Early Tooth Development

• What signalling is essential for bud-to-cap transition?

  BMP signalling

  
• What is the primary enamel knot?

  A structure which is histologically visible as a localised mass of cells at the centre of the inner enamel epithelium which will act as a signalling centre for crown development
• What can be identified in the late cap stage in terms of cell types?

  4 distinct cell populations in the enamel organ:Stellate reticulum- formed by central cells (star-shaped cells separated by large intercellular spaces)Inner enamel epithelium- formed from columnar cells & ameloblasts will differentiate from hereOuter enamel epithelium- the cells of the cap in contact with the dental follicle (cuboidal cells) form thisStratum intermedium- contains flattened cells lying perpendicular to those of the inner enamel epithelium
• Where does the epithelium get its nutrients from?

  Blood vessels present in the mesenchyme at the interface between the epithelium and the mesenchyme
• Is the epithelial part of the tooth germ avascular?


  Yes, like all epithelia in the body
• What will the dental follicle give rise to?

  Cementum

  Periodontal ligament

  Alveolar bone socket
• What will the dental papilla give rise to?

  Dentin

  Dental pulp
• What can be identified at the late cap stage in terms of mesenchyme?

  2 populations of condensed mesenchyme:

  Dental papilla- condensed mesenchyme lying beneath the epithelial cap

  Dental follicle- condensed mesenchyme that surrounds the tooth germ
• What happens in the 12th week of embryonic development?

  Late cap stage. Characterised by deeper epithelial folding

  
• What happens in the 11th week of embryonic development?

  Early cap stage

  
• How does the cap shape change to a bell shape?

  Epithelial folding increases, leading to a bell stage where you can recognise the shape of the future tooth crown by looking at the shape of the dental mesenchyme that's enclosed within the epithelium
• How does the bud shape change to a cap shape?

  The tip of the epithelial bud folds inwards & the condensed mesenchyme becomes progressively enclosed inside the dental epithelium
• What is tooth morphogenesis?

  Determination of tooth crown shape by epithelial folding- due to a combination of cell proliferation & cell movements
• What does the bud stage look like from a sagittal view?

  
• What does the bud stage look like from a coronal view?

  
• What does condensation of the mesenchyme result from?

  Increase in cell proliferation
• Describe the bud stage of tooth development.

  Mesenchyme around the epithelial bud condenses and is called the dental mesenchyme

  
• What will the epithelial swellings and dental lamina then do?

  Proliferate and will successively acquire the shape of a bud, cap and bell
• What is 1 of the early changes that takes place in the mesenchyme that surrounds the epithelial placodes?

  Expression of transcription factor Pax9- it labels the site of tooth developments
• What does a lack of Shh signalling lead to?

  Arrest of tooth development

  
• What does ectopic Shh in a diastema lead to?

  Ectopic tooth thickening
• What is a diastema?

  Space between teeth
• How was it shown that signals from the oral ectoderm control tooth initiation?

  
• What are these epithelial thickenings also known as?

  Dental placode
• What does each epithelial swelling correspond to?

  A developing deciduous tooth
• What happens at 8th week of embryonic development?

  Initiation of tooth formation at specific sites of the dental lamina. A series of swellings develop on the deep surface of the dental lamina
• What does the dental lamina then do?

  Elongate
• What does each primary epithelial band give rise to (6th-7th week)?

  2 subdivisions:

  Vestibular lamina on the buccal side

  Dental lamina on lingual side
• What is the formation of the epithelial thickening a result of?


  A change in orientation of cleavage plane of dividing cells
• What does the primary epithelial band correspond to?

  A thickening of the oral epithelium
• What is the primary epithelial band?

  Continuous band of thickened epithelium which forms in the position of the future dental arches
• What does the initiation stage start with?

  The formation of the primary epithelial band at ~6 weeks of embryonic development along the oral side of the maxilla & mandible
• Where do teeth form?

  On the oral side of the 1st branchial arch & frontonasal process
• What is Treacher Collins syndrome and how is it characterised?

  Associated with mutation in TCOF1 gene essential for NCC survival

  Defects in structures derived from 1st & 2nd branchial arches so:

  Hypoplastic maxilla & mandible

  Lower eyelid coloboma

  Cleft palate

  Ear defect

  Tooth agenesis in 33% of cases
• Are CNCCs multipotent cells?

  Yes

  
• What is EMT?

  Epithelial to mesenchymal transition. NCCs undergo this process as they originate from ectodermal epithelium and then they transform into mesenchymal cells
• What do cranial neural crest cells (CNCCs) do?

  Delaminate at the border of the neural & non-neural ectoderm. They migrate in streams from the neural folds into the branchial arches
• How do we know there is epithelial-mesenchymal communication?


  Because when they were separated from each other, no tooth was produced
• What is epithelial-mesenchymal communication?

  During tooth development, there is constant and reciprocal interactions between the oral epithelium and mesenchyme
• What will the mesenchyme give rise to?

  Dentin

  Dental pulp

  Cementum

  Periodontal ligament

  Alveolar bone socket