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FRP - Crowns/Bridges/Wear/TMD/SDA/IMPLANTS > Dental development > Flashcards

Flashcards in Dental development Deck (15)
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3 primary embryonic layers





what is the only part of a tooth that develops from ectoderm layer.
-what layer are all other parts of the tooth from

-other parts from ectomesenchyme layer


Stages in tooth development

-dental lamina
-root formation


what is the primary epithelial band

Primary epithelial band develops at approx 6 wks IUL

Appears as thickening in epithelium of embryonic mouth (stomodaeum)


what is the dental lamina
-vestibular lamina what does it breakdown to...

Approx. 7 wks IUL

The PEB has grown into the jaw and divided into 2 parts:

Vestibular lamina, which will break down to form the buccal sulcus, and the dental lamina, from which the enamel organ develops


enamel organ - bud stage

Approx. 8–10 wks IUL
Dental lamina thickens into a ‘bud’ stage enamel organ (A)
An ectomesenchymal condensation (B) appears and this is the dental papilla


enamel organ - cap stage

Approx 11 wks IUL

The enamel organ forms a ‘cap’ over the papilla

“Cap stage” enamel organ:

External enamel epith. - top of cap

Internal enamel epith. - underside of cap

EEE and IEE meet at the Cervical Loop


enamel orgal bell stage

approx 14 wks IUL

“Bell-stage” enamel organ

More cell layers differentiated

Tooth shape is being defined


4 cell layers of bell stage

stratum intermedium
stellate reticulum
internal enamel epithelium
external enamel epithelium


permanent tooth germ

At approx. 12th week, an extension appears on the lingual side of the dental lamina

This is the dental lamina for the permanent successor

At about 16th week, the 1st permanent molar germ develops as a backwards extension of the dental lamina


enamel organ - late bell stage

Approx 18 weeks IUL
Late bell stage EO

Crown shape is well defined (‘crown’ stage EO)

Apposition of enamel and dentine begins

In this picture:

Dentine formation established

Enamel formation beginning



Odontoblast differentiation from IEE

Deposition of dentine matrix (mainly collagen)

This unmineralised dentine is predentine

Mineralisation of dentine (hydroxyapatite)


enamel formation

Enamel is very highly mineralised (96%)

It is made in two stages
1. Protein matrix deposited
Matrix is partially mineralised (30%)
2. Once this framework is established, the organic part is removed,
and mineralisation is completed (‘maturation’)

The ameloblasts change form and function several times during amelogenesis


amelogenisis stages

Ameloblast differentiation:
1. Dentine induces IEE cells to differentiate into ameloblasts they elongate, becoming columnar
the nucleus migrates to the basal end of the cell
2. Secretory phase:
Ameloblasts become secretory cells
They synthesise and secrete the enamel matrix proteins (amelogenins)
The matrix is then partially mineralised (30% mineral)
3. Maturation phase:
Most of the matrix proteins are removed
Mineral content of enamel is increased
Mature enamel is 95% mineral
4. Protection phase:
Ameloblasts regress to form a protective layer – the reduced enamel epithelium
Involved in eruption
Formation of epithelial attachment


how are roots formed

1. The enamel organ maps out the shape of the crown
The EEE and IEE meet at the cervical loop
Migration of the cervical loop maps the crown shape

2.The root shape is defined by apical growth of the cervical loop, which is now called:
Hertwig’s epithelial root sheath
This is a 2-cell-layered structure, in contrast to the 4-layered enamel organ

3.Hertwig’s epithelial root sheath (HERS) induces formation of root dentine
Once the initial layer of root dentine is formed, Hertwig’s sheath breaks up (no enamel in root)
Remains of HERS persist as ‘debris of Malassez’, which may develop into a cyst
Mesenchymal cells from the follicle contact the dentine, and differentiate into cementoblasts
These form cementum
Fibres from the developing PDL are embedded in the cementum (“Sharpey’s fibres”)