Dental Development Flashcards
What are the 3 primary embryonic layers?
- ectoderm
- mesoderm
- endoderm
What tooth germ is tooth enamel derived from?
ectoderm
Which one of the 4 primary embryonic layers are all the parts of the teeth and supporting structure apart from tooth enamel derived from?
ectomesenchyme
What is the first stage of tooth development?
intiation
What tissue migrates?
neural crest migrates into the developing face and jaws
What is the ectomesenchyme
A fourth cell type forms between the ectoderm and the neural tube
part of the ‘neural crest’ that develops beside the primitive nervous system (ectoderm)
What disorder is the failure of ectomesenchymal cells to migrate?
Mandibulofacial Dysostosis
What is a depression between the brain and the pericardium in an embryo which is the precursor to the mouth called?
Stomodaeum
Approximately when does the primary epithelial band develop?
6 weeks
What does the primary epithelial band appear as?
thickening of epithelium at the embryonic mouth (stomodaeum)
What 2 parts does the primary epithelial band divide into?
What week?
7 weeks
Vestibular lamina, which will form the buccal sulcus
Dental lamina, from which the enamel organ develops
What shape is the dental lamina?
What week does it take this shape?
horseshoe
What is the second stage in tooth development?
morphogenesis (bud stage)
When does the enamel organ - ‘bud’ stage 2 occur?
8-10 weeks
What happens at the ‘bud’ stage of dental development?
- Dental lamina thickens into a ‘bud’ stage enamel organ
- An ectomesenchymal condensation
appears and this is the dental papilla
When does the enamel organ - ‘cap’ stage 3 occur?
11 weeks
What 2 epitheliums are present in the enamel ‘cap stage’?
Where do they meet?
External enamel epithelium
Internal enamel epithelium
EEE and IEE meet at the cervical loop
What is the acculmation of ectomesencymal cells around the enamel organ called?
NOT UNDER
dental folluicle
What is the fourth stage of tooth development?
bell stage
What is ectodermal dysplasia?
a group of genetic syndromes deriving from abnormalities of ectodermal structures
What happens in hypohidrotic ectodermal dysplasia concerning teeth?
hypodontia (absence) of multiple teeth
How can ectodermal dysplasia be treated?
gene therapy - can reverse a genetic disorder
When does the enamel organ - ‘bell’ (cytodifferentiation) stage occur?
14 weeks
At what stage is the tooth shape starting to be defined?
bell stage
What are the 4 cell layers present in the ‘bell’ stage?
Stratum intermedium
Internal enamel epithelium
External enamel epithelium
Stellate reticulum
What is the function of stellate reticulum in the bell stage?
keeping storage of nutrients for tissues
comprises of glycoaminosglycans (attract water) which allows space for developing crown
glycogen is energy for ameloblasts as blood vessels are far
At what time does an extension appear on the lingual side of the dental lamina?
this is the dental lamina for the adult tooth
12 weeks
At what time does the 1st permanent molar germ develop as a backwards extension of the dental lamina?
16th week
What is the fifth stage of tooth development?
What time does it occur?
enamel organ matrix secretion (late bell)
18 weeks IUL
In what stage does the positioning of enamel and dentine begin?
late bell stage within matrix secretion
At what stage do cells become specialised?
late bell stage within matrix secretion
What do dental papilla cells (adjacent to the internal enamel epithelium) differentiate into?
odontoblasts
What do odontoblasts do?
lay down dentine matrix which is later mineralised (predentine)
What do IEE cells differentiate into and when?
Once dentine formation has begun, IEE cells differentiate into ameloblasts, which form enamel
What is the process of dentinogenesis?
Odontoblast differentiation from dental papilla cells near IEE
Deposition of dentine matrix (mainly collagen)
This unmineralised dentine is predentine
Mineralisation of dentine (hydroxyapatite)
What is the role of stem cells?
stem cells have capability to become odontoblasts and produce tertiary dentine
What are the 2 phases of formation of enamel?
- Protein matrix deposited
Matrix is partially mineralised (30%) - Once this framework is established, the organic part is removed
What are the 7 stages of ameloblast differentiation?
- Morphogenic
- Histodifferentiation
- Secretory (initial)
- Secretory (tomes process)
- Maturative (ruffle-ended)
- Maturative(smooth)
- Protective
What happens in step 1 of amelogenesis?
Ameloblast differentiation:
- Dentine induces IEE cells to differentiate into ameloblasts
- they elongate, becoming columnar
- the nucleus migrates to the basal end of the cell
What happens in step 2 of amelogenesis?
Secretory phase:
- Ameloblasts become secretory cells
- They synthesise and secrete the enamel matrix proteins (amelogenins)
- The matrix is partially mineralised (30% mineral as seeded crystallites)
What happens in step 3 of amelogenesis?
Maturation phase:
- Most of the matrix proteins are removed
- Mineral content of enamel is increased
- Mature enamel is 95% mineral
What happens in step 4 of amelogenesis?
Protection phase:
- Ameloblasts regress to form a protective layer – the reduced enamel epithelium
- Involved in eruption
- Formation of epithelial attachment
What is the full name of amelogenesis imperfecta?
Autosomal recessive hypoplastic hypomaturation amelogenesis imperfecta
What gene does amelogensis imperfecta affect?
Matrix metallopeptidase 20 gene or MMP20
What does MMP20 gene do?
Provides instructions for making enamelysin
Enamelysin cleaves other proteins, such as amelogenin and ameloblastin, into smaller pieces (easier to remove)
Why do teeth look dull in amelogenesis imperfecta?
not shiny due to low mineralisation of enamel
enamel becomes similar to dentine composition and becomes indistingushable on radiographs
What has to finish for root formation to begin?
crown formation
What is the 5th stage in tooth development?
root formation
Where do the EEE and IEE meet?
cervical loop
What does migration of the cervical loop map out?
crown shape
What is the apical growth (proliferation of cervical root cells) of cervical root known as?
hertwig’s epithelial root sheath
How many layers is hertwig’s epithelial root sheath?
How many layers is the enamel organ?
This is a 2-cell-layered structure, in contrast to the 4-layered enamel organ
What does the Hertwig’s epithelial root sheath induce?
formation of root dentine
What is ‘debris of Malassez’?
epithelial cells on the PDL that are remains of HERS -may develop into cyst
What are cementoblasts?
differentiated ectomesenchymal cells from the follicle
What are fibres from the developing PDL that are embedded into cementum called?
sharpeys fibres
What are rests of malassez cysts called?
odontogenic cysts - happen during formation of dentine
What is the type of tissue, origin and product of the enamel organ?
epithelium, ectoderm, enamel
What is the type of tissue, origin and product of the dental papilla?
ectomesenchyme, neural crest, dentine, pulp
What is the type of tissue, origin and product of the dental follicle?
ectomesenchyme, neural crest, cementum, PDL, alv bone
How can teeth developmental abnormalities occur?
Prenatal
Postnatal
Inherited
Acquired
What is gemination
one tooth divided into two and fused together
What is fusion?
two different teeth fused together with hypodontia of one
What is concrescence?
joining of adjacent teeth by cementum.
Which epithelium is found in the primary epithelial band?
Stratified squamous epithelium
Notice the primary epithelial band in both the mandibular and maxillary processes. What relationship do they have to each other?
Maxilla labial to mandible
The enamel organ is apparently connected by a stalk-like structure to the oral surface. This stalk like structure in 3D is U-shaped.
What is the connecting stalk called?
dental lamina
Where are the ectomesenchymal cells derived from?
neural crest
What is the organic matrix of dentine called?
predentine
What name is given to the layer of dentine formed first, which lies next to the future ADJ?
mantle dentine
The epithelial cells next to the forming dentine
What are they called?
IEE
internal enamel epithelium
The IEE cells can receive their nutrients from the blood vessels of the dental papilla.
However, after dentine and enamel matrices are created, this is not possible.
Therefore, the ameloblasts gather nutrients from a different source
What is the evidence of that?
The presence of a rich vascular bed near the enamel organ
a decrease in blood flow to the dental papilla after the matrix hardens.
Predentine is the most recent secretion of the odontoblasts which has not yet had time to mineralise.
Within this pale zone, look for globules which are stained darker pink.
What are these ?
Calcospherites
A spherical zone of hydroxyapatite formed during the mineralization phase of dentine formation
Fuse together to form mineralised dentine
Now look at the layer of columnar ameloblasts forming enamel. It is a single, much more regular layer than the odontoblast layer.
Are these ameloblasts taller or shorter than the odontoblasts ?
taller
Notice 2-3 rows of cells lying close to the ameloblasts. This is the stratum intermedium.
Are the ameloblast nuclei nearer or further away from the stratum intermedium?
nearer
What is globular dentine also known as?
calcospherites
In the protective phase of amelogenesis, what happens to the ameloblast remains before/after eruption?
The reduced enamel epithelium forms the remains of the ameloblast cell layer and protects the enamel during eruption. After eruption it becomes the junctional epithelium.
