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Oral Biology - Year 3 > Tooth development (I) Odontogenesis > Flashcards

Tooth development (I) Odontogenesis Flashcards

0
Q

What are the three phases of tooth development?

A
  1. Initiation (AKA induction)
  2. Morphogenesis (change in shape)
  3. Histogenesis (differentiation of cells)
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1
Q

What are the five basic structures within a tooth and from which histological origin do they arise?

A
  1. Enamel -> the only part with an epithelial component (enamel organ)
  2. Dentine }
  3. Cementum } -> these structures are all ectomesenchymal,
  4. Pulp chamber } derived from neural crest cells
  5. Periodontal ligament }
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2
Q

What components do you need for successful tooth development?

A

Multiple interactions between epithelial cells and ectomesenchymal cells (derived from neural crest cells) are essential for successful tooth development -> you need BOTH. Tooth development involves many growth factors and transcription factors which give rise to homeobox gene codes.

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3
Q

What are neural crest cells? From which branchial arch does tooth ectoderm arise?

A

They are pluripotent cells derived from the border of the neural plate to become ectomesenchyme.
Branchial arch 1 epithelium.

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4
Q

By what is the fate of an individual cell determined? In what order do tooth germs receive instruction?

A

Both the environment to which it migrates and then a combination of Homeobox gene expression. Epithelial-mesenchymal interactions are vital for normal tooth development. Initially the epithelium is instructive for early events which commit neural crest cells to tooth initiation (epithelium instructs mesenchyme); then the mesenchyme instructs the epithelium for tooth specificity.

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5
Q

How does the scientific community know that both neural crest cells and oral epithelium are necessary to form teeth?

A

Neural crest cells + oral epithelium = tooth

Neural crest calls + other epithelium = bone or cartilage but NO tooth

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6
Q

Expression of which transcription factor is restricted to oral/dental epithelium?

A

Pituitary homeobox 2 (PITX-2)

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7
Q

Restricted expression of which signalling protein within the dental epithelium interacts with Wnt signalling molecules to increase cell proliferation?

A

Sonic hedgehog (Shh)

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8
Q

Give an example of a Wnt signalling molecule.

A

Wnt/7b

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9
Q

Over-expression of Wnt/7b leads to…

A

Supernumerary teeth.

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10
Q

Lack of Wnt/7b leads to…

A

Complete arrest of tooth development.

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11
Q

Give examples of two proteins (not Shh, PITX-2 or Wnt) that are required for the early tooth germ to progress from bud stage.

A

Pax9 and Msx1

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12
Q

After epithelium relinquishes control, mesenchyme takes over. What happens if you swap the following components of these organs?
Skin: epithelium and mesenchyme
Tooth: epithelium and mesenchyme

A

Skin epithelium + dental mesenchyme = tooth
Dental epithelium + skin mesenchyme = skin

-> proves mesenchyme is now controlling events.

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13
Q

After epithelium relinquishes control, mesenchyme takes over. What happens if you swap the following components of these organs?
Incisor germ: epithelium and mesenchyme
Molar germ: epithelium and mesenchyme

A

Molar epithelium + incisor mesenchyme = incisor
Incisor epithelium + molar mesenchyme = molar

-> wherever the mesenchyme component came from, organ forms

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14
Q

A combination of which Homeobox genes lead to the formation of an incisor?

A

Msx-1
Msx-2
Alx-3

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15
Q

A combination of which Homeobox genes lead to the formation of an molar?

A

Dlx-1
Dlx-2
Barx-1

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16
Q

What happens in the absence of Dlx-1 and Dlx-2?

A

There is a high possibility of no maxillary molars forming.

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17
Q

What is the primary epithelial band?

A

A thickening of the oral epithelium occurring around 6th/7th week of development in utero.

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18
Q

What does the primary epithelial band divide into?

A

The band invaginates into the mesenchyme and divides into the buccal vestibular lamina and the lingual dental lamina..

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19
Q

What are the placodes on the dental lamina?

A

A dental placode is an area of thickening of the epithelium in the embryonic head ectoderm layer that gives rise to teeth.

20
Q

What are the stages of tooth development?

A

Bud stage; Cap stage; Bell stage (early and late)

21
Q

Explain the term initiation.

A

The bud stage of tooth germ formation where the enamel organ is in bud stage and the mesenchymal cells of the neural crest are condensing.

22
Q

Explain the term morphogenesis.

A

Morphogenesis is the biological process that causes an organism to develop its shape.

23
Q

Explain the term histogenesis.

A

Histogenesis is the formation of different tissues from undifferentiated cells.

24
Q

Describe the bud stage of tooth formation.

A

The enamel organ resembles a bud; the mesenchymal cells from the neural crest are condensing around the bud. The stage is poorly morphodifferentiated and histodifferentiated.

25
Q

What layers are visible histologically at the cap stage?

A
  1. Stellate reticulum
  2. External enamel epithelium
  3. Internal enamel epithelium
  4. Dental papilla
    E. Dental follicle
26
Q

Describe the cap stage.

A

By 11th/12th week in utero morphogenesis has progressed to form a cap-like structure with distinct epithelial layers within the enamel organ . The dental papilla and dental follicle are defined regions of the mesenchyme.

27
Q

Which epithelial layer is present in the early bell stage but NOT in the cap stage?

A

Stratum intermedium

28
Q

What do glycosaminoglycans do in the stellate reticulum?

A

They protect the developing tooth from mechanical pressure which cause bony defects.

29
Q

How many layers are there of the dental follicle?

A

3

30
Q

Describe the differentiation of the tooth germ in early bell stage of 14 weeks in utero.

A

Further morphodifferentiation and a high degree of histodifferentiation.

31
Q

Give an example of a transitory structure formed during the cap stage of development.

A

Enamel knot

32
Q

Give an example of a transitory structure formed in the early bell stage of tooth development.

A

Enamel cord

33
Q

What is the responsibility of the inner enamel epithelium?

A

It broadly maps out the occlusal pattern of the tooth crown.

34
Q

What may bone resorption defects result in during the early bell stage?

A

Restricted space leading to alterations in tooth shape.

35
Q

How does the enamel organ loose connection with the oral epithelium?

A

Dental lamina breaks down.

36
Q

Remnants of the dental lamina beyond the end of tooth development are known as what? What may they be involved in?

A

Epithelial pearls of Serrs - involved in the aetiology of cysts.

37
Q

What is the furthermost outer layer of the late bell stage?

A

External enamel epithelium.

38
Q

What is the point called where the internal and external enamel epithelium meet? What do these cells go onto form?

A

Cervical loop -> Hertwig’s epithelial root sheath -> root formation

39
Q

What are the two layers between the internal and external enamel epithelium at the late bell stage?

A

Stellate reticulum (at its most differentiated) and a very thin stratum intermedium layer.

40
Q

What does the internal enamel epithelium surround?

A

The dental papilla.

41
Q

What are the four layers of the enamel organ?

A
  1. External enamel epithelium
  2. Stellate reticulum
  3. Stratum intermedium
  4. Internal enamel epithelium
42
Q

What are the three layers of the dental papilla?

A
  1. Odontoblasts
  2. Fibroblasts
  3. Undifferentiated mesenchymal cells/pulp stem cells
43
Q

What does the dental papilla become?

A

Dentine and dental pulp.

44
Q

What are the layers of the dental follicle?

A
  1. Osteoblasts
  2. Cementoblasts
  3. Fibroblasts
  4. PDL stem cells
45
Q

What does the dental follicle become?

A

Alveolar bone, cementum and the periodontal ligament.

46
Q

What does the stratum intermedium and possibly the stellate reticulum become, helped by ameloblasts? What does this go on to form?

A

Reduced enamel epithelium goes onto form primary junctional epithelium and epithelial attachment.

47
Q

What are the cells of the internal enamel epithelium also known as?

A

Pre-ameloblasts

48
Q

What are the sequence of early events for the formation of enamel and dentine?

A
  • Inner enamel epithelium -> pre-ameloblasts
  • Pre-ameloblasts stimulate dental papilla to pre-odontoblasts -> odontoblasts
  • Basal lamina between them breaks down
  • Odontoblasts produce the first layer of dentine matrix (dentinogenesis)
  • Dentine stimulates pre-ameloblasts -> ameloblasts
  • Ameloblasts produce enamel (amelogenesis)
  • Amelodentinal junction is thus defined

Oral Biology - Year 3 (3 decks)

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