dentinogenesis Flashcards
When does dentinogenesis begin?
what teeth does it begin with?
- 17-18 weeks
- late bell stage
- after enamel knot has disappeared
- after odontoblast differentiation
- before amelogenesis
- starts with the central incisors
How does dentinogenesis begin in late bell stage?
- odontoblast differentiation starts at future cusp tip and spreads apically
- ameloblasts retreat into enamel organ
what are odontoblasts differentiated from?
ecto-mesenchymal cells of the dental papilla
How do ectomesenchymal cells/pre-odontoblasts differ from mature odontoblasts?
pre-odontoblasts
- high nucleus:cytoplasm ratio
- little RER and little mitochondria
- low synthentic capacity
odontoblasts
- lower nucleus:cytoplasm ratio
- high synthetic capacity
- polarised cells - not symmetrical
Which cells signal for odontoblast differentiation?
Inner enamel epithelial cells
How do IEE cells signal for odontoblast differentiation?
BMPs
FGFs
how is ameloblast differentiation signalled for?
Occurs when IEE cells are exposed to predentine
cells are signalled to differentiate into ameloblasts
what is competency and how is it achieved?
- a signal cells must be competent to respond to a signal for differentiation
- achieved by undergoing the correct number of cell cycles (cell divisions)
- after final division - cells receive signal and differentiate into odontoblast (e.g.)
are odontoblasts able to undergo cell division?
no, they are post-mitotic cell
no further cell division
What is mantle dentine
the first formed dentine
around 0.15mm thick
matrix from new odontoblasts and existing dental papilla cells (the rest of dentine is only from odontoblasts)
how is mantle dentine formed?
- the cells - odontoblasts and existing dental papilla cells
- secrete extracellular matrix
- rich in collagen type I / III fibres perpendicular to the IEE
- fibres interdigitate with cells of the IEE - bonding with the scalloped ADJ
- collagen scaffold forms a network which accepts the deposition of HAP mineral crystals
how is mantle dentine mineralised?
by matrix vesicles
- carry lots of calcium and phosphate
- matrix mediated mineralisation
- vesicles bud off from plasma membrane of odontoblast
- deposition of hydroxyapatite mineral in the collagen fibres
- odontoblasts have not fully developed enough to mineralise the matrix yet
how does mantle dentine differ from dentine?
mantle dentine
- collagen fibres are thicker
- mineralised by matrix vesicle mediated mineralisation
- made from new odontoblasts and dental papilla cells
what occurs after mantle dentine is formed?
odontoblasts secrete the matrix and retreat pulpally
cell process and micro-filaments help migrate proteins, calcium and phosphate into the matrix to bring about the formation of dentine
What is circumpulpal dentine and how is it formed?
- circumpulpal dentine forms the bulk of the tooth structure
- always secrete a layer of unmineralised pre-dentine first which mineralises into dentine
As odontoblast retreats pulpally the odontoblast process is left “entombed” within the mineralised matrix
- Allows odontoblast to communicate with matrix
- They are still present
- Significant for response of the pulpal tissue to insult and dentine hypersensitivity
- Can make repairs to the dentine
- Dentinal tubules run
- S-shape course in crown
- Straight course in root
what patterns of mineralisation are there?
globular
- associated with primary dentine formation
linear
- associated with secondary dentine formation within a mature tooth
- globules called calcospherites form at the dentine predentine interface and grow in size
- the globules fuse together + mineralise
- when they do not fuse together, there is uncalcified dentine
- called interglobular dentine
- risk of caries
explain the levels of odontoblast secretion
- 2 levels of secretion from odontoblast
- unique structure of dentine matrix
- Intertubular Dentine
- Main secretion of structural components (collagen, PGs) into pre-dentine from cell body
- Produced by matrix mediated mineralisation
- Peritubular Dentine
- Surrounds odontoblast process and encases the odontoblast tubule
- Secretion of dentine matrix rich in tissue-specific matrix components at mineralisation front WITHIN dentinal tubules (no collagen)
- High level of mineral in the dentine
characteristics of peritubular dentine and intertubular dentine
which is secreted first?
- Peritubular Dentine:
- Immediately surrounding tubule.
- Highly mineralised with no collagen
- Much stronger dentine
- Intertubular Dentine:
- Remainder of matrix rich in collagen
- Tubule first secretes intertubular dentine
- Then infills with peritubular dentine
- Higher mineralised content
- Then infills with peritubular dentine
what characteristics does dentine have? and how are these characteristics beneficial?
- elasticity
- strength and elasticity against masticatory forces
- prevents it breaking away from enamel
- small tubules
- do not let much bacteria into the matrix
- protection against erosion/insult through caries
how does dentine form in time?
- forms rhythmically
- alternatures between secretion and quiescence
- incremental lines at 90 degrees to tubules
- daily rate = 4mm/day
- lines of Von Ebner
- 5 day pattern
- Andersen lines
dentinogenesis during root formation
- Presence of mantle dentine
- Interacts with cells that make cementum
- Reflect a major interruption in the deposition of dentin due to a metabolic distruption during odontogenesis
- All signalling is different
- Significant levels of interglobular dentine
- See granular layer of tomes
what are the granular layer of tomes?
- small air spaces
- granular area in root
- just below dentine surface
- where root is covered by cementum
differences between mantle dentine and pre-dentine
Mantle dentine
- Closest layer to enamel
- Secreted by immature odontoblasts
- Mantle dentin is separated from the circumpulpal dentin by globular dentin,
Predentine
- Innermost layer
- Near pulp
draw odontoblast and dentine it forms pls
