Dentinogenesis

Question 1

What are the dentine types in the crown and in the root?

Answer 1

Crown: mantle dentine and circumpulpal denine

Root: Hyaline layer, Granular layer, circumpulpal

Question 2

Where is mantle dentine found?

Answer 2

Found adjacent to the enamel dentine junction as it forms near birth

Question 3

What happens in terms of enamel and epithelium during the bell stage?

Answer 3

• Well defined dental papilla
• Enamel organ fully formed
• Internal enamel epithelium differentiated

Question 4

What are the 3 parts in dentinogenesis?

Answer 4

1. Odontoblast differentiation
2. Dentine matrix deposition
3. Mineralisation

Question 5

What do cells signals ensure?

Answer 5

Odontoblasts differentiate at the same time as ameoloblasts

Question 6

What does the basement membrane separate?

Answer 6

The ameloblasts and the odontoblasts

Question 7

What cells respond in terms of injury to produce dentine?

Answer 7

Preodontoblasts

Question 8

What happens to differentiating odontoblasts?

Answer 8

Undergo rapid changes in size and polarisation

Question 9

What do newly formed odontoblasts develop and begin to do?

Answer 9

Develop multiple small cell processes and being secretion of matrix.
Nucleus moves away from the secretory part of the cell (increases the secretion potential). Pulp chamber shrinks over time as more odontoblast form.

Question 10

Explain what cyto-differentiation is

Answer 10

Starts at tips of cusps or incisal margins

Travels rootwards and forms the outside of the tooth.

Question 11

What are odontonblasts?

• organelles
• cell junctions
• attachments between cells - why?

Answer 11

• Large nucleus at basal part of cell
• Large golgi complex
• Rough endoplasmic reticulum parallel to long axis of cell
• Process development
  
  • Initially many small cell processes directed towards basement membrane
• Cell-cell junction (between odontoblasts and sub-odontoblast). Desmosomal attachments between cells to stop matrix from seeping between cells so the cells mineralise

Question 12

Give the main headings (main components) under the organic matrix

Answer 12

• Collagen type 1
• Phosphoproteins
• Glycoproteins
• Proteoglycans
• Growth factors
• Metalloproteinases
• Serum-derived proteins

Question 13

Initial matrix deposition: late bell stage

Composition is different from the rest of dentine —-.
Has contributions from dental pulp cells beneath developing —-.
Collagen fibres at —- angles to internal enamel epithelium (eventually forms the enamel-dentine junction)
Also known as “corkscrew fibres” of Von Korff

• Numerous processes lead to branching dentine tubules in this area. Leads to a —- layer.
• 20 to 150um
• Different —- process
  
  • Matrix vesicles compared to nucleation on collagen fibres
    These —- trigger mineralisation.

Answer 13

Matrix

Odontoblasts

Right

Porous

Mineralisation

Vesicles

Question 14

Collagen fibres in the dental matrix lay at what angle to the internal enamel epithelium?

Answer 14

Right angles

Question 15

Explain the matrix deposition of circumpulpal dentine

Answer 15

• Collagen type 1 fibres laid down parallel to dentine-pulpal dentine
• Slight changes in orientation every 6-10 days (perpendicular to parallel)
• These changes are possibly due to long-period lines (Andresen lines)

Question 16

What part of the tooth is predentine laid down?

Answer 16

Dental pulp

Question 17

When is the predentine matrix formed?
What appearance does this give under a microscope?

What two types of mineralising front could there be?

Answer 17

Formed prior to mineralisation

Pale staining appearance (not mineralised)

Either globular or linear

Question 18

What are the 4 main parts of the matrix around the tooth?

Answer 18

DPP
Proteoglycans
Gla-protein
Collagen

Question 19

Give the approx measurements of the different sides of the tooth for predentine

Answer 19

Proximal 20nm
Central 40nm
Distal 70-80nm

Question 20

What is another name for the mineralisation front?
What is it rich in?
Thickness?
What are calcospherites that are present here?

Answer 20

Metadentine
Rich in dentine phosphoprotein, dentine sialoprotein, proteoglycans
2.5-5um
These are globules formed from calcium salts.

Question 21

Explain the daily variation in rate of deposition

Answer 21

Due to circadian (24h) variation in acid-base balance.
Visible as light-dark paired bands.
Between 2-4um apart.

Question 22

Rate of deposition = rate of ?

Answer 22

Mineralisation

Question 23

What organelles is the cause of mineralisation?
What process do the cells undergo?

What diameter does mineralisation occur to?

What is the role of enzymes here?

What dentine has crystalline structures?

Answer 23

Matrix vesicles

Cell budding or fragmentation

30-200nm

Alkaline phosphate to increase phosphate concentration to develop crystal.

Mantle dentine

Question 24

How do odontoblasts control mineralisation?

Where does mineralisation occur?

Answer 24

Controlling influx of calcium ions.
Controlling secretion of metabolism of matrix proteins.

Occurs by calcium ion nucleation at spaces present within bundles of collagen?

Question 25

What are the properties and functions of DPP?

Answer 25

Properties: Highly acidic and so binds calcium ions Can change shape and bind calcium ions to allow crystal growth Functions: 1. Transports calcium ions to mineralisation front 2. Location of nucleation to specific areas of collagen 3. Stabilisation of the formed crystals 4. Inhibits crystal formation in high concentration

Question 26

What proteins are present that can contribute to mineralisation in vitro?

Answer 26

Osteonectin (inhibits growth of hydoxyapatite) Osteopontin (promotes mineralisation) Bone sialoprotein (found in early mineralising dentine, predentine and peritubular dentine) Proteoglycans (absorbed onto collagen, decreases as mineralisation proceeds)

Question 27

What are calcospherites? If they fail to fuse?

Answer 27

Spheres which mineral come from - formed from calcium salts. Interlobular dentine

Question 28

Explain peritubular dentine mineralisation - When does it start to form? - Does external stimuli alter rate of deposition? - Where is the matrix probably derived from? - Where is dentine laid down here?

Answer 28

- Starts to form at almost the same time as interlobular dentine - No - Odontoblast and suffused plasma proteins - Laid down around the outside of the tubule (hollow part of tooth) and between the tubules.

Question 29

What is root dentine formation similar to? What is it initiated by? Rate of growth in proportion to coronal dentine? First formed root dentine may have ---- mineralisation to later root dentine.

Answer 29

Coronal dentine formation Initiated by formation of epithelial root sheath. Forms slower than coronal dentine but is continuous and simultaneous with it (multirooted teeth may be an exception with isolated areas of mineralisation). Delayed

Question 30

Give features of the hyaline layer of root dentine

Answer 30

``` Relatively structureless (no tubules) Non-collagenous fine, fibrillar matrix Proteins are enamel-like 10um thick Obscure origin May serve to bond cementum to dentine ```

Question 31

Explain secondary and tertiary dentine formation

Answer 31

Secondary = Formation starts as completion of root formation is same as primary circumpulpal dentine. Preprogrammed age change. Tubular pattern are a little less regular as ... odontoblasts become more crowded. slower rate of deposition. Border usually due to change in direction of tubules. Rate of formation can be increased by altering blood flow to tooth. Forms once the tooth is fully developed by there is still dentine being laid down. Tertiary = “dentine more or less irregular in structure deposited at sites or pulpal aspects of 1 dentine corresponding to areas of external irritation” It can be stimulated by caries or attrition. It is laid down in response to injury.

Question 32

What are the two types of tertiary dentine formation? Signals involved?

Answer 32

Reactionary = mild irritant, odontoblasts survive and are upregulated Reparative = strong irritant, odontoblasts die, there is progenitor cell recruitment, induction of odontoblasts differentiation, odontoblast upregulation Dentine chips in a tissue culture of dental papillae include growth around the caps. Suggests the signal molecule is in the dentine matrix.