Tooth Morphogenesis Flashcards
What are the 2 stages of tooth development where the tooth is physically created?
Cap and bell
Tooth development: Explain the tissues present at each stage
Bud - mainly neural crest derived mesenchyme and the oral epithelium (ectoderm) sitting above. Some condensing mesenchyme.
Cap - same as before except there is lot more condensing dental mesenchyme
Bell - the presence of odontoblasts and ameloblasts
Erupted tooth - enamel and dentine here
Explain the role of the homeobox code
6 weeks into human embryo all the teeth look the same.
The homeobox code adds gene expression. Transcription factors are produced here which bind to the DNA to cause changes in tooth shape.
What is the typical gene which defines cusp number?
Barx1 - the more complex the tooth, the higher the level.
Give the conclusions on tooth shape formation
- Tooth type is determined very early on in development prior to any morphological sign of tooth development
- The tooth type that forms depends on the expression of homeobox genes in the mesenchyme into which the tooth germ invaginate.
- The developing tooth reads the level of expression of the genes
- Although mice do not have premolar teeth, the information regarding their patterning is still in place
- The homeobox predates the development of the heterodont dentition and was co-opted to be used in tooth patterning.
The role of the enamel knot in tooth shape - explain the initiation
- The primary enamel knot is induced at the bud stage of tooth development by signals from the mesenchyme
Group at cells at the tip of the bud turn on a load of signals. A host of genes are turned on at the bud stage
What happens to the role of the enamel knot at the cap stage?
Cap stage - Role of the enamel knot as a signalling centre
The primary enamel knot expresses a number of signalling molecules.
What genes stimulate growth and proliferation of dental epithelium?
Fgf4 and Shh
Signals pumped out create the cap shape from bud shape.
What can happen to some growth factors from the enamel knot?
Expresses them but does not express the receptors so cannot respond to its own signal
Give details on the proliferation stage
Where does the dental papilla form from?
High proliferation outside the enamel now and low within it. This results in folding of the dental epithelium.
The cap stage is formed by the enamel knot not dividing.
Flatterning out of the bottom of the tooth which is not causes by proliferation. Proliferation increases the size but not any change in shape.
The dental papilla forms from a small population of mesenchymal cells position under the enamel knot.
What happens to the enamel knot after the cap shape?
Silencing of the signalling centre: death of the enamel knot in apoptosis
The enamel knot is a transient structure.
Bmp4 in the enamel knot stimulates cell death in these cells leading to eventual los of the enamel knot and silencing of the signalling centre.
How many enamel knots do the teeth have?
Premolars and incisors have PEK
Only molars go on to develop secondary and tertiary ones.
What does the formation of the secondary enamel knots do in molar teeth?
Act to control cusp morphogenesis.
At the tips of cusps we get growth factors. This creates new enamel knots to generate more signalling molecules, This created the complex shape fo the tooth.
How many pockets of expression of Fgf4 do we get in secondary enamel knots and what stage?
2 pockets
Late cap stage
What does the lay out of the secondary and tertiary enamel knot determine?
The final cusp pattern.
