Dental Development 2 (embryology)

Question 1

what is the purpose of the dental papilla cells adjacent to the IEE?

Answer 1

the differentiate into odontoblasts

Question 2

what is the function of odontoblasts in tooth formation?

Answer 2

they lay down dentine matrix, which is later mineralised

Question 3

what occurs to internal enamel epithelium cells once dentine formation begins?

Answer 3

they differentiate into ameloblasts

Question 4

what is the function of ameloblasts?

Answer 4

they form enamel

Question 5

what is are the steps of dentinogenesis?

Answer 5

1. odontoblast differentiation from IEE
2. deposition of dentine matrix (mainly collagen)
   - this unmineralised dentine is predentine
3. mineralisation of dentine (hydroxyapatite)

Question 6

what percentage of enamel is mineralised (roughly)?

Answer 6

96%

Question 7

describe the stages of enamel formation:

Answer 7

1. protein matrix deposited (this matrix is partially mineralised 30%)
2. once this framework is established, the organic part is removed & mineralisation is completed (‘maturation’)

Question 8

what are the different phases of ameloblasts throughout their differentiation lifetime?

Answer 8

1. morphogenic
2. histodifferentiation
3. secretory (initial)
4. secretory (tomes process)
5. maturative ruffle-ended)
6. maturative (smooth)
7. protective

Question 9

how can the change of the ameloblast cell be described during the first stages of differentiation?

Answer 9

• dentine induces IEE cells to differentiate into ameloblasts
• they ELONGATE, becoming COLUMNAR
• the nucleus migrates to the basal end of the cell

Question 10

what process occurs when ameloblasts become secretary cells?

Answer 10

— they synthesise and secrete the enamel matrix proteins

— the matrix is partially mineralised (30% mineral as seeded crystallites)

Question 11

what occurs during the maturation phase of amelogenesis?

Answer 11

• most of the matrix proteins are removed
• mineral content of the enamel is increased
• mature enamel is 95% mineral

Question 12

what occurs during the protection phase of amelogenesis?

Answer 12

• ameloblasts regress to form a protective layer (the reduced enamel epithelium)
• this epithelium is involved in eruption and formation of epithelial attachment

Question 13

what does the term hypoplastic mean?

Answer 13

reduction of the plasticity of enamel

Question 14

what gene is involved in the clinical condition Amelogenesis Imperfecta? where is this gene located?

Answer 14

• matrix metallopeptidase 20 gene (MMP20)

- located on the long arm of chromosome 11 (position 22.3)

Question 15

what type of disease is amelogenesis imperfecta?

Answer 15

an AUTOSOMAL disease

Question 16

what is enamelysin?

Answer 16

• an enzyme that breaks enamel

- also cleaves proteins such as amelogenin and ameloblastin into smaller pieces

Question 17

what are the clinical signs of Amelogenesis Imperfecta?

Answer 17

• dull and rough enamel (teeth appear yellow)
• LOW MINERALISATION of enamel
• on radiograph it is hard to distinguish between enamel and dentine (due to low mineral enamel content)

Question 18

what is Dentinogenesis Imperfecta?

Answer 18

a condition that causes dentine to be unmineralised (or less mineralised than normal)

Question 19

what clinical findings would be seen in a patient suffering from dentinogenesis imperfecta?

Answer 19

• dark coloured teeth

- on radiograph the pulp cannot be seen (as dentine is so unmineralised you cannot differentiate between the two)

Question 20

what must be completed before root formation can begin?

Answer 20

crown formation!

Question 21

what is the role of the enamel organ in root formation?

Answer 21

the enamel organ maps out the shape of the crown

Question 22

where do the EEE and IEE meet?

Answer 22

the cervical loop!

Question 23

what is the function of the cervical loop in root formation?

Answer 23

the ROOT SHAPE is defined by apical growth of the cervical loop… which has a different name at this stage

Question 24

what is the cervical loop called during root formation?

Answer 24

Hertwig’s epithelial root sheath (2-cell-layered structure)

Question 25

what does Hertwig’s epithelial root sheath induce?

Answer 25

formation of root dentine

Question 26

what occurs once the initial layer of root dentine is formed?

Answer 26

Hertwig’s sheath breaks up (remains of HERS persist as ‘debris of Malassez)

Question 27

what type of cells go on to differentiate into cementoblasts when they come into contact with dentine?

Answer 27

Mesenchymal cells from the follicle

Question 28

what is the function of cementoblasts?

Answer 28

to form cementum

Question 29

what are ‘Sharpey’s fibres’?

Answer 29

fibres from the developing PDL that are embedded in the cementum

Question 30

what are the different groups of teeth developmental abnormalities?

Answer 30

• prenatal
• postnatal
• inherited
• acquired

Question 31

what is gemination of teeth?

Answer 31

• a tooth that divides into two! (like a twin)

Question 32

what is fusion of teeth?

Answer 32

• merging of two teeth during development

Question 33

what is concrescence?

Answer 33

joining of teeth via cementum