OE L4 Dentine Structure Flashcards
Describe the composition of dentine.
- 70% inorganic: hydroxyapatite + small amounts of non-crystalline amorphous calcium phosphate
- 20% organic: 90% collagen + 10% lipids
- 10% water
Describe the physiology of dentine.
- Hard tissue
- Elastic properties due to tubular structure, supports brittle enamel
- Yellow
Circumpulpal dentine refers to…
Primary, secondary and predentine.
Doesn’t include predentine or tertiary dentine.
Describe mantle dentine.
First type of dentine formed, seen at outer edges and mineralised through matrix vesicles.
Describe primary dentine.
Refers to all of the dentine formed during tooth development. Includes mantle dentine and cirumpulpal dentine.
Describe secondary dentine.
Dentine laid down post eruption.
Made after root formation.
Odontoblasts continue to secrete dentine at a slow rate of 3-4microns a day.
Tubular structure.
Describe predentine.
The layer closest to pulp chamber (opposite of mantle dentine).
Unmineralised.
Secreted by odontoblasts as organic matrix, later remodelled to allow for mineralisation.
Describe tertiary dentine.
Formed in response to disease or trauma e.g. caries, abrasion. Aka. noxious stimuli.
Response is directly beneath region of disease or pathology.
Increases distance between noxious agent and pulp cells.
Divided into reactionary and reparative.
Describe reactionary dentine.
- Mild stimulus
- Pre-existing odontoblasts secrete dentine
Describe reparative dentine.
- Strong stimulus
- Odontoblasts killed and stem cell population recruited from pulp
- Odontoblast-like cells secrete a dysplastic dentine with irregular/no tubules
Also called osteodentine
Does pulp respond to restorative materials?
Yes.
Dental materials can trigger responses such as sensitivity, chronic inflammation and cellular toxicity.
This is because materials can leak through dentinal tubules and reach the pulp.
Describe the appearance of carious dentine.
Heavily stained brown with soft texture.
Bacteria demineralising the dentine can be visualised as dark staining lines in tubules under microscope, also note presence of demineralisation front.
What 2 types of curvature do dentinal tubules show?
Primary curvature- sigmoidal path of dentinal tubules due to crowding towards pulp
Secondary curvature- of the dentinal tubule walls themselves (wobbly)
Where are there more tubules, at the pulp or ADJ?
At the pulp (45,000/mm^2).
At enamel it is 20,000mm^2.
Consequences of branched tubules.
- Good for elasticity and nutrient supply
- However, not so good for caries development and response to restorative materials
Describe peritubular dentine.
- The dentine immediately surrounding the tubule
- Hypermineralised ring of dentine providing integrity and strength to tubule
- Little collagen, mostly hydroxyapatite and calcium phosphate
What is sclerotic dentine?
Describes dentine wtih occluded tubules from age or pathology.
- A normal feature of aging
- Thought to be caused by continued secretion of peritubular dentine
- Gradual decrease in size of tubule lumen
- Also acts as line of defence: prevents bacteria travelling down tubules
What is the appearance of sclerotic dentine?
Transparent, glossy.
What are dead tracts?
As the odontoblast process retracts in sclerotic dentine, it leaves behind an empty tubule that may become filled with air, appears as dark stained area (dead tracts).
Describe intertubular dentine.
Located between tubules. Network collagen fibres embedded in ground substance in which HAP crystals are deposited.
- Bulk of dentine
- Main product of odontoblast cell bodies
- Tight network of type 1 collagen fibrils arranged at right angles to tubules
- Crystals deposited into these fibrils
Describe the ground substance of the intertubular dentine.
- Plasma proteins
- Glycosaminoglycans
- Phosphoproteins
- Growth factors
Compare lines of Von Ebner and Anderson lines.
Lines of Von Ebner:
- Daily growth lines
- Closer together
Anderson Lines:
- 5 day growth lines
- More obvious
What is the granular layer of Tomes?
- Seen only in ground sections
- Black dots in root
- Just below dentine where root is covered by cementum
Possible explanation: air trapped in tubules causing air pockets
What is the significance of the ruffled appearance of the ADJ?
Increased surface area for enamel and dentine to bind together tightly.
What age related and envrionmental changes affect dentine?
- Age: volume of pulp chamber decrease, increased tubule occlusion by peritubular dentine
- Environment: increased tertiary dentine due to caries, trauma, abrasion, attrition
