Uitwerkingen van de kennisclips van Cyclus 1.1.3 Celbiologie WEEK 15 (LTK 1.2 De Gezonde Mens) aan de Rijksuniversiteit Groningen uit Bachelor 1/ Propedeuse Collegejaar .
AANLEG VAN TANDEN EN KIEZEN: EMBRYONIC DEVELOPMENT OF THE TEETH
In the future mouth region there is tissue developing.
There are 2 layers of tissue developed:
- ectomesenchyme
- epithelium
In the beginning phase of tooth development the oral epithelium layer gets thicker.
Oral epithelium contains dividing cells (white ones).
Originally in the beginning the cells divide horizontally.
In this beginning phase of tooth development the cells begin to divide also vertically.
Which generates this kind of bulge of cells, also deepening of the oral epithelium and early thickening.
Key points are:
- there is localized proliferation of the epithelial cells
- at the point where the future teeth will rise
- ectomesenchymal cells condense around the growths of cells
Wherever you put the epithelium from before 5 weeks of development with any ectomesenchyme in the
embryo, you’ll get a tooth.
Wherever you put ectomesenchyme from after 5 weeks of development with any epithelium in the embryo,
you’ll get a tooth.
So before or after 5 weeks one of the cell types has control over the formation of teeth.
Odontogenesis comes first from epithelium cells then switches to ectomesenchymal cells.
,Knop/ bud phase is around ~ 8 weeks of embryo development.
The structure is bigger now.
The epithelial cells become thicker and round (green arrow).
Underneath the epithelial cells are the ectomesenchymal cells.
Bud phase can be recognised through the round phase of tooth development.
In the bud phase there are epithelial cells and mesenchymal cells.
If you separate the epithelial cells or mesenchymal cells and try to make a new tooth somewhere else, it will no
longer work.
Because these two cell types now need each other for this phase of tooth formation.
They are critical for the development of teeth that they work together.
Kap/ cap phase is from 11-12th weeks.
Now we have the presence of extremely important cell types:
1. outer enamel epithelium/ external enamel epithelium
2. inner enamel epithelium/ internal enamel epithelium
3. stellate reticulum
4. dental lamina
5. dental papilla/ pulp
6. dental follicle
Outer enamel epithelium/ external enamel epithelium is more flatted, cubic epithelial cell type.
Outer enamel epithelium/ external enamel epithelium defines the shape of enamel organ.
Inner enamel epithelium/ internal enamel epithelium is more deeper, columnar cell type.
Inner enamel epithelium/ internal enamel epithelium become very proliferated in the next few phases.
Between the stellate reticulum there is a lot of space filled with protein and ECM.
Protein en ECM helps with cushioning and gives protection for the developing tooth.
Dental lamina is an epithelial structure which connects the developing tooth to the original oral epithelium.
Dental papilla/ pulp lies in the middle.
Dental follicle are more around the outside of the dental papilla.
,From the cap stage we move into the early klok/ bell phase.
Early klok/ bell phase is in the 14th week.
There is the presence of a new type of cells: stratum intermedium.
Stratum intermedium is a thin layer of cells on the top of the internal enamel epithelium.
Function of stratum intermedium is still unclear.
They think it is a sort of stem cell to help repair the tooth if the development does not go well.
There is also the presence of odontoblast layer.
Odontoblasts come from a differentiation from cells in the dental papilla.
Odontoblasts are long cells.
Odontoblast produces a precursor of dentine.
Odontoblast always arises before the counterparts cells, the ameloblasts, arise.
Ameloblasts are the cell types which eventually make enamel.
First you always have odontoblasts differentiation from the dental papilla cells and later you’ll have ameloblasts
differentiation from the internal enamel epithelium.
14th weeks in the early klok/ bell phase there are 4 layers of enamel organ visible:
1. external enamel epithelium
2. stellate reticulum
3. stratum intermedium
4. internal enamel epithelium → ameloblast
Stratum intermedium is new.
,There is no particular hard tissue in the early klok/ bell phase.
In the late klok/ bell phase you’ll start to see production op predentine by the odontoblasts.
Odontoblasts have been differentiated from the dental pulp.
Odontoblasts are visible as these long thin cells.
Odontoblasts started to function.
Odontoblast started to secrete a precursor of dentin (yellow).
Precursor because odontoblast will never be able to secrete dentin.
Dentin is a hard substance.
Odontoblasts will die.
Precursor dentin will be modified outside of the cell.
In the late klok/ bell phase the dental lamina is gone.
Dental lamina connects the developing tooth to the oral epithelium.
In the late klok/ bell phase it always starts with predentin production from the odontoblasts.
It is never in a healthy situation that the ameloblast begins first with enamel production!
The ameloblasts need stimuli from de dentin to be activated!
So it needs to start with dentinogenesis.
,
,
,AANLEG VAN TANDEN EN KIEZEN DENTINOGENESIS
Dentin is the blue, stripy structure.
Dentin forms the bulk of the tooth body.
Dentin is a huge portion of the tooth.
Dentin is harder than bone.
Dentin is softer than enamel.
Dentin is made of closely packed tubules.
Dentin is:
- 70% hydroxyapatite
- 20% organic components (mostly collagen I)
- 10% water
There is also a bound stuck to the enamel at the dentinoenamel junction.
, In the late bell stage odontoblasts make precursor dentin (yellow).
Odontoblasts are differentiated from the dental papilla/ dental pulp.
On the outside of the precursor dentin there are ameloblasts.
Ameloblast makes enamel.
Ameloblast is derived from the inner enamel epithelium.
Dentin is made by odontoblasts starting in the late bell stage.
Dental papilla cells receive a signal from the inner enamel epithelium cell.
There is a cross talk between these 2 cell types.
This signal stimulates the division/ proliferation of the dental papilla into 2 cells.
When these cells are divided, you’ll see a change in morphology.
One cell looks like the dental papilla cell, this cell is saved for the future.
One cell differentiate in a pre-odontoblast.
Pre-odontoblasts have a longer, bigger cell volume than dental papilla cells.
Pre-odontoblasts have more cytoplasm volume.
Logically this is useful, because pre-odontoblasts need to be producing a lot of protein.
Protein needs to be secreted from the cells.
Then there is full differentiation in odontoblasts producing the protein that makes pre-dentin.
Pre-dentin is mineralized in dentin itself.
Dentin is a very hard tissue.
Odontoblast have an early stage (during differentiation) and late stage.
Late stage is the mature form of odontoblasts.
Mature form of odontoblasts have a really long cell body with cytoplasmic extension (branching).
Steps are:
1. dental papilla cells
2. division
3. differentiation into pre-odontoblasts
4. pre-dentin production
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