What are the physical properties of dentine?
- harder than bone, softer than enamel
- cannot withstand masticatory forces
- permeable
- compressive
What are the chemical properties of dentine?
Mineralised connective tissue
Inorganic:
- hydroxyapatite crystals (more impurities than enamel)
Organic:
- collagen I (embedded within mineralised matrix)
- Non-collagenous proteins (dentine phosphoproteins)
How is dentine different to enamel.
(-structural
-physical
-chemical)
- dentine has dentinal tubules, enamel has prismatic microstructure of hydroxyapatite crystals arranged in rods/prisms
- dentine is less mineralised
- dentine has collagen I
What does dentine consist of mainly…
Hydroxyapatite crystals in an organic fibrillar matrix
What are the constituent of the organic matrix (+specifics of fibrils included) in dentine .
- collagen type 1
What is tubular dentine?
- tooth structure that consists of dentinal tubules
What is peritubular dentine? (what can this cause)
- dentine deposited on walls of dentinal tubule in maturation
- narrowing of lumen
What is intertubular dentine?
Dentine located between dentinal tubules
How can changes in dentinal tubules affect dentine permeability?
- tubule diameter (increased deposition of peritubular dentine can limit permeability)
Explain the mineralisation process of dentine.
- Odontoblast process deposit unmineralised pre-dentine and organic matrix
- Mineralisation occurs fast after deposition
- Calcium and phosphorus ions from surrounding fluid in the pulp combine to form hydroxyapatite crystals
- Nucleation of hydroxyapatite crystals
- As mineralisation progresses, dentinal tubules form
Explain what calcospherites are and their formation.
- spherical hydroxyapatite formed during the mineralisation of dentine
- CHECK DISCUSSION BOARD
What is sclerotic dentine, and when may it be produced?
- dentine that contains dentinal tubules that are completely full of peritubular dentine
- appears transparent
-in response to ‘insult’
How can translucent dentine be used to estimate age?
-translucent dentine deposited with age
-the more transparent the dentine looks, the older the patient is
Where is Circumpulpal dentine located and what’s a characteristic of it.
- the bulk of dentine between predentine and ADJ
- uniform structure
What’s the role of odontoblasts in dentine formation + maintenance?
- odontoblast processes in odontoblasts secrete organic matrix (predentine)
- mineralisation of predentine occurs
- secondary dentine is deposited throughout life
What are the 2 types of tertiary dentine and when are they deposited?
Reactionary (some cells not died so they produce reparative dentine)
Reparative (all cells have died, stem cells differentiate into ‘odontoblast-like-cells’ and produce reparative dentine)
Explain the hydrodynamic theory.
- stimulus triggers flow of fluid (dentinal fluid) within dentinal tubules
- the movement depolarises nerve endings
Why is dentine more susceptible to acid dissolution than enamel?
- dentine is softer
- dentine has lower mineral content
- dentinal tubules allow penetration of acid
Why does caries spread faster in dentine than enamel?
- lower mineral content
- dentinal tubules allow penetration of acid
Where’s the hyaline layer
Between Circumpulpal dentine and cementum
