Tooth Development Flashcards
what are the 3 primary embryonic layers?
ectoderm, mesoderm and endoderm
what layer is tooth enamel derived from?
ectoderm
apart from enamel, what are all parts of teeth and supporting structures derived from?
ectomesenchyme
what is the ectomesenchyme
part of the neural crest that develops beside the primitive nervous system (ectoderm)
what do teeth develop from
tooth germs
what is the neural crest also called?
ectomesenchyme
what does the neural crest tissue migrate into?
the developing face and jaws
what is mandibulofacial dysostosis
failure of ectomesenchymal cells to migrate
what are the stages in tooth development?
initiation, morphogenesis, cytodifferentiation, matrix secretion, root formation
when does the primary epithelial band form?
6 weeks IUL
what does the primary epithelium band appear as?
thickening in epithelium of embryonic mouth (stomodaeum)
what happens to the primary epithelial band at 7 weeks IUL?
it grows into the jaw and divides into vestibular lamina and dental lamina
what does vestibular lamina form?
buccal sulcus
what does dental lamina form?
enamel organ
at 8 weeks what is the dental lamina shaped like?
a horse shoe
when does the enamel bud stage take place
8-10 weeks IUL
what happens during the enamel bud stage?
dental lamina thickens into bud stage enamel organ and ectomesenchymal condensation appears (dental papilla)
when is the enamel cap stage?
11 weeks
what happens in the enamel cap stage?
enamel organ forms a cap over dental papilla - EEE and IEE meet at the cervical loops
what are placodes?
different ways that different tissues forms a bud stage
what can ectodermal dysplasia affect?
not only teeth but also hair and other tissues
how can you treat ectodermal dysplasia?
gene therapy
when is the enamel bell stage
14 weeks IUL
what happens in the bell stage
the tooth is being refined
what are the cell layers in the bell stage
stratum intermedium, stellate reticulum, internal enamel epithelium and external enamel epithelium
which layer of the enamel bell stage holds sugars (glycogen) which is necessary for cells to develop enamel matrix from?
stellate reticulum
why can enamel not use the energy coming from the odontoblasts in the dental papilla
there is a matrix between them
what does matrix formation follow?
differentiation of cells
what happens at the 12th week IUL?
an extension appears on the lingual side of the dental lamina (permanent tooth germ)
when does the permanent tooth germ of the 1st primary molar start to develop?
16th week as a backwards extension of the dental lamina
when is the late bell stage?
18th week
what does the tooth look like in the late bell stage?
well defined crown
what happens in the late bell stage?
apposition of enamel and dentine
which cells differentiate into odontoblasts?
dental papilla cells adjacent to IEE
what do odontoblasts do?
lay down dentine matrix which is later mineralised
what happens once dentine formation has begun?
the IEE can differentiate into ameloblasts to form enamel
what are the steps of dentinogenesis?
odontoblast differentiation from IEE, deposition of dentine matrix, unmineralised dentine is predentine, mineralisation of dentine
what are the 2 stages of enamel formation?
protein matrix deposited and matrix partially mineralised
organic part removed and mineralisation complete
what are the stages of ameloblast differentiation?
morphogenic, histodifferentiation, secretory (initial), secretory (tomes process), maturative (ruffle-ended), maturative (smooth), protective
what happens during ameloblast differentiation stage 1
dentine induces IEE cells to differentiate to ameloblasts, they elongate becoming columnar, nucleus migrates to the basal end of the cell
what happens during the secretory phase of amelogenesis?
ameloblasts become secretory cells, they synthesis and secrete enaml matrix proteins (amelogenins) and the matrix is partially mineralised (30%)
what happens during the maturation phase of amelogenesis?
matrix proteins removed, mineral content increased to 95%
what happens during the protection phase of amelogenesis
ameloblasts regress to form a protective layer (reduced enamel epithelium) which is involved in eruption and formation of epithelial attachment
what is amelogenesis imperfecta?
autosomal recessive hypoplastic hypomaturation amelogenesis imperfecta
what do teeth appear like with amelogenesis imperfecta
yellow and difficult to see on radiograph due to loss of mineral content
what is dentinogenesis imperfecta
dentine is not mineralised to expected level
what can occur as a result of dentinogenesis imperfecta
tooth wear as there is no base for the enamel
what is the root shape defined by?
apical growth of the cervical loop
with root formation what name does the cervical loop take?
Hertwig’s epithelial root sheath
how many cells are in HERS
2
what does HERS do?
induce formation of root dentine and then breaks up
what are the remains of HERS called?
debris of Malassez
once HERS is broken down what happens with the mesenchymal cells?
they contact the dentine and differentiate into cementoblasts to form cementum
which type of fibres are embedded in cementum?
Sharpey’s fibres
what does the dental follicle produce?
cementum, PDL, alveolar bone
what does the dental papilla produce?
dentine and pulp
what are the developmental abnormalities?
prenatal, postnatal, inherited, acquired, number, shape, size, structure, eruption
what happens with acquired enamel defects?
only incisal area formed and not cervical
what is gemination
teeth that join together as one tooth breaks down to 2
what is fusion?
separate teeth which join during development
what is concresence?
when teeth join together by the cementum
