Dentin Flashcards
What do the tubules in dentin contain
- odontoblastic processes
- dentinal fluid
- nerve endings
What stage of tooth formation does dentin formation begin
Bell stage
What colour is dentin, is it permeable/impermeabe
Dentin = pale yellow in colour and permeable
Is dentin harder/softer than bone, cementum and enamel
Harder than bone and cementum but softer than enamel
Describe the chemical structure of dentin
Calcium hydroxyapatite crystals are found between type 1 collagen fibrils, the crystals are much smaller than those in enamel
What shape do the dentinal tubules make and why
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
What are the contour lines of owen and how do they form
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.
Where are the secondary curves of dentin normally found
Usually found at the junction of primary and secondary dentin
How might dentinal tubules appear differently in the periphery near the DEJ
They branch profusely, many small side branches, some may unite with branches of other tubules
What is the purpose of the lateral branches (Canaliculi) of dentinal tubules
This is where odontoblastic processes can communicate with one another
What is intra/peritubular dentin and what is interlobular dentin
Peri = dentin that forms the wall of each tubule, more mineral that interlobular dentin Inter = Dentin between tubules
Does peri or interlobular dentin have more collagen
Inter
Is peri or inter dentin more mineralised
Peri
How are the type 1 collagen fibres arranged in inter dentin
Arranged perpendicular to the tubule
What is the circumpulpal dentine and describe its structure(s)
Forms the bulk of the dentin
Uniform in structure except
- Outer surface - interlobular
- inner surface - mineralisation front
How might the tubules of circumpulpal dentin be modified
Modified with age by secondary dentin deposition in pulp
Modified by disease by tertiary dentin
Where are the hyaline and granular layers of the dentin
These are found in the periphery of the root
Describe the dentin and dentinal tubules found in the Hyaline and granular layers of the dentin
- Hypo-mineralised in comparison to circumpupal dentin
- Dentinal tubules branch more profusely and loop back creating air spaces
Where is interglobular dentin found
Found just below the mantle zone in the crown or granular layer of tomes in the root.
Describe the features of the interglobular dentin and dentinal tubules
It is less calcified and appears as irregularly shaped crescents
Tubules pass through but peritubular dentin is absent in these areas
Why is interglobular dentin less calcified
Results from uneven fusion of the mineralisation front
What is the prevention
• Initially laid down dentine matrix before
mineralization
• The innermost layer of the dentine
• The mineralising front-globular or linear
How does mineralisation occur in dentin
• 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
What is linear and globular mineralisation of dentin
- Linear – deposition by apposition onto existing calcified areas
- Globular – deposition occurs in spheres (calcospherites)
How does globular calcification of dentin happen
Begins in small spherical areas that become larger and fuse with one another to form a calcification front.
What are von Ebner lines
Incremental lines associated with matrix deposition and mineralisation
• Daily alterations in the formation of dentine
• Seen as banding along the dentinal tubules
• Perpendiculartothedentinaltubules.
What happens to primary dentin with age
Can become translucent with age (increased deposition of peritubular dentine occludes tubule)
When does secondary dentin deposition occur
begins after eruption - often as tooth comes into occlusion.
In time will reduce pulp chamber and root canal size
What is the structural difference between primary and secondary dentin
Structurally similar to primary dentine but with fewer tubules
When is tertiary dentin produced and what is its role
Produced in response to external stimuli (attrition, caries, cavity preparation, trauma).
It has a protective role
When is sclerotic dentin formed and describe its structure
- Formed in response to external challenge
- Appears translucent – due to increased mineralisation
- Tubules filled in to block ingress of bacteria in caries
What are dead tracts of dentin
Empty tubules following death of odontoblast or retraction of process
What effect can tertiary dentin have on the pulp cavity
Tertiary dentin can totally obliterate the pulp cavity with ageing or severe damage.
What causes the sensitivity of dentin
Exposed dentine is often painful (sensitive): when dentinal fluid moves it compresses nerve endings on dentinal tubules transmitting sense of pain
