Tooth Morphogenesis

Question 1

What tooth type is present in humans but not mice?

Answer 1

Premolars

Question 2

When is the tooth type determined?

Answer 2

Initiation stage

Question 3

When does the homeobox code activate in the lower jaw?

Answer 3

6 weeks in utero

Question 4

What are homeobox genes?

Answer 4

Genes with ‘homeobox domains’ within their sequence which combine to other parts of DNA to control expression of other genes

Question 5

Where in the dental mesenchyme is Barx1 expressed during the initiation stage?

Answer 5

Molar region

Question 6

Where in the dental mesenchyme is Msx1 expressed during the initiation stage?

Answer 6

Incisor region

Question 7

In the shrew, what do the levels of Barx1 determine?

Answer 7

Number of cusps (high levels = more cusps)

Question 8

What is the function of the homeobox code in the context of teeth?

Answer 8

Decides what tooth (gene) and how complex (level)

Question 9

In what tissue are homeobox genes expressed?

Answer 9

Dental mesenchyme

Question 10

When does the PEK appear?

Answer 10

Bud stage

Question 11

What causes the formation of the PEK?

Answer 11

Signals from mesenchyme: BMP4 and activin

Question 12

What do FGF4 and SHH do (PEK)?

Answer 12

Stimulate growth of dental epithelium to form cap shape

Question 13

What two factors are important in moving from the bud stage to the cap stage?

Answer 13

Juxtaposition of proliferating and non-proliferating cells

Rearrangement of cells (involves focal adhesion kinases)

Question 14

What happens if focal adhesion kinases are lost?

Answer 14

Cells cannot rearrange in bud so cap stage is not reached

Question 15

How is the PEK lost?

Answer 15

Apoptosis

Question 16

What molecule is involved in apoptosis of the EK?

Answer 16

BMP4 (in EK)

Question 17

What does the number of SEKs determine?

Answer 17

Number of cusps

Question 18

What does the timing of initiation of SEKs relate to?

Answer 18

Height of the cusps formed

Question 19

How could you increase cusp number?

Answer 19

Stimulate enamel knot-inducing pathways using activin, EDA, SHH

Question 20

What makes a tooth more likely to have a cusp of Carabelli?

Answer 20

Larger crown area with more compact cusps

Question 21

Why might bigger jaws result in larger teeth?

Answer 21

Alveolar bone surrounding tooth can give more space

Question 22

How does hypohidrotic ectodermal dysplasia affect the teeth?

Answer 22

Reduced number (hypodontia)

Flattened cusps (strange peg-shaped morphology)

Abnormal enamel knot shape

Question 23

What does ectodysplasin A do in tooth development?

Answer 23

Binds to EDAR in EK to turn on EDARADD (EDAR-associated death domain protein)

Question 24

What do enamel knots express? (5)

Answer 24

EDAR

FGF4

P21

SHH

WNT10B

Question 25

What does overexpression of EDAR cause?

Answer 25

Too many SEKs

Additional sharp cusps

Severe enamel defects

Question 26

What happens if the PEK is too small?

Answer 26

Reduced folding so shallower and fewer cusps