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
Explain the ‘odontoblasts acting as receptors’ theory
- Response is triggered in the odontoblast process
- There’s synapses between odontoblast cell bodies and adjacent nerves
- Impulse travels down to cell body where it triggers a synapse + onto nerve plexus
Explain the hydrodynamic theory
- Stimulus applied to dentine triggers a flow of fluid within tubules
- Movement is sufficient to depolarise nerve endings
Why is it generally accepted that hydrodynamics is the most likely mechanism
- It would act regardless of precise position or number of nerve endings
- As tubules are narrower, the further away from the pulp one goes, any given volume of fluid would flow at a faster rate, hence a greater stimulus and greater sensitivity in that reigon
- Dentine sensitivity can be reduced or removed by occluding the tubules as evidenced by anti-sensitivity toothpastes
What are the arguments against the ‘stimulation on nerves’ theory
- Nerve axons appear to be absent in the outer parts of dentine - most sensitive reigon in dentine
- Application of local anaesthetics to the surface of dentine doesn’t remove the sensitivity
What are the arguments against ‘odontoblasts acting as receptors’ theory
- Odontoblast processes may not extend to the ADJ
- Odontoblasts have not been shown to have synaptic junctions with nerve fibres
How does dentine maintain is vitality
- Through odontoblasts
- The cell bodies which lie at the periphary of the dental pulp
- Their processes extending into the dentinal tubules
What do the odontoblast cells do
- Lay down + mineralise dentine matrix
- Help maintain its integrity when dentine structure is damaged through disease or trauma
Where is the extracellular dentinal fluid that passes along the dentinal tubules derived from
Why may this be important
- The vasculature of the dental pulp
- May be important in maintaining the health of the cellular and hard tissue environment in dentine
How does odontoblasts acting as a selective barrier help
- Allow tissue fluid to enter dentinal tubules
- May slow the inward movement of toxins during the progression of dental caries
What is the relationship between odontoblasts and the formation of tertiary dentine
The responsiveness of dentine to external stimuli resulting in the formation of tertiary dentine is mediated by odontoblasts
What are odontoblasts capable of producing
Pro-inflammatory mediators in response to bacterial toxins such as lipopolysaccharides
Where do dentinal tubules commonly fill in as a response to an external stimulus
- Under slowly advancing caries
- Beneath areas of severe attrition
How can occlusion of groups of dentinal tubules by deposition of sclerotic dentine offer protection
By slowing down progression of lesion towards the pulp
What is the mineral in sclerotic dentine
The mineral is crystalline and possibly an apatite, although plate-like crystals of octocalcium phosphate have also been reported
Whats the difference in mineral concentration in sclerotic dentine and young dentine
Sclerotic dentine has a significantly higher mineral concentration
Whats the difference between sclerotic dentine and normal dentine
Sclerotic dentine exhibits almost no yielding before failure
What happens when primary odontoblasts are killed by an external stimulus
- Empty dentinal tubules are left
- Tubules may be sealed at their pulpal end by tertiary dentine
What happens when the mounting medium dont enter the sealsed-off tubules when ground sections are prepared and mounted?
The tubules remain air-filled, so they will appear dark under a microscope and are histologically termed dead tracts
What is tertiary dentine used to describe
All hard tissue deposited on the pulpal surface in response to an external stimulus:
Stimuli may include caries, tooth surface loss and damage to dentine
What is tertiary dentine: a response tissue or an age change
- Response tissue
- Deposited at specific sites, providing a barrier to the progress of caries and toxins
Where can tertiary dentine be found in older teeth
On the pulpal aspect of secondary dentine
Where is tertiary dentine restricted to
The reigon behind the irriatation
What does the appearance and composition of tertiary dentine depend on
The types and severity of the stimulus applied to dentine
How might tertiary dentine resemble secondary dentine
Having a regular tubular structure
How might tertiary dentine resemble bone
May have a few/irregularly arranged tubules or be atubular
What does the term ‘reactionary dentine’ refer to
The dentine forming in response to an insult in which existing odontoblasts recover and continue to form dentine, although dentine will have an irregular apperance with fewer tubules
What does the term ‘reparative dentine’ relate to
Dentine forming after a stimulus in which the original odontoblasts in the associated reigon have been destroyed and new calcified tissue has been formed by newly differentiated ‘odontoblast-like’ cells
How do you form reparative dentine
Odontoblast-like cells differentiate from a stem cell population
Whats allows for the divison of dentine into different reigons
The properties and composition of mineralised dentine between the predentine adjacent to the pulp and the ADJ
What is the bulk of dentine in the crown and root called
Circumpulpal dentine
What is circumpulpal dentine’s structure like?
Uniform, except at its periphery where interglobular dentine may be found. Where interglobular dentine is absent, mantle dentine forms its peripheral boundary
Where is the granular layer of Tomes found
At the peripheral reigon in root dentine
What are the 2 explanations for the existance of the granular layer
- Dentinal tubules in the area branch more profousely and loop back on themselves creating air spaces in ground sections, resulting in internal reflection of transmitted light
- Due to the incomplete fusion of calcospherites (much smaller than those found in the crown
Describe the hyaline layer
Sits outside of the granular layer & appears as a narrow structureless band - may have a role in bonding cementume to dentine
What is predentine
Unmineralised intermost layer in the crown and root - represents the initially laid down dentine matrix before its mineralisation
What colour is predentine in demineralised sections stained with haematoxylin and eosin
Why is it this colour
Distinct pale-staining apperance due to a difference in the composition of its matrix
Where is secondary dentine found
- In older teeth
- Inner, pulpal part of the circumpulpal dentine
How different is the structure of primary and secondary dentine
They have a very similar structure
What is secondary dentine laid down by
Original odontoblasts as an age-related change in the rate of dentine formation
As dentine deposition continues, what happens to pulp volume
Decreases
What percentage of odontoblasts die over a 4-year period
50%
What does the death of odontoblasts likely lead to in relation to the contour line
There is a change in the direction of the tubules
What does a slower rate of deposition of dentine do to the tubular pattern
Makes the pattern a little less regular than that of primary dentine
What may the continuing deposition of secondary dentine throughout life contribute to
May contribute to the barrier function of the tissue
What is mantle dentine
- First-formed layer of dentine
- Most peripheral layer of dentine
- Found beneath the enamel
What is the width of mantle enamel
Varies from 20-150 microns
How does mantle dentine differ from the bulk of curcumpulpal dentine
- Mantle dentine is lightly less mineralised
- Mantle dentine displays branching of dentinal tubules
- Mantle dentine has collagen fibrils orientated perpendicular to the ADJ
What do the speical properties of mantle dentine help to prevent
Small cracks developing in the enamel near the ADJ from speading into the dentine
Where is interglobular dentine found
Beneath the mantle layer in the crown and beneath the granular layer in root areas where dentine mineralisation is incomplete
How do uncalcified, interglobular areas appear when ground sections are viewed in transmitted light
They appear dark due to the internal reflection of light
What are Schrenger lines
Lines associated with the primary curvatures of the dentinal tubules - where peaks of the sigmoid primary curvatures concide, they form broad bands known as Schrenger lines
What are Contour lines of Owen
Lines associated with the secondary curvatures of the dentinal tubules - They give rise to an optical effect resulting in the apperance of lines known as the Contour lines of Owen
Why are lines seen at the junction of primary and secondary dentine
There is a coincident change in tubule direction
What are the daily incremental lines
Where dentine is laid down at about 4µm per day in a diurnal rhythm
Describe von Ebner’s lines
Short-period markings may be seen as alternating dark and light bands, each pair reflecting the diurnal rhythm of dentine formation
What are Andresen lines
Lines which are superimposed on von Ebner’s lines and are more prominent
What is between each long-period line
6-10 paids of short period lines with an average 1 week periodicity similar to the long-period striae of Retzius in enamel
