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BDS2: Oral Biology > Dental Development > Flashcards

Dental Development Flashcards

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1
Q

What are the three embryonic layers from which all body tissues are developed?

A
  1. Ectoderm
  2. Mesoderm
  3. Endoderm
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2
Q

Where is tooth enamel derived from?

A

Ectoderm

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3
Q

Where do all other parts of the teeth (except enamel) derive from?

A

Ectomesenchyme

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4
Q

What is the ectomesenchyme?

A

Part of the ‘neural crest’ that develops beside the primitive nervous system (ectoderm)

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5
Q

Briefly describe the neural crest

A
  1. A 4th cell type forms between the ectoderm and the neural tube
  2. It is called the neural crest
  3. Neural crest tissue is also known as ‘ectomesenchyme’
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6
Q

What part of the body does the neural crest migrate and develop into?

A

The developing face and jaws

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7
Q

What condition occurs when ectomesenchymal cells fail to migrate?

A

Mandibulofacial Dysostosis

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8
Q

What problems can occur in mandibulofacial Dysostosis?

A
  1. Increased inter pupillary space
  2. Position of the ears is lower than usual
  3. No formation of the ears
  4. Reduced mandible and maxilla size
    - results in overcrowding (associated with other deficiencies)
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9
Q

What are the 5 stages of tooth development?

A
  1. Initiation
  2. Morphogenesis
  3. Cytodifferentiation
  4. Matrix secretion
  5. Root formation
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10
Q

What 3 features are present in tooth initiation in a 5-6 week human embryo?

A
  1. Maxillary process
  2. Stomodaeum
  3. Mandibular process
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11
Q

What is the embryonic mouth also known as?

A

Stomodaeum

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12
Q

When does the primary epithelial band develop and how does it appear?

A
  • Approx 6 weeks of intra uterine life

- Appears as a thickening in epithelium of embryonic mouth

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13
Q

What is the primary epithelial band known as after thickening has occurred?

A

Dental lamina

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14
Q

When does the dental lamina develop?

A

Approx 7 weeks IUL

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15
Q

What develops from the dental lamina?

A

Enamel organ

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16
Q

When the dental lamina develops, the PEB has grown into the jaw and divided into two parts:

A
  1. Vestibular lamina
    - breaks down to form the buccal sulcus
  2. Dental lamina
    - from which enamel organ develops
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17
Q

Describe the appearance of the dental lamina after 8 weeks IUL

A

Horse shoe shaped structure with thick regions known as tooth germs

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18
Q

What is the first stage of morphogenesis known as?

A

‘Bud’ stage

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19
Q

When does the bud stage occur?

A
  • 8-10 weeks IUL
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20
Q

Briefly describe what happens in the bud stage

A
  1. Dental lamina thickens into a ‘bud’ stage which is known as the enamel organ
  2. An ectomesenchymal condensation appears and this is the dental papilla
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21
Q

What occurs after the bud stage?

A

Cap stage

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22
Q

When does the cap stage occur?

A

11 weeks IUL

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23
Q

Briefly describe the cap stage

A
  1. Enamel organ forms a ‘cap’ over the papilla
  2. ‘Cap stage’ enamel organ:
    - external enamel epithelium
    - internal enamel epithelium
  3. EEE and IEE meet at the cervical loop
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24
Q

What disease is associated with absence of some teeth?

A

Hypohidrotic ectodermal dysplasia

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25
Q

What other tissue formation is affected by severe hypohydrotic ectodermal dysplasia?

A

Absence of hair

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26
Q

What treatment options are available for genetic disorders such as HED?

A

Gene therapy

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27
Q

What is the first stage of cytodifferentiation?

A

Bell stage

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28
Q

When does the bell stage occur?

A

14 weeks IUL

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29
Q

Briefly describe the bell stage

A
  1. More cell layers differentiated

2. Tooth shape is being defined

30
Q

What are the 4 cell layers of the bell stage enamel organ?

A
  1. External enamel epithelium
  2. Internal enamel epithelium
  3. Stratum Intermedium
  4. Stellate reticulum
31
Q

What molecule is present in the stellate reticulum during the early bell stage?

A

Glycogen

32
Q

When does the dental lamina for the permanent successor appear?

A

12 weeks IUL

33
Q

What does the dental lamina for the permanent successor look like?

A

An extension on the lingual side of the dental lamina

34
Q

What significant feature develops after approx 16 weeks IUL

A

The 1st permanent molar germ develops a backwards extension of the dental lamina

35
Q

When does the enamel organ late bell stage occur?

A

18 weeks IUL

36
Q

Briefly describe the late bell stage

A
  1. Crown shape is well defined

2. Apposition of enamel and dentine begins

37
Q

What happens to dental cells adjacent to the IEE

A

They differentiate into odontoblasts

38
Q

What happens to IEE cells after dentine formation has begun

A

They differentiate into ameloblasts which form enamel

39
Q

What function do the newly differentiated odontoblasts carry out?

A

They lay down dentine matrix (mainly collagen) which is later mineralised

40
Q

What term is given to the unmineralised dentine?

A

Predentine

41
Q

What causes mineralisation of dentine?

A

Hydroxyapatite

42
Q

What percentage of enamel is mineralised?

A

96%

43
Q

Briefly Describe the two main stages of enamel formation

A
  1. Protein matrix deposited
    - matrix is partially mineralised (30%)
  2. Once this framework is established, the organic part is removed and mineralisation is completed (maturation)
    - the ameloblasts change form and function several times during amelogenesis
44
Q

List the stages of amelogenesis

A
  1. Morphogenic
  2. Histodifferentiation
  3. Secretory (initial)
  4. Secretory (tomes process)
  5. Maturative (ruffle ended)
  6. Maturative (smooth)
  7. Protective
45
Q

Describe the ameloblast appearance during ameloblast differentiation

A
  1. Dentine induces IEE cells to differentiate into ameloblasts
  2. They elongate, becoming columnar
  3. The nucleus migrated to the basal end of the cell
46
Q

Describe the ameloblasts during the secretory phase

A
  1. Ameloblasts become secretory cells
  2. They synthesise and secrete the enamel matrix proteins (amelogenins)
  3. The matrix is partially mineralised (30% mineral as seeded crystallites)
47
Q

Briefly describe the maturation phase of amelogenesis

A
  1. Most matrix proteins are removed
  2. Mineral content of enamel is increased
  3. Mature enamel is 95% mineral
48
Q

Briefly describe the protection phase of amelogenesis

A
  1. Ameloblasts regresa to form a protective layer - the reduced enamel epithelium
  2. Involved in eruption
  3. Formation of epithelial attachment (due to enamel epithelium reduction)
49
Q

Describe Autosomal recessive hypoplastic hypomaturation amelogenesis imperfecta

A
  1. Matrix Metallopeptidase 20 gene or MMP20
  2. Located on the long arm of chromosome 11 at position 22.3
  3. Provides instructions for making enamelysin
  4. Enamelysin cleaves other proteins, such as amelogenin and ameloblastin, into smaller pieces (easier to remove)

(Multiple phenotypes)

50
Q

What are the effects of amelogenesis imperfecta?

A
  1. Results in dull, frail enamel which is more susceptible to caries
  2. (On radiographs) enamel is much harder to differentiate from dentine due to its lower mineral content
51
Q

What are differences between amelogenis imperfecta and dentinogenesis imperfecta?

A

(For dentinogenisis imperfecta)
1. On radiographs pulp cannot be seen as mineralisation in dentine is so low that it matches that of pulp

  1. Toothwear is very damaging as there is no cushioning for the enamel
52
Q

What is responsible for the mapping of the crown shape in tooth development?

A

Enamel organ

53
Q

What is the root shape defined by?

A

Apical growth of the cervical loop which is now called:

Hertwig’s epithelial root sheath

54
Q

What is the cell structure of hertwig’s epithelial root sheath?

A

2-cell-layered structure

55
Q

What substance does Hertwig’s epithelial root sheath (HERS) induce formation of?

A

Root dentine

56
Q

What happens to HERS after the initial layer of root dentine is formed?

What potential complication can arise from this?

A
  1. HERS breaks up (no enamel in root)

2. Remains of HERS persist as ‘debris of Malassez’ which may develop into a cyst

57
Q

After the breakdown of HERS, mesenchymal cells from the follicle contact the dentine and ____________?

A

Differentiate into cementoblasts

- these form cementum

58
Q

What name is given to the fibres from the developing PDL which are embedded in the cementum?

A

Sharpey’s fibres

59
Q

Write a brief summary of root formation

A
  1. migration of cervical loop (now HERS) apically provides the shape of the root
  2. HERS cells induce odontoblasts to form dentine
  3. Once dentine is formed the HERS breaks down and leftover cells are called ‘debris (or cell rests) of Malassez
    - these can produce odontogenic cysts
  4. Breakdown of HERS cells allow follicle cells to make contact with dentine
    - this stimulates differentiation of follicle cells into cementoblasts
60
Q

How is the dental follicle identified on a histology slide?

A

Appears as a circle surrounding the enamel organ and dental papilla

  • all of these features combined makes up the tooth germ
61
Q

What 3 components make up the tooth germ?

A
  1. Enamel organ
  2. Dental papilla
  3. Dental follicle
62
Q

Describe the enamel organ in terms of:

  1. Type of tissue
  2. Origin
  3. Products
A
  1. Epithelium
  2. Ectoderm
  3. Enamel
63
Q

Describe the dental papilla in terms of:

  1. Type of tissue
  2. Origin
  3. Product
A
  1. Ectomesenchyme
  2. Neural crest
  3. Dentine, pulp
64
Q

Describe the dental follicle in terms of:

  1. Type of tissue
  2. Origin
  3. Product
A
  1. Ectomesenchyme
  2. Neural crest
  3. Cementum, PDL, alveolar bone (partly)
65
Q

What are the 4 main types of tooth development abnormalities?

A
  1. Prenatal
  2. Postnatal
  3. Inherited
  4. Acquired
66
Q

What aspects of the teeth do developmental abnormalities affect?

A
  1. Number
  2. Shape
  3. Size
  4. Structure
  5. Eruption
67
Q

What can cause an acquired enamel defect?

A

Infection

68
Q

What is gemination?

A

When two twin teeth develop instead of 1

69
Q

What name is given to the defect in which two separate teeth are combined together during development?

A

Fusion

70
Q

What name is given to the defect in which two teeth are bound together at the cementum?

A

Concrescence

BDS2: Oral Biology (1 decks)

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