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BDS1 > Tooth development > Flashcards

Tooth development Flashcards

1
Q

What alternative to implants and dentures is being researched?

A

Stem-cell research to develop tooth germs that can be implanted and grown in the mouth

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2
Q

Drawbacks of possible tooth germ technology to replace missing teeth

A
  • might not be commercially viable
  • might not be able to compete with dentures/implants
  • method of implanting tooth bud
  • alveolar bone resorbed, PDL lost, soft tissue lost, occlusion changes after extraction
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3
Q

What are the 3 primary embryonic layers that all body tissues develop from?

A

ectoderm, mesoderm, endoderm

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4
Q

What dental tissue is formed from the ectoderm?

A

Enamel

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5
Q

What are all parts of the teeth (except enamel) derived from?

A

ectomesenchyme / neural crest tissue that migrates into the developing face and jaw (forms dentine, pulp, cementum, PDL, jaw bones)

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6
Q

Where does the ectomesenchyme originate?

A

From the neural crest that develops between the ectoderm and neural tube. Migrates to developing head.

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7
Q

What is the cause of Treacher-Collins Syndrome phenotype?

A

Failure of ectomesenchyme / neural crest tissue to migrate into the developing face and jaw.

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8
Q

Name of the structure teeth develop from

A

tooth germs

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9
Q

What is the first stage in tooth development?

A

initiation

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10
Q

Name of the oral epithelial tissue covering the primitive mouth

A

stomodaeum

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11
Q

Appearance of primitive mouth at week 5-6

A

2 maxillary processes separated by a frontal nasal process. 2 mandibular processes. Covered by stomodaeum.

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12
Q

How is the maxilla formed?

A

Joining together of the frontal nasal process and the 2 maxillary processes

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13
Q

How is the mandible formed?

A

Joining together of the 2 mandibular processes

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14
Q

What is the congenital abnormality caused by the failure of the 2 maxillary processes and the frontal nasal process to fuse?

A

Cleft lip and palate

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15
Q

What is the first stage of tooth initiation?

A

At 6 weeks, the stomodaeum (oral epithelium) thickens and invaginates into the mesenchyme to form the primary epithelial band.

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16
Q

What is the primary epithelial band?

A

The thickening and invagination of the stomodaeum into the mesenchyme at 6 weeks IUL.

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17
Q

What happens by week 7?

A

The primary epithelial band divides into 2 processes: the vestibular lamina (buccally located) and the dental lamina (lingually located).

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18
Q

What does the vestibular lamina form?

A

Forms the vestibule / buccal sulcus

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19
Q

What is the vestibule?

A

Horse-shoe shaped space between the lips/cheeks and teeth/gingiva

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20
Q

What does the dental lamina form?

A

enamel organ

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21
Q

What shape is the dental lamina?

A

Horse-shoe shaped, following the line of the vestibular fold

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22
Q

How is the vestibule of the oral cavity formed?

A

Cells of the vestibular lamina proliferate followed by apoptosis of the central epithelial cells to produce the sulcus of the vestibule.

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23
Q

How do the early tooth germs appear by week 8?

A

as a series of swellings on the deep surface of the dental lamina.

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24
Q

What is the second stage of tooth development after initiation?

A

Morphogenesis

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25
Q

What is the first stage of morphogenesis?

A

Bud stage

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26
Q

What happens in the bud stage?

A

The dental lamina thickens to form the bud shaped enamel organ

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27
Q

What surrounds the bud shaped enamel organ?

A

ectomesenchymal condensation which is the dental papilla

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28
Q

What cells make up the dental papilla?

A

Ectomesenchymal cells that have migrated. (failure of migration will lead to an underdeveloped dental papilla)

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29
Q

When is the enamel organ at the bud stage?

A

8-10 weeks

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30
Q

What follows the bud stage of the enamel organ?

A

Cap stage

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31
Q

At which week does the enamel organ form the cap stage?

A

11 weeks

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32
Q

What structure is below the internal enamel epithelium in the cap stage?

A

dental papilla

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33
Q

What are the two layers of the cap stage enamel organ?

A

External enamel epithelium makes up the outside of the cap, the internal enamel epithelium makes up the inside of the cap.

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34
Q

Where do the external and internal enamel epithelia meet?

A

At the cervical loop

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35
Q

Which stage follows morphogenesis (bud and cap stages)?

A

Cytodifferentiation (cell specialisation) (bell stage)

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36
Q

When does the bell stage of the enamel organ occur?

A

Approx 14 weeks - depends on which tooth is being formed.

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37
Q

What happens during the bell stage enamel organ?

A

more cell layers differentiate and the internal enamel epithelium starts to define the occlusal shape of the crown.

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38
Q

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

A

Stellate reticulum, stratum intermedium, internal enamel epithelium and external enamel epithelium.

39
Q

Where is the stellate reticulum found?

A

star shaped cells at the centre of the bell stage of the enamel organ

40
Q

Where is the stratum intermedium found?

A

Lies over the IEE (at the location of future cusps) between the IEE and the stellate reticulum in the bell stage enamel organ.

41
Q

How does the permanent tooth germ form?

A

The dental lamina for the permanent tooth forms as an extension of the lingual side of the dental lamina for the deciduous tooth germ. Approx week 12

42
Q

Which permanent teeth do not form from an extension of the dental lamina of their deciduous counterpart?

A

the 12 permanent molars because there are no previous deciduous teeth.

43
Q

How do the enamel organs for the permanent molars form?

A

The dental lamina grows backwards to bud off successively (don’t have deciduous predecessor) at around week 16

44
Q

What is the stage of tooth development after cytodifferentiation?

A

Matrix secretion (late bell stage)

45
Q

What week is the late bell stage?

A

week 18

46
Q

What happens during the late bell stage?

A

Apposition of dentine and enamel begins

47
Q

Name of the junction between dentine and enamel

A

Amelo-dentinal junction

48
Q

At which stage of tooth development is the crown shape well defined?

A

Late bell stage of the enamel organ

49
Q

In which directions is enamel and dentine formed?

A

Dentine forms inwards while enamel forms outwards

50
Q

Is enamel or dentine formed first?

A

Dentine is formed before enamel

51
Q

How do odontoblasts differentiate?

A

Developing ameloblasts (preameloblasts) influence mesenchymal dental papilla cells adjacent to IEE to differentiate into odontoblasts.

52
Q

Which cells differentiate into odontoblasts?

A

the dental papilla cells adjacent to the IEE

53
Q

Which cells differentiate into ameloblasts?

A

IEE cells

54
Q

Process of dentinogenesis

A

Odontoblasts deposit unmineralised dentine matrix (mainly collagen) which is predentine. This is then mineralised by the deposition of hydroxyapatite to form dentine.

55
Q

Which cells produce dentine (predentine initially)?

A

odontoblasts

56
Q

Which cells form enamel?

A

Ameloblasts

57
Q

When do ameloblasts differentiate and secrete enamel?

A

Internal enamel epithelial (IEE) cells differentiate into ameloblasts once dentine formation has begun. The presence of dentine induces the ameloblasts to secrete enamel.

58
Q

How do the IEE cells differentiate into ameloblasts?

A

they elongate, becoming columnar and the nucleus migrates to the basal end of the cell.

59
Q

What is an enamel knot?

A

Cluster of cells associated with the stratum intermedium that form during the bud stage and establish the crown shape.

60
Q

How many enamel knots would an incisor have?

A

4 - 3 form the mamelons on the incisal edge while 1 forms the cingulum.

61
Q

How many enamel knots might a 16/26 have?

A

5 - 4 knots form the cusps while 1 forms the tubercle of Carabelli

62
Q

Which disorder is associated with a mutation / lack of the Edgar gene?

A

Amelogenesis imperfecta - enamelins and amelogenins (enamel proteins) are not broken down during enamel maturation which leads to the enamel being softer.

63
Q

Does the enamel organ or dental papilla define the shape of the tooth?

A

Enamel organ - although ameloblasts fully differentiate/secrete enamel later, they determine the conversion of mesenchymal cells into odontoblasts.

64
Q

How do the dentinal tubules form?

A

As each odontoblast recedes, it grows a longer projection within the secreted matrix which becomes a dentinal tubule.

65
Q

Similarity between ultrastructure of ameloblasts and odontoblasts

A

Both are polarised with their nuclei in the opposite end of the cell (basal end) to where matrix is secreted from.

66
Q

Which structure secretes enamel crystals in ameloblasts?

A

Tomes process

67
Q

What are the 2 stages of enamel formation?

A
  1. a protein matrix is deposited which partially mineralises enamel to 30%
  2. maturation - once this framework is formed, the organic part breaks down to complete mineralisation (96%)
68
Q

Stages of ameloblast differentiation

A

Differentiation, Secretion, Maturation, Regression

69
Q

Why is the regression stage of amelogenesis differentiation important?

A

As ameloblasts regress they form a group of cells that later develop into the junctional epithelium (periodontium)

70
Q

What happens during the secretory phase of amelogenesis?

A

Ameloblasts become secretory cells which synthesise and secrete enamel matrix proteins (e.g. amelogenins)

71
Q

What level of mineralisation is reached during the secretory phase of amelogenesis?

A

Partial mineralisation (30% - out of 95%)

72
Q

What happens during the maturation phase of amelogenesis?

A

Most of the matrix proteins are removed and the mineral content of enamel is increased to 95%

73
Q

What happens during the protection/regression phase of amelogenesis?

A

ameloblasts regress to form a protective layer called the reduced enamel epithelium

74
Q

Function of the reduced enamel epithelium

A

involved in eruption and the formation of epithelial attachment (junctional epithelium)

75
Q

What is the final stage of tooth development after matrix secretion?

A

Root formation

76
Q

When does root formation begin?

A

After the crown formation is completed

77
Q

What maps the root shape?

A

Apical growth / migration of the cervical loop.

78
Q

What is the name of the cervical loop as it grows apically to create the root?

A

Hertwig’s epithelial root sheath (2-cell-layered structure as opposed to 4 layered enamel organ)

79
Q

Function of Hertwig’s epithelial root sheath

A

induces the formation of root dentine

80
Q

What happens to Hertwig’s epithelial root sheath once the initial layer of root dentine forms?

A

Hertwig’s epithelial root sheath breaks down to form cell rests / debris of Malassez and a connection now forms between the dental follicle and root dentine.

81
Q

Which cells do cysts develop from?

A

cell rests / debris of Malassez

82
Q

How is cementum formed?

A

When Hertwig’s epithelial root sheath breaks down, the mesenchymal cells from the dental follicle contact the dentine and differentiate into cementoblasts which form cementum.

83
Q

Name of the PDL fibres that are embedded into cementum

A

Sharpey’s fibres

84
Q

What type of tissue is the enamel organ formed from?

A

Epithelium originating from ectoderm

85
Q

What tooth component does the enamel organ form?

A

Enamel

86
Q

What type of tissue are the dental papilla and dental follicle formed from?

A

ectomesenchyme tissue originating from the neural crest

87
Q

What tooth structures are formed by the dental papilla?

A

Dentine and pulp

88
Q

What tooth structures are formed by the dental follicle?

A

Cementum, periodontal ligament, part of the alveolar bone

89
Q

Name of dental developmental disorder in which patients may have fewer teeth and the teeth can appear conical and smaller

A

hypodontia

90
Q

Name of dental developmental disorder in which an extra tooth is present between the 2 central incisors

A

supernumerary mesio-dens

91
Q

What is gemination?

A

Dental developmental disorder in which 2 teeth develop from one tooth bud, creating an extra tooth

92
Q

What is fusion?

A

dental developmental disorder in which 2 tooth germs unite creating a larger tooth with a single root

93
Q

Name of dental developmental disorder of improper dentine formation

A

dentinogenesis imperfecta

BDS1 (50 decks)

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