AMELOGENESIS

• Epithelial Enamel Organ consists of:

  • Outer Enamel Epithelium
  • Stellate Reticulum
  • Stratum Intermedium
  • Inner Enamel Epithelium
  • Cervical Loop
• Life Cycle of Ameloblasts includes stages:

  • Morphogenic Stage
  • Organizing Stage
  • Formative Stage
  • Maturative Stage
  • Protective Stage
  • Desmolytic Stage
• Morphogenic Stage characteristics:

  • Cell Short Columnar
  • Large oval nucleus
  • Golgi apparatus and mitochondria located at proximal end
• Organizing Stage changes:

  • Cells become longer
  • Reversal of Polarity occurs by migration of Golgi apparatus and centrioles
  • Nuclei shifts to the proximal part of the cell
  • Amount of Rough E. R. increases
  • Basal lamina supporting ameloblasts disintegrates after dentin formation
  • Change in nutritional supply of ameloblasts occurs
• Formative Stage details:

  • Starts after first layer of Dentin is laid down
  • Development of a blunt process occurs on ameloblast surface
  • Penetrates basal lamina to enter predentin
• Maturative or Mineralizing Stage features:

  • Enamel maturation occurs after most of Enamel Matrix is laid down
  • Ameloblasts are slightly reduced in length with appearance of microvilli
  • Organelles associated with formation of enamel are enclosed in phagocytic vacuoles and digested by lysosomal enzymes
• Protective Stage information:

  • After mineralization of Enamel is complete, ameloblasts lose their striated border and shape
  • Form the reduced enamel epithelium over the newly formed enamel to prevent connective tissue contact until eruption
• Desmolytic Stage effects:

  • Reduced enamel epithelium induces atrophy of connective tissue
  • Premature degeneration can result in soft tissue impaction of tooth
• Amelogenesis consists of two processes:

  • Formation of Enamel Matrix
  • Mineralization
• Development of Tomes Processes:

  • Ameloblasts' surface is rough and inter-digitates with enamel rods
  • Projections into enamel Matrix are called Tomes’ Processes
  • Secretion of Enamel matrix occurs via narrow channels
• Distal Terminal Bars:

  • Separate Tomes processes from cell proper
  • Localized condensations of cytoplasmic substance
  • Closely associated with thickened cell wall
• Mineralization and Maturation of Enamel Matrix occurs in two stages:

  • First stage: partial mineralization of matrix segments
  • Second stage or maturation: completion of mineralization
• Clinical Considerations include:

  • Enamel Caries
  • Cavity Preparation
  • Shade Selection
  • Acid Etching
  • Fluoridation
  • Bleaching
  • Lateral Spread of Caries at DEJ
  • Dens Invaginatus