ODONTOGENESIS Flashcards by ELIZA NICOLE ATA

4 STAGES REQUIRED FOR TOOTH FORMATION

Initiation Stage
Morphodifferentiation Stage
Histodifferentiation Stage
Apposition Stage

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Bud stage
Formation of tooth germs
along the dental lamina

Initiation Stage

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Differential
growth causes change in shape

Morphodifferentiation Stage

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Bell stage
Specialization of cells

Histodifferentiation stage

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Mineralization of tissues

Apposition Stage

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Tooth Formation is dependent on:

*Genetic Factors
*Environmental Factors

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Tooth Formation is dependent on:
hundreds to several
thousand genes likely involved

Genetic Factors

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Tooth Formation is dependent on:
nutrition,
physical phenomenon, infection

Environmental Factors

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 Oral epithelium thickens and
invaginates in to the mesenchyme to form a primary epithelial band
 Future dental arches

6TH week

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 Primary epithelial band divides into two
processes: dental lamina and vestibular lamina

7th week

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lingual; 1st to appear
contributes to the tooth
development

Dental lamina

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facial/buccal
cells rapidly enlarge to form a clef o vestibule between the cheeks and the tooth-bearing areas

Vestibular lamina

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series of swellings develop on the deep
surface of the dental lamina
 tooth development proceeds in three stages: the bud, cap, and bell stages
 enamel organ appears as simple
spherical to avoid epithelial
condensation
 poorly morphodifferentiated and
histodifferentiated

8th week

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 8th week
 dental lamina is a knob-like projection toward the mesoderm
 beginning of dental organ formation

BUD STAGE

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 10th week
 morphogenesis has progressed
 the deeper surface of the dental organ
invaginating to form a cap-shaped structure
 enamel organ appearing poorly
histodifferentiated
 at this early stage, tooth development is
already possible to identify the
formative element of tooth and its
supporting tissues:  dental organ/ enamel organ  dental papilla  dental follicle/ dental sac

CAP STAGE

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CAP STAGE

10TH WEEK

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3 COMPONENTS OF THE TOOTH BUD AT CAP STAGE:

Dental organ
Dental papilla
Dental follicle

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COMPONENT OF THE TOOTH BUD AT CAP STAGE:
forms the enamel

Dental organ

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COMPONENT OF THE TOOTH BUD AT CAP STAGE:
forms the dentin and
pulp

Dental papilla

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COMPONENT OF THE TOOTH BUD AT CAP STAGE:
forms the supporting structures of teeth

Dental follicle

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3 COMPONENTS OF THE TOOTH AT EARLY CAP STAGE:

Dental organ
Dental papilla
Dental follicle

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COMPONENT OF THE TOOTH AT EARLY CAP STAGE:
eventually forms enamel

Dental organ

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COMPONENT OF THE TOOTH AT EARLY CAP STAGE:

Odontoblasts (periphery) =
dentin  Fibroblasts (center) = pulp

Dental papilla

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COMPONENT OF THE TOOTH AT EARLY CAP STAGE:

Cementoblasts (inner) = cementum  Fibroblasts (middle) =
periodontal ligament  Osteoblasts (outer) = alveolar
bone

Dental follicle

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Late during cap stage, dental organ histodifferentiated into morphogically and functionally different components:

Stellate reticulum External or outer enamel epithelium Internal or inner enamel epithelium Stratum intermedium

- cells at the center of the dental organ

Stellate reticulum

tall cuboidal cells at the periphery of the dental organ

External or outer enamel epithelium

columnar cells immediately adjacent to the dental papilla

Internal or inner enamel epithelium

epithelial cells between the internal dental epithelium and the newly formed stellate reticulum

Stratum intermedium

14th week Further morphodifferentiation and histodifferentiation  Dental organ increases in size changes in shape  Invagination (IEE) becomes deeper

BELL STAGE

14th week Area where the inner and the outer enamel epithelium come together  Established the CEJ

CERVICAL LOOP

 During the early stages of tooth development three transitory structures may be seen: A. Enamel knot (Ahern’s knot) B. Enamel navel C. Enamel cord

TRANSITORY STRUCTURES

Localized mass cells in the center of IEE

Enamel knot (Ahern’s knot)

 Slight indentation to the outer enamel epithelium caused by the inward pull of the enamel cord

Enamel navel

 Strand of cells seen at the early bell stage extending from the stratum intermedium towards the outer enamel epithelium  Together with the enamel knot, form the site of the future cusp tip or incisal edge

Enamel cord

 Associated with the formation of the dental hard tissues, commencing at about the 18th week  Dentin formation always precedes enamel formation

LATE BELL STAGE (appositional stage)

Also known as cup stage

Proliferation stage

primitive oral cavity ○ Lined by stratified squamous epithelium - oral ectoderm

Stomodeum

Stomodeum lined by stratified squamous epithelium called ___.

oral ectoderm

○ oral ectoderm endoderm contacts with the foregut

Buccopharyngeal membrane

- the buccopharyngeal membrane ruptures

27th day of gestation

○ connective tissue cells underlying the oral ectoderm ○ Essential for the face and the teeth

Neural crest or ectomesenchyme

first deciduous teeth to erupt

Mandibular Central Incisors

○ Appears at the 37th day of development ○ A band of odontogenic epithelium that forms around the mouth ○ Horseshoe shaped

Primary Epithelial band

○ Localized thickenings within the primary epithelial bonds ○ Key feature of initiation of tooth development

Placodes

PEB gives rise to:

Dental lamina Vestibular lamina

It first forms from PEB

Dental lamina

forms after Dental lamina

Vestibular lamina

○ Embryo is 6 weeks wold certain areas of basal cell of the oral ectoderm proliferate rapidly ○ Leads to dental lamina invading the underlying ectomesenchyme ○ Serves as primordium of the ectodermal portion

Dental Lamina

- first recognizable stage in embryonic development

Primordium

6 or 6 ½ weeks of tooth development

First sign of tooth development

When is development of first permanent molar initiated?

at the fourth month of utero

When does deciduous teeth develop from lingual extension of the free end of the dental lamina

5th month in utero to the 10th month of age

Fate of the dental lamina

Extends over 5 years

It hollows and forms the oral vestibule

Vestibular Lamina/Lip furrow band

What develops first in the tooth development

Mandibular teeth

The tooth are named after ___________

the shape of epithelium

Earliest evidence of tooth

Tooth Germ

Development stages

1. Growth stage 2. Calcification stage 3. Eruption stage

Under growth stage:

a. Initiation stage b. Proliferation stage c. Histodifferentiation stage d.Morphodifferentiation stage e. Apposition stage

The epithelium of the dental lamina is separated from the underlying ectomesenchyme

Initiation Stage (bud stage)

Ovoid swellings arise from 10 different points -> future position ○ Primordia of enamel organ

Initiation Stage (bud stage)

○Consist of : ■ Low columnar cells ■ Centrally located polygonal cell

Enamel organ

○ Cells around the tooth bud undergo mitosis ■ Results to migration of migration of neural crest cells to ectomesenchymal cells that surrounds the tooth bud

Enamel organ

○ Area of ectomesenchymal condensation, subjacent to the enamel organ

Dental Papilla

Cells of dental papilla forms:

Dentin and pulp

condensed mesenchyme that surrounds the tooth bud

Dental sac

Dental sac forms

■ Cementum ■ Periodontal ligament

Parts of tooth bud:

■ dental/ enamel organ ■ Dental papilla ■ Dental sac

Part of tooth bud: produce enamel

dental/ enamel organ

Part of tooth bud: produce pulp and dentin

Dental papilla

Part of tooth bud: produce cementum and periodontal ligament

Dental sac

a soft connective tissue between the inner wall of the alveolar socket and the roots of the teeth.

Periodontal ligament

Embryonic cells of dental/enamel organ-ameloblasts-enamel

ectoderm

Embryonic cells of dental papilla-connective tissue- odontoblast - dentin and pulp

ectomesenchyme

Embryonic cells of dental sac or follicle-connective tissue-cementum and periodontal ligament

ectomesenchyme

A slight indentation to the outside epithelium

Enamel navel

○ Reservoir of dividing cells ○ Cells in the center of the enamel organ

Enamel knot

○ Vertical extension of the enamel knot ○ seems to divide the dental organ into two

Enamel cord(temporary structure)

○ Concavity filled with connective tissue

Enamel niche

○ Formative organ of the dentin and pulp

Dental papilla

○ Surrounds the dental organ ○ Made up of mesenchymal sac ○ Important in the formation of cementum and periodontal ligament

Dental Sac

○ Basement membrane that separates the enamel organ and the dental papilla ○ Future DEJ (dentino enamel junction)

Membrana preformativa

○ Consist of cells that differentiate prior to amelogenesis

Inner enamel epithelium

○ Cells in the center of the organ ○ Star shaped cells

Stellate reticulum

○ Flattened low cuboidal cells ○ Provides a rich nutritional supply for intense metabolic activity

Outer epithelium

Advance bell stage: ○ Rises from the cervical portion of the enamel organ ○ Enamel organ forms the HERS which is essential for root formation

Hertwig’s epithelial root sheath (HERS)

Advance bell stage: Where inner and outer epithelia comes together

Cervical loop

Advance bell stage: ○ Periodontal ligament of an erupted teeth where remnants are found ■ Remnants - lost structure of HERS

Rest of malassez

Fusion of crown

Fusion

Globule of enamel is present

Dens Evaginatus

○ Hypoplasia ○ Notches are present

Hutchinson’s teeth

○ Small island of enamel usually present in the CEJ

Enamel pearls

○ Angulation of tooth

Dilaceration