tooth development

Question 1

when do deciduous teeth begin formation

Answer 1

week 6-7 of interuterine life

Question 2

when do permanent teeth begin developing

Answer 2

week 14

Question 3

when do permanent molars begin developing

Answer 3

week 20

Question 4

what two tissue components begin the development of teeth

Answer 4

primitive oral epithelium
underlying ectomesenchyme

Question 5

what is the ectomesenchyme derived from

Answer 5

craniofacial neural crest cells

Question 6

what is the purpose of the primitive oral epithelium and the ectomesenchyme

Answer 6

they instruct each other to determine the formation and location of the teeth

Question 7

how does tooth formation begin

Answer 7

thickening of the primitive oral epithelium to form the primary epithelial bands, with one on each jaw

Question 8

what happens after the formation of the primary epithelial bands

Answer 8

each one splits into two - the inner dental lamina and the outer vestibular lamina

Question 9

what does the vestibular lamina do

Answer 9

it hollows out to form the vestibule of the mouth, which is the space between the alveolar bone and the labial/buccal surfaces

Question 10

which signal proteins causes the dental lamina cells to proliferate

Answer 10

FGFs
BMPs
ectodisplacin

Question 11

what are dental placodes

Answer 11

localised projections in the dental lamina which are invaginations for the positions of the future teeth. form the enamel organ

Question 12

what happens when the dental placodes proliferate

Answer 12

the teeth undergo morphogenesis, resulting in different tooth shapes.

Question 13

what guides the proliferation of the dental placode

Answer 13

interactions between the epithelial and mesenchymal tissues

Question 14

what are the three main stages of tooth morphogenesis

Answer 14

bud
cap
bell

Question 15

describe the bud stage

Answer 15

this is when the dental placodes form bud like structures attached to the oral epithelium by the dental lamina
ectomesenchymal cells cluster around the bud to form a condensation of the ectomesenchyme right beneath the bud

Question 16

what are the cell types forming the enamel organ at the bud stage

Answer 16

outer layer of low columnar cells and an inner bundle of polygonal cells

Question 17

why is the bud stage unique

Answer 17

due to differential proliferation, ie the cells at the centre are slower to differentiate than those at the peripherals

Question 18

what makes the bud shape of the enamel organ become a cap shape

Answer 18

the differential proliferation of the bud stage cells

Question 19

describe the cells found in the cap stage of the enamel organ

Answer 19

inner enamel epithelium
outer enamel epithelium
stellate reticulum

Question 20

where is the inner enamel epithelium of the cap stage found

Answer 20

as a low columnar lining of the inner surface of the central depression of the cap

Question 21

describe the outer enamel epithelial lining of the cap

Answer 21

cuboidal lining around the side of the cap on the outside

Question 22

what is the stellate reticulum

Answer 22

cells linked by desmosomes that secrete glycosaminoglycans into the extracellular space, which attracts water in the ECS, pushing on their membranes to turn them into the shape of a star

Question 23

what are the enamel knots

Answer 23

non dividing cells at the inner enamel epithelium which are the signalling centre that functions to regulate the formation of the cusps of the developing tooth

Question 24

describe the change from cap to bell stage in the tooth formation

Answer 24

• ectomesenchymal cells continue to accumulate, particularly by the invagination of the cap
• dense condensation beneath the cap is known as the dental papilla
• accumulation encircling the dental papilla and the enamel organ is the dental follicle
• as the enamel organ grows, the invagination deepends, forming the cervical loop where the inner and outer enamel epithelium meet

Question 25

what is the stratum intermedium formed by

Answer 25

epithelial cells between the stellate reticulum and the inner enamel epithelium that differentiate into a layer of spindle shaped cells - this is the stratum intermedium

Question 26

function of the stratum intermedium

Answer 26

glycogen storage

Question 27

what does the bell shaped structure of the enamel organ represent

Answer 27

the shape of the crown of the tooth

Question 28

what happens in the late bell stage of the enamel formation

Answer 28

future shape of the crown is determined

Question 29

what happens to the stellate reticulum in the bell stage

Answer 29

collapses to reduce the distance between the inner and outer enamel epithelium

Question 30

what forms odontoblasts

Answer 30

dental papilla

Question 31

what forms ameloblasts

Answer 31

inner enamel epithelium

Question 32

what happens to the dental lamina as the ameloblasts and odontoblasts are secreting their mineralised matrixes

Answer 32

it disintegrates to detach the tooth germ from the oral epithelium

Question 33

what does the disintegration of the dental lamina lead to

Answer 33

epithelial pearls being left over, which can give rise to supernumerary teeth, odontoma and eruption cysts

Question 34

when does root formation begin

Answer 34

after crown development

Question 35

describe root formation

Answer 35

- cervical loop cells proliferate downward to form HERS - HERS migrates downward to guide root formation and induce the differentiation of odontoblasts - limited growth potential determines the length of the root - distintegration of hers leads to rests of malassez, which allows cells of the dental follicle to come in contact with root dentine and their differentiation into cementoblasts

Question 36

what forms periodontal ligament

Answer 36

fibroblasts which differentiate from the dental follicle cells

Question 37

what does the dental follicle give rise to

Answer 37

fibroblasts and osteoblasts to form the periodontal ligament and alveolar bone

Question 38

describe development of the permanent teeth

Answer 38

- extension of a tiny bit of dental lamina behind the deciduous tooth bud - this is the successional lamina - gives rise to all permanent teeth except the molars - dental lamina in the posterior regions of the jaw bury into the oral epithelium and give off tooth buds that undergo the same stages of development as deciduous tooth buds

Question 39

what forms the enamel organ

Answer 39

dental placodes

Question 40

what process allows formation of ameloblasts and odontoblasts

Answer 40

histodifferentiation

Question 41

when do the permanent molars develop

Answer 41

from week 20 to five years after birth

Question 42

where do the permanent molars develop from

Answer 42

directly from the dental lamina