Dentinogenesis

Dentinogenesis

1. Odontoblast differentiation

   • Ecto-mesenchymal cells of DP -> OD
   • Pre-OD to OD transformation - STRUCTURE RELATED TO FUNCTION
   • 1) IEE induces DP -> OD (BM presents signal via growth factors)
     • RECIPRICOL INDUCTION
     • Signal is required but also cells must have undergone certain number of cell divisions to be COMPETENT to receive the signal.
   • 2) OD secrete first pre-dentine, causes DBM to breakdown
   • 3) Pre-dentine is now in contact with IEE, causes IEE -> Ameloblast
     • RECIPRICOL INDUCTION
   • OD's are said to be post-mitotic - cannot proliferate further

2. Dentine secretion

   • MANTLE dentine (first formed)
     • Matrix contributions come from newly differentiated odontoblasts and cells of the dental papilla
     • Mantle dentine is mineralised by MATRIX vesicles as OD have not fully developed the ability to mineralise dentine yet.
   • Circumpulpal dentine
     • As the OD secrete matrix, they move pulpally (downwards), leaving a single OD process in dentinal tubule running through matrix. This permits communication with rest of matrix.
     • S-shape in crown, Straight course in root
     • Two main sites (vary in composition, not just orientation - > i.e. different to prismatic/interprismatic variations of enamel)
     • ITD - inbetween the tubules - rest of the matrix that isn't PTD. Secretion of COLLAGEN + PG's into PreD from CELL BODY of OD - NOT secretory process. Essentially -> a collagenous matrix.
     • PTD - immediately surrounding the tubular process of OD. Secretion of tissue specific matrix components at mineralisation front - e.g. PG's + phosphoproteins. LACKS collagenous fibres of ITD. >15% more mineralised. Essentially -> highly mineralised, ground substance rich matrix.

3. Background info

   • Begins at 17-18 weeks in utero
   • LATE bell stage in tooth development
   • Starts at cusp tips (gradient of secretion cervically - same as enamel)
   • Dentine secretion begins straight after DP -> OD
   • OD always on FORMATIVE SURFACE (OD-preD-Dentine)
   • Vital tissue - important to maintain D/P complex for functional dentition/tooth

4. Types of dentinogenesis

   • Primary dentine - until completion of root formation
   • Secondary dentine - much more slowly secreted than primary dentine. Secreted throughout life -> leads to pulp chamber occlusion.
   • Tertiary dentine (REACTIONARY) - if OD's survive caries attack
   • Tertiary dentine (REPARATIVE) - if OD's killed, generation of new OD-like cells to produce 3° dentine

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