Tooth development - Wright

Question 1

Neural crest cells originate from…
Neural crest cells are _____ in origin

What they do, what they form

Answer 1

Originate from neuro ectoderm
Neural crest cells are ectoderm in origin

They migrate to various parts of body, form various things like heart, ganglia, melanocytes

Neural crest cells that migrate to head / neck region form ecto-mesenchyme

Question 2

Formation of Dental (general) Lamina:

Answer 2

increased mitotic activity in certain regions of epithelial bands.

Question 3

4 types of lamina:

Answer 3

Dental lamina (aka general lamina)
vestibular lamina
lateral lamina
successional lamina

Answer 4

Each tooth bud will grow on a lateral lamina, associated with all the primary teeth, you’re going to have a successional lamina, where the succedaneous tooth will grow later on.

between dental ridge and lip, there is an oral vestibule, where vestibular lamina is.

So all primary teeth grow from dental lamina.
Successional teeth grow from successional lamina that grows off the dental lamina.

However, permanent molars grow out of general lamina just like the primary teeth.

Question 5

Each tooth bud will grow on a

Answer 5

lateral lamina

Question 6

all primary teeth grow from:
all succedaneous teeth grow from
permanent molars grow from:

Answer 6

dental lamina
successional lamina
dental lamina

Question 7

key feature of mandible in histology:

Answer 7

Meckel’s cartilage

Question 8

different stages of tooth development:

Answer 8

bud stage -> cap stage -> bell stage

Question 9

Bud stage

facts:

Answer 9

begins 8th week
10 mandib / max buds
surrounding ectomesenchyme proliferates / condenses
basement membrane still intact

Question 10

cap stage :

facts

Answer 10

begins 9th week
epithelial enamel organ becomes concave
enamel knot / cord appear. enamel knot helps development of cusps of tooth.

extra: can see dental lamina, successional lamina, lateral lamina, outer / inner enamel epithelium, stratum intermedium, stellate reticulum

Question 11

bell stage:

processes that go on, and some facts

Answer 11

hisodifferentiation: inner epithelial cells will transform into ameloblasts.
mesenchymal cells go into odontoblasts

morphodifferentiation: tooth shape determined. what type of tooth itll be. Can tell shape.

stellate reticulum: star structure. as glycosaminoglycans accumulate, spreads these cells apart and gives them the star appearance. glycosaminoglycans allow nutrient supply

cervical loop: forms all around tooth bud, where crown / pulp junction (cervical region) is.

Question 12

The enamel organ at bell stage:

Answer 12

Outer enamel made of epithelial cells
dental papilla / follicle are connective tissue
stellate reticular cells: makes up bulk of enamel organ.

Question 13

Stratum intermedium cells:

Answer 13

layer of cells between stellate reticulum and inner enamel epithelium

Question 14

When does the dental papilla become pulp?

Answer 14

papilla becomes pulp when the first calcified tissue appears in the cusp region of the tooth.

Question 15

dental follicle:

Answer 15

found in peripheral area of developing tooth.

lots of collagen fibrils

Question 16

When does the dental lamina begin to fragment and disappear?

Answer 16

Bell stage. When this happens, tooth bud will no longer be connected to oral epithelium.

Question 17

Formation of dentin and enamel:

Answer 17

It takes ameloblasts to get odontoblasts, but it takes dentin to get enamel.

1.) Ameloblasts differentiate from inner enamel epithelial cells starting at cusp region
2.) Ameloblasts release signals to neighbors, making ectomesenchymal cells to differentiate into odontoblasts.
3.) odontoblasts secrete dentin
4.) presence of dentin stimulates ameloblasts to secrete enamel.

Thus, this is known as reciprocal induction.

Also, dental lamina begins to degenerate during this time.

Question 18

Layers in the formation of dentin and enamel:

Answer 18

dental follicle, stellate reticulum, then stratum intermedium, then ameloblasts, enamel, dentin, predentin, odontoblasts, dental papilla

Question 19

Enamel organ relies on what to get nutrients?

Answer 19

Enamel organ = epithelial so therefore no direct blood supply.
Relies on CT nearby to provide nutrients.

2 sources: prior to hard tissue formation:
BVs in dental papilla, dental follicle.

after hard tissue formation:
dental follicle only. (note: odontoblasts still receive from pulp)

Question 20

Ameloblasts separated with blood vessels due to huge stellate reticulum.

Answer 20

stellate reticulum collapses to bring follicular blood supply closer to ameloblasts.

outer enamel eipthelial cells come into contact with stratum intermedium, blood vessels now much closer to ameloblast layer.

Question 21

Hertwig’s epithelial root sheath:

Answer 21

When stellate reticulum collapses, outer enamel epithelial cells and inner epithelial cells come together.

distal end of root sheath: epithelial diaphragm.

Question 22

role of epithelial root sheath:

Answer 22

the role of epithelial root sheath is to induce the formation of odontoblasts from the pulp in the root area.

It is the root sheath that is responsible for forming the root, because root is made primarily out of dentin, and dentin is secreted by odontoblasts

Question 23

epithelial rests of malassez

Answer 23

as the as the root elongates the root sheath begins to disintegrate and little clusters
of cells drift away from the root out into where the periodontal ligament is developing.

Question 24

support structures: dental follicle becomes:

cementoblasts
osteoblasts
fibroblasts

Answer 24

cementoblasts: secrete cementum on surface of root
osteoblasts: secrete alveolar bone
fibroblasts: produce PDL