AMELO222

• Life cycle of the ameloblasts can be divided into six stages based on their function:
• Morphogenic stage:

  • Ameloblasts interact with adjacent mesenchymal cells (Dental Papilla) before full differentiation
  • Cells are short and columnar with large oval nuclei
  • Golgi apparatus and centrioles located in the proximal end of the cell
  • Basal lamina separates inner enamel epithelium from dental papilla connective tissue
• Organizing stage:

  • Cells of inner enamel epithelium become longer
  • Nucleus-free zones at distal ends of cells elongate
  • Clear cell-free zone between inner enamel epithelium and dental papilla disappears
  • Preameloblasts secrete proteins similar to enamel matrix
• Formative stage:

  • Ameloblasts enter formative stage after first layer of dentin is formed
  • Development of blunt cell processes on ameloblast surfaces
  • Junctional complexes control substances passing between ameloblast and enamel
• Maturative stage:

  • Enamel maturation occurs after most of enamel matrix is formed
  • Ameloblasts slightly reduced in length and closely attached to enamel matrix
  • Ameloblasts display microvilli and cytoplasmic vacuoles during maturation
• Protective stage:

  • Enamel fully developed and fully calcified
  • Ameloblasts form reduced enamel epithelium to protect mature enamel
  • Reduced enamel epithelium separates enamel from connective tissue until tooth erupts
• Desmolytic stage:

  • Reduced enamel epithelium proliferates and induces atrophy of connective tissue
  • Fusion of reduced enamel epithelium with oral epithelium occurs
  • Epithelial cells elaborate enzymes to destroy connective tissue fibers
• Formation of the enamel matrix:

  • Ameloblasts lose projections that penetrated basal lamina
  • Islands of enamel matrix deposited along predentin
  • Amelogenin is major component of enamel matrix proteins
• Mineralization and maturation of the enamel matrix:

  • Mineralization occurs in two stages: immediate partial mineralization and gradual completion of mineralization
  • Maturation progresses from crown to cervix
  • Maturation characterized by growth of crystals in primary phase
• Age changes in teeth:

  • Attrition or wear of occlusal surfaces and proximal contact points
  • Localized increases of elements like nitrogen and fluorine in older teeth
  • Teeth may become darker and more resistant to decay
  • Reduced permeability of older teeth to fluids
• Fluoridation:

  • Incorporation of fluoride ions into hydroxyapatite crystal for acid resistance
  • Excess fluoride can lead to mottled enamel or chronic endemic fluorosis
  • Acid etching used for conditioning enamel for various dental procedures
• Pathologic amelogenesis:

  • Hypoplasia can lead to pitting, furrowing, or absence of enamel
  • Hypocalcification results in opaque or chalky areas on enamel
  • Causes of defective enamel formation can be systemic, local, or genetic
• Functions of IEE cells in tooth development and amelogenesis:

  • Establish crown morphological pattern during bell stage
  • Induce adjacent surface cells of dental papilla to differentiate into coronal odontoblasts
  • Differentiate into ameloblasts and maturation ameloblasts
  • Form reduced enamel epithelium to protect enamel surface until tooth erupts
  • Contribute to formation of dentogingival junction of teeth