Tooth development - Wright Flashcards
Neural crest cells originate from…
Neural crest cells are _____ in origin
What they do, what they form
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
Formation of Dental (general) Lamina:
increased mitotic activity in certain regions of epithelial bands.
4 types of lamina:
Dental lamina (aka general lamina)
vestibular lamina
lateral lamina
successional lamina
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.
Each tooth bud will grow on a
lateral lamina
all primary teeth grow from:
all succedaneous teeth grow from
permanent molars grow from:
dental lamina
successional lamina
dental lamina
key feature of mandible in histology:
Meckel’s cartilage
different stages of tooth development:
bud stage -> cap stage -> bell stage
Bud stage
facts:
begins 8th week
10 mandib / max buds
surrounding ectomesenchyme proliferates / condenses
basement membrane still intact
cap stage :
facts
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
bell stage:
processes that go on, and some facts
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.
The enamel organ at bell stage:
Outer enamel made of epithelial cells
dental papilla / follicle are connective tissue
stellate reticular cells: makes up bulk of enamel organ.
Stratum intermedium cells:
layer of cells between stellate reticulum and inner enamel epithelium
When does the dental papilla become pulp?
papilla becomes pulp when the first calcified tissue appears in the cusp region of the tooth.
dental follicle:
found in peripheral area of developing tooth.
lots of collagen fibrils
When does the dental lamina begin to fragment and disappear?
Bell stage. When this happens, tooth bud will no longer be connected to oral epithelium.
Formation of dentin and enamel:
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.
Layers in the formation of dentin and enamel:
dental follicle, stellate reticulum, then stratum intermedium, then ameloblasts, enamel, dentin, predentin, odontoblasts, dental papilla
Enamel organ relies on what to get nutrients?
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)
Ameloblasts separated with blood vessels due to huge stellate reticulum.
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.
Hertwig’s epithelial root sheath:
When stellate reticulum collapses, outer enamel epithelial cells and inner epithelial cells come together.
distal end of root sheath: epithelial diaphragm.
role of epithelial root sheath:
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
epithelial rests of malassez
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.
support structures: dental follicle becomes:
cementoblasts
osteoblasts
fibroblasts
cementoblasts: secrete cementum on surface of root
osteoblasts: secrete alveolar bone
fibroblasts: produce PDL
