Tooth development (I) Odontogenesis Flashcards
What are the three phases of tooth development?
- Initiation (AKA induction)
- Morphogenesis (change in shape)
- Histogenesis (differentiation of cells)
What are the five basic structures within a tooth and from which histological origin do they arise?
- Enamel -> the only part with an epithelial component (enamel organ)
- Dentine }
- Cementum } -> these structures are all ectomesenchymal,
- Pulp chamber } derived from neural crest cells
- Periodontal ligament }
What components do you need for successful tooth development?
Multiple interactions between epithelial cells and ectomesenchymal cells (derived from neural crest cells) are essential for successful tooth development -> you need BOTH. Tooth development involves many growth factors and transcription factors which give rise to homeobox gene codes.
What are neural crest cells? From which branchial arch does tooth ectoderm arise?
They are pluripotent cells derived from the border of the neural plate to become ectomesenchyme.
Branchial arch 1 epithelium.
By what is the fate of an individual cell determined? In what order do tooth germs receive instruction?
Both the environment to which it migrates and then a combination of Homeobox gene expression. Epithelial-mesenchymal interactions are vital for normal tooth development. Initially the epithelium is instructive for early events which commit neural crest cells to tooth initiation (epithelium instructs mesenchyme); then the mesenchyme instructs the epithelium for tooth specificity.
How does the scientific community know that both neural crest cells and oral epithelium are necessary to form teeth?
Neural crest cells + oral epithelium = tooth
Neural crest calls + other epithelium = bone or cartilage but NO tooth
Expression of which transcription factor is restricted to oral/dental epithelium?
Pituitary homeobox 2 (PITX-2)
Restricted expression of which signalling protein within the dental epithelium interacts with Wnt signalling molecules to increase cell proliferation?
Sonic hedgehog (Shh)
Give an example of a Wnt signalling molecule.
Wnt/7b
Over-expression of Wnt/7b leads to…
Supernumerary teeth.
Lack of Wnt/7b leads to…
Complete arrest of tooth development.
Give examples of two proteins (not Shh, PITX-2 or Wnt) that are required for the early tooth germ to progress from bud stage.
Pax9 and Msx1
After epithelium relinquishes control, mesenchyme takes over. What happens if you swap the following components of these organs?
Skin: epithelium and mesenchyme
Tooth: epithelium and mesenchyme
Skin epithelium + dental mesenchyme = tooth
Dental epithelium + skin mesenchyme = skin
-> proves mesenchyme is now controlling events.
After epithelium relinquishes control, mesenchyme takes over. What happens if you swap the following components of these organs?
Incisor germ: epithelium and mesenchyme
Molar germ: epithelium and mesenchyme
Molar epithelium + incisor mesenchyme = incisor
Incisor epithelium + molar mesenchyme = molar
-> wherever the mesenchyme component came from, organ forms
A combination of which Homeobox genes lead to the formation of an incisor?
Msx-1
Msx-2
Alx-3
A combination of which Homeobox genes lead to the formation of an molar?
Dlx-1
Dlx-2
Barx-1
What happens in the absence of Dlx-1 and Dlx-2?
There is a high possibility of no maxillary molars forming.
What is the primary epithelial band?
A thickening of the oral epithelium occurring around 6th/7th week of development in utero.
What does the primary epithelial band divide into?
The band invaginates into the mesenchyme and divides into the buccal vestibular lamina and the lingual dental lamina..
What are the placodes on the dental lamina?
A dental placode is an area of thickening of the epithelium in the embryonic head ectoderm layer that gives rise to teeth.
What are the stages of tooth development?
Bud stage; Cap stage; Bell stage (early and late)
Explain the term initiation.
The bud stage of tooth germ formation where the enamel organ is in bud stage and the mesenchymal cells of the neural crest are condensing.
Explain the term morphogenesis.
Morphogenesis is the biological process that causes an organism to develop its shape.
Explain the term histogenesis.
Histogenesis is the formation of different tissues from undifferentiated cells.
