Dentinogenesis

Question 1

Give an overview of Dentine:

Answer 1

Dentine:

• specialised connective tissue
• hard KHN - 75
• strong and resilient
• tubular - porous
• vital
• embryologically, physically and functionally linked to pulp - derived from papilla

Question 2

What is pre-dentine?

What is the composition of Dentine?

Answer 2

Pre-dentine:

• organic matrix only
• beside pulp

Dentine:

• 70% mineral (hydroxyapatite)
• 20% organic matrix: extracellular matrix, type I collagen
• 10% water

Question 3

How is dentine formed in summary?

What are the stages of dentine formation?

Answer 3

• formed by odontoblasts: derived from dental papilla, ectomesenchymal in nature
• begins at end of bell stage
• starts at cusp tip

Stages of dentine formation:

• cytodifferentiation
• matrix formation
• mineralisation

Question 4

What is the first signal at the cervical loop in dentine formation?

Next?

Finally?

What does the interface between IEE and DP represent?

Answer 4

Dental papilla to IEE:

• epithelial cells are dividing
• papilla sends messenger signals to tell IEE cells how much to divide - governs shape and size of tooth

IEE to dental papilla:

• papilla cells to divide and mature to odontoblasts

DP to IEE:

• IEE cells to mature to form ameloblasts

Interface between IEE and DP represents position of future ADJ

Question 5

Answer 5

Question 6

Describe Dentinogenesis:

Answer 6

1. Dental papilla cells divide and migrate (triggered by signal from IEE to DP)
2. Cells enlarge and cross acellular space and line up along basal lamina, adjacent to epithelial cells (2 daughter cells, 1 forms odontoblast, other is undifferentiated ectomesenchymal cell - can restimulate tertiary dentine)
3. Increased synthetic/secretory organelles (secrete collagen, RER, mitochondria etc)
4. Organic matrix secreted = pre-dentine
5. Odontoblasts retreat inwards secreting pre-dentine forming dentinal tubules (odontoblast process)
6. Pre-dentine mineralises forming dentine, basal lamina disintegrates, then enamel formation commences

Question 7

What is matrix secretory phase?

How does initial mineralisation commence?

Dentine Mineralisation?

What is interglobular dentine?

Answer 7

Matrix secretory phase: odontoblast secretes the organic matrix = pre-dentine

Initial Mineralisation:

• matrix vesicles involved
• crystals grow and aggregate obscuring collagen
• basal lamina disintegrates - signals start of enamel formation

Dentine Mineralisation:

• once hydroxyapatite crystals formed, hydroxyapatite grows in a spherical form - globular = calcospherites - these eventually fuse

Interglobular dentine: failure of calcospherites to fuse

Question 8

What is mantle dentine?

Answer 8

Mantle dentine:

• 1st formed
• adjacent to enamel
• ~150 microns thick
• characterised by: large collagen fibrils at 90 degrees to the ADJ, matrix vesicles, ground substance not all of odontoblast origin, slightly less mineralised by ~5%

Question 9

What is circumpulpal dentine?

Answer 9

Circumpulpal dentine:

• rest of dentine
• ground substance from odontoblasts
• collagen fibrils - smaller, closely packed and interwoven, parallel to ADJ
• mineralisation: no matrix vesickes, heterogeneous nucleation (crystal growth)

Question 10

How is dentine laid down?

How do odontoblasts migrate?

Answer 10

Dentine is laid down incrementally, ~5 microns of matrix per day

• subtle changes in collagen fibre orientation
• incremental lines of von Ebner

Odontoblast migration:

• odontoblast retreats centripetally in S-shaped track
• leaves behind a process - the odontoblast process in a tubule
• odontoblast track is S-shaped