CFD 12 - odontogensis 1a Flashcards
What is histogenesis?
differentiation of undifferentiated cells to make new tissues
What is the vestibular lamina?
contributes to the vestibule of the mouth, delineating the lips and cheek from the teeth, formation of sulcus
What are the stages of tooth development?
- initiation stage
- bud stage
- cap stage
- bell stage
4/5. crown stage (late bell stage)
What is the external enamel epithelium?
outer layer of cuboidal cells that limites the enamel organ
What is the stellate reticulum?
of epithelial origin but behave like mesenchymal cells
- synthesis of collagen I, II and III
What is the stratum intermedium?
two or three layers of cells sitting above IEE
- express Alkaline Phosphatase like SR but not IEE
What is the inner enamel epithelium?
columnar shaped cells rich in RNA
- connected by desmosomes to each other
What is ectomesenchyme?
interesting group of cells whose origin is very controversial
- some think neural crest others mesodermal somites
At what point in development does an area get ready for a tooth to develop?
around week 6
What happens during week 6 of development to get the area ready for tooth development?
- condensation of ectomesenchyme and a primary epithelial band being formed
- the band is starting to push inwards towards this condensation of mesenchyme
What does the primary epithelial band give rise to?
- dental lamina
- vestibular lamina
What does the vestibular lamina do?
- grows and then breaks down
- forms vestibule between teeth and lips/cheeks (the sulcus)
When the primary epithelial band pushes in, what causes the condensation of the mesenchyme to be triggered?
Fgf8
What do signals coming from the labial/buccal side of the primary epithelial band form?
the vestibular lamina
What do signals coming from the lingual side of the primary epithelial band form?
the dental lamina
By week 7 of development, what is the dental lamina doing?
interacting with the ectomesenchyme
By week 7 of development, what is the vestibular lamina doing?
pushing down and migrating into the mesenchyme, and proliferating quite a lot
By week 8 of development, what are the 2 distinct things going on in terms of tooth development?
- the bud of the dental lamina growing down, interacting with and causing the ectomesenchyme to start differentiating as well
- the vestibular lamina continuing to grow
By week 9 of development, what is happening in terms of tooth development?
signals have told the cells in the vestibular lamina to start dying off
By week 12 of development, what is happening in terms of tooth development?
- the cells of the vestibular lamina have died off, leaving a gap (the labial/buccal sulcus or vestibule)
- dental lamina is going through more and more processes for tooth formation
What are the 3 overlapping phases of tooth development?
initiation, morphogenesis and histogenesis
What 2 things are there interactions between during tooth development?
epithelium (ectoderm) and mesenchyme (ectomesenchyme)
What does the epithelium (ectoderm) give rise to?
- enamel
- hyaline layer of the root
What does the mesenchyme (ectomesenchyme) give rise to?
- dentine
- pulp
- cementum
- periodontium - PDL and bone
When and where are the first signs of initiation of tooth development?
- first signs: 6 weeks iul
- localised epithelial thickening in incisor and molar regions
Which tissue initiates tooth development?
- epithelium initiation has the odontogenic potential, then the ectomesenchyme
- 1st arch epithelium is what generates the initial signal (tissue recombination experiments)
Describe the bud stage of the tooth germ
- initiation of epithelial proliferation down into the mesenchyme causing the mesenchyme to condense into a small bell type shape
- looks like a small bud or droplet
Describe the cap stage of the tooth germ
- migration and proliferation within the mesenchyme by the epithelium and starting to surround the condensed ectomesenchyme of this area
- signals are going backwards and forwards between the two tissues, so you’re getting an interaction and different layers of the enamel organ which are going to form the pulp and the periodontium (the follicle)
- looks like a hat
Describe the bell stage of the tooth germ
- starting to get the shape of the tooth, differentiation in middle and around it
- the signals going on between these 2 areas are quite intense, and we’re seeing what’s being made and what’s forming
- matrix is starting to be formed
looks the shape of a tooth
Describe the late bell stage of the tooth germ
- dental lamina becomes removed from the external source so the tooth is now in an area of its own and is differentiating through
Describe the crown stage of the tooth germ
- starting to get hard tissue formation, dentin and enamel being formed
- more and more enamel and dentine being formed as we progress through, and the enamel organ starts to shrink and push down as the hard tissue growth
- at this point almost ready for tooth eruption
What are they components of the tooth germ?
- enamel organ
- dental papilla
- dental follicle
During the bud stage, what cell processes etc are happening?
No differentiation, mainly proliferations and interactions between the dental lamina and the dental papilla
During the cap stage, what cell processes etc are happening?
- cells of enamel organ still poorly differentiated epithelial cells, but they are interacting with the cells of the condensed ectomesenchyme
- there is some differentiation beginning to happen
During cap stage, what is happening to the dental lamina?
growing down but still attached to the oral epithelium
During the bell stage, what is happening to the dental lamina?
starting to shrink, it’s served its purpose and is now starting to disappear
During the bell stage, what is happening to the dental papilla?
it is differentiated
During the bell stage, what is happening to the outer mesenchyme?
Outer mesenchyme now becoming the dental follicle and is starting to surround and differentiate round the enamel organ
By the bell stage, what are the 4 distinct layers of the enamel organ?
- inner enamel epithelium
- stratum intermedium
- stellate reticulum
- outer enamel epithelium
By early bell stage, what has the ectomesenchyme differentiated to into?
- the dental papilla
- the dental follicle
What does the dental papilla form?
odontoblasts (dentine) and pulp
What does the dental follicle form?
cementum, PDL, and alveolar bone
What does the basal lamina of the inner enamel epithelium conform to?
future ADJ
What are the cells of the inner enamel epithelium like?
columnar cells at cusp tips
What is the role of the inner enamel epithelium?
forms ameloblasts —> enamel
What are the cells of the stratum intermedium like?
flattened cells
What is the role of the stratum intermedium?
synthesis and transport to and from IEE
- make matrix growth factors to allow them to interact and go on to form what they are
What are the cells of the stellate reticulum like?
star shaped - lots of desmosomes
- fluid filled extracellular space
- osmotic gradient due to extracellular GAGs
What is the role of the stellate reticulum?
maintenance of shape and protection of enamel organ once it’s formed
What are the cells of the outer enamel epithelium like?
cuboidal cells
What is the role of the outer enamel epithelium?
maintenance of shape and exchange
- allow exchange between the ectomesenchyme and the enamel organ
What are cells rests and cell nests?
- left after the break down of the dental lamina
- have cystic potential
What are the 3 transitory structures of the tooth germ?
- enamel knot
- enamel niche
- enamel septum
What is the enamel knot?
area of developing enamel which seems to send out signals
What is the enamel niche?
as dental lamina starts to break down, a hole or depression can be seen
What is the enamel septum?
seems to form between the outer and inner enamel epithelium
By what week of development is bud stage seen?
8th week
By what week of development is cap stage seen?
11th week
By what week in development is bell stage seen?
14th week
By what week in development is late bell stage seen (dental lamina is starting to break down)?
17th week
