tooth development Flashcards
what are the 3 embryonic layers all body tissue develop from
- ectoderm
- mesoderm
- endoderm
what is tooth enamel derived from
- ectoderm
what are the supporting elements of the teeth 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
- a fourth cell type that forms between the ectoderm and the neural tube
what is the neural crest tissue also called
- ectomesenchyme
how does the neural crest form
- the neural plate folds into a groove
- then becomes the neural tube
- the top of this is the neural crest
what does the neural crest form
- ectomesenchymal cells
what does neural crest tissue migrate to form
- the developing face and jaws
- finger like projections form the face
what can failure of the neural crest projections to migrate lead to
- pathological situations that affect the formation of the tooth
- mandiblofacial dysostosis
what is mandibulofacial dysostosis
- mandible looks smaller
- eye sockets are further apart than normal
- ears position is not in the same place as normal = lower
what cause mandibulofacial dysostosis
- failure of cells creates a specific phenotype seen in the reduction of size of mandible and absence of teeth
- in both permanent and deciduous teeth
what are the stages in tooth development
- initiation
- morphogenesis
- cytodifferentiation
- matrix secretion
what occurs during initiation
- brachiosaurus arches project themselves to form the face
- mandible is formed by 2 process that join together
does the mandible or maxillary processes fuse first
- mandible
at what time of development does intitiation take place
- 5-6 weeks development
at what time does the primary epithelial band form
- 6 weeks IUL
what does the primary epithelial band look like
- a thickening in epithelium of the embryonic mouth (stomadeum)
- thickening of the surface of the mandible
at what time does the dental lamina form
- approx 7 weeks IUL
- the primary epithelial band has grown into the jaw and divided into 2 parts
what is the dental lamina
- vestibular lamina which will break down to form the buccal sulcus and the dental lamina, from which the enamel organ develops
what is needed for the vestibular lamina to form the vestibule
- a space is needed which is formed by apoptosis
what shape is dental lamina
- horse shoe shaped structure
what is the second stage of tooth development
- morphogenesis
what is the first stage of tooth development
- initiation
what occurs in the second stage of tooth development
shape formation of organs
at how many weeks is the bud stage within morphogenesis
approx 8 weeks IUL
what happens in the bud stage
- dental lamina thickens into a bud stage enamel organ
- ectomesenchymal condensation appears and this is the dental papilla = cells around the bud condensate
- first event of the shape seen by the dental papilla
what is the shape of the tooth determined by
enamel organ
at how many weeks is the cap stage within morphogenesis
approx 11 weeks
what happens during the cap stage
- the enamel organ forms a ‘cap’ over the papilla
- ‘cap stage’ enamel organ
how many types of epithelium does the cap stage have
- external enamel epithelium (EEE)
- internal enamel epithelium (IEE)
where do IEE and EEE meet
- meet at the cervical loop
what is the cervical loop
- where the formation of the root starts
what is the general term for the enamel organ
- placode
what are placodes also seen for
- nails, hair and mammary glands
- it is the same process for all organs: hair, nails, mammary glands and teeth
what is hypohidrotic ectodermal dysplasia
- absence of teeth
- shape of teeth are different
- some teeth can be impacted and not erupt
- changes can also impact other areas of the body as well = absence and reduction in number and size of hair, nails and mammary glands
- is a genetic disease = means it can help with those who are pregnant as can give baby gene therapy treatment early on
what can prevent hypohidrotic ectodermal dysplasia
- gene therapy
- must be done at an early stage of development
what is the third stage of tooth development
- cytodifferentiation
what happens during cytodifferentiation
- formation of tooth into a ‘bell’
- enamel organ ‘bell stage’
- more cell layers differentiate
- tooth shape is being defined = have whole shape of tooth
at how many weeks is the bell stage
- approx 14 weeks
how many cell layers does the bell stage enamel organ have
- 4
- stratum intermedium
- internal enamel epithelium
- external enamel epithelium
- stellate reticulum
what is the function of stratum intermedium and stellate reticulum
- protect and maintain
- define the shape of the tooth
where does the process of crown formation take place
- process doesnt occur throughout the whole structure
- starts at cusp area = differentiated cells form dentine then enamel
- differentiation occurs from cusp downward to cervical area
why is tetracycline not allowed for children or pregnant women
- causes tooth staining during development and will show as a line on the tooth
at how many weeks is the permanent tooth germ present
- approx 12th week, an extension appears on the lingual side of the dental lamina
- this is the dental lamina for the permanent successor
at what week does the 1st permanent molar develop as backwards extension of dental lamina
- around 16th week
what is the 4th stage of tooth development
- matrix secretion
what happens in the matrix secretion stage
- enamel organ late bell stage
- crown shape is well defined
- apposition of enamel and dentine begins
at how many weeks is the enamel organ late bell stage
- approx 18 weeks IUL
what forms first between enamel and dentine
- always have initial formation of dentine before enamel
- enamel organ defines the process and dental papilla follows
what is the process of formation of enamel and dentine
- dental papilla cells adjacent to the IEE differentiate into odontoblasts
- odontoblasts lay down dentine matrix, which is later mineralised
- once dentine formation has begun, IEE cells differentiate into ameloblasts, which form enamel
- for dental papilla to differentiate, it requires the presence of the enamel organ
what is dentinogeneis
- formation fo dentine
what happens in dentinogenesis
- odontoblast differentiation form IEE
- deposition of dentine matrix (mainly collagen)
- this un mineralised dentine is called pre-dentine
- mineralisation of dentine
what happens in stage 3 of dentinogenesis
- cell division of ectomesenchymal cells and keeps one ectomesenchymal cell waiting to become the stem cell
what is secondary dentine
- a slowed down version of primary dentine
what is tertiary dentine
- dentine formed in response to trauma
what 2 ways can tertiary dentine be formed
- 1 = by odontoblast recognising the threat and then begin to make it
- 2 = or the threat is too bad that the odontoblasts die so the ectomesenchymal cells that were dormant are recruited to form tertiary dentine
what does tertiary dentine formation depend on
- presence or absence of those primary odontoblasts
what is the matrix
- major nutritional source coming from the vascularised side
how is enamel made
- enamel is very highly mineralised
- made in two stages
- ameloblasts change form and function several times during amelogensis
what are the 2 stages of enamel formation
- 1 - protein matrix is deposited = matrix partially mineralised (30%)
- 2 - once this framework is established, the organic part is removed, and mineralisation is complete (‘maturation’)
what are the 4 main stages of ameloblast differentiation
- differentiation
- secretion
- maturation
- regression
what occurs during the first stage of ameloblast differentiation
- differentiation
- change in position on basement membrane and the cell becomes polarised to produce the organic matrix
what occurs during the second stage of ameloblast differentiation
- secretion
- effective arrangement to create energy/protein
what happens in the third stage of ameloblast differentiation
- maturation
- protein is removed
what happens in the fourth stage of ameloblast differentiation
- regression
- ameloblasts stop having active functional process but instead a protective function
- these cells that are formed in the regression stage form the junctional epithelium
what are other stages of ameloblast formation
- morphogenic
- histodifferentiation
- secretory (initial)
- secretory (tomes process)
- maturative (ruffle-ended)
- maturative (smooth)
- protective
where do the stages of ameloblast formation take place
- all stages happen at the same time but in different regions
- late stages occur at the cusp, early stages occur at the cervical region
what occurs during ameloblast differentiation
- dentine induces IEE cells to differentiate into ameloblasts
- they elongate, becoming columnar
- the nucleus migrates to the basal and of the cell
what occurs during the secretory phase of amelognenesis
- ameloblast become secretory cells
- they synthesise and secrete the enamel matrix proteins (amelogenins)
- the matrix is partially mineralised (30% mineral as seeded crystallites)
what allows crystallisation of ameloblasts
- when the ameloblasts become secretory cells and secrete and synthesis the enamel matrix this allows crystallisation
what occurs during maturation phase of amelogenesis
- most of the matrix proteins are removed to allow mineral content to increase to 95%
- mineral content of enamel is increased
- erupted teeth have increased carbonated hydroxyapatite and that is reduced as you age and so you get more hydroxyapatite
does mature enamel have pure hydroxyapatite
- no
- although mineral content is matured it doesn’t mean you have pure hydroxyapatite
- still have a mixture of carbonated apatite
what occurs during protection phase of amelogenesis
- ameloblasts regress to form a protective layer = the reduced enamel epithelium
- involved in eruption
- formation of epithelial attachment
why do we prescribe fissure sealants at school age
- as newly erupted teeth are more susceptible to caries
- around 6 years old look to give sealant as they are effective at that age when teeth have just erupted
what are the 3 times when there is a peak of caries
- starting primary school
- secondary school
- college/uni
what is amelogenesis imperfecta
- genesis of enamel if not perfect
- autosomal recessvie hypoplastic hypomaturation amelogenesis imperfecta
- can get different types
- matrix metallopeptidase 20 gene or MMP20 = located on long arm of chromosome 11 at position 22.3
what does gene MMP20 do
- provides instruction lion for proteins for making enamelysin
- creates proteins that make crystallites
- absorbed protein content so that the mineral content increases
what does enamelysin do
- cleaves other proteins such as amelogenin and ameloblastin into smaller pieces = means it is easier to remove
why are teeth more yellow than normal in amelogenesis imperfecta
- protein
- staining
- translucency may be decreased = it is based on mineral content and if that is reduced then so is the translucency so can see the colour of dentine shining through the enamel
what do teeth look like in amelogenesis imperfecta
- look rough, dull
- premolars look weird, they don’t have that round shape
what do you do when the 1st molar erupts in those with amelogenesis imperfecta
- place a stamp crown on it
- used as it is too difficult to do large restorations in that tooth
what is a stamp crown
- hollow pieces of stainless steel stamped into the shape of the tooth
why are stamp crowns sued
- restoring teeth on patients with amelogenesis imperfecta is very difficult as composite doesn’t adhere the same
- it is good as it covers the whole tooth
why is vertical bone loss called vertical bone loss
- doesn’t follow the reach of the bone
what is bad about the stamp crown
- can cause vertical bone loss
- crown is larger than needed so invade biological space
- they are not made to be perfect = why they work well with paediatric dentistry as the teeth will be lost anyway
why can’t you see the interface between the dentine and enamel in amelogenesis imperfecta
- enamel is so mineralised that it has the same density as dentine so shows the same
how do you know if the absence of gene MMP20 is complete
- if the tooth still looks slightly shiny then the gene is not completely gone as still have some level of mineralisation
what is the only treatment that will work on patients with amelogenesis imperfecta
- crown
- everything else will probably fail
what are amelogenesis imperfecta patients more at risk of
- caries
- but means they know how to prevent it as much as they can
what is dentinogenesis imperfecta
- enamel is properly formed but the dentine hasn’t
- there is lots of tooth wear =
how does dentinogenesis imperfecta cause tooth wear
- enamel relies on the resilience of dentine and without then enamel can’t flex as well and so tooth wear is quick
how does dentinogenesis imperfecta show on a x-ray
- can see the different between enamel and dentine as enamel is mineralised
- can’t really see root canal as the density of the dentine is lower and quite similar to absence of dentine all together
- don’t see the difference between dentine and pulp
what is the 4th stage in tooth development
- root formation
when does root formation begin
- when crown formation is complete
what maps out the shape of the crown
- the enamel organ
- migration of the cervical loop maps the crown shape
where do the IEE and EEE meet
- at the cervical loop
what is apical growth of the cervical loop now called
- Hertwig’s Epithelial root sheath (HERS)
- defines root shape
what is Hertwig’s epithelial root sheath
- 2-cell-layered structure, in contrast to the 4 cell layered enamel organ
what does HERS induce formation of
- root dentine
when does HERS break up
- once the initial layer of root dentine is formed it breaks up as no enamel is formed in the root
what do remains of HERS be
- debris of Malassez
what can debris of Malassez become
- can develop into a cyst
- called odontogenic cysts
what differentiates into cementoblasts
- mesenchymal cells from the follicle contact the dentine and differentiate into cementoblasts
what do cementoblasts do
- form the cementum
what are Sharpay’s fibres
- fibres from developing PDL than are embedded in the cementum
- embedded and then they form the true fibre cementum
what are true cysts
- have a direct connection with epithelium
what type of tissue s enamel organ and what is its origin and products
- type of tissue = epithelium
- origin = ectoderm
- products = enamel
what type of tissue is dental papilla and what is its origin and products
- type = ectomesenchyme
- origin = neural crest
- products = dentine, pulp
what type of tissue is dental follicle and what is its origin and products
- type = ectomesenchyme
- origin = neural crest
- products = cementum, PDL, alveolar bone (partly)
when can you get tooth developmental abnormalities
- prenatal
- postnatal
- inherited
- acquired = enamel defects
what are the effects of tooth developmental abnormalities
- number
- shape
- size
- structure
- eruption
what is gemination
- means twins
- from one tooth, 2 are born
- can be difficult to distinguish between fusion
what is fusion
- two teeth have fused together
- difficult to tell between gemination and fusion
what is concrescence
- connection between cementum
what is the vestibule lamina
- projection of epithelium cells entering the mesenchymal structure
- apoptosis drives shape and formation
how many processes form the palate
- 3
why is cleft palate more common than cleft lip
- palate has longer to grow and there is a tongue that is to grow as well
when is the first surgery for cleft palate done
- as soon as the baby is born
- because they are still growing, and baby needs to breast feed and can’t do that without a plate
- first surgery gives baby a soft structure at this stage
what is cartilage responsible for forming
- 2 bones in the ear
- has nothing to do with the formation of the mandible
what is the function of the dental papilla
- to produce the dentine and pulp
what is a cysts
- it is a balloon of epithelium cells filled with a liquid inside allowing them to expand
- ability to expand is the issue with cysts
what do cysts have their name of
- have their name after genesis of tooth
