Development of the Teeth Flashcards
what is making the potential for dentures to become redundant
stem cell research is being undertaken to develop tooth germs that could be implanted in mouths
these could be grown to replace missing teeth
what are the three primary embyronic layers that all body tissues develop from
ectoderm
mesoderm
endoderm
which embryonic layer is enamel derived from
ectoderm
what are all the parts of the teeth and supporting structures derived from apart from the enamel
the ectomesenchyme
what is the ectomesenchyme part of
the neural crest which develops bside the primitive nervous system developed from the ectoderm
what do teeth develop from
tooth germs
what is the neural crest
a fourth cell type that forms between the ectoderm and the neural tube
what is the neural crest tissue called
the ectomesenchyme
what does the neural crest tissue migrate to form
the developing face and jaws
what are the stages in tooth development
- initiation
- morphogenesis
- cytodifferentiation
- matrix secretion
- root formation
at what point does the primary epithelial band develop
6 weeks
what is the stomadoaeum
a thickening in the epithelium of the embryonic mouth
when does the dental lamina form
7 weeks of interuterine life
what is PEB
the primary epithelial band
what happens to the primary epithelial band at week 7
- grows into the jaw and divided into two parts
- vestibular lamina
- dental lamina
what is the vestibular lamina
this breaks down to form the buccal sulcus
what is the dental lamina
this is where the enamel organ develops
what do the vestibular lamina and dental lamina have in common
they are derived from the primary epithelial band
how can the shape of the dental lamina be described
horse shoe shaped
what is the bud stage
the enamel organ formation
when does the bud stage occur
at 8-10 weeks of interuterine life
what does the dental lamina thicken to become
the bud stage enamel organ
what is the dental papilla
an ectomesenchymal condensation
when does the cap stage occur
11 weeks interuterine life
what are the main stages to the formation of the enamal organ
bud > cap > bell
describe the cap stage
the enamel organ forms a cap over the dental papilla
there is now an external and internal enamel epithelium, which meet at the cerivcal loop
when does the enamel organ bell stage occur
14 weeks inter uterine life
what occurs in the bell stage of the enamel organ
more cell layers are differentiated and the tooth shape begins to be defined
what are the four cell layers of the bell stage enamel organ
- stratum intermedium
- stellate reticulum
- internal enamel epithelium
- external enamel epithelium
when does the permanent tooth germ appear and how
12th week, as an extension on the lingual side of the dental lamina
what is the extension that forms on the lingual side of the dental lamina at 12 weeks
the dental lamina for the permanent successor
when does the first permanent molar gern develop as a backward extension of the dental lamina
week 16
when does the late bell stage occur
18 weeks interuterine life
describe the late bell stage of the enamal organ
- crown shape is well defined
- apposition of the enamel and dentine begins
when does the crown shape of a tooth become well defined
at 18 weeks in the late bell stage of the enamel organ
what forms the odontoblasts
dental papilla cells found adjacent to the internal enamel epithelium differentiate to become the odontoblasts
function of odontoblasts in dentine formation
they lay down the dentine matrix, which is later mineralised
do odontoblasts or ameloblasts come first
the odontoblasts. once dentine formation begins the ameloblasts form
what forms the ameloblasts
the internal enamel epithelial cells differentiate into ameloblasts
what is the dentine matrix composed mainly of
collagen
what is predentine
unmineralised dentine
what causes the mineralisation of dentine
hydroxyapatite
how mineralised is enamel
96%
what are the two stages of enamel formation
- protein matrix depositied
- organic part removed, mineralisation complete
how mineralised is the protein matrix of enamel before maturation
30%
do ameloblasts remain the same throughout enamel formation
no, their form and function changes several times
describe ameloblast differentiation
- dentine induces the internal enamel epithelial cells to differentiate into ameloblasts
- they elongate, become columnar
- the nucleus migrates to the basal end of the cell
describe the secretory phase of amelogenesis
- ameloblasts become secretory cells
- they synthesise and secrete the enamel matrix proteins
- the matrix is then partially mineralised
what are amelogenins
the enamel matrix proteins
in the secretory phase how mineralised is the enamel
30%
describe the maturation phase of amelogenesis
- most of the matrix proteins are removed
- mineral content of the enamel is increased
- mature enamel is 95% mineral
describe the protection phase of amelogenesis
- ameloblasts regress to form a protective layer called the reduced enamel epithelium
- involved in eruption
- formation of epithelial attachment (junctional epithelium)
does crown formation complete before or after the beginning of root formation
before
what is responsible for mapping out the shape of the crown
the enamel organ
the cervical loop is where the internal and external enamel epithelia meet, and the migration of this loop maps out the crown shape
where do the external and internal enamel epitheliums meet
at the cervical loop
what is hetwigs epithelial root sheath
the apical growth of the cervical loop, with two layers
how many cell layers on the root sheath
two
how many layers on the enamel organ
four
what induces the formation of the root dentine
the hertwigs epithelial root sheath
describe root formation
- HERS induces the formation of root dentine
- once this initial layer of root dentine is formed, HERS breaks up as there is no enamel in the root
- remains of the HERS are the cell rests of malassez which can become cysts
- mesenchymal cells from the follicle contact the dentine and differentiate into cementoblasts
- fibres from the developing periodontal ligament are embedded in the cementum
what type of tissue is the enamel organ
epithelium
what type of tissue is the dental papilla
ectomesenchyme
what type of tissue is the dental follicle
ectomesenchyme
what is the origin of the enamel organ
ectoderm
what is the origin of the dental papilla
neural crest
what is the origin of the dental papilla
neural crest
what is the origin of the dental follicle
neural crest
what are the products of the enamel organ
enamel
what are the products of the dental papilla
dentine and pulp
what are the products of the dental follicle
cementum, periodontal ligament, alveolar bone
what are some different dental development disorders
- hypodontia
- supernumerary
- gemination
- fusion
- dentinogenesis imperfecta
which features of teeth can be defective
- their presence - some are absent
- number
- size
- shape
- structure
- eruption
how does the neural crest migrate
from the neural groove, they migrate via the brachial arches to the front portion to form the face, including the teeth
where does the primary epithelial bed form
within the stomadaeum as there is the thickening of the cells
where does the primary epithelial band grow
in the jaw
what is the dental lamina
a horse shoe shape of structures through the somatodaeum
when do tooth germs form in the dental lamina
at 8 weeks
what is morphogenesis
when the tooth gains shape, begins in the bud stage of the enamel organ development
why is it called the bud stage
the appendices of the epithelial cells looks like a bud
what is the dental papilla in the bud stage of the enamel organ
the ectomesenchymal concentration which then becomes the internal tissues of the tooth
what is cytodifferentiation
this is when the cells become specialised
what is the sinusoidal shape
the bell shape of the enamel organ in the cytodifferentiation stage
what do enamel and dentine have in common
they are both formed from an organic matrix produced by the cells that form them
where is the formation of dentine and enamel initiated
the dental papilla
where does the formation of dentine and enamel finish
at the internal enamel epithelium
where are the projections of the odontoblasts
in the space of the predentine matrix
what does mineralisation of dentine require
hydroxyapatite
what is a typical characteristic of differentiating cells
polarisation
what is hypodontia
reduction in the size of the teeth
what is supernumerary
an extra tooth
what is gemination
twin teeth - two teeth joined together - coming out of the same root space
what is fusion
fusion of two teeth
what is dentinogenesis imperfecta
this is when the dentine is not laid down properly and there is no mineral content. because the enamel is unsupported it breaks down, meaning restorations would break and fracture. high sensitivity
