Dental Development

Question 1

What are the 3 primary embryonic layers?

Answer 1

• ectoderm
• mesoderm
• endoderm

Question 2

What tooth germ is tooth enamel derived from?

Answer 2

ectoderm

Question 3

Which one of the 4 primary embryonic layers are all the parts of the teeth and supporting structure apart from tooth enamel derived from?

Answer 3

ectomesenchyme

Question 3

What is the first stage of tooth development?

Answer 3

intiation

Question 3

What tissue migrates?

Answer 3

neural crest migrates into the developing face and jaws

Question 3

What is the ectomesenchyme

Answer 3

A fourth cell type forms between the ectoderm and the neural tube

part of the ‘neural crest’ that develops beside the primitive nervous system (ectoderm)

Question 4

What disorder is the failure of ectomesenchymal cells to migrate?

Answer 4

Mandibulofacial Dysostosis

Question 5

What is a depression between the brain and the pericardium in an embryo which is the precursor to the mouth called?

Answer 5

Stomodaeum

Question 6

Approximately when does the primary epithelial band develop?

Answer 6

6 weeks

Question 7

What does the primary epithelial band appear as?

Answer 7

thickening of epithelium at the embryonic mouth (stomodaeum)

Question 8

What 2 parts does the primary epithelial band divide into?

What week?

Answer 8

7 weeks

Vestibular lamina, which will form the buccal sulcus

Dental lamina, from which the enamel organ develops

Question 9

What shape is the dental lamina?

What week does it take this shape?

Answer 9

horseshoe

Question 10

What is the second stage in tooth development?

Answer 10

morphogenesis (bud stage)

Question 11

When does the enamel organ - ‘bud’ stage 2 occur?

Answer 11

8-10 weeks

Question 12

What happens at the ‘bud’ stage of dental development?

Answer 12

• Dental lamina thickens into a ‘bud’ stage enamel organ
• An ectomesenchymal condensation
  appears and this is the dental papilla

Question 13

When does the enamel organ - ‘cap’ stage 3 occur?

Answer 13

11 weeks

Question 14

What 2 epitheliums are present in the enamel ‘cap stage’?

Where do they meet?

Answer 14

External enamel epithelium
Internal enamel epithelium
EEE and IEE meet at the cervical loop

Question 15

What is the acculmation of ectomesencymal cells around the enamel organ called?

NOT UNDER

Answer 15

dental folluicle

Question 16

What is the fourth stage of tooth development?

Answer 16

bell stage

Question 17

What is ectodermal dysplasia?

Answer 17

a group of genetic syndromes deriving from abnormalities of ectodermal structures

Question 18

What happens in hypohidrotic ectodermal dysplasia concerning teeth?

Answer 18

hypodontia (absence) of multiple teeth

Question 19

How can ectodermal dysplasia be treated?

Answer 19

gene therapy - can reverse a genetic disorder

Question 20

When does the enamel organ - ‘bell’ (cytodifferentiation) stage occur?

Answer 20

14 weeks

Question 21

At what stage is the tooth shape starting to be defined?

Answer 21

bell stage

Question 22

What are the 4 cell layers present in the ‘bell’ stage?

Answer 22

Stratum intermedium Internal enamel epithelium External enamel epithelium Stellate reticulum

Question 23

What is the function of stellate reticulum in the bell stage?

Answer 23

keeping storage of nutrients for tissues comprises of glycoaminosglycans (attract water) which allows space for developing crown glycogen is energy for ameloblasts as blood vessels are far

Question 24

At what time does an extension appear on the lingual side of the dental lamina? | this is the dental lamina for the adult tooth

Answer 24

12 weeks

Question 25

At what time does the 1st permanent molar germ develop as a backwards extension of the dental lamina?

Answer 25

16th week

Question 26

What is the fifth stage of tooth development? | What time does it occur?

Answer 26

enamel organ matrix secretion (late bell) 18 weeks IUL

Question 27

In what stage does the positioning of enamel and dentine begin?

Answer 27

late bell stage within matrix secretion

Question 28

At what stage do cells become specialised?

Answer 28

late bell stage within matrix secretion

Question 29

What do dental papilla cells (adjacent to the internal enamel epithelium) differentiate into?

Answer 29

odontoblasts

Question 30

What do odontoblasts do?

Answer 30

lay down dentine matrix which is later mineralised (predentine)

Question 31

What do IEE cells differentiate into and when?

Answer 31

Once dentine formation has begun, IEE cells differentiate into ameloblasts, which form enamel

Question 32

What is the process of dentinogenesis?

Answer 32

Odontoblast differentiation from dental papilla cells near IEE Deposition of dentine matrix (mainly collagen) This unmineralised dentine is predentine Mineralisation of dentine (hydroxyapatite)

Question 33

What is the role of stem cells?

Answer 33

stem cells have capability to become odontoblasts and produce tertiary dentine

Question 34

What are the 2 phases of formation of enamel?

Answer 34

1. Protein matrix deposited Matrix is partially mineralised (30%) 2. Once this framework is established, the organic part is removed

Question 35

What are the 7 stages of ameloblast differentiation?

Answer 35

1. Morphogenic 2. Histodifferentiation 3. Secretory (initial) 4. Secretory (tomes process) 5. Maturative (ruffle-ended) 6. Maturative(smooth) 7. Protective

Question 36

What happens in step 1 of amelogenesis?

Answer 36

Ameloblast differentiation: * Dentine induces IEE cells to differentiate into ameloblasts * they elongate, becoming columnar * the nucleus migrates to the basal end of the cell

Question 37

What happens in step 2 of amelogenesis?

Answer 37

Secretory phase: * Ameloblasts become secretory cells * They synthesise and secrete the enamel matrix proteins (amelogenins) * The matrix is partially mineralised (30% mineral as seeded crystallites)

Question 38

What happens in step 3 of amelogenesis?

Answer 38

Maturation phase: * Most of the matrix proteins are removed * Mineral content of enamel is increased * Mature enamel is 95% mineral

Question 39

What happens in step 4 of amelogenesis?

Answer 39

Protection phase: * Ameloblasts regress to form a protective layer – the reduced enamel epithelium * Involved in eruption * Formation of epithelial attachment

Question 40

What is the full name of amelogenesis imperfecta?

Answer 40

Autosomal recessive hypoplastic hypomaturation amelogenesis imperfecta

Question 41

What gene does amelogensis imperfecta affect?

Answer 41

Matrix metallopeptidase 20 gene or MMP20

Question 42

What does MMP20 gene do?

Answer 42

Provides instructions for making enamelysin Enamelysin cleaves other proteins, such as amelogenin and ameloblastin, into smaller pieces (easier to remove)

Question 43

Why do teeth look dull in amelogenesis imperfecta?

Answer 43

not shiny due to low mineralisation of enamel enamel becomes similar to dentine composition and becomes indistingushable on radiographs

Question 44

What has to finish for root formation to begin?

Answer 44

crown formation

Question 45

What is the 5th stage in tooth development?

Answer 45

root formation

Question 46

Where do the EEE and IEE meet?

Answer 46

cervical loop

Question 47

What does migration of the cervical loop map out?

Answer 47

crown shape

Question 48

What is the apical growth (proliferation of cervical root cells) of cervical root known as?

Answer 48

hertwig’s epithelial root sheath

Question 49

How many layers is hertwig's epithelial root sheath? | How many layers is the enamel organ?

Answer 49

This is a 2-cell-layered structure, in contrast to the 4-layered enamel organ

Question 50

What does the Hertwig’s epithelial root sheath induce?

Answer 50

formation of root dentine

Question 51

What is ‘debris of Malassez’?

Answer 51

epithelial cells on the PDL that are remains of HERS -may develop into cyst

Question 52

What are cementoblasts?

Answer 52

differentiated ectomesenchymal cells from the follicle

Question 53

What are fibres from the developing PDL that are embedded into cementum called?

Answer 53

sharpeys fibres

Question 54

What are rests of malassez cysts called?

Answer 54

odontogenic cysts - happen during formation of dentine

Question 55

What is the type of tissue, origin and product of the enamel organ?

Answer 55

epithelium, ectoderm, enamel

Question 56

What is the type of tissue, origin and product of the dental papilla?

Answer 56

ectomesenchyme, neural crest, dentine, pulp

Question 57

What is the type of tissue, origin and product of the dental follicle?

Answer 57

ectomesenchyme, neural crest, cementum, PDL, alv bone

Question 58

How can teeth developmental abnormalities occur?

Answer 58

Prenatal ž Postnatal Inherited ž Acquired

Question 59

What is gemination

Answer 59

one tooth divided into two and fused together

Question 60

What is fusion?

Answer 60

two different teeth fused together with hypodontia of one

Question 61

What is concrescence?

Answer 61

joining of adjacent teeth by cementum.

Question 62

Which epithelium is found in the primary epithelial band?

Answer 62

Stratified squamous epithelium

Question 63

Notice the primary epithelial band in both the mandibular and maxillary processes. What relationship do they have to each other?

Answer 63

Maxilla labial to mandible

Question 64

The enamel organ is apparently connected by a stalk-like structure to the oral surface. This stalk like structure in 3D is U-shaped. What is the connecting stalk called?

Answer 64

dental lamina

Question 65

Where are the ectomesenchymal cells derived from?

Answer 65

neural crest

Question 66

What is the organic matrix of dentine called?

Answer 66

predentine

Question 67

What name is given to the layer of dentine formed first, which lies next to the future ADJ?

Answer 67

mantle dentine

Question 68

The epithelial cells next to the forming dentine What are they called?

Answer 68

IEE internal enamel epithelium

Question 69

The IEE cells can receive their nutrients from the blood vessels of the dental papilla. However, after dentine and enamel matrices are created, this is not possible. Therefore, the ameloblasts gather nutrients from a different source What is the evidence of that?

Answer 69

The presence of a rich vascular bed near the enamel organ a decrease in blood flow to the dental papilla after the matrix hardens.

Question 70

Predentine is the most recent secretion of the odontoblasts which has not yet had time to mineralise. Within this pale zone, look for globules which are stained darker pink. What are these ?

Answer 70

Calcospherites A spherical zone of hydroxyapatite formed during the mineralization phase of dentine formation Fuse together to form mineralised dentine

Question 71

Now look at the layer of columnar ameloblasts forming enamel. It is a single, much more regular layer than the odontoblast layer. Are these ameloblasts taller or shorter than the odontoblasts ?

Answer 71

taller

Question 72

Notice 2-3 rows of cells lying close to the ameloblasts. This is the stratum intermedium. Are the ameloblast nuclei nearer or further away from the stratum intermedium?

Answer 72

nearer

Question 73

What is globular dentine also known as?

Answer 73

calcospherites

Question 74

In the protective phase of amelogenesis, what happens to the ameloblast remains before/after eruption?

Answer 74

The reduced enamel epithelium forms the remains of the ameloblast cell layer and protects the enamel during eruption. After eruption it becomes the junctional epithelium.