1
Q
Name the embryonic layers that all body tissues develop from (3)
A
- Ectoderm
- Mesoderm
- Endoderm
2
Q
What arises from Ectoderm? (3)
A
- CNS
- Tooth enamel
- Skin
3
Q
What arises from Mesoderm? (4)
A
- Connective tissue
- Blood vessels
- Reproductive system
- kidney/urinary system
4
Q
What arises from Endoderm?
A
- Alimentary canal
2. Respiratory system
5
Q
What do teeth develop from?
A
Teeth germs
6
Q
What is the name of the 4th cell type?
A
Neural crest/ Ectomesenchyme
7
Q
How does the 4th cell type form?
A
Forms between the ectoderm and the neural tube (neural crest)
8
Q
How is the neural tube formed? (2)
A
- Neural crest tissue migrates into the developing face and jaw
- Neural plate folds and forms a neural groove and the neural groove folds and forms a neural tube
9
Q
What arises from Ectomesenchyme? (5)
A
- Dentine
- Cementum
- Pulp
- PDL
- Jaw bones
10
Q
How does Mandibulofacial Dystosis occur?
A
Failure of ectomesenchymal cells to migrate
11
Q
List the stages in tooth development (5)
A
- Initiation
- Morphogenesis
- Cytodifferentiation
- Late Bell stage
- Root formation
12
Q
What happens in the initiation phase? (4)
A
- PEB develops at approx 6wks IUL
- Appears as a thickening in epithelium of the embryonic mount (stomadeum)
- This results in the growth of dental lamina into the connective tissue
- The PEB grows into the jaw and divides into 2 parts
13
Q
What 2 parts does the PEB divide into during the initiation phase?
A
- Vestibular lamina
- Which breaks down to form the buccal sulcus - Dental Lamina (approx 7wks)
- Develops enamel organ
- Has tooth germs
- Formation of dental lamina initiated by neural crest cells
14
Q
What happens to the dental lamina formed?
A
The lamina grows and then apoptosis will separate the 2 epithelial tissues, forming the teeth
15
Q
What happens in the Morphogenesis phase?
A
BUD STAGE (8-10wks):
- Dental lamina thickens into a ‘bud’ stage enamel organ
- Ectomesenchymal condensation forms the dental papilla
CAP STAGE (11wks):
- The enamel organ forms a ‘cap’ over the papilla
- EEE + IEE meet at the cervical loop
16
Q
What is the cervical loop a reference for?
A
Formation of the root
17
Q
What does the dental papilla form?
A
All the other tissues apart from enamel:
- Dentine
- Cementum
- PDL
- Pulp
18
Q
Function of the dental follicle?
A
Sac that holds tissue together
19
Q
Function of the enamel organ?
A
Epithelial tissue that forms enamel
20
Q
What is Hypohyidrotic Ectodermal Dysplasia? (2)
A
- HED is a genetic skin disease resulting in missing teeth/irregular teeth shape
- Coronoid teeth may be formed
21
Q
How does Severe Hypohidotic Ectodermal Dysplasia differ from the usual? (3)
A
- Changes not always associated with teeth
- Associated with the absence/reduction in number/size/shape of teeth
- Also affects hair nails formation
22
Q
What happens in the Cytodifferentiaton phase? (3)
A
BELL STAGE (14wks):
1. Enamel organ bell stage at approx 14wks
2 More cell layers differentiate into a more defined tooth shape
3. Bell stage forms 4 different cell layers
23
Q
What cell layers are formed during the Bell stage of Cytodifferentiation (4)
A
- Stratum Intermedium
- Stellate Reticulum
- IEE
- EEE
24
Q
When does the permanent tooth germ form during Cytodifferentiation? (2)
A
- At approx 12wks appears as an extension on the lingual side of the dental lamina
- This is the dental lamina for the permanent successor
25
When does the 1st permanent molar form?
At roughly 16wks the 1s permanent molar forms as a backwards extension of the dental lamina
26
What happens in the Late Bell Stage (4)
1. Approx 18wks IUL
2. Crown shape well defined
3. Apposition of enamel + dentine begins
4. Dental formation is established and enamel formation begins
27
Describe the steps to the formation of dentine + enamel (4)
1. Dental papilla cells adjacent to IEE differentiate into odontoblasts
2. Odontoblasts lay down dentine matrix (which is later mineralised
3. Once dentine formation has begun, IEE cells differentiate into amelobasts (which form enamel)
28
When is primary dentine formed?
Formed while the tooth is still forming (but hasn't completely formed)
29
When is secondary dentine formed?
Formed after the tooth is completely formed
30
When is tertiary dentine formed?
Formed in response to trauma (odontoblasts recognise trauma)
31
When does the formation of primary dentine stop?
After the 3rd molar has formed
32
Dentinogenesis steps (4)
Odontoblast differentiation from IEE
2. Deposition of dentine matrix (mainly collagen)
3. This unmineralised dentine is predentine
4. Mineralisation of dentine (hydroxyapatite) occurs
33
Mineralisation content of enamel
96%
34
Describe the enamel formation stages (2)
STAGE 1:
- Protein matrix deposited
- Matrix is partially mineralised (30%)
STAGE 2:
- Organic part is removed and mineralisation is completed (maturation)
35
Define regression
When ameloblastsstop having active functions processes, but they still have a protective epithelial function
36
What is junctional epithelium/
Tissue that holds gingiva to enamel
37
Outline the steps to root formation (3)
1. The EEE and IEE meet at the cervical loop
2. Migration of cervical loop for crown shape
3. Apical growth of the cervical loop (HERS) defines root shape
38
What maps the crown shape during root formation?
The migration of the cervical loop
39
What maps the root shape during root formation?
The apical growth of the cervical loop (which is now called the Hertwigs Epithelial Root)
40
What is HERS?
2 cell layered structure in comparison to the 4 layered enamel organ
41
Function of HERS (3)
1. Induces formation of root dentine
2. Once the initial layer of root dentine is formed HERS breaks up (no enamel in root)
3. Remains of HERS persist as debris of malassez, which may develop into a cyst
42
How is cementum formed?
Mesenchymal cells from the follicle contact dentine and differentiate into cementoblast (which form cementum)
43
List the ameloblast differentiation stages (7)
1. Morphogenic
2. Histodifferentiation
3. Secretory (initial)
4. Secretory (tomes process)
5. Maturative (ruffled ended)
6. Maturative (smooth)
7. Protective
44
What happens in the Ameloblast Differentiation stage of amelogenesis? (3)
1. Dentine induces IEE cells to differentiate into ameloblasts
2. They elongate and become columnar
3. The nucleus migrates to the basal end of the cell
45
What happens in the Secretory Phase of amelogenesis? (3)
1. Ameloblasts become secretory cells
2. They synthesise and secrete the enamel matrix proteins (amelogenins)
3. The matrix is partially mineralised (30% mineral), mature enamel is 95% mineral
46
What happens in the Maturation Phase of amelogenesis? (2)
1. Most of the matrix proteins are removed
2. Mineral content of enamel is increased (but we still don't have pure hydroxyapatite, still a mix of carbonated apatite + hydroxyapatite
47
What happens in the Protection Phase of amelogenesis? (3)
1. Ameloblasts regress to form a protective layer (the reduced enamel epithelium)
2. Involved in eruption
3. Formation of epithelial attachment
48
Why are fissure sealants used after early stage tooth eruption? (3)
1. Erupted tooth has high conc of hydroxyapatite
2. This will be reduced by the demineralisation/remineralisation process
3. Fissure sealants used as its very susceptible to cavity formation
49
What is Amelogenesis Imperfecta?
When enamel fails to develop properly, leading to small yellow teeth
50
Why is Enamelysin protein essential for proper maturation? (3)
1. Enamelysin breaks down other proteins like amelogenin/amelobastin into smaller pieces so they are easier to remove
2. This allows the protein breakage to be absorbed and to remove the protein content, allowing the minerals to actually mature the enamel
3. Absence of this proteins leads to inadequate maturation
51
How do the teeth appear opaque due to Amelogenesis Imperfecta? (2)
1. Reduced mineral content leads to reduced translucency (so becomes opaque)
2. Opacity brings the colour of dentine through
52
How does Amelogenesis Imperfecta affect the restoration process?
Restoring teeth is harder as composite won't adhere with the same strength as it would, due to lack of mineral
53
How does Amelogenesis Imperfecta present on a radiograph?
Can't see the interface between enamel and dentine - as enamel is so demineralised that it has similar density to dentine
54
What is Dentinogenesis Imperfecta? (2)
- Genetic disorder of tooth development
- Type of dentin dysplasia that leads to discoloured grey tooth
- Enamel is properly formed but dentine hasn't reached sufficient maturation
55
How does Dentinogenesis Imperfecta affect teeth?
Teeth are weaker than normal, making them more prone to rapid wear, breakage and loss
56
How can we distinguish Dentinogenesis Imperfecta from Amelogenesis Imperfecta?
We can see the interface between enamel and dentine (as enamel is still mineralised although dentine is less mineralised)
57
ENAMEL ORGAN:
1. Type of tissue
2. Origin
3. Product
1. Epithelium
2. Ectoderm
3. Enamel
58
DENTAL PAPILLA:
1. Type of tissue
2. Origin
3. Product(s)
1. Ectomesenchyme
2. Neural Crest
3. Dentine, Pulp
59
DENTAL FOLLICLE:
1. Type of tissue
2. Origin
3. Product(s)
1. Ectomesenchyme
2. Neural Crest
3. Cementum, PDL, alv bone
60
Teeth development abnormalities can appear during (4)
1. Prenatal
2. Postnatal
3. Inherited
4. Acquired
61
Affected characteristics from teeth development abnormalities (5)
1. Number
2. Shape
3. Size
4. Structure
5. Eruption
62
What is hypodontia?
Less teeth
| Incorrect shape
63
What is gemination?
2 teeth combined
Oral Biology
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