tooth development 1:) Flashcards
primary dentition
5 teeth 2 incisors 1 canine 2 motors tooth morphology different between jaws
permanent dentition
8 teeth 2 incisors 1 canine 2 premolars 3 molars
tooth development stages
initiation
morphodifferentiation
cytodifferentiation
initiation stage
starts tooth formation
correct number in correct location in jaw
morphodifferentiation stage
formation in correct shape
cytodifferentiation stage
differentiation of cells to produce specific dental tissue
what is the fist sign of tooth deelopment
primary epithelial band
thickened band of ectoderm along each dental arch
when does the primary epithelial band appear
7 weeks post fertilisation after maxillary arch formed
what gives rise to Md/Mx
pharyngeal arch
what does the primary epithelial band do
tooth buds grow downwards into dental lamina to form buds
induces condensation of ectomesenchymal cells beneath the band
cells gather round and become denser due to signals from ecotoderm
what happens after condensation of ectomesenchymal cells
epithelual band divides into dental laminar and vestibular lamina
continue to proliferate
the superficial cells of vestibular lamina degenerate to form a vestibule/sulcus
what are signalling molcules and what are they expressed by
BMPs and FGFs
ectoderm
what do the growth factors interact with
first arch ectomesenchyme to form the correct number of tooth buds in each quadrant
chronological order from ectoderm formation
- Ectoderm thickens to give primary epithelial band
- Epithelium proliferates and grows into the lamina propria underneath
- Underneath the band are ecto-mesenchyme cells which condense (get thicker)
originate from the neural crest - Epithelial band divides and grows downwards into 2 sections
Dental lamina
Vestibular lamina:
proliferates down, superfial cells then degenerate to form a vestibule/sulcus (gutter on lingual and buccal side)
what does the epithelial band divide into
dental lamina
vestibular lamina
where does the ectoderm originate from
facial processes
what do mesenchymal cells originate from
neural crest
what do the ectoderm and mesenchymal cells undergo
epithelial mesenchymal interactios to differentiate Into particular cells
what does the oral ectoderm form
teeth in combination with first arch ectomesenchyme
what is DLX gene coding
expression of homeobox genes at specific parts of the arch defines each type of tooth
how does expression of genes affect the teeth
- each gene is expressed in a decreasing gradient from anterior to posterior i.e. 4 is more likely to be formed than 5
what is it called when you introduce genes into a tissue
electroporation
what is the effect of disruption to the initiation stage
anodontia
hyperdontia
hypodontia
anodontia
no teeth are formed
hypodontia
few teeth don’t develop
occurs at the end of expression domain
commonly affects 8>5>3
hyperdontita
extra teeth
what are extra teeth known as
supernumerary
what do supernumerary teeth look like
atypically shaped teeth (accessory) normal teeth (supplemental teeth)
what happens after initiation
differentiation of oral ectodermal components into EO
ectomesenchymal components into dental papilla
what differentiates into EO
oral ectoderm
what differentiates into dental papilla
ectomesenchymal components
what happens after differentiation into the EO ad DP
tooth bud grows into the CT
Tip of EO grows around the DP
now tooth germ not a bud
how is determination of the shape of inidiviaul shape produced
selective division in the internal dental epithelial layer of EO
morphodifferentation
internal layer of EO undergoes mitosis
leads to buckling of the future ADJ
where do the signals for mitosis of the IDE of EO come from
DP and enamel knot
what is and does the enamel knot do
tight group of cells
refines signals from the DP
controls selective mitosis of IDE
what induces the enamel knot to form
BMP4
what determines the basic tooth shape
dental papilla
what separates the EO from the DP in recombination experiments
trypsin
what singnals are sent from the DP and EK
BMPs 2 and 7
FGFs
Wnt
EK:
SHH
what happens after the shape of future junction of enamel and dentine is mapped out
EK disappears
permanent tooth bud arises from side of EO of primary teeth
dental follicle around whole tooth
dental lamia disintegrates
what are the layers in the EO
external dental epithelium
stellate reticulum
stratum intermedium
internal dental epithelium
stellate reticulium
largest area of the EO
star shaped cells joined by desmosomes
network, cells widley scattered
stratum intermedium
sits on top of the IDE
squamous cells layered
function of the EDE
regulates entry of nutrients
thin layer of cuboidal cells
function of stellate reticulum
space packing with ECM
nutrients to the IDE
protects the tooth
lots of Ca and phosphate needed for enamel
function of stratum intermedium
essential for enamel formation
function of IDE
differentates into amelolasts to form enamel
what happens if morphodifferentaiton is no carried out correctly
bizzare shaped teeth
permanent molar orgin
primary epithelial band grows posterially as jaws grow
three new buds arise
