epithelium cells are columnar

• C= outer enamel epithelium cells

• D= stellate reticulum

• E= stratum intermedium

• F= outer cells of dental papilla or differentiating odontoblasts

Future crown patterning occurs in the bell stage, by folding of the inner dental epithelium.

Bell Stage

B. Advanced bell stage• A= odontoblasts• B= dental papilla• C= dentin• D= organizing

ameloblast layer of inner dental epithelium

• E= outer enamel epithelium

• F= stellate reticulum• G = stratum intermedium

Formation of hard tissue structure

Dr Hesham Dameer

Histological structure of the tooth germ during advanced bell stage

STRATUM

INTER.

STELLATE RETICULUM

INNER DENT. EPITH.

PREDENTIN

ODONTOBLASTS

Ameloblast & odontoblast

• Ameloblast and Odontoblast layers move apart, leaving enamel and dentine between them

Dr Hesham Dameer

Advanced bell stage

Advanced bell stage

• 1 - ameloblasts2 - enamel3 - dentine (predentine)4 - odontoblasts5 - dental pulp

Dr Hesham Dameer

Dentin

Predentin

Odontoblasts

Enamel

Ameloblas

Advanced bell stage Histological structure of the tooth germ

ENAMEL

DENTIN

PREDENTIN

OUTER DENTAL EPITHELIUM

CAPILLARY LOOP

Dr Hesham Dameer

Root Stage

After complete formation of the crown , both the inner and outer enamel epithelium at the cervical end of the crown is known cervical loop . The vertical cervical loop grows in horizontal direction to form the epithelial diaphragm . The epithelial cells, at the cervical area or cervical to the epithelial diaphragm proliferate leading to the formation of the first portion of the root sheath . Both the root sheath and the epithelial diaphragm only consists of outer and inner enamel epithelium . The inner enamel epithelium cells of the root sheath will

induce the adjacent ectomesenchymal cells to differentiate into odontoblasts .

The odontoblasts deposit dentin on the inner side of the root sheath . As a result of dentin deposition , the root sheath will degenerate , thus exposing newly for dentin surface into the adjacent ectomesenchyme . The surrounding ectomesenchymal cells begin to differentiate to cementoblasts . Cementoblasts start cementum formation , to which the fibers of the dental sac will be embedded . Occasionally , an incomplete degeneration of root sheath may occur, resulting in the presence of some epithelial cells in the form of nests which known epithelial rests of Malassez . In case of multiroot formation, tongue like processes arise from the margin of epithelial diaphragm, thus dividing the primitive apical foramen into more one, corresponding to the number of the growing processes . At first these processes grow in horizontal direction, but later their free ends grow vertically .

The inner enamel epithelial cells of the processes induce the the adjacent mesenchymal cells to differentiate into odontoblasts that in turn deposit dentin . The margins of the process will grow downwards with downgrowth of the root sheath, resulting in the formation of multiroot .

Dr Hesham Dameer

FORMATION OF SUPPORTING TISSUES• Supporting tissues develops during root formation from dental follicle.• As the root sheath fragments ectomesenchymal cells of thedental follicle penetrate between the epithelial fenestrations and become opposed to the newly formed dentine of root. • These cells differentiate into cementoblasts.• Cementoblasts elaborate an organic matrix that become mineralize.• Collagen fiber bundles of periodontal ligament become anchored . • Cells of PDL and fiber bundles differentiate from dental follicle.• Cells forming the bone in which PDL fibers anchored also differentiate from dental follicle.

Dr Hesham Dameer

A= Epithelial root sheathB= Ectomesenchymal cellsC=Dental follicleD= Odontoblast

Dr Hesham Dameer

• A= cervix of tooth

• B= epithelial diaphragm (part of root sheath) – these cells don’t become tall (columnar) because they are not going to be secreting anything like in the crown.

• C= odontoblast layer

• D= dentin• E= pulp• F = alveolar bone

Dr Hesham Dameer

• Developmental process: eruptive stage of tooth development

• Region or location: Root shealth• A= crown• B = root• C= DEJ (artifact space)• D= ameloblasts• E= dentin• F = odontoblast layer• G = Hertwig’s epithelial root sheath• Specific components or positional

parts of HERS:• 1= epithelial diaphragm (curve

between root sheath and diaphram)• 2= root sheath• 3= cervix of tooth

Dr Hesham Dameer

Cell rest (of Malassez)

Differentiation of dental follicle cells

Dr Hesham Dameer

Root Formation (Cervical loop forms the epithelialroot sheath of Hertwig)

Cervical loop

Dental papilla

Cervical loop

Hertwig’s epithelial root sheath

Tongue-like extentions

Dr Hesham Dameer

Tongue like processes arise from the margin of epithelial diaphragm, thus dividing the primitive root trunk into more one, corresponding to the number of the growing processes .

Root Formation

Dr Hesham Dameer

Root Formation

Dr Hesham Dameer

• Developmental process: Late crown or early eruptive stage of tooth development. This tooth is erupted, however apical foramen are still open.

• Region or location: Multirooted tooth

• A= what’s left of root sheath

• B= apical foramen• C= dentin• D= interradicular

septum (furcation area)

• E= pulp

• Interradicular septum is in the middle (D)