Dentine Flashcards
Why is the dentine that covers the bulk of the crown not visible
It is covered by the enamel
What does the deep surface of dentine form?
Forms the walls of the pulp chamber
Which tissue has a thicker crown: dentine or enamel
Dentine
What’s the advantage of dentine being thick
- Helps protect the pulp tissue at the core of the tooth
- Provides room for replacement
When can dentine be exposed
When cementum and enamel fail to meet at the CEJ
What can expose dentine
- Gingival recession
- Significant tooth surface loss
- Caries
- Crown fracture
What can exposed coronal and root dentine cause
Can cause clinical symptoms
What colour is dentine
Dentine is pale yellow
What is dentine
Mineralised connective tissue
What are dentinal tubules
Channels running from the pulp to the outer dentine at the ADJ
How hard is dentine in relation to other mineralised coinnective tissue
Dentine is harder than bone and cementum but softer than enamel
Where does dentine obtain its rigidity from and why is this useful
- Mineral content
- Support enamel
- Maintain the shape of the tooth
Explain the relationship between dentine and mastication
Exposed dentine cannot withstand abrasive forces of mastication
What provides dentine with greater compressive, tensile and flexural strength than enamel
Why is this important
- The organic matrix and tubular architecture
- This provides dentine flexible support needed by the overlying brittle enamel
What does dentine’s permability depend on
- Size and patency of tubules
- Age change
- Pathalogical processes affecting the tooth
Why is the mineral in dentine more soluable in acid than in enamel
Dentine contains hydroxyapatite crystallites, however there are more impurities than in enamel
What is the structural difference between hydroxyapatite crystallites in dentine and enamel
In dentine:
- Much smaller in cross section
- Shorter
How are the hydroxyapatite crystals arranged
- Along and in-between collagen fibrils
- Fibrils form a meshwork
What is the principal collagen fibril
Type 1 collagen
How do most collagen fibrils run in relation to the ADJ
Parallel to the ADJ
Why is the mineral content in dentine lower than in enamel
- Dentine tubules and collagen meshwork take up a significant proportion of the tissue volume
- Hydroxyapatite crystals aren’t as tightly packed together as in enamel
What do non-collagenous proteins include
- Phosphoproteins
- Proteoglycans
- Glycoproteins
- Growth factors
What are the main non-colagenous proteins
- Dentine phosphoprotein (DPP)
- Dentine matrix proteins 1 (DMP-1)
- They have different actions during mineralisation
What role do proteoglycans have in collagen fibril assembly
- Cell adhesion
- Migration
- Proliferation
- Differentiation
Where are lipids detected?
Detected at the mineralising front and are thought to play a role in mineralisation
What are lipids in the form of
- Phospholipids
- Cholesterol
Where are phospholipids found
The spaces between collagen fibrils along with the proteoglycans
How quickly is the peritubular dentine laid down
Slowly throughout life
Why does dentine become transluscent
- As groups of tubules become totally filled, reigons become transluscent
- Tubules and the intertubular dentine have approx the same refractive index
What happens when a ground section of a root is placed in water
Reigons blocked by peritubular dentine will appear translucent, while reigons with patent tubules will fill with water and appear opaque
Where do dentinal tubules first come occluded
What happens during physiological ageing
- Tubules first become occluded at the root apex
- Transluscent areas gradually extend cervically and towards the root canal with physiological ageing
Describe how secondary dentine can be used to determine the age of a person from their teeth
The extent of transluscent dentine is related to chronological ageing so the feature is used in forensic age
What does sclerotic dentine produce and how does it differ from transluscent dentine?
- Produces transparent reigons
- Differs from transluscent dentine as it isn’t related to chronological age
What type of dentine is sensitive
Exposed dentine
What are the proposed mechanisms of dentine sensitivity
- Direct innervation
- Odontoblasts act as sensory endings
- Hydrodynamics (fluid flow)
Which nerves may suggest simple direct simulation of the nerves
Nerves within dentinal tubules
What are the 3 theories of dentine sensitivity
- Direct stimulation on nerves theory
- Odontoblasts acting as receptors theory
- Hydrodynamic theory
Explain the ‘direct stimulation on nerves’ theory
- Stimulus trigers direct response in nerve
- Impulse passing down to the nerve and onto central nervous system via Raschkow’s plexus