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tooth development Flashcards

1
Q

what week is bud stage

A

8 weeks

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2
Q

what week is cap stage

A

10-12 weeks

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3
Q

at week is early bell stage

A

14 weeks

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4
Q

what week is late bell stage

A

18 weeks

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5
Q

8 stages of tooth development

A

Initiation
Inductive stage
Bud stage
Cap stage
Bell stage
Apposition
Root formation
PDL, cementum, AV bone development

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6
Q

week 2

A

-after fertilisation occurs, zygote cell undergoes mitosis and develops into blastocyst=cell that implants itself into endometrium of uterus—develops into bilaminar disc (bi=week 2)

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7
Q

week 3

A

-week 3 -bilaminar disc transfers into trilaminar disc—ectoderm, mesoderm and endoderm. Ectoderm sits above mesoderm, ectoderm forms a neural tube (made out of ectoderm cells)-contains neural crest cells, which migrate down towards mesoderm cells and form hybrid cell layer mixture known as ectomesenchyme cells. Neural crest cells assist the whole process

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8
Q

week 4

A

-week 4-formaiton of 5 key facial features-mouth, upper jaw and lower jaw

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9
Q

Where is oral epithelium derived from?

A

-ectoderm

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10
Q

Where is ectomesenchyme derived from?

A

-neural crest

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11
Q

what happens at week6

A

6-inititation: * First sign seen at week 6 is thickening of embryos oral epithelium forming 2 horseshoe shape bands in maxillary and mandibular. Epithelium and ectomesenchyme separated by primary epithelial band/basement membrane
Initiation stage
-ectoderm cells give rise to oral epithelium cells which thicken to form primary oral epithelium band
-continues to thicken and grows to underlying ectomesenchyme cells
-primary epithelium band is induced to split into dental vestibule and dental lamina

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12
Q

what happens at week 7

A
  • primary oral epithelium subdivides into (lump) vestibular lamina (give rise to oral vestibule) and dental lamina (future dentition)
    • Lamina begins to form in midline and progresses/proliferates posteriorly-
      -dental laminar is a protrusion inside the lower and upper jaw that will eventually initiate formation of teeth
    • Dental lamina formed by further thickening and growth of arch shaped epithelial band into ectomesenchyme
    • localised thickenings called germs, initiation of tooth formation
      By week 8-series of swellings on deep surface of lamina which are early developing tooth germs
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13
Q

what is orphogenesis

A
  • crown from/shape is determined. Occurs due to differential rates of mitosis and diff cell differentiation times
    Gives rise to individual tooth shape e.g. incisor, canine under influence of genetic programming and cell signalling from interactions between epithelial and mesenchymal cells
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14
Q

what is histogenesis

A
  • Differentiation of diff type of cell types which allow mineralised tissue to be formed
    histodifferentiation (cells of dental papilla differentiate into odontoblasts (produce dentine). Short columnar cells of enamel epithelium will diff into long columnar cells ameloblasts-form enamel)
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15
Q

Explain induction during initiation

A

-proteins pass between primary epithelium band and ectomesenchyme cells
-proteins bind onto specific cell receptors and attract specific transcription factors to initiate gene expression–causes formation of 10 placodes to form per jaw
* Bioactive signalling molecules are produced in specific sequence
* pass between epithelium and mesenchyme binding to cell receptors and set off series of intracellular cascades that regulate gene expression and alter cell behaviour
* A key gene expressed is SHH. Forms little packs of proteins that will help cell expression of genes, which will determine type of tooth/root length etc, leads to formation of dental placodes. 10 codes upper and 10 lower—determine structure
* These signals operate throughout development and regulate expression of genes in the responding tissues

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16
Q

what are homeobox genes

A

genes that specify identity of cells and positioning

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17
Q

what are neural crest cells

A

form tissues of ectomesenchyme which instruct tooth germ to tooth type.

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18
Q

Explain early bud stage

A

-7+ weeks
-Dental placodes goes further into ectomesenchyme and makes shape of bud, Germ attached to oral epithelial layer via the dental lamina
-ectomesenchyme cells surround the bud and condense beneath it
-no morpho differentiation/hist

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19
Q

bud stage

A

week 8
-growing enamel organ ovoid shape
-Density of ectomesenchyme increases and becomes more condensed near bud.
-ectomesenchyme undergoing proliferation-surrounds enamel organ and is growing and condensing
-Dental papilla=condensed ectomesenchyme (gives rise to future dentine and pulp).
-Enamel organ=tooth bud (look at pic)
-bud has differential proliferation-cells in centre proliferate slower leading bud shape to make cap shape

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20
Q

early cap stage

A

week 10
Early cap stage=histogenesis
-early histogenesis =3 new types of cells: inner enamel epithelium, outer enamel epithelium stellate reticulum

* Cross section of enamel looks like a cap. Enamel organ drags the dental lamina and makes shape of a cap. No morpho yet
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21
Q

Stellate reticulum

A

-continuous with superficial layer, linked by desmosomes
-form network in enamel organ
-have cushioning and nutrient role for cells of Inner and outer EE
-lies between the stratum intermedium and the outer enamel epithelium.
-protects underlying dental tissues and maintains tooth shape
-will differentiate into cementum, periodontal ligament and alveolar process
-supports production of enamel matrix

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22
Q

Stratum intermedium

A

-more inner compressed layer of flat cells
-supports production of enamel matrix

23
Q

What is tooth germ

A

dental papilla, follicle, enamel organ

24
Q

Enamel knots

A

-Non dividing cells, sit at bottom of epithelium=signalling centre that regulates formation of cusps of tooth.
-Number and location of enamel knots determine number and location of cusps)

25
Q

Outer enamel epithelium

A

-outer cuboidal cells of enamel organ, serves as protective bar for enamel organ, line sides of cap

26
Q

Inner enamel epithelium

A

Tall, columnal cells of enamel organ, will diff into ameloblast, line inner surface of caps central depression

27
Q

late cap stage

A

week 12
more histogenesis-SR develops into star shaped cells, IEE start to fold into a shape development of papilla BUT still no morphogenesis, dental follicle and papilla forms

28
Q

what happens to SR in late cap stage

A

-SR produce glycosaminoglycans which attracts water between the cells, pushing the cells apart but contact still maintained by desmosomes
-IEE begin to fold-they grow/taller, more cuboidal. Enamel knots (toe of cells that influence formation of cusps) migrate near the IEE and influence the folding near the IEE to influence folding via mitogenic factors

29
Q

-development of Dental papilla

A

dense condensation of ectomesenchyme cells beneath cap, formed from ectomesenchyme cells found just beneath the germ.
-This papilla responsible for forming dentine and pulp.

30
Q

Ectomesenchyme cells found a round cap will specialise into dental follicle cells

A

-increasing amount of collagen fibres around enamel organ, serves protective bar for enamel organ
-ectomesenchyme cells surrounding enamel organ and dental papilla
and responsible for forming separate structures such as cementum, PDL and AV bone

31
Q

Outer cells of dental papilla

A

-Outer layer of cells of dental papilla nearest to IEE and enamel organ. Basement membrane between outer layer and IEE
-will diff into ondoblasts that form dentine matrix

32
Q

Central cells of dental papilla

A

central cell mass of dental papilla, will differentiate into pulp tissue

33
Q

when is
Early bell stage

A

week 14

34
Q

what happens at early bell stage

A

-morpho differentiation-recognisable tooth shape determined, occurs due to differential rates of mitosis and diff cell differentiation times

35
Q

what happens to IEE at early bell stage

A

-histodifferentiation visible- cell type differentiation as IEE cells become tall columnar cells, Cells of IEE will stop dividing and start diff into ameloblasts. Pressure exerted on ameloblasts due to continuous cell division so ameloblasts pushed into future cusp tip area and make enfolding which gives rise to molar tooth

36
Q

what happens to OEE at early bell stage

A

short columnar OEE cells of enamel epithelium will diff into ameloblasts

37
Q

what happens to SR cells ay early bell stage

A

-few epithelial cells between stellate reticulum and inner enamel epithelium differentiate into layer of spindle shaped cells called stratum/stellate intermedium cells, assist enamel formation. This reduces distance between IEE and OEE, creating bell shape. SR starts to collapse eventually

38
Q

what happens to -dental papilla at early bell stage

A

cells on outer surface form odontoblasts, inner cells form pulp

39
Q

what happens to -Dental follicle at bell stage

A

composed of several layers of ‘flattened’ cells from which cementum, periodontal ligament and some alveolar bone formed

40
Q

when is Late bell stage

A

week 18

41
Q

what happens at late bell stage

A

-morpho differentiation of crown is complete, histodiff continuing
-Histodifferentiation of ameloblasts from IEE leads to differentiation of odontoblasts from ectomesenchyme peripheral cells of dental papilla, which lays down dentine, after this the ameloblasts create enamel
-odontoblasts lay first layer of dentine, after first layer formed, enamel formation begins
-Enamel and dentine formation starts at tips of future cusps/incisal edges
-Alveolar bone is deposited around developing tooth
-Am and od continue to secrete mineralised matrix, dental lamina disintegrates and detaches tooth germ from oral epithelium

42
Q

Dentinogenesis late bell stage/how is dentine formed

A

-enamel organ fully formed with differentiated IEE, but no enamel laid down
-differentiation of odontoblasts from peripheral cells of dental papilla is initiated by series of epithelial signals from IEE
-dental matrix deposited first by odontoblasts that start differentiating
-fully differentiated odontoblasts have an odontoblastic process–they secrete mineralised dentine matrix

43
Q

Direction of odontoblast and dentine formation

A

-odontoblast differentiation and dentine formation begins where cusps will later form and continues uniformly down slopes of cusps and walls of crown to cervical loop
-dentine gradually forms bulk of tooth tissue. As dentine thickness increases, odontoblast cell bodies at dentine-pulp interface are pushed inwards towards pulp, so move away from future ADJ
-following crown formation, process continues in an apical direction to form root dentine

44
Q

Amelogenesis-formation of enamel

A

-amelogenesis and dentinogenetic occur almost simultaneously
-the site where they both begin is the future amelodentinal junction ADJ
-at this stage, cells of inner enamel epithelium have undergone histodifferentiation into tall columnar cells, the IEE outlines the shape of the crown
-deposition of dentine matrix induces IEE cells to differentiate further into secretory ameloblasts
-ameloblasts have a tomes process, they deposit and later modify enamel
-enamel is formed incrementally (in stages) similar to dentine
-as enamel thickness increases ameloblast cell bodies are pushed outwards away from future ADJ
-amelogenesis is under genetic control, the thickness, morphology, colour and surface characteristics of teeth conferred by enamel are inherited
-ameloblast differentiation and enamel formation seen first at future cusp tips/incisal edges, then progresses cervically towards crown-root junction

45
Q

What is reduced enamel epithelium

A

-as ameloblasts move away from ADJ towards OEE and after enamel appositional growth ceases in the crown of each primary/permanent tooth, the layers of enamel organ become compressed, forming the reduced enamel epithelium

46
Q

How is crown formed

A

-crown emerges through an epithelium-lined pathway intro oral cavity due to fusion of REE with oral epithelium lining the oral cavity, followed by disintegration of central parts of this tissue

47
Q

What are rests of serres

A

-remnants of the dental lamina may persist in adult mucosa as epithelial rests of Serres
-some of these may proliferate to produce clusters of epithelial cells with tightly packed keratin–these may udnergo cystic change and are then referred to as a gingival cysts of new born

48
Q

What is apposition

A

Apposition-breakage of dental lamina-lamina detaches from tooth germ, this releases enamel organ from OEE-this can sometimes leave epithelial pearls. Epithelial pearls may rise to form abnormalities/become part of the adult OE/produce clusters of epithelial cells

49
Q

Root formation

A

Cervical loop proliferates downwards to produce 2 layer structure called root sheath.
Root formation-involves interaction of follicle cells, papilla cells and Hertwigs epithelial root sheath (HERS)
-HERS is a 2 layered structure made by combo of IEE and OEE, guides formation and length, induces differentiation of odontoblasts into dentine for root
-(this encloses dental papilla and grows apically to outline shape of future root and form apical foramen
-HERS turns medially before it grows vertically e.g. like root sheath as skirt hanging down from enamel organ.)

50
Q

What does disintegration of root sheath lead to?

A

Disintegration of root sheath results in epithelial rests of which allows dental follicle to come contact with dentine and their differentiation into cementoblasts which deposit cementum (lines root).
-remaining cells of dental follicle form periodontal ligament
-alveolar bone of tooth socket is developing

51
Q

cementum

A

-cementum-dental follicle cells interact and differentiate into cementoblasts which deposit cementum over top of root, this is a weak structure and is usually exposed when a patient does not look after their teeth

52
Q

Pdl

A

-PDL is a glue/connection between tooth and bone. Follicle cells rise to fibroblasts which forms the ligament, the bone holds the teeth in place and acts as a socket

53
Q

Alveolar bone

A

follicle cells rises to osteoblasts which form the bone

tooth development (1 decks)

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