tooth development Flashcards
when do deciduous teeth begin formation
week 6-7 of interuterine life
when do permanent teeth begin developing
week 14
when do permanent molars begin developing
week 20
what two tissue components begin the development of teeth
primitive oral epithelium
underlying ectomesenchyme
what is the ectomesenchyme derived from
craniofacial neural crest cells
what is the purpose of the primitive oral epithelium and the ectomesenchyme
they instruct each other to determine the formation and location of the teeth
how does tooth formation begin
thickening of the primitive oral epithelium to form the primary epithelial bands, with one on each jaw
what happens after the formation of the primary epithelial bands
each one splits into two - the inner dental lamina and the outer vestibular lamina
what does the vestibular lamina do
it hollows out to form the vestibule of the mouth, which is the space between the alveolar bone and the labial/buccal surfaces
which signal proteins causes the dental lamina cells to proliferate
FGFs
BMPs
ectodisplacin
what are dental placodes
localised projections in the dental lamina which are invaginations for the positions of the future teeth. form the enamel organ
what happens when the dental placodes proliferate
the teeth undergo morphogenesis, resulting in different tooth shapes.
what guides the proliferation of the dental placode
interactions between the epithelial and mesenchymal tissues
what are the three main stages of tooth morphogenesis
bud
cap
bell
describe the bud stage
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
what are the cell types forming the enamel organ at the bud stage
outer layer of low columnar cells and an inner bundle of polygonal cells
why is the bud stage unique
due to differential proliferation, ie the cells at the centre are slower to differentiate than those at the peripherals
what makes the bud shape of the enamel organ become a cap shape
the differential proliferation of the bud stage cells
describe the cells found in the cap stage of the enamel organ
inner enamel epithelium
outer enamel epithelium
stellate reticulum
where is the inner enamel epithelium of the cap stage found
as a low columnar lining of the inner surface of the central depression of the cap
describe the outer enamel epithelial lining of the cap
cuboidal lining around the side of the cap on the outside
what is the stellate reticulum
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
what are the enamel knots
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
describe the change from cap to bell stage in the tooth formation
- 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
what is the stratum intermedium formed by
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
function of the stratum intermedium
glycogen storage
what does the bell shaped structure of the enamel organ represent
the shape of the crown of the tooth
what happens in the late bell stage of the enamel formation
future shape of the crown is determined
what happens to the stellate reticulum in the bell stage
collapses to reduce the distance between the inner and outer enamel epithelium
what forms odontoblasts
dental papilla
what forms ameloblasts
inner enamel epithelium
what happens to the dental lamina as the ameloblasts and odontoblasts are secreting their mineralised matrixes
it disintegrates to detach the tooth germ from the oral epithelium
what does the disintegration of the dental lamina lead to
epithelial pearls being left over, which can give rise to supernumerary teeth, odontoma and eruption cysts
when does root formation begin
after crown development
describe root formation
- 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
what forms periodontal ligament
fibroblasts which differentiate from the dental follicle cells
what does the dental follicle give rise to
fibroblasts and osteoblasts to form the periodontal ligament and alveolar bone
describe development of the permanent teeth
- 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
what forms the enamel organ
dental placodes
what process allows formation of ameloblasts and odontoblasts
histodifferentiation
when do the permanent molars develop
from week 20 to five years after birth
where do the permanent molars develop from
directly from the dental lamina
