dentinogenesis

Question 1

When does dentinogenesis begin?

what teeth does it begin with?

Answer 1

• 17-18 weeks
• late bell stage
• after enamel knot has disappeared
• after odontoblast differentiation
• before amelogenesis
• starts with the central incisors

Question 2

How does dentinogenesis begin in late bell stage?

Answer 2

• odontoblast differentiation starts at future cusp tip and spreads apically
• ameloblasts retreat into enamel organ

Question 3

what are odontoblasts differentiated from?

Answer 3

ecto-mesenchymal cells of the dental papilla

Question 4

How do ectomesenchymal cells/pre-odontoblasts differ from mature odontoblasts?

Answer 4

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

Question 5

Which cells signal for odontoblast differentiation?

Answer 5

Inner enamel epithelial cells

Question 6

How do IEE cells signal for odontoblast differentiation?

Answer 6

BMPs

FGFs

Question 7

how is ameloblast differentiation signalled for?

Answer 7

Occurs when IEE cells are exposed to predentine

cells are signalled to differentiate into ameloblasts

Question 8

what is competency and how is it achieved?

Answer 8

• 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.)

Question 9

are odontoblasts able to undergo cell division?

Answer 9

no, they are post-mitotic cell

no further cell division

Question 10

What is mantle dentine

Answer 10

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)

Question 11

how is mantle dentine formed?

Answer 11

• 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

Question 12

how is mantle dentine mineralised?

Answer 12

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

Question 13

how does mantle dentine differ from dentine?

Answer 13

mantle dentine

• collagen fibres are thicker
• mineralised by matrix vesicle mediated mineralisation
• made from new odontoblasts and dental papilla cells

Question 14

what occurs after mantle dentine is formed?

Answer 14

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

Question 15

What is circumpulpal dentine and how is it formed?

Answer 15

• 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

Question 16

what patterns of mineralisation are there?

Answer 16

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

Question 17

explain the levels of odontoblast secretion

Answer 17

• 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

Question 18

characteristics of peritubular dentine and intertubular dentine

which is secreted first?

Answer 18

• 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

Question 19

what characteristics does dentine have? and how are these characteristics beneficial?

Answer 19

• 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

Question 20

how does dentine form in time?

Answer 20

• 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

Question 21

dentinogenesis during root formation

Answer 21

• 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

Question 22

what are the granular layer of tomes?

Answer 22

• small air spaces
• granular area in root
• just below dentine surface
  
  • where root is covered by cementum

Question 23

differences between mantle dentine and pre-dentine

Answer 23

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

Question 24

draw odontoblast and dentine it forms pls

Answer 24