6. Tooth Development

Question 1

Types of primary embryonic layers (3)

Answer 1

Ectoderm
Mesoderm
Endoderm

Question 2

Definition of ectomesenchyme (2)

Answer 2

Part of the neural crest that develops beside the primitive nervous system (ectoderm)
Fourth cell type (also called the neural crest)

Question 3

From which primary embryonic layers are tooth structures derived (2)

Answer 3

Enamel from ectoderm

All others from ectomesenchyme

Question 4

Cause of mandibular dysostosis

Answer 4

Failure of ectomesenchymal cells to migrate

Question 5

Stages in tooth development (5)

Answer 5

Initiation
Morphogenesis
Cytodifferentiation
Matrix secretion
Root formation

Question 6

First part of tooth development (3)

Answer 6

Development of primary epithelial band
At 6wks iul
Appears as a thickening in epithelium of the embryonic mouth

Question 7

Second part of tooth development (3)

Answer 7

Development of the dental lamina
At 7wks iul
PEB has grown into the jaw and divided into two parts

Question 8

At 7wks iul, what has the PEB divided into (2)

Answer 8

Vestibular lamina (breaks down to form buccal sulcus)
Dental lamina (from which enamel organ forms)

Question 9

Third part of tooth development (4)

Answer 9

Bud stage, 8-10wks iul
Enamel organ forms
Dental lamina thickens into a bud stage enamel organ
Ectomesenchymal condensation appears (dental papilla)

Question 10

Fourth part of tooth development (3)

Answer 10

Cap stage, 11wks iul
Enamel organ forms a cap over papilla
Cap stage enamel organ is IEE and EEE

Question 11

Where do IEE and EEE meet

Answer 11

At the cervical loop

Question 12

Fifth part of tooth development (3)

Answer 12

Bell stage, 14wks iul
More cell layers differentiated
Tooth shape is being defined

Question 13

Cell layers of the bell stage enamel organ (4)

Answer 13

Stratum intermedium
Stellate reticulum
Internal enamel epithelium
External enamel epithelium

Question 14

Definition of enamel knot

Answer 14

Where cusps, mammelons and cingulums are established

Question 15

What happens at 12wks iul and what is this

Answer 15

Extension appears on the lingual side of the dental lamina

This is the dental lamina for the permanent successor

Question 16

What happens at 16wks iul (2)

Answer 16

First permanent molar germ develops

Develops as a backwards extension of the dental lamina

Question 17

Sixth part of tooth development (3)

Answer 17

Late bell stage, 18wks iul
Crown shape is well defined
Apposition of enamel and dentine begins

Question 18

Dental papilla cells adjacent to IEE differentiate into

Answer 18

Odontoblasts

Question 19

What happens when dentine formation has begun (2)

Answer 19

IEE cells differentiate into ameloblasts

Ameloblasts form enamel

Question 20

Process of dentinogenesis (3)

Answer 20

Odontoblast differentiation from IEE
Deposition of unmineralised dentine matrix (predestine)
Mineralisation of dentine (hydroxyapatite)

Question 21

Process of ameloblast formation (4)

Answer 21

Differentiation
Secretion
Maturation
Regression

Question 22

Stages in ameloblast differentiation (7)

Answer 22

Morphogenic
Histodifferentation
Secretory (initial)
Secretory (Tomes process)
Maturative (ruffle-ended)
Maturative (smooth)
Protective

Question 23

Process of ameloblast differentiation (3)

Answer 23

Dentine induces IEE cells to differentiate into ameloblasts
Elongation, they become columnar
Nucleus migrates to basal end of the cell

Question 24

Process of secretory phase (3)

Answer 24

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

Question 25

Process of maturation phase (2)

Answer 25

Removal of most matrix proteins | Enamel mineral content increased (95%)

Question 26

Process of protection phase (3)

Answer 26

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

Question 27

Definition of amelogenesis imperfecta, AI

Answer 27

Congenital disease, abnormal formation of enamel | Unreleated to any systemic/generalised conditions

Question 28

Cause of AI

Answer 28

Malfunction of proteins in enamel due to abnormal enamel formation via amelogenesis

Question 29

Types of enamel proteins (4)

Answer 29

Ameloblastin Enamelin Tuftelin Amelogenin

Question 30

Type of condition of AI

Answer 30

Autosomal recessive hypoplastic hypomaturation AI

Question 31

Genetics of AI (2)

Answer 31

MMP20 gene located on long (q) arm | On chromosome 11, position 22.3

Question 32

Definition of dentinogenesis imperfecta, DI (2)

Answer 32

Genetic disorder of tooth development | Dentine dysplasia that causes teeth to be discoloured

Question 33

Causes of DI (3)

Answer 33

``` Genetic factors (mainly) Any environmental/systemic upset that impedes calcification or metabolism of Ca ```

Question 34

Function of enamel organ

Answer 34

Map out shape of crown

Question 35

How is the crown shape mapped out

Answer 35

Migration of the cervical loop

Question 36

How is the root shape defined (2)

Answer 36

By apical growth of the cervical loop | Cervical loop is now called Hertwig's epithelial root sheath (HERS)

Question 37

Difference between enamel organ and HERS

Answer 37

Enamel organ - 4 cell layers | HERS - 2 cell layers (IEE and EEE)

Question 38

HERS induces

Answer 38

Formation of root dentine

Question 39

Root formation process (4)

Answer 39

Once initial layer of root dentine is formed, HERS breaks up Remains of HERS persist as debris of Malassez (may develop into a cyst) Mesenchymal cells from the follicle contact dentine, differentiating into cementoblasts Fibre's from developing PDL (Sharpey's) are embedded into cementum

Question 40

Why does HERS break up so soon

Answer 40

No enamel in the root

Question 41

Type of tissue, origin and products for enamel organ (3)

Answer 41

Epithelium Ectoderm Enamel

Question 42

Type of tissue, origin and products for dental papilla (3)

Answer 42

Ectomesenchyme Neural crest Dentine, pulp

Question 43

Type of tissue, origin and products for dental follicle (3)

Answer 43

Ectomesenchyme Neural crest Cementum, PDL, part of alveolar bone

Question 44

Types of tooth development abnormalities (9)

Answer 44

``` Prenatal Postnatal Inherited Acquired Number Shape Size Structure Eruption ```