Tooth organogenesis

Question 1

What is tooth organogenesis?

Answer 1

žInductive signals are exchanged between the dental epithelium and the neural crest cells

žMulti-step process culminating in the differentiation of the tissues

Question 2

What is tooth patterning?

Answer 2

žInductive signals are exchanged between the dental epithelium and the neural crest cells

žDifferent signals depending on spatial positioning

Question 3

What is the odontogenic homeobox code ‘field’ theory?

Answer 3

žDistal expression of BMP4 in oral epithelium = incisors

žProximal expression of FGF8 & FGF9 = molars

Question 4

What do BMP4 & FGF8/9 control?

Answer 4

žBMP4 & FGF8/9 control expression of homeobox genes in underlying mesenchyme

žMSX1 & MSX2 restricted to incisor region

žBARX1 & DLX2 restricted to molar region

Question 5

Define heterodont and homodont

Answer 5

• Homodont- all teeth are same shape
• Heterodont- all teeth are different shape
• Both fall in to either three families: incisiform, caniniform, maloriform.

Question 6

Which 2 models explain how different shaped teeth are formed?

Answer 6

Field and clone

Question 7

What is the field model?

Answer 7

• Factors responsible for tooth shape are in the ectomesenchyme in distinct graded and overlapping fields for each tooth family.
• The fact that each field expresses different combos of patterning homeobox genes supports this

Question 8

What is the clone model?

Answer 8

• Each tooth class is derived from a clone of ectomesenchymal cells programmed by epithelium to produce teeth of a given pattern.
• Support: Isolated presumptive first molar tissues have been shown to continue development to from 3 molar teeth in their normal positional sequence.

Question 9

Which tissue eventually assumesthe dominant role in crown pattern formation?

Answer 9

Ectomesenchymal

Question 10

What does molar development result from?

Answer 10

recombo of molar papilla with incisor dental organ

Question 11

What does incisor development result from?

Answer 11

• recombo of incisor papilla with molar dental organ

Question 12

Which genetic expression results in the formation of incisors?

Which genetic expression results in the formation of molars?

Answer 12

• Distal expression of BMP4 in oral epithelium leads to formation of incisors while proximal expression of FGF8 & FGF9 lead to the formation of molars.

Question 13

What are homeobox genes?

Answer 13

Homeobox genes are a large family of similar genes that direct the formation of many body structures during early embryonic development. In humans, thehomeobox gene family contains an estimated 235 functional genes and 65 pseudogenes (structurally similar genes that do not provide instructions for making proteins

Question 14

What causes teeth to have different shapes?

Answer 14

• Teeth develop different shapes depending on their exact position in the mouth and the pattern of homeobox genes being expressed in underlying mesenchyme.
• Knockout of DLX1/DLX2 causes loss of upper molars but not mandibular. In mandibular loss of 1 or 2 is compensated for by DLX5/DLX6