Dental Development (embryology)

Question 1

what are the three primary embryonic layers that all body tissues develop from?

Answer 1

• ectoderm
• mesoderm
• endoderm

Question 2

what embryonic layer is tooth enamel derived from?

Answer 2

the ectoderm

Question 3

what embryonic structure are the teeth and supporting structures derived from? (EXCLUDING ENAMEL)

Answer 3

the ectomesenchyme

Question 4

what is the ectomesenchyme?

Answer 4

it is part of the neural crest that develops beside the ectoderm

Question 5

what can the ectoderm also be referred to as?

Answer 5

the primitive nervous system

Question 6

what do teeth develop from?

Answer 6

tooth germs

Question 7

what is the neural crest?

Answer 7

a fourth cell type that forms between the ectoderm and the neural tube!

Question 8

how is the neural crest relevant to tooth formation?

Answer 8

neural crest tissue migrates into the developing face and jaws

Question 9

what is a failure of ectomesenchymal cells to migrate also known as?

Answer 9

mandibulofacial dysostosis

Question 10

what are examples of clinical signs of failed migration of ectomesenchymal cells?

Answer 10

• large interpupillary distance
• underdeveloped mandible and maxilla
• TEETH CROWDING!!! (as a result)

Question 11

what are the 5 main stages of tooth development?

Answer 11

1. initiation
2. morphogenesis
3. cytodifferentiation
4. matrix secretion
5. root formation

Question 12

what occurs during tooth initiation?

Answer 12

formation of the dental lamina

Question 13

what is the primary epithelial band?

Answer 13

• a thickening in the epithelium of the embryonic mouth (stomodaeum)

Question 14

when does the primary epithelial band develop?

Answer 14

approx 6 weeks IUL (intra uterine life)

Question 15

what does the primary epithelial band go onto form?

Answer 15

• vestibular lamina

- dental lamina

Question 16

when does the dental lamina form?

Answer 16

approx 7 weeks IUL

Question 17

what does the vestibular lamina go onto form?

Answer 17

breaks down to form the buccal sulcus

Question 18

what does the enamel organ develop from?

Answer 18

the dental lamina

Question 19

describe the shape of the dental lamina?

Answer 19

horse shoe shaped structure

Question 20

what is meant by morphogenesis in relation to tooth development?

Answer 20

• the shape of the structure begins to form

Question 21

what stages fall under the morphogenesis aspect of tooth development?

Answer 21

• bud stage

- cap stage

Question 22

when does the ‘bud stage’ occur?

Answer 22

approx 8-10 weeks IUL

Question 23

what occurs during the bud stage?

Answer 23

the dental lamina thickens into a ‘bud’ stage enamel organ

Question 24

what is the bud to cap stage?

Answer 24

rearrangement of shape to look like a cap!

Question 25

when does the ‘cap’ stage occur?

Answer 25

approx 11 weeks IUL

Question 26

what occurs during the cap stage?

Answer 26

the enamel organ forms ‘a cap’ over the papilla

Question 27

what is the ‘cap stage’ enamel organ composed of?

Answer 27

- external enamel epithelium | - internal enamel epithelium

Question 28

what are placodes?

Answer 28

embryonic structures that give rise to structures such as hair follicles, teeth, nails etc.

Question 29

what is meant by ectodermal dysplasia?

Answer 29

a group of disorders in which two or more of the ectodermally derived structures (teeth, hair, nails etc.) develop abnormally

Question 30

what is hypohidrotic ectodermal dysplasia?

Answer 30

a condition that causes hypodontia of the teeth

Question 31

what is hypodontia?

Answer 31

the developmental absence of one or more teeth

Question 32

what occurs in a patient that has severe hypoidrotic ectodermal dysplasia?

Answer 32

absence of TEETH and HAIR

Question 33

when does the ‘bell stage’ occur?

Answer 33

approx 14 weeks IUL

Question 34

what is the purpose of the bell stage?

Answer 34

- more cell layers are differentiated | - tooth shape is being defined

Question 35

what are the 4 cell layers of the ‘bell stage’ enamel organ?

Answer 35

- stratum intermedium - stellate reticulum - internal enamel epithelium - external enamel epithelium

Question 36

what is found in the stellate reticulum?

Answer 36

glycogen (energy) for the amelloblasts to create the matrix

Question 37

when the crown of the tooth is being formed, explain the patter of differentiation:

Answer 37

- differentiation starts at the apical portion of the tooth | - the differentiation continues down towards the cervical loop

Question 38

what occurs at approximately 12 weeks in relation to the dental lamina?

Answer 38

an extension appears on the lingual side of the dental lamina - this is the dental lamina for the future permanent tooth

Question 39

what occurs as a backwards extension of the dental lamina?

Answer 39

the 1st permanent molar germ

Question 40

what occurs at approx. 18 weeks IUL?

Answer 40

the ‘late bell stage’ of the enamel organ

Question 41

what occurs during the late bell stage?

Answer 41

apposition of enamel and dentine begins