Amelo

• At the bell stage of tooth development, 4 distinct layers are observed:

  1. Outer enamel epithelium

  2. Stellate reticulum

  3. Stratum intermedium

  4. Inner enamel epithelium
• Outer Enamel Epithelium:

  • Cuboidal cells
  • Highly vascularized
  • Contains villi, cytoplasmic vesicles, and numerous mitochondria
• Stellate Reticulum:

  • Star-shaped cells with long processes separated by intercellular substance
  • Renders the enamel organ elastic and resistant to physical forces that may disturb amelogenesis
• Stratum Intermedium:

  • Flat and cuboidal cells
  • Controls fluid diffusion into and out of ameloblasts and contributes formative elements or enzymes
• Inner Enamel Epithelium:

  • Columnar shaped cells that differentiate into ameloblasts, which produce enamel
• Cervical Loop:

  • Where the outer and inner enamel epithelium meet at the rim of the enamel organ
  • Cuboidal cells elongate to form the Hertwig’s epithelial root sheath
• Life cycle of ameloblast:

  1. Morphologic

  2. Organizing

  3. Formative

  4. Maturative

  5. Protective

  6. Desmolytic
• Morphologic stage of ameloblast:

  • Low columnar cells with large centrally located nucleus
  • Receive nutrients from dental papilla
• Organizing stage/Differentiation stage:

  • Differentiation of odontoblasts and ameloblasts
  • Reversal of functional polarity and nutritional source
• Formative/secretory stage:

  • Mutual interaction between enamel and dentin
  • Active organelles for secretion
  • Ameloblasts migrate away from DEJ as enamel matrix is laid down
• Maturation/Maturative stage:

  • Mineralization stage after full thickness of enamel is laid down
  • Development of microvilli, numerous vacuoles, and striated border at the proximal ends of ameloblast
• Protective stage:

  • Formation of REE (reduced enamel epithelium) from OEE and IEE
  • REE separates mature enamel from surrounding connective tissue as tooth erupts
• Desmolytic stage:

  • REE produces enzymes to destroy connective tissue as tooth erupts
  • Fusion of REE and oral epithelium
• 2 processes involved in amelogenesis:

  1. Enamel matrix formation

  2. Mineralization and maturation
• Enamel Matrix Formation:

  • Starts after a thin layer of dentin is formed
  • Includes Dentinoenamel membrane, Tomes processes, and Distal terminal bars
• Mineralization and maturation:

  • Immediate partial mineralization in the 1st stage
  • Maturation stage in the 2nd stage with a further decrease of inorganic content
• Clinical considerations:

  • Factors that can disturb enamel formation: systemic diseases, nutritional deficiencies, endocrinopathies, febrile diseases, and chemical intoxications
• Excess fluoride content in the enamel can cause fluorosis, manifesting as a moth-eaten appearance
• Tetracycline may produce discoloration of enamel and dentin