Root Development and Eruption Flashcards
When does root eruption start?
When does it finish?
After crown formation - at the bud stage.
Finishes 3 years after the tooth has erupted.
How many different cell populations are there at the early bell stage?
What are cervical loops?
4 different ones
Cervical loops are where there are two epithelia which come together (outer epithelium surrounding the bell and inner (ameleoblasts)). These loops proliferate and form Hertwig’s epithelial root sheath.
What are the 3 roles of HERS (Hertwig’s epithelial root sheath)?
- Maps out root shape
- Initiates odontoblast differentiation
- Break-down initiates cementum and PDL formation
Is HERS permanent or temporary?
Why?
Temporary
Break down initiates the formation of the periodontal ligament which enables cementum development.
Explain how HERS maps out root shape
what do mesenchymal cells next to HERS differentiate to?
Dentine of the crown is shown and next to this is HERS formed of two layers of epithelium which have proliferated and start moving downwards.
Mesenchymal cells differentiate to rootoblasts.
Explain how HERS initiates odontoblast differentiation
HERS grows down and as this happens it secretes molecules which act as signals on surrounding cells (especially mesenchymal cells of the dental papilla which will be included in the future dental pulp).
The signals induce the differentiation of the mesenchymal cells next to HERS to form odontoblasts.
Explain what happens once predentine is laid down
Predentine is laid down and mineralised to dentine.
After this, HERS is broken down and this then goes to form the periodontal ligament and cementum.
Cells come in contact with the dentine and either secrete collagen to form the periodontal ligament or become cementoblasts.
HERS grows down until the full length of the root is obtained.
What is the difference between acellular cementum and cellular cementum?
Acellular = coronal 2/3 of the root
Cellular = apical 1/3 of root
Give detail on HERS break down initiating cementum and PDL formation?
There are cluster of epithelial cells which remain from HERS. These remain around the root and can be reactivated and form cysts in later life.
Cell signalling is then what goes on to initiate PDL.
How does formation of the root apex occur?
HERS grow at a right angle to form an epithelial diaphragm. This does not completely close (leaves an open tip) called the apical foreman so the blood vessels can get in and vascularise the tooth.
How is HERS structures in a two root tooth?
Three root?
HERS forms around the two roots. It changes orientation and forms two tongues of epithelium which come together by moving at right angles and then fusing together.
Epithelium changes orientation and forms towards the centre of the tooth to separate the root into 3 parts.
Where does the tooth move from during eruption?
From its development position in the bony crypt to tis functional position in the occlusal plane.
How does the periodontal ligament form?
Fibroblasts secrete collagen which organises into bundles of fibres.
Some bundles change orientation.
Primary dentition:
What is the tooth covered by?
What do these cells fuse with?
All epithelial layers surrounding the cell types (4 cell types from ETD lecture).
These cells form the reduced enamel epithelium.
These cells then fuse with the oral epithelium and the cells degenerate.
When the reduced enamel epithelium and the —- —- fuse and the inner cells degenerate means the tooth will then erupt into the —- —-.
Cells which form the enamel will then be lost. When there is tooth decay later, there are no cells to replace the lost —- material as the cells laying down the enamel are now lost when the tooth —-.
Formation of the dental —- junction when the tooth erupts formed by two types of epithelium.
oral epithelium
oral cavity
mineralised
erupts
gingival
