OE L3 Dentinogenesis Flashcards
When does dentinogenesis begin for central incisors?
17-18 weeks iu. Late bell stage.
Where does dentine formation begin?
At the cuspal tip, progresses down to the cervical loops
Which cells produce the dentine matrix?
Odontoblasts.
Therefore, there are always odontoblast cell bodies at the pulpal aspect lining the newly formed dentine.
What are pre-odontoblast cells?
Ectomesenchymal cells of the dental papilla.
What changes do the ectomesenchymal cells undergo when becoming odontoblasts?
- Change from low synthetic capacity to high synthetic/secretory capacity
- Increased RER, golgi, mitochondria
- Cell becomes polarised and columnar with a basal nucleus
- Change from high nucleus : cytoplasm ratio to low nuclear : cytoplasm ratio
How do the ectomesenchymal cells of the dental papilla change to odontoblasts?
- Cells of the IEE produce signalling molecules (FGFs, BMPs) which pass through the BM to reach ectomesenchymal cells
- The cells differentiate and undergo a number of cell cycles until they become odontoblasts
What happens to the basement membrane when the odontoblasts secrete pre-dentine?
Pre-dentine stimulates the breakdown of the basement membrane.
Now the IEE cells are exposed to pre-dentine, which signals it is now time for them to differentiate into ameloblasts.
What is the first type of dentine formed?
Mantle dentine.
Describe mantle dentine.
- 0.15mm thick
- Odontoblasts secrete an ECM rich in collagen type I and III
- The fibres act as a scaffold to accept deposition of hydroxyapatite crystals
- Has a scalloped edge at junction between dentine and enamel matrices (amelodentinal junction)
- Matrix vesicle mediated mineralisation: odontoblasts produce matrix vesicles which bud off and carry calcium and phosphate and deposit this amongst collagen fibres. This process is unique to mantle dentine.
What is the second type of dentine to be laid down?
Circumpulpal dentine.
Forms the bulk of the tooth.
Describe the action of odontoblasts after mantle dentine formation.
- The cell body retreats down into the pulp
- The cell body and cell process are seperated by the terminal web apparatus
- The cell process has few organelles and has a mainly secretory role (process = dentinal tubule)
- The cell body has a mainly synthetic role
Describe circumpulpal dentine formation.
- Requires a collagen scaffold
- Firstly lays down a layer of unmineralised pre-dentine
- Matrix mediated mineralisation: remodelling of the matrix allows deposition of mineral into dentine. Collagen and tissue specific glycoproteins are involved.
Described as heterogeneous mineralisation.
Mineralisation of circumpulpal dentine can be divided into 2 patterns depending on rate of growth; what are these?
- Globular pattern
- Linear pattern (secreted slowly)
Descirbe globular dentine.
- Associated with primary dentine formation
- Globules called calcospherites form at dentine/predentine interface
- Calcospherites grow in size and fuse with eachother
What term describes dentine where globules fail to fuse?
Absence of fusion creates hypocalcified/uncalcified dentine with a browner appearance under a microscope.
It is called interglobular dentine.