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Dental Development Flashcards

1
Q

What are the 3 primary embryonic layers

A

Ectoderm
Mesoderm
Endoderm

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2
Q

What are the tooth structures derived from

A

Enamel is derived from ectoderm

All other parts of the teeth and supporting structures are derived from the endoderm

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3
Q

What is the ectomesenchyme

A

Part of the neural crest that develops beside the ectoderm

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4
Q

What do teeth develop from

A

Tooth germs

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5
Q

Where does the neural crest form

A

Between the neural tube and the ectoderm

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6
Q

Describe the movement of neural crest cells

A

Migrate towards the front from dorsal portion to ventral portion

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7
Q

What is mandibulofacial dysostosis

A

Failure of ectomesenchymal cells to migrate

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8
Q

What are common signs of mandibulofacial dysostosis

A

Distance between pupils becomes greater
Ears are positioned lower
Malformation of the ears
Maxilla and mandible small in relation to the skull which relates to crowding of the teeth

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9
Q

What are the stages of tooth development

A 
Initiation
Morphogenesis
Cytodifferentiation
Matrix secretion
Root formation
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10
Q

When does tooth initiation occur

A

5-6 weeks

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11
Q

Describe the events of tooth initiation

A

Mandibular processes seam together in the midline to form the mandible
Maxillary processes will seam with the frontal nasal process, working the nose

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12
Q

When does the primary epithelial band develop and what does it appear as

A

6 weeks

Appears as thickening in epithelium of embryonic mouth (stomodeum)

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13
Q

What does the primary epithelial band form

A

Vestibular lamina, which will break down to form the buccal sulcus
Dental lamina, from which the enamel organ develops

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14
Q

When does the dental lamina develop

A

7 weeks

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15
Q

Describe the dental lamina

A

Horseshoe shaped structure with regions of thickness called tooth germs

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16
Q

When does the bud stage occur

A

8-10 weeks

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17
Q

Describe the events of the bud stage

A

Dental lamina thickens into a bud stage enamel organ

An ectomesenchymal condensation appears, this is the dental papilla

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18
Q

When does the cap stage occur

A

11 weeks

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19
Q

Describe the events of the cap stage

A

The enamel organ forms a cap over the papilla made from the external enamel epithelium and the internal enamel epithelium
The EEE and IEE meet at the cervical loop

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20
Q

What are placodes

A

Embryonic structures that give rise to structures such as hair follicles, feathers and teeth
Different ways that a tissue will form its bud stage

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21
Q

What is hypohidrotic ectodermal dysplasia

A

A genetic skin disease that can cause absence of teeth and hair

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22
Q

Why are both hair follicles and teeth affected by hypohidrotic ectodermal dysplasia

A

The dental placodes are formed from the same process as the hair follicle placodes

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23
Q

How can genetic disorders be cured

A

By gene therapy, the condition may be reversed

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24
Q

When does the bell stage occur

A

14 weeks

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25
What are the 4 cell layers of the enamel organ during the bell stage
Stellate reticulum Stratum inter medium External enamel epithelium Internal enamel epithelium
26
What is the purpose of the stellate reticulum
Holds the energy, materials and sugars necessary for the ameloblasts to develop the enamel matrix
27
Where do odontoblasts acquire their nutrients from
The dental papilla
28
Describe the pattern in which the crown is formed
Differentiation starts at the incisal region and then proceeds towards the cervical loop Matrix formation will follow the differentiation of those cells
29
Describe the stages of permanent tooth germ formation
At 12 weeks, an extension will appear on the lingual side of the dental lamina - the permanent successor At 16 weeks, the first permanent molar starts to develop in a backwards extension of the dental lamina
30
Why does the permanent first molar develop in the way it does
It doesn’t have a deciduous counterpart
31
When does the late bell stage occur
18 weeks
32
Describe the late bell stage
Crown shape is well defined | Apposition of enamel and dentine begins
33
Describe the key events in the formation of dentine and enamel
Dental papilla cells adjacent to the IEE differentiate into odontoblasts Odontoblasts lay down dentine matrix, which is later mineralised Once dentine formation has begun, IEE cells differentiate into ameloblasts which form enamel
34
What is the purpose of stem cells in dentinogenesis
Will be responsible for the formation of tertiary dentine if the odontoblasts die
35
What happens in dentinogenesis
Odontoblasts differentiate from dental papilla cells Dentine matrix is deposited (mainly collagen) Unmineralised dentine is predentine Dentine is mineralised by hydroxyapatite
36
What happens in enamel formation
Protein matrix is deposited which is partially mineralised (30%) 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
37
What are the stages of ameloblast differentiation
``` Morphogenic Histodifferentiation Secretory (initial) Secretory (tomes process) Maturative (ruffle-ended) Maturative (smooth) Protective ```
38
Describe the position of ameloblasts during differentiation
In early stages they’re closer to the cervical region | In later stages they’re closer to the cusp
39
What happens during the initial stages of ameloblast differentiation
Dentine induces IEE cells to differentiate into ameloblasts They elongate, becoming columnar The nucleus migrates to the basal end of the cell (away from the ADJ)
40
What happens during the secretory phase of ameloblast differentiation
Ameloblasts become secretory cells They synthesis and secrete the enamel matrix proteins (amelogenins) The matrix is partially mineralised (30% mineral as seeded crystallites)
41
What happens during the maturation phase of ameloblast differentiation
Most of the matrix proteins are removed | Mineral content of enamel is increased
42
What happens during the protection phase of ameloblast differentiation
Ameloblasts regress to form a protective layer - the reduced enamel epithelium Involved in eruption and formation of epithelial attachment
43
What is amelogenesis imperfecta and what is it caused by
A group of genetic conditions where the enamel fails to develop properly Caused by a mutation in the MMP20 gene which provides instruction for making enamelysin
44
Describe a radiograph of a patient with amelogenesis imperfecta
Can’t tell when enamel stops and dentine starts because enamel has lost so much mineral content so it becomes very similar to dentine
45
What is dentinogenesis imperfecta
Dentine is not developed or mineralised to the level that it should be
46
Describe a radiograph of a patient with dentinogenesis imperfecta
Cannot see the pulp
47
Why is the root formed last
Need to have the correct shape, arrangement and cervical loop before the root is formed
48
What happens to the cervical loop in root formation
Apical growth of the cervical loop which becomes Hertwig’s epithelial root sheath - a 2 cell-layered structure
49
Describe how root formation occurs
HERS induces formation of root dentine Then HERS breaks up as there is no enamel in the root Remainder of HERS persists as ‘debris of Malassez
50
How is the cementum formed
The breakdown of HERS allows the follicle to come into contact with dentine Mesenchymal cells from the follicle contact the dentine and differentiate into odontoblasts Fibres from the developing PDL are embedded in the cementum - Sharpey’s fibres
51
What may happen to the debris of Malassez
May produce a cyst | Because they are associated with odontogenesis they are called odontogenic cysts
52
Name the type of tissue, origin and products of the enamel organ
Epithelium Ectoderm Enamel
53
Name the type of tissue, origin and products of the dental papilla
Ectomesenchyme Neural crest Dentine and pulp
54
Name the type of tissue, origin and products of the dental follicle
Ectomesenchyme Neural crest Cementum, PDL and part of the alveolar bone
55
What are the different types of teeth developmental abnormalities
Prenatal Postnatal Inherited Acquired
56
What can teeth development abnormalities have an effect on
``` Number Shape Size Structure Eruption ```
57
What is germination
Teeth that are together because a tooth has broken down into two
58
What is fusion
When teeth have joined together
59
What is concrescence
When teeth get together by the cementum
60
What type of epithelium is found in the primary epithelial band
Stratified squamous

Oral Biology (12 decks)

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