Dental development

Question 1

3 primary embryonic layers

Answer 1

Ectoderm
–
Mesoderm
–
Endoderm

Question 2

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

Answer 2

Enamel

-other parts from ectomesenchyme layer

Question 3

Stages in tooth development

Answer 3

• dental lamina
• bud
• cap
• bell
• root formation

Question 4

what is the primary epithelial band

-when

Answer 4

Primary epithelial band develops at approx 6 wks IUL
•
Appears as thickening in epithelium of embryonic mouth (stomodaeum)

Question 5

what is the dental lamina

• when
• vestibular lamina what does it breakdown to…

Answer 5

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

Question 6

enamel organ - bud stage

Answer 6

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

Question 7

enamel organ - cap stage

Answer 7

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

Question 8

enamel orgal bell stage

Answer 8

approx 14 wks IUL
•
“Bell-stage” enamel organ
•
More cell layers differentiated
•
Tooth shape is being defined

Question 9

4 cell layers of bell stage

Answer 9

stratum intermedium
stellate reticulum
internal enamel epithelium
external enamel epithelium

Question 10

permanent tooth germ

Answer 10

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

Question 11

enamel organ - late bell stage

Answer 11

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

Question 12

dentinogenesis

Answer 12

•
Odontoblast differentiation from IEE
•
Deposition of dentine matrix (mainly collagen)
•
This unmineralised dentine is predentine
•
Mineralisation of dentine (hydroxyapatite)

Question 13

enamel formation

Answer 13

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

Question 14

amelogenisis stages

Answer 14

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

Question 15

how are roots formed

Answer 15

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”)