Dentinogenesis

• What is dentinogenesis?

  Formation of dentin
• what is the embryonic origin of the dentine and dental pulp?

  dental papilla
• what are the stages of dentinogenesis?

  1. Odontoblast differentiation

  2. Dentine matrix production

  3. Dentine mineralisation- mantle dentine
• where does Odontoblast differentiation occur?


  Occurs in the dental papilla, along the boundary between the epithelial cells of the enamel organ and the ectomesenchymal cells of the dental papilla (some of which will become the odontoblasts)
• what occurs during Odontoblast differentiation?


  A)

  Undifferentiated cells of the dental papilla (ectomesenchyme) are attracted to the boundary by signalling molecules and growth factors originating from the epithelial cells of the developing enamel organ

  
  

  B)

  • The epithelial cells orient themselves relative to the boundary with the enamel organ

  • Ectomesenchymal cells rapidly enlarge and divide to forma a layer of at least two types of cells:

  
  

  C)

  cell type 1 produced:

  The ectomesenchymal cells adjacent to the epithelial boundary are influenced by the growth factors and signalling molecules of the epithelial cells.

  -> These ectomesenchymal cells elongate, develop organelles for protein synthesis, polarize, and differentiate into odontoblasts (F), which will secrete the dentine matrix.

  
  

  E)

  cell type 2 produced:

  cell E will remain undifferentiated (G) but in close association with the odontoblasts

  -> this is a vital source of cells that can be used to create for example reparative dentine

  
• what will the spot between the newly formed odontoblasts and the inner enamel epithelium cells become?


  it will become the EDJ
• dentine matrix production begins BEFORE enamel matrix production.

  TRUE/FALSE

  TRUE
• what occurs during Dentine matrix production?

  • Odontoblasts secrete the mantle predentine matrix (type III collagen- von Korff's fibers)

  • As odontoblasts increase in size during dentinogenesis, they begin secreting type I collagen fibrils of the circumpulpal predentine

  • These fibrils are oriented parallel to the secretory surface (unlike the vK fibers)

  • Odontoblasts do not become entombed in the collagen matrix they produce.

  • They leave behind a cellular extension (the odontoblast process) in the matrix, leading to the formation of a dentine tubule

  • The unmineralized, collagen-rich predentine matrix always separates the odontoblast layer from the mineralised dentine.

  • The mineralization of the dentine front lags behind from the production of the collagen matrix.
• what occurs during Dentine mineralisation?

  • Odontoblasts secrete matrix vesicles containing phosphate-sequestering enzymes and proteins to promote hydroxyapatite crystal growth

  • These act as "seeds" for matrix mineralization

  • Odontoblasts can continue to produce matrix vesicles that locally mineralize dentine matrix (calcospheric mineralization)

  • But they also appear to pump mineral ions into the matrix directly (linear mineralization)
• what are Incremental growth lines?

  • Lines of von Ebner:

  daily variations in dentine production

  
  

  ---> can be due to:

  Daily changes in metabolism or sleep/awake cycles

  ---> Incremental line widths in humans ~4-5 µm suggest that dentine matrix is deposited at this rate à this is variable depending on age and region of the tooth!

  ---> these lines also represent structural variations in the collagenous matrix, not the hydroxyapatite crystals

  
  

  
  

  • Andresen lines:

  multi-day incremental lines spaced 6-10 days apart

  
  

  ---> these lines represent structural variations in the collagenous matrix, not the hydroxyapatite crystals
• what forms Incremental growth lines?

  Fluctuations in odontoblast activity produces incremental growth lines that are observable in the dentine

  
  

  - there is a consistent rate at which the lines form and so they are incremental
• incremental lines are in the soft part of dentine, not the hard part.

  TRUE/FALSE

  TRUE

  - it is still present if the dentin is demineralized (turned into a soft tissue section)

  - so incremental lines are preserved in the collagen matrix of the dentine
• what are non-Incremental growth lines?

  Countour lines of Owen:

  supra-daily, non-rhythmic variations in dentine production

  
  

  - not a consistent rate at which the lines form and so they are non-incremental.
• what forms non-Incremental growth lines?


  • Physiological changes (e.g., illness)

  • Variations in nutrition (e.g., malnutrition)

  • Birth (neonatal line)

  • Can be caused by coincidence of secondary curvatures of dentine tubules during dentinogenesis, and/or hypomineralisation

  -> causes might be multiple!