OB D6 - Dentinogenesis

Question 1

what are properties of dentine?

Answer 1

-Specialised connective tissue
-Hard (KHN 75)
-Strong and resilient
-Tubular – porous
-Vital
-Embryologically, physically and functionally linked to
pulp

Question 2

what is predentine?

Answer 2

• organic matrix only

- beside pulp

Question 3

where does dentine formation start and what direction does it go in?

Answer 3

starts at ADJ and works inwards so always being laid down at papillan apsect

Question 4

what is the composition of dentine?

Answer 4

70% Mineral : Hydroxyapatite
20% Organic Matrix:
– Collagen (mainly type I)
– Extracellular Matrix/Ground substance: 
• Dentine Phosphoproteins
• Proteoglycans
• Lipids
10% Water

Question 5

what is dentine formed by?

Answer 5

odontoblasts

Question 6

what are odontoblasts derived from?

Answer 6

– derived from cells of dental papilla

– ectomesenchymal

Question 7

when does dentine formation begin?

Answer 7

end of bell stage

Question 8

where does dentine formation start?

Answer 8

cusp tip

Question 9

what are the 3 stages of dentine formation?

Answer 9

– Cytodifferentiation
– Matrix formation
– Mineralisation

Question 10

describe the signalling between dental papilla cells and inner enamel epithelium.

Answer 10

-DP to IEE:
number of cell divisons
-IEE to DP : papilla cells divide and mature to odontoblasts
-DP to IEE:
IEE cells mature to ameloblasts

Question 11

what is the significance of the basal lamina?

Answer 11

position of future ameldodentinal junction

Question 12

what is the first stage of dentinogenesis?

Answer 12

Dental papilla cells divide

Question 13

what is the second stage of dentinogenesis?

Answer 13

cells enlarge and cross acellular space

Question 14

what is the third stage of dentinogenesis?

Answer 14

increased synthetic/ secretory organelles

Question 15

what is the forth stage of dentinogenesis?

Answer 15

organic matrix secreted = pre dentine

Question 16

what is the fifth stage of dentinogenesis?

Answer 16

odontoblasts retreat secreting pre dentine

Question 17

what is the sixth stage of dentinogenesis?

Answer 17

Pre dentine mineralises forming dentine

basal lamina disintegrates and enamel formation commences

Question 18

what is the matrix secretory phase?

Answer 18

odontoblasts secrets the organic matrix -pre dentine

Question 19

what is the initial mineralisation stage?

Answer 19

-Matrix vesicles involved
-Crystals grow and aggregate obscuring
collagen
-Basal lamina disintegrates
– signals start of enamel formation

Question 20

Describe mineralisation of dentine.

Answer 20

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

Question 21

what is interglobular dentine?

Answer 21

failure of calcospherite fusion

Question 22

what are the 2 types of dentine?

Answer 22

• mantle dentine

- circumpulpal dentine

Question 23

Describe mantle dentine.

Answer 23

-The 1st formed dentine
- adjacent to enamel
-~ 150μm thick
-characterised by:
– large collagen fibrils at 90° to the ADJ
– MVs
– ground substance not all of Odontoblast origin – Slightly less mineralised (by ~5%)

Question 24

Describe circumpulpal dentine.

Answer 24

-Rest of the dentine
-Ground substance from Odontoblasts
-Collagen fibrils are closely packed + interwoven and small collagen fibrils parallel to the ADJ
-Mineralisation:
– No Matrix vesicles
– heterogeneous nucleation

Question 25

Describe incremental nature.

Answer 25

• ~5μm of matrix per day
• subtle changes in collagen fibre orientation
• Incremental lines of von Ebner

Question 26

Describe odontoblasts migration.

Answer 26

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