Embryology

Question 1

From what embryonic layer is enamel derived?

Answer 1

Ectoderm

Question 2

What are all parts of teeth and supporting tissues (except enamel) derived from?

Answer 2

Ectomesenchyme

Question 3

From what do teeth develop?

Answer 3

‘Tooth germs’

Question 4

Where is the neural crest located?

Answer 4

Between the ectoderm and neural tube

Question 5

What is mandibulo facial dysostosis

Answer 5

Failure of ectomesenchymal cells to migrate (into the developing face and jaws)

Question 6

What is the first stage of tooth development and what 2 features develop?

Answer 6

Tooth initiation:
Primary epithelial band (PEB) develops at approx 6 weeks IUL
Appears as thickening in epithelium of embryonic mouth (stomodaeum)

Dental lamina develops at approx 7 weeks
The PEB has grown into the jaw and divided into 2 parts:
- vestibular lamina (will break down to form buccal sulcus)
- dental lamina (from which enamel organ develops)

Question 7

Describe the ‘bud’ stage of tooth development

Answer 7

Approx 8-10 weeks

Dental lamina thickens into a ‘bud’ stage enamel organ
An ectomesenchymal condensation appears (dental papilla)

Question 8

Describe the ‘cap’ stage of tooth development

Answer 8

Approx 11 weeks

The enamel organ forms a ‘cap’ over the papilla
The cells of the enamel organ differentiate into the external enamel epithelium (EEE) and internal enamel epithelium (IEE)

The EEE and IEE meet at the cervical loop

Question 9

Describe the ‘bell’ stage of tooth development

Answer 9

Approx 14 weeks
More cell layers differentiated
Tooth shape being defined

‘Bell’ stage enamel organ has 4 layers

• IEE
• EEE
• stellate reticulum (between the IEE and EEE)
• stratum intermedium (lies adjacent to IEE)

Question 10

Describe the late ‘bell’ stage of tooth development

Answer 10

Approx 18 weeks

Crown shape is well defined
Apposition of enamel and dentine begins

Question 11

Describe the formation of dentine during tooth development

Answer 11

Dental papilla cells adjacent to IEE differentiate into odontoblasts, which lay down dentine matrix (mainly collagen), which is later mineralised.
The unmineralised dentine is predentine

Question 12

Describe the formation of enamel in tooth development

Answer 12

Two stages:
1. Protein matrix deposited by ameloblasts
Matrix is partially mineralised (30%)

2. Once this framework is established, the organic part is removed and mineralisation is completed (96%)

Question 13

Describe the ameloblast differentiation stage of amelogenesis

Answer 13

Dentine induces IEE cells to differentiate into ameloblasts
They elongate, becoming columnar
The nucleus migrates to basal end of cell

Question 14

Describe secretory phase of amelogenesjs

Answer 14

Ameloblasts become secretory cells
They synthesise and secrete the enamel matrix proteins (amelogenins)
The matrix is then partially mineralised (30% mineral)

Question 15

Describe the maturation phase of amelogenesis

Answer 15

Most of matrix proteins removed
Mineral content of enamel increased
Mature enamel is 95% mineral

Question 16

Describe the protection phase of amelogenesis

Answer 16

Ameloblasts regress to form protective layer- the reduced enamel epithelium
Involved in eruption
Formation of epithelial attachment

Question 17

How is root shape defined?

Answer 17

Defined by apical growth of cervical loop

Question 18

What is the new name of the cervical loop during root formation?

Answer 18

Hertwig’s epithelial root sheath (HERS)

Question 19

What does HERS induce?

Answer 19

Induces formation of root dentine

Question 20

What is the fate of Hertwig’s epithelial root sheath once the root dentine is formed?

Answer 20

HERS breaks up

Some remains may persist as ‘debris of Malasiez’, which may develop into a cyst

Question 21

Describe the final steps of root formation once root dentine has been placed

Answer 21

Mesenchymal cells from the follicle contact dentine and differentiate into cementoblasts, which form cementum

Fibres from developing PDL are embedding in the cementum (Sharpey’s fibres)

Question 22

Name the type of tissue, origin and product(s) of the enamel organ

Answer 22

Epithelium, ectoderm, enamel

Question 23

Name the type of tissue, origin and product(s) of the dental papilla

Answer 23

Ectomesenchyme
Neural crest
Dentine, pulp

Question 24

Name the type of tissue, origin and product(s) of the dental follicle

Answer 24

Ectomesenchyme
Neural crest
Cementum, PDL, alveolar bone

Question 25

Name the 3 embryonic layers all body tissues develop from

Answer 25

Ectoderm
Mesoderm
Endoderm

Question 26

What is the stomatodeum?

Answer 26

Mouth

Question 27

What does the 1st pharyngeal arch grow into?

Answer 27

Lips and muscles of mastication

Question 28

What does 2nd pharyngeal arch grow into?

Answer 28

Muscles of facial expression

Question 29

What are somites?

Answer 29

Ectoderm cells for spine, ribs etc.

Question 30

What does the medial nasal process become?

Answer 30

Tissue between nostrils and cuspids bow

Question 31

What does anterior naris become?

Answer 31

Nostril

Question 32

What does lateral nasal process become?

Answer 32

Ala of nose

Question 33

Define cleft lip

Answer 33

Developmental defect of maxillary process and medial nasal process

Fusing failure

Can cause excess tissue

Question 34

Define cleft palate

Answer 34

Palatal folds fail to fuse and form correctly