OE L3 Dentinogenesis Flashcards

1
Q

When does dentinogenesis begin for central incisors?

A

17-18 weeks iu. Late bell stage.

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2
Q

Where does dentine formation begin?

A

At the cuspal tip, progresses down to the cervical loops

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3
Q

Which cells produce the dentine matrix?

A

Odontoblasts.

Therefore, there are always odontoblast cell bodies at the pulpal aspect lining the newly formed dentine.

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4
Q

What are pre-odontoblast cells?

A

Ectomesenchymal cells of the dental papilla.

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5
Q

What changes do the ectomesenchymal cells undergo when becoming odontoblasts?

A
  • 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
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6
Q

How do the ectomesenchymal cells of the dental papilla change to odontoblasts?

A
  • 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
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7
Q

What happens to the basement membrane when the odontoblasts secrete pre-dentine?

A

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.

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8
Q

What is the first type of dentine formed?

A

Mantle dentine.

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9
Q

Describe mantle dentine.

A
  • 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.
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10
Q

What is the second type of dentine to be laid down?

A

Circumpulpal dentine.

Forms the bulk of the tooth.

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11
Q

Describe the action of odontoblasts after mantle dentine formation.

A
  • 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
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12
Q

Describe circumpulpal dentine formation.

A
  • 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.
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13
Q

Mineralisation of circumpulpal dentine can be divided into 2 patterns depending on rate of growth; what are these?

A
  • Globular pattern

- Linear pattern (secreted slowly)

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14
Q

Descirbe globular dentine.

A
  • Associated with primary dentine formation
  • Globules called calcospherites form at dentine/predentine interface
  • Calcospherites grow in size and fuse with eachother
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15
Q

What term describes dentine where globules fail to fuse?

A

Absence of fusion creates hypocalcified/uncalcified dentine with a browner appearance under a microscope.
It is called interglobular dentine.

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16
Q

Describe dentine with a linear pattern of mineral deposition.

A
  • Associated with secodnary dentine formation after eruption.
  • Secreted very slowly.
  • Tubules run in sigmoidal pattern in crown, straight pattern in root
  • Forms the bulk of the tooth structure
17
Q

Secretion of circumpulpal dentine can be divided into 2 patterns; what are these?

A
  • Intertubular dentine secretion

- Peritubular dentine secretion

18
Q

Describe intertubular dentine.

A
  • Main bulk of the dentine
  • Found between tubules
  • Matrix rich in collagen
19
Q

Describe peritubular dentine.

A
  • Encircles each tubule (cell process)

- Highly mineralised with no collagen

20
Q

Is dentine elastic?

A

Dentine does have a degree of elasticity. If it didn’t, it would be too rigid and put the enamel at risk of breaking away from dentine.

21
Q

Describe tubule size at the ADJ.

A
  • At the ADJ the
    tubules have a thinner and smaller structure
    This means caries will have less of an impact as they tuubles aren’t wide enough to let as much bacteria and noxious acids travel down deeper into the tooth.
22
Q

Describe the incremental growth of dentine.

A
  • Dentine alternates between periods of secretion and quiescence
23
Q

Describe Lines of Von Ebner.

A
  • Shows daily rate of secretion
  • Faint lines showing periods of secretion and quiescence
  • 4um
24
Q

Describe Anderson lines.

A
  • Shows secretion over 5 day period

- 20mm

25
Q

Describe dentinogenesis during root formation.

A
  • Presence of mantle dentine interacring with cells which will form cementum
  • No enamel in the root
  • Granular layer of Tomes lies adjacent to cementum, it is effectively interglobular dentine that has not minerlaised properly- present at start of root but not further down
26
Q

Is dentine a vital tissue?

A

Yes dentine is a vital tissue, enamel is not.

Odontoblasts are a vital cell and continue living throughout the life of the tooth, ameloblasts are not.