Dentinogenesis

Question 1

Where are coronal and radicular dentin found?

Answer 1

Coronal = crown

Radicular = root

Question 2

What are the two layers of coronal dentin?

Answer 2

Mantle dentin

Circumpulpal dentin

Question 3

Where is mantle dentin found?

Answer 3

Adjacent to the EDJ

Question 4

What are the three layers of radicular dentin?

Answer 4

Hyaline layer (Hopewell-Smith)

Granular layer of Tomes

Circumpulpal dentin

Question 5

Where is circumpulpal dentin found?

Answer 5

Around pulp

Question 6

Describe the process of dentinogenesis. (5)

Answer 6

1. IEE differentiates into preameloblasts
2. Peripheral dental papilla cells start to differentiate into preodontoblasts and odontoblasts
3. Differentiating odontoblasts undergo elongation and polarisation and secretory organelles develop
4. Newly formed odontoblasts develop multiple small cell processes and begin predentin secretion
5. Odontoblast cell body moves toward pulp as matrix is deposited and process retracts over time

Question 7

Where does cytodifferentiation (amelo/odontoblasts) start?

Answer 7

Tips of cusps/incisal edge

Question 8

Describe odontoblasts. (5)

Answer 8

Large nucleus at base

Large Golgi complex

RER parallel to long axis of cell

Long process with many smaller ones

Cell-cell junctions (desmosomes)

Question 9

Why do odontoblasts have desmosomes between each other?

Answer 9

Prevent leakage of predentin between cells

Question 10

What is the function of a preodontoblast?

Answer 10

Resides in pulp tissue and responds to injury

Question 11

What are the substances present in predentin? (7)

Answer 11

Collagen type I

Phosphoproteins

Glycoproteins/sialoproteins

Proteoglycans

Growth factors

Matrix metalloproteinases

Serum-derived proteins

Question 12

Give three examples of phosphoproteins which are present in predentin. (3)

Answer 12

Dentin phosphoproteins

Carboxyglutamate-containing proteins (Gla-proteins)

Dentin matrix protein 1

Question 13

What glycoproteins/sialoproteins are present in predentin? (4)

Answer 13

Osteonectin

Osteopontin

Bone sialoprotein

Dentin sialoprotein

Question 14

What proteoglycans are present in predentin? (3)

Answer 14

Decorin (CS rich)

Biglycan (CS rich)

Lumican (KS)

Question 15

What growth factors are present in predentin? (4)

Answer 15

TGF β-family

Insulin-like GF1/2

FGF

BMP

Question 16

What matrix metalloproteinases are present in predentin? (5)

Answer 16

Collagenases (MMP1)

Gellatinases A/B (MMP2/9)

Stromelysin (MMP3)

Enamelysin (MMP20)

Tissue inhibitors metalloprotein

Question 17

What serum-derived proteins are present in predentin?

Answer 17

Albumin

α2HS-glycoprotein

Question 18

How thick is mantle dentin?

Answer 18

20-150um

Question 19

Describe mantle predentin. (4)

Answer 19

Different composition as has contributions from pulp cells

Collagen fibres at right angles to IEE

Numerous processes lead to porous dentin

Matrix vesicles form on collagen fibres which trigger mineralisation

Question 20

Describe circumpulpal predentin. (3)

Answer 20

Collagen fibres parallel to dentin-pulpal border

Incremental lines present

Sinusoidal path of odontoblasts (primary curvature)

Question 21

How thick are the collagen fibres in dentin?

Answer 21

100nm

Question 22

What two types of mineralising fronts are there (dentin)?

Answer 22

Linear

Globular

Question 23

How thick are the collagen fibres in proximal and distal predentin?

Answer 23

20nm proximally and thicken to 70nm distally (thickens through predentin)

Question 24

What is the metadentin?

Answer 24

Mineralising front

Question 25

Describe metadentin. (3)

Answer 25

2.5-5um thick Rich in DPP, dentin sialoprotein, proteoglycans Calcospherites are 2.5-5um thick in globules

Question 26

What is interglobular dentin?

Answer 26

Areas between unevenly fused calcospherites found in the globular layer (fast mineralisation) Between mantle and circumpulpal dentin

Question 27

What does the diurnal variation in odontoblast secretion result in?

Answer 27

Incremental lines of von Ebner (light and dark paired bands, 2-4um apart)

Question 28

How big are the matrix vesicles in predentin mineralisation and what do they contain?

Answer 28

30-200nm Enzymes (alkaline phosphatase) which increase phosphate concentration

Question 29

How can the matrix vesicles in predentin mineralisation be formed?

Answer 29

Cell budding or fragmentation

Question 30

How is mineralisation of predentin controlled by odontoblasts?

Answer 30

Controlling influx of Ca2+ Controlling secretion and metabolism of matrix proteins

Question 31

How is circumpulpal predentin mineralised?

Answer 31

Ca2+ nucleation at spaces present between collagen fibres under principle control of DPP

Question 32

What are the properties of dentin phosphoprotein?

Answer 32

Highly acidic so binds Ca2+ Can change shape to bind more Ca2+ to allow crystal growth

Question 33

What are the functions of dentin phosphoprotein? (4)

Answer 33

Transports Ca2+ to mineralisation front Location of nucleation to specific areas of collagen Stabilisation of formed crystals Inhibits crystal formation when DPP concentration is high

Question 34

What role does osteonectin play in mineralisation in vitro?

Answer 34

Inhibits growth of hydroxyapatite Promotes Ca2+ and phosphate binding to collagen

Question 35

What role does osteopontin play in mineralisation in vitro?

Answer 35

Promotes mineralisation

Question 36

Where is bone sialoprotein found in dentin? (3)

Answer 36

Early mineralising dentin Predentin Peritubular dentin

Question 37

What role do proteoglycans play in mineralisation in vitro?

Answer 37

Predentin - transport; hydroxyapatite inhibitors Mineralising dentin - absorbed onto collagen and promotes hydroxyapatite initiation

Question 38

What are calcospherites?

Answer 38

Circular areas of mineralised dentin seen under polarised light

Question 39

What initiates the formation of root dentin?

Answer 39

Hertwig's epithelial root sheath

Question 40

How does radicular dentin formation differ to coronal dentin?

Answer 40

Slower Calcospherites are smaller initially with more interglobular areas

Question 41

Describe the hyaline/Hopewell-Smith layer.

Answer 41

Relatively structureless (no tubules) Non-collagenous, fine, fibrillar matrix with enamel-like proteins 10um thick

Question 42

When is primary dentin formed?

Answer 42

During tooth development

Question 43

When is secondary dentin formed?

Answer 43

After root is fully formed

Question 44

Why does secondary dentin have a less regular tubular pattern?

Answer 44

Odontoblasts become more crowded Slower rate of deposition

Question 45

Why is there a contour line at the edge of the secondary dentin?

Answer 45

Change in tubule direction

Question 46

How can the rate of secondary dentin formation be increased?

Answer 46

By denervation

Question 47

When is tertiary dentin laid down?

Answer 47

In response to stimulus

Question 48

Describe reactionary dentin. (3)

Answer 48

Tertiary dentin laid down in response to mild irritants Original odontoblasts survive and upregulation of odontoblasts More time = more regular structure

Question 49

Describe reparative dentin.

Answer 49

Tertiary dentin laid down in response to strong irritants Odontoblasts die - progenitors recruited and differentiate Preodontoblasts differentiate into odontoblast-like cells

Question 50

What might the appearance of tertiary dentin be like? (3)

Answer 50

Secondary dentin Atubular Few and irregularly arranged tubules

Question 51

What signal molecules are present in dentin matrix?

Answer 51

TGF-β 3 and 1 BMP

Question 52

What type of dentin would TGF-β3 and 1 result in?

Answer 52

Reactionary-like dentin

Question 53

What type of dentin would TGF-β3 result in?

Answer 53

Reparative-like dentin

Question 54

What type of dentin would BMP result in?

Answer 54

Bone-like dentin