L4-Tooth Development 1 (Odontogenesis)

Question 1

At ~5 wks the epithelial bands form in upper and lower jaws. What does this site mark?

Answer 1

The epithelial bands are sites of future tooth development

Question 2

If the teeth form from epithelial bands what role do ectomesenchyme cells play in tooth development?

Answer 2

Ectomesenchyme cells have the ability to signal epithelial layer to thicken and begin tooth development.

Question 3

What do the dental and vestibular lamina form? Which is closer to the midline?

Answer 3

Dental lamina forms teeth. Closest to midline

Vestibular lamina forms space.

Question 4

The three stages of Odontogenesis are named for the morphological appearances of the teeth. What are the first three stages in tooth development?

Answer 4

1. Bud stage. 6-8 wks. Ingrowth.
2. Cap stage. 8-12 wks. Morphogenesis.
3. Bell Stage. 12-16 wks. Differentiation.

Question 5

In what stage of tooth development do epithelial cells move into the underlying ectomesenchyme, followed by the ectomesenchyme cells packing closer together around the bud?

Answer 5

Bud stage. 6-8 wks. Ingrowth.

Question 6

The process of CONDENSATION during the Cap stage forms what?

Answer 6

The ectomesenchymal dental papilla. During the cap stage of odontogenesis the ectomesenchyme aggregates around the enamel (dental) organ to form the dental papilla.
Ectomesenchyme also forms the dental follicle (sac), which surrounds the enamel organ and dental papilla.

Question 7

What structure that forms within the enamel organ during late cap stage signals the formation of cusps? What cell type is this structure composed of? What happens after signal is transduced?

Answer 7

The ENAMEL KNOT, formed by epithelial cells within the enamel body, signals the formation of cusps. Specifically, the shape & number of cusps. After signal is transduced the enamel knot undergoes apoptosis.

Question 8

What gene is expressed by the enamel knot that is essential for cusp formation?

Answer 8

Fgf-4.

Question 9

Epithelial cell differentiation is a major part of the Bell stage. What 4 types of epithelial cells are observed during bell stage? What is the cell shape?

Answer 9

1. Outer dental epithelium - cuboidal cells
2. Stellate reticulum - star shaped cells
3. Stratum intermedium - several flattened layers
4. Inner dental epithelium - short columnar cells

Question 10

The inner dental epithelium formed during the bell stage has a storage form of energy that is the energy source for tooth development. What is it?

Answer 10

Glycogen

Question 11

The Inner dental epithelial cells and the dental papilla cells that are back to back against the basement membrane stop proliferating, reverse polarity and through a two step process become what cells? This process forms what junction?

Answer 11

After the reversal of polarity, the Inner Dental Epithelial cells become Preameloblast cells and the Dental Papilla cells attached to the basement membrane become Odontoblast cells (make dentin). Then the preameloblast cells become ameloblast cells (make enamel).
-This forms the DEJ.

Question 12

Which epithelial cell type folds according to tooth type during the bell stage?

Answer 12

The Inner Dental Epithelium

Question 13

What happens to the dental lamina during the bell stage of tooth development?

Answer 13

Breaks down cutting connection with oral epithelium.

Question 14

During the late bell stages the stellate reticulum is reduced in thickness at locations of mineral formation. Why might this be?

Answer 14

Thought to bring outer dental epithelium closer to sites of tooth formation for access to blood supply (nutrition).

Question 15

Permanent molar tooth germs begin to develop how?

Answer 15

When the dental lamina burrows back from the second premolar to the first molar then second then third.

Question 16

Reciprocal reactions, such as the FGF8, Pax9, BMP4 reaction, are important in determining the location at which teeth will develop. How does the Pax9 reaction represent this?

Answer 16

Pax9, a transcription factor, is important in initiation of tooth development. When produced by FGF8, Pax9 will cause tooth develpoment. However, FGF8 will only produce Pax9 in the absence of BMP4 (bone morphogenetic protein), which antagonistically reacts with FGF8. Thus, both Pax9 and BMP4 reciprocally control where tooth development occurs.