Odontogenesis

• Odontogenesis

  Tooth development

  
• Stages of odontogenesis

  1. Primary epithelial band

  2. Dental and Vestibular laminae

  3. Bud stage

  4. Cap stage

  5. Bell stage

  6. Apposition

  7. Maturation
• Primary epithelial band

  • Horse-shoe shaped thickenings of epithelium
  • Located at the future maxillary and mandibular arches
  • In the 6th week of development
  • Gives rise to dental lamina and vestibular lamina

  
• Dental lamina and vestibular lamina


  • Derived from the primary epithelial band
  • Dental lamina (lingually = teeth)
  • Vestibular lamina (buccally = vestibule)

  
• Bud stage

  1. Dental lamina grows into a bud shape penetrating the underlying ectomesenchyme

  2. Individual epithelial swellings on the deep surface of the dental lamina are recognisable

  3. Little change in shape or function of epithelial cells

  4. Presumptive enamel organs roughly spherical

  5. No morphogenesis

  6. Little histogenesis - cells have less RNA and glycogen but more oxidative enzymes than the oral epithelium

  7. Ectomesenchyme closely packed around epithelial bud

  
• Cap stage

  1. Enamel organ surrounds inner mass of dental papilla and outer mass of dental sac

  2. Proliferation of epithelial bud & invagination of the deeper surface of the epithelial bud forms the cap shape

  3. Condensation of ectomesenchyme

  4. Morphogenesis

  5. Early histogenesis

  6. Central cells of enamel organ spherical while peripheral cells become cuboidal

  
• Cap stage

  • Enamel organ cells differentiated
  • Central area of star-shaped, desmosomes, intercellular spaces
  • Outer layer cells cuboidal
  • Inner layer cells columnar
  • Proliferation of mesenchyme
  • Dental papilla
  • Dental follicle

  
• Bell stage

  1. Enamel organ differentiates into bell shape

  2. Shape has changed and epithelial component shape resembles the final occlusal shape

  3. Enamel organ now has histologically distinct components: inner enamel epithelium, stratum intermedium, stellate reticulum, outer enamel epithelium
• Inner enamel epithelium

  • Columnar cells, linked by desmosomes to each other and stratum intermedium
  • Have rich RNA content
  • Responsible for enamel formation
  • Differing mitotic rates of inner enamel epithelium cells result in folds producing the future crown shape

  
• Stratum intermedium

  • 2-3 layers of flat cells overlying internal enamel epithelium
• Stellate reticulum

  • Centre of enamel organ, separated from internal enamel by stratum intermedium
  • Star-shaped cells, obvious nucleus
  • Synthesise and secrete glycosaminoglycans into the extracellular compartment
  • Protect internal enamel epithelium and dental papilla
  • Maintain shape

  
• Outer enamel epithelium

  • Cuboidal cells on basement membrane
  • Large nuclei but small number protein synthetic organelles
  • Responsible for helping to maintain shape of enamel organ
  • Exchange of substances
• Dental papilla

  • Vascular connective tissue

  
• Dental follicle

  • Inner vascular, fibrocellular layer
  • Loose connective tissue
  • Outer layer of vascular mesenchyme

  
• During bell stage the dental lamina breaks down to leave separate tooth germs
• Enamel organs lose their connections with the oral epithelium
• Remnants of the lamina in adult mucosa adjacent teeth = Rests of Serres

  
• Enamel knot

  • Localised focus of non-dividing cells in the central part of the internal enamel epithelium
  • Forms a bulge in the dental papilla, visible during cap stage of development
  • Contributes to the enamel cord
  • May be an important centre involved in tooth development

  
• Enamel cord

  • Overlies developing incisal edge or first cusp that develops
  • Function unclear

  
• Enamel niche

  • Where the developing tooth has a double attachment to the dental lamina
  • Function unclear
  • May be sectioning artefact

  
• Bell stage

  1. Dental lamina breaks down to leave separate tooth germs

  2. Enamel organs lose their connections with the oral epithelium

  3. Remnants of the lamina in adult mucosa adjacent teeth = Rests of Serres
• Other (transitory) histological structures

  • Enamel knot
  • Enamel cord
  • Enamel niche
• Enamel knot

  • Localised focus of non-dividing cells in the central part of the internal enamel epithelium
  • Forms a bulge in the dental papilla, visible during cap stage of development
  • Contributes to the enamel cord
  • May be an important centre involved in tooth development

  
• Enamel cord

  Cells extend from the enamel knot to the outer enamel epithelium

  
• Enamel niche

  • Where the developing tooth has a double attachment to the dental lamina
  • Function unclear
  • May be sectioning artefact

  
• Tooth development

  1. Bud stage

  2. Cap stage

  3. Bell stage

  4. Apposition

  5. Maturation

  
• Dental hard tissue matrices secreted during bell stage
• Cellular processes in early odontogenesis

  • Initiation
  • Proliferation
  • Differentiation
  • Morphogenesis
  • Maturation
• Initiation

  • Induction
  • Reciprocal induction
• Epithelial-mesenchymal interactions


  • Tooth development involves interaction between epithelial and ectomesenchymal elements
  • Reciprocal induction of tissue
  • May involve chemical messengers, direct cell contact, effect of extracellular matrix

  
• At cap stage

  Dental papilla appears to control tooth development

  
• Dental papilla

  Influences tooth shape (morphogenesis)

  
• Hypothetical models of tooth development

  • Field model
  • Clone model

  
• Field model

  • Factors responsible for tooth development exist in the ectomesenchyme
  • Distinct overlapping fields for each type of tooth
  • Cells within each field express specific genes

  
• Clone model

  Each tooth class is derived from a clone of ectomesenchymal cells programmed by the epithelium to produce teeth of a different pattern

  
• Experimental recombination of molar ectomesenchyme with incisor enamel organ → molar tooth, and incisor ectomesenchyme with molar enamel organ → incisor tooth

  
• Proliferation

  • Controlled cellular growth
  • 8th Week through to maturation
  • The plane/axis of division results in thickening in certain planes
  • Differential proliferation or patterning helps shape the tooth germ

  
• Differentiation

  • Cells become more specialised
  • A change in the amount of organelles
  • A change in cell shape
  • 9th-10th weeks through to apposition
• Morphogenesis

  • Development of specific tissue structures
  • The process by which the tooth attains its shape
  • Aided by differential proliferation and inhibition
  • 9th to 10th weeks through to apposition

  
• Maturation

  • Attainment of adult/final function and size
  • Complete mineralisation of dental hard tissues
  • Aided by all the other cellular processes
  • Various times