root formation

• Root development and cementogenesis

  The process of root and cementum formation
• Root development

  1. Occurs after crown formation (late bell stage)

  2. Interactions between dental follicle, epithelial root sheath, and dental papilla

  3. Coincides with tooth eruption

  
• Dental follicle

  • 3 layers in association with developing root
  • Inner layer differentiates into cementoblasts
  • Outer layer adjacent to developing alveolar bone
  • Intermediate layer possibly mesodermal in origin and contributes to periodontal ligament

  
• Root formation

  1. Junction of OEE and IEE forms cervical loop which proliferates in an apical direction

  2. Epithelial root sheath of Hertwig forms

  3. Dentine formation in the root resembles the process that occurs in the crown

  
• Cells on the internal layer of the root sheath

  Induce dental papilla cells to differentiate into odontoblasts

  
• Root sheath fragment

  Occurs after onset of root dentinogenesis

  
• Dental follicle mesenchymal cells

  Differentiate into cementoblasts and start laying down cementum

  
• Epithelial rests of Malassez

  • Remain within the periodontal ligament into adult life as a fenestrated network around root
  • They are active in periodontal repair and regeneration
  • Can give rise to odontogenic cysts

  
• In multirooted teeth, the location of ingrowths seems to be determined by areas of low vascularity

  
• Tooth eruption

  1. Starts soon after initiation of root development

  2. Formed enamel covered by a layer of reduced enamel epithelium

  3. Resorption of overlying bone

  4. Crown passes through connective tissue

  5. Outer cells of reduced enamel epithelium proliferate

  6. Degeneration of overlying fibroblasts within the connective tissue

  7. Reduced enamel epithelium fuses with oral epithelium forming a "knot" of epithelium

  8. Central cells degenerate to form an epithelial-lined pathway