Dental Development Flashcards
3 primary embryonic layers
ectoderm
mesoderm
endoderm
what embryonic tissue is enamel derived from?
ectoderm
all other tooth structures and supporting structures are derived from the ectomesenchyme
what structure do teeth develop from
tooth germs
what is the ectomesechyme part of?
the neural crest that develops beside the primitive nervous system (ectoderm)
what is the neural crest
A fourth cell type forms between the ectoderm and the neural tube (folds onto the neural grove)
- ectomesenchyme
what does the neural crest tissue migrate into
Neural crest tissue migrates into the developing face and jaws
- Brachial arches
- Projections below midbrain from face
Have migrating ectomesenchyme cells
- Can radioactively label
Depending on migration of those cells can develop a number of pathological situations – consequence on teeth formation
what is mandibulofacial dysostosis
failure of ectomesenchyme cells to migrate
phenotype of mandibulofacial dysostosis
Mandible is smaller (reduction of size)
Sometimes absence of deciduous or permanent teeth
Eyes look more apart than expected
- Lower than normal person
might have hindered/lighter presentation - some but not all phenotype
5 stages in tooth development
tooth initiation
morphogenesis
cytodifferentiation
matrix secretion
root formation
tooth initation
first stage in tooth development
Brachial arches project themselves
2 mandibular process - 2 process that join together
- Join in early stage compared to maxilla
Stomodaeum - space which forms the mouth
Primary epithelium band
develops at approx 6 wks IUL
- Appears as thickening in epithelium of embryonic mouth (stomodaeum)
Dental lamina
- Approx. 7 wks IUL
- The PEB has grown into the jaw
- —Invaginating on ectomesenchyme surface
Divided into 2 parts:
- Vestibular lamina, which will break down to form the buccal sulcus, and
- The dental lamina, from which the enamel organ develops
Vestibule space is formed by apoptosis
Horse shoe shaped in structure
Tooth germs in key places where teeth form
primary epithelial band
develops at approx 6 wks IUL
- Appears as thickening in epithelium of embryonic mouth (stomodaeum)
dental lamina
- Approx. 7 wks IUL
- The PEB has grown into the jaw
- —Invaginating on ectomesenchyme surface
Divided into 2 parts:
- Vestibular lamina, which will break down to form the buccal sulcus, and
- The dental lamina, from which the enamel organ develops
Vestibule space is formed by apoptosis
morphogenesis
second stage in tooth development
generation of enamel organ itself
- bud stage (8-10 weeks)
- cap stage (11 weeks)
bud stage
part of morphogenesis
Approx. 8–10 wks IUL
Dental lamina thickens into a ‘bud’ stage enamel organ (A)
An ectomesenchymal condensation appears and this is the dental papilla
- Tooth shape and structured is determined by enamel organ (first events from dental papilla)
- Separate dental papilla and EO and place different tooth EO on top – so different tooth formed in place
cap stage
part of morphogenesis
3D cap shape of ectomesenchyme cells
Approx 11 wks IUL
The enamel organ forms a ‘cap’ over the papilla
“Cap stage” enamel organ:
- External enamel epithelium
- Internal enamel epithelium
EEE and IEE meet at the Cervical Loop
- Reference for root formation
cytodifferentiation
third stage in tooth development
- bell stage (14 weeks)
- crown pattern formation
- permanent tooth germ (12 weeks)
bell stage
approx 14 wks IUL
More cell layers differentiated
- 4 layers
- —Stellate reticulum
- —-Stratum intermedium
- —-Internal enamel epithelium
- —-External enamel epithelium
Tooth shape is being defined
- Seen more in incisors than molars
function of stellate reticulum and stratum intermedium
protect and maintain
stellate reticulum has nutrients present
4 cell layers in bell stage
- stellate reticulum
- stratum intermedium
- internal enamel epithelium
- external enamel epithelium
crown pattern formation
Process of forming the tooth doesn’t occur all the way through structure
- Start in teeth cusps area downwards to cervical
Dentine forming Then enamel
what can cause changes/disruptions in tooth formation
Avoid prescribing certain antibiotics to children with developing teeth
- Tetracycline
- —-Stains the tooth during the formation
- —-Will show in your teeth as a line
- —–Impregnant the content of enamel and dentine in a specific part of process of formation
Infectious disease that greatly produces fever (measles) creates specific line on toots
permanent tooth germ formation
in cytodifferentiation
At approx. 12th week, an extension appears on the lingual side of the dental lamina
- This is the dental lamina for the permanent successor
At about 16th week, the 1st permanent molar germ develops as a backwards extension of the dental lamina
matrix secretion
fourth stage in tooth development
late bell stage (18 weeks)
late bell stage
Approx 18 weeks IUL
Crown shape is well defined (‘crown’ stage EO)
Apposition of enamel and dentine begins
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
- EO defines the process and dental papilla follows
But Dentine formation before enamel
- For IEE to differentiate requires EO presence
what forms first dentine or enamel
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
root formation
fifth stage in tooth development
Crown formation is complete before root formation begins
The enamel organ maps out the shape of the crown
The EEE and IEE meet at the cervical loop
The root shape is defined by apical growth of the cervical loop, which is now called:
- Hertwig’s epithelial root sheath
This is a 2-cell-layered structure, in contrast to the 4-layered enamel organ
- In EO need for to maintain ameloblasts (not present in root)
Hertwig’s epithelial root sheath (HERS) induces formation of root dentine
- Once the initial layer of root dentine is formed, Hertwig’s sheath breaks up (no enamel in root)
Remains of HERS persist as ‘debris of Malassez’, which may develop into a cyst
- Odontogenic cysts
Mesenchymal cells from the follicle contact the dentine, and differentiate into cementoblasts
- These form cementum
Exposure of area to cells of ectomesenchyme
Fibres from the developing PDL are embedded in the cementum (“Sharpey’s fibres”)
Hertwig’s epithelial root sheath
apical growth of the cervical loop defines root shape
2-cell-layered structure
induces formation of root dentine
- Integration of IEE and EE
migrate and differentiate into odontoblast
- Forms dentine layer - cells break apart (no enamel in root)
- Ones with contact with dentine are used to form cementoblasts
- Remains of HERS persist as ‘debris of Malassez’, which may develop into a cyst
—- Odontogenic cysts
what is a general term for an enamel organ
placode
certain genes highlighted with development process
what 3 other organs (bar enamel organ) are placodes
hair
nail
mammary gland
what is the common feature in placodes
epithelial tissue forms 4 organs with initial bud stage the same
hypohidrotic ectodermal dysplasia
Pathology
Obvious strange occurrence in teeth
- Less teeth than expected - absence
- Shape is different
- —-Canin is Conoid (cone like)
- Some of teeth are impacted —- not erupted
Changes are not only related to the teeth
- Placode formation issue
- —Absence of reduction in number of size or shape of teeth
- —But also effect hair and mammary gland formation
what type of therapy can be used for ectodemal dysplasia
gene therapy as it is a genetic pathology
can correct gene issue with gene replacement therapy but need to carry out in very early stage of development
- embryonic (prenatal)
dentinogenesis
Ectomesenchyme cells differentiate into odontoblasts
- Odontoblast differentiation from IEE
Deposition of dentine matrix (mainly collagen)
This unmineralised dentine is predentine
- Mineralisation of dentine (hydroxyapatite)
one ectomesenchymal cell is left in waking (undifferentiated)
- stem cell
formation of tertiary dentine
Formed in response of traumatic or aggressive event
Fracture, caries
- Sometimes induced by dentine
—–Remove caries partially - leave some not to expose pulp
Formed 2 ways
- Reactionary
- —-Odontoblast recognise threat and form tertiary dentine
- Reparative
- —-Aggression so harsh odontoblast dies
- —-Dormant ectomesenchyme cells are recruited to form tertiary dentine
what cells deposits dentine
odontoblasts
primary dentine Vs secondary dentine
Primary while the tooth is being formed
Secondary when tooth completely formed
- Root formation 2-3 years after eruption
If formation of primary at same speed continues for secondary will close pulp area quickly
- Secondary dentine is slowed down formation
where is the major nutritional source for the enamel organ
the highly vascularised dental papilla
- need complex structure of cell layers to maintain itself as cannot reach EO
what percentage is enamel mineralised to
96%
2 basic stages of enamel formation
Protein matrix deposited
- Matrix is partially mineralised (30%)
Once this framework is established, the organic part is removed, and mineralisation is completed (‘maturation’)
The ameloblasts change form and function several times during amelogenesis
what cells make enamel
ameloblasts
7 ameloblasts differentiation stages (amelogenesis)
- Morphogenic
- Histodifferentiated
- Secreted (initial)
- Secretory (tomes)
- Maturative (ruffle-ended)
- Maturative (smooth)
- Protective
why does enamel need etched
Crystallite more sensitive on side of crystallite
- Create a rough surface
Liquid adhesive attaches to rough surface
direction of enamel formation
from the crown to cervical region (downwards)
ameloblast differentiation
Dentine induces IEE cells to differentiate into ameloblasts
- they elongate, becoming columnar
- the nucleus migrates to the basal end of the cell
secretory phase
Ameloblasts become secretory cells
They synthesise and secrete the enamel matrix proteins (amelogenins)
- Proteins organised in a way that allows super saturation
The matrix is partially mineralised (30% mineral as seeded crystallites)
- Removal of all protein allows mineral content to be increased with external introduction of calcium and phosphate
maturation phase
Most of the matrix proteins are removed
Mineral content of enamel is increased
Mature enamel is 95% mineral
- Not pure HA
- —-Mixture carbonated apatite and HA
Fluoride presence in important
carbonated apatite properties
part of mature enamel mix (carbonated and HA/FA)
Carbonated apatite is more susceptible to acid environments – removed easier
Reduced through lifetime by de- re-mineralisation process into HA and FA
why is the use of fluoride sealant important in amelogenesis maturation stage
Use sealant in early stage when tooth is erupted as it is susceptible to cavity formation (facilitate and create a better environment for the teeth)
Higher risk – first permanent molar as longest exposed
No use of sealant in adult as tooth matured, diet is well established (would alter diet if need to change something)
times of caries incidence peak
start primary, secondary school and uni/college
what tooth has the highest caries risk
first permanent molar as longest exposed
protection phase of amelogenesis
Ameloblasts regress to form a protective layer – the reduced enamel epithelium
Involved in eruption
- Formation of epithelial attachment (junctional epithelium)
amelogenesis imperfecta
Autosomal recessive hypoplastic hypomaturation amelogenesis imperfecta
- Different types
Matrix metallopeptidase 20 gene or MMP20
- Located on the long (q) arm of chromosome 11 at position 22.3.
Provides instructions for making enamelysin
Enamelysin cleaves other proteins, such as amelogenin and ameloblastin, into smaller pieces (easier to remove)
- Allows minerals to mature enamel and removes protein content
No Enamelysin = incorrect maturation of enamel
phenotypic features of amelogenesis imperfecta
Yellow in colour than what would expect
- Presence of protein and stain
- Enamel translucency is based on mineral content - become more opaque
Not smooth - rough
Dull looking
Irregularities
- due to higher failure on eating
- More prone to chipping
Premolars look odd
- Not rounded - Formation not occurred normally
what is the issue of stainless steel stock crowns
Crown is invading biological space - Stamp crown not made to space
- not suitable for permanent
teeth
Hard to restore large areas in deciduous teeth
- Enamel is more frail - weaker adhesive nature
what is the difficulty of restoring teeth with amelogenesis imperfecta
enamel is not 95% mineralised
- composite doesn’t adhere to same strength
X ray evidence of amelogenesis imperfecta (2)
vertical bone loss
- valley towards root - not following reach of bone
cannot see interface between enamel and dentine
- similar density as enamel decreased mineral content
dentinogenesis imperfecta
enamel is properly formed
dentine doesn’t have required level of maturation
is there a scale with amelogenesis imperfecta
Absence of the gene is not absolute
Genetic recession penetration is not complete (100%)
differing degrees of mineralisation
enamel issues due to dentinogeneisis imperfecta
Can flex more than it should
Can cause dentine to flake and break down
X ray evidence of dentiogenesis imperfecta
can see interface of enamel and dentine
since dentine is less mineralised/lower density cannot visually ID root canal
type of tissue of enamel organ
epithelium
type of tissue of dental papilla
ectomesenchyme
type of tissue of dental folllicle
ectomesenchyme
origin of enamel organ
ectoderm
origin of dental papilla
neural crest
origin of dental follicle
neural crest
product of enamel organ
enamel
2 products of dental papilla
denine
pulp
3 products of dental follicle
cementum
PDL
alveolar bone (part)
4 categories of teeth development abnormalites
prenatal
postnatal
inherited
acquired
teeth development abnormalities can affect (5)
number size shape structure eruption
how can you tell an enamel defect is acquired and not inherited
line on incisal third canine to canine
Lesion couldn’t have happened in genetics as on section not whole tooth
- Permanent teeth - early stage development effected
Infectious disease potentially - measles
gemination
site of one tooth but two formed
- e.g. central incisor divided into 2 right centrals
fusion
2 or more teeth join together
- likely multiple roots on x-ray
concrescence
connection between cementum of teeth
