CFD 12 - odontogensis 1a

Question 1

What is histogenesis?

Answer 1

differentiation of undifferentiated cells to make new tissues

Question 2

What is the vestibular lamina?

Answer 2

contributes to the vestibule of the mouth, delineating the lips and cheek from the teeth, formation of sulcus

Question 3

What are the stages of tooth development?

Answer 3

1. initiation stage
2. bud stage
3. cap stage
4. bell stage
   4/5. crown stage (late bell stage)

Question 4

What is the external enamel epithelium?

Answer 4

outer layer of cuboidal cells that limites the enamel organ

Question 5

What is the stellate reticulum?

Answer 5

of epithelial origin but behave like mesenchymal cells
- synthesis of collagen I, II and III

Question 6

What is the stratum intermedium?

Answer 6

two or three layers of cells sitting above IEE
- express Alkaline Phosphatase like SR but not IEE

Question 7

What is the inner enamel epithelium?

Answer 7

columnar shaped cells rich in RNA
- connected by desmosomes to each other

Question 8

What is ectomesenchyme?

Answer 8

interesting group of cells whose origin is very controversial
- some think neural crest others mesodermal somites

Question 9

At what point in development does an area get ready for a tooth to develop?

Answer 9

around week 6

Question 10

What happens during week 6 of development to get the area ready for tooth development?

Answer 10

• condensation of ectomesenchyme and a primary epithelial band being formed
• the band is starting to push inwards towards this condensation of mesenchyme

Question 11

What does the primary epithelial band give rise to?

Answer 11

• dental lamina
• vestibular lamina

Question 12

What does the vestibular lamina do?

Answer 12

• grows and then breaks down
• forms vestibule between teeth and lips/cheeks (the sulcus)

Question 13

When the primary epithelial band pushes in, what causes the condensation of the mesenchyme to be triggered?

Answer 13

Fgf8

Question 14

What do signals coming from the labial/buccal side of the primary epithelial band form?

Answer 14

the vestibular lamina

Question 15

What do signals coming from the lingual side of the primary epithelial band form?

Answer 15

the dental lamina

Question 16

By week 7 of development, what is the dental lamina doing?

Answer 16

interacting with the ectomesenchyme

Question 17

By week 7 of development, what is the vestibular lamina doing?

Answer 17

pushing down and migrating into the mesenchyme, and proliferating quite a lot

Question 18

By week 8 of development, what are the 2 distinct things going on in terms of tooth development?

Answer 18

• the bud of the dental lamina growing down, interacting with and causing the ectomesenchyme to start differentiating as well
• the vestibular lamina continuing to grow

Question 19

By week 9 of development, what is happening in terms of tooth development?

Answer 19

signals have told the cells in the vestibular lamina to start dying off

Question 20

By week 12 of development, what is happening in terms of tooth development?

Answer 20

• the cells of the vestibular lamina have died off, leaving a gap (the labial/buccal sulcus or vestibule)
• dental lamina is going through more and more processes for tooth formation

Question 21

What are the 3 overlapping phases of tooth development?

Answer 21

initiation, morphogenesis and histogenesis

Question 22

What 2 things are there interactions between during tooth development?

Answer 22

epithelium (ectoderm) and mesenchyme (ectomesenchyme)

Question 23

What does the epithelium (ectoderm) give rise to?

Answer 23

• enamel
• hyaline layer of the root

Question 24

What does the mesenchyme (ectomesenchyme) give rise to?

Answer 24

• dentine
• pulp
• cementum
• periodontium - PDL and bone

Question 25

When and where are the first signs of initiation of tooth development?

Answer 25

- first signs: 6 weeks iul - localised epithelial thickening in incisor and molar regions

Question 26

Which tissue initiates tooth development?

Answer 26

- epithelium initiation has the odontogenic potential, *then* the ectomesenchyme - 1st arch epithelium is what generates the initial signal (tissue recombination experiments)

Question 27

Describe the bud stage of the tooth germ

Answer 27

- initiation of epithelial proliferation down into the mesenchyme causing the mesenchyme to condense into a small bell type shape - **looks like a small bud or droplet**

Question 28

Describe the cap stage of the tooth germ

Answer 28

- migration and proliferation within the mesenchyme by the epithelium and starting to surround the condensed ectomesenchyme of this area - signals are going backwards and forwards between the two tissues, so you're getting an interaction and different layers of the enamel organ which are going to form the pulp and the periodontium (the follicle) - **looks like a hat**

Question 29

Describe the bell stage of the tooth germ

Answer 29

- starting to get the shape of the tooth, differentiation in middle and around it - the signals going on between these 2 areas are quite intense, and we’re seeing what’s being made and what’s forming - matrix is starting to be formed **looks the shape of a tooth**

Question 30

Describe the late bell stage of the tooth germ

Answer 30

- dental lamina becomes removed from the external source so the tooth is now in an area of its own and is differentiating through

Question 31

Describe the crown stage of the tooth germ

Answer 31

- starting to get hard tissue formation, dentin and enamel being formed - more and more enamel and dentine being formed as we progress through, and the enamel organ starts to shrink and push down as the hard tissue growth - **at this point almost ready for tooth eruption**

Question 32

What are they components of the tooth germ?

Answer 32

- enamel organ - dental papilla - dental follicle

Question 33

During the bud stage, what cell processes etc are happening?

Answer 33

No differentiation, mainly proliferations and interactions between the dental lamina and the dental papilla

Question 34

During the cap stage, what cell processes etc are happening?

Answer 34

- cells of enamel organ still poorly differentiated epithelial cells, but they are interacting with the cells of the condensed ectomesenchyme - there is some differentiation beginning to happen

Question 35

During cap stage, what is happening to the dental lamina?

Answer 35

growing down but still attached to the oral epithelium

Question 36

During the bell stage, what is happening to the dental lamina?

Answer 36

starting to shrink, it’s served its purpose and is now starting to disappear

Question 37

During the bell stage, what is happening to the dental papilla?

Answer 37

it is differentiated

Question 38

During the bell stage, what is happening to the outer mesenchyme?

Answer 38

Outer mesenchyme now becoming the dental follicle and is starting to surround and differentiate round the enamel organ

Question 39

By the bell stage, what are the 4 distinct layers of the enamel organ?

Answer 39

- inner enamel epithelium - stratum intermedium - stellate reticulum - outer enamel epithelium

Question 40

By early bell stage, what has the ectomesenchyme differentiated to into?

Answer 40

- the dental papilla - the dental follicle

Question 41

What does the dental papilla form?

Answer 41

odontoblasts (dentine) and pulp

Question 42

What does the dental follicle form?

Answer 42

cementum, PDL, and alveolar bone

Question 43

What does the basal lamina of the inner enamel epithelium conform to?

Answer 43

future ADJ

Question 44

What are the cells of the inner enamel epithelium like?

Answer 44

columnar cells at cusp tips

Question 45

What is the role of the inner enamel epithelium?

Answer 45

forms ameloblasts —> enamel

Question 46

What are the cells of the stratum intermedium like?

Answer 46

flattened cells

Question 47

What is the role of the stratum intermedium?

Answer 47

synthesis and transport to and from IEE - make matrix growth factors to allow them to interact and go on to form what they are

Question 48

What are the cells of the stellate reticulum like?

Answer 48

star shaped - lots of desmosomes - fluid filled extracellular space - osmotic gradient due to extracellular GAGs

Question 49

What is the role of the stellate reticulum?

Answer 49

maintenance of shape and protection of enamel organ once it’s formed

Question 50

What are the cells of the outer enamel epithelium like?

Answer 50

cuboidal cells

Question 51

What is the role of the outer enamel epithelium?

Answer 51

maintenance of shape and exchange - allow exchange between the ectomesenchyme and the enamel organ

Question 52

What are cells rests and cell nests?

Answer 52

- left after the break down of the dental lamina - have cystic potential

Question 53

What are the 3 transitory structures of the tooth germ?

Answer 53

- enamel knot - enamel niche - enamel septum

Question 54

What is the enamel knot?

Answer 54

area of developing enamel which seems to send out signals

Question 55

What is the enamel niche?

Answer 55

as dental lamina starts to break down, a hole or depression can be seen

Question 56

What is the enamel septum?

Answer 56

seems to form between the outer and inner enamel epithelium

Question 57

By what week of development is bud stage seen?

Answer 57

8th week

Question 58

By what week of development is cap stage seen?

Answer 58

11th week

Question 59

By what week in development is bell stage seen?

Answer 59

14th week

Question 60

By what week in development is late bell stage seen (dental lamina is starting to break down)?

Answer 60

17th week