Dentin

Question 1

What do the tubules in dentin contain

Answer 1

• odontoblastic processes
• dentinal fluid
• nerve endings

Question 2

What stage of tooth formation does dentin formation begin

Answer 2

Bell stage

Question 3

What colour is dentin, is it permeable/impermeabe

Answer 3

Dentin = pale yellow in colour and permeable

Question 4

Is dentin harder/softer than bone, cementum and enamel

Answer 4

Harder than bone and cementum but softer than enamel

Question 5

Describe the chemical structure of dentin

Answer 5

Calcium hydroxyapatite crystals are found between type 1 collagen fibrils, the crystals are much smaller than those in enamel

Question 6

What shape do the dentinal tubules make and why

Answer 6

S shapes
due to the crowding of odontoblasts as they get squeezed into a smaller and smaller space within the pulp cavity, known as the primary curve

Question 7

What are the contour lines of owen and how do they form

Answer 7

These are the appearance of a line crossing the dentin and are caused by subtle changes in direction during dentin depositions that creates wavy dentinal tubules, these are known as the secondary curves.

Question 8

Where are the secondary curves of dentin normally found

Answer 8

Usually found at the junction of primary and secondary dentin

Question 9

How might dentinal tubules appear differently in the periphery near the DEJ

Answer 9

They branch profusely, many small side branches, some may unite with branches of other tubules

Question 10

What is the purpose of the lateral branches (Canaliculi) of dentinal tubules

Answer 10

This is where odontoblastic processes can communicate with one another

Question 11

What is intra/peritubular dentin and what is interlobular dentin

Answer 11

Peri = dentin that forms the wall of each tubule, more mineral that interlobular dentin
Inter = Dentin between tubules

Question 12

Does peri or interlobular dentin have more collagen

Answer 12

Inter

Question 13

Is peri or inter dentin more mineralised

Answer 13

Peri

Question 14

How are the type 1 collagen fibres arranged in inter dentin

Answer 14

Arranged perpendicular to the tubule

Question 15

What is the circumpulpal dentine and describe its structure(s)

Answer 15

Forms the bulk of the dentin
Uniform in structure except
- Outer surface - interlobular
- inner surface - mineralisation front

Question 16

How might the tubules of circumpulpal dentin be modified

Answer 16

Modified with age by secondary dentin deposition in pulp

Modified by disease by tertiary dentin

Question 17

Where are the hyaline and granular layers of the dentin

Answer 17

These are found in the periphery of the root

Question 18

Describe the dentin and dentinal tubules found in the Hyaline and granular layers of the dentin

Answer 18

• Hypo-mineralised in comparison to circumpupal dentin

- Dentinal tubules branch more profusely and loop back creating air spaces

Question 19

Where is interglobular dentin found

Answer 19

Found just below the mantle zone in the crown or granular layer of tomes in the root.

Question 20

Describe the features of the interglobular dentin and dentinal tubules

Answer 20

It is less calcified and appears as irregularly shaped crescents
Tubules pass through but peritubular dentin is absent in these areas

Question 21

Why is interglobular dentin less calcified

Answer 21

Results from uneven fusion of the mineralisation front

Question 22

What is the prevention

Answer 22

• Initially laid down dentine matrix before
mineralization
• The innermost layer of the dentine
• The mineralising front-globular or linear

Question 23

How does mineralisation occur in dentin

Answer 23

• Organic matrix laid down by odontoblasts
• Calcium transported through odontoblast to area of calcification
• Calcium becomes crystalline in dentine after deposition onto collagen fibrils
• As matrix deposition and mineralisation continue,
a zone of calcification will nearly always be visible

Question 24

What is linear and globular mineralisation of dentin

Answer 24

• Linear – deposition by apposition onto existing calcified areas
• Globular – deposition occurs in spheres (calcospherites)

Question 25

How does globular calcification of dentin happen

Answer 25

Begins in small spherical areas that become larger and fuse with one another to form a calcification front.

Question 26

What are von Ebner lines

Answer 26

Incremental lines associated with matrix deposition and mineralisation
• Daily alterations in the formation of dentine
• Seen as banding along the dentinal tubules
• Perpendiculartothedentinaltubules.

Question 27

What happens to primary dentin with age

Answer 27

Can become translucent with age (increased deposition of peritubular dentine occludes tubule)

Question 28

When does secondary dentin deposition occur

Answer 28

begins after eruption - often as tooth comes into occlusion.

In time will reduce pulp chamber and root canal size

Question 29

What is the structural difference between primary and secondary dentin

Answer 29

Structurally similar to primary dentine but with fewer tubules

Question 30

When is tertiary dentin produced and what is its role

Answer 30

Produced in response to external stimuli (attrition, caries, cavity preparation, trauma).
It has a protective role

Question 31

When is sclerotic dentin formed and describe its structure

Answer 31

• Formed in response to external challenge
• Appears translucent – due to increased mineralisation
• Tubules filled in to block ingress of bacteria in caries

Question 32

What are dead tracts of dentin

Answer 32

Empty tubules following death of odontoblast or retraction of process

Question 33

What effect can tertiary dentin have on the pulp cavity

Answer 33

Tertiary dentin can totally obliterate the pulp cavity with ageing or severe damage.

Question 34

What causes the sensitivity of dentin

Answer 34

Exposed dentine is often painful (sensitive): when dentinal fluid moves it compresses nerve endings on dentinal tubules transmitting sense of pain