Dental development Flashcards
All body tissues develop from 3 primary embryonic layers. What are these?
- Ectoderm
- Mesoderm
- Endoderm
Which primary embryonic layer does tooth enamel derive from?
- Ectoderm
Tooth enamel is derived from ectoderm. Where are all other parts of the teeth and supporting structures derived from?
- Ectomesenchyme
What is Ectomesenchyme?
Part of the neural crest that develops beside the primitive nervous system (ectoderm)
What do teeth develop from?
‘tooth germs’
A fourth cell type forms between the ectoderm and the neural tube. What is this called?
The ‘neural crest’
What is the neural crest tissue also called?
Ectomesenchyme
Do neural crest tissues migrate into the developing face and jaw?
- Yes
Neural crest tissue migrates into the developing face and jaw which causes projections that will form the face. What occurs if there is failure of the migration of these cells?
- This will cause a deficiency in the formation of the face
What is mandibulofacial dysostosis caused by?
Failure of ectomesenchymal cells to migrate
What are common signs of mandibulofacial dysostosis? (4 points)
- Mandible is smaller
- Eye sockets are fur ther apart
- Ear position is lower than normal
- Abscence of permanent teeth is possible
What is the first stage in tooth development?
- Initiation
the dental lamina
What is the Stomodaeum?
The space that will form the mouth
When does the primary epithelial band develop?
At approx. 6 weeks IUL
What does the primary epithelial band appear as?
- Appears as a thickening in epithelium of the embryonic mouth (stomodaeum)
- Multiplication of oral epithelium cells projection of the epithelium onto Ectomesenchymeal surface
When does the dental lamina form?
- Approx. 7 weeks IUL
The primary epithelial band will grown into the jaw and divide into 2 parts at approx. 7 weeks IUL. What are the 2 parts?
- Vestibular lamina: which will break down to form the buccal sulcus
- Dental lamina: from which the enamel organ develops
What is the shape of the structure of the dental lamina?
Horseshoe shape
What is the second stage of tooth development?
- Morphogenesis
bud and cap stage
When does the ‘bud’ stage occur?
At approx. 8 weeks IUL
What is the process of the ‘bud’ stage? (2 points)
- Dental lamina thickens into a ‘bud’ stage enamel organ
- An ectomesenchymal condensation appears and this is the dental papilla
What is the shape of a tooth determined by?
- The enamel organ
When does the ‘cap’ stage occur?
- Approx. 11 weeks IUL
Then enamel organ forms a ‘cap’ over the papilla. What does the ‘cap stage’ enamel organ include? (2 points)
- External enamel epithelium
- Internal enamel epithelium
In the ‘cap’ stage where do the external enamel epithelium and the internal enamel epithelium meet?
- At the cervical loop
- This is the reference point formation of the root (this is the cervical region of the tooth)
The enamel organ can be called a placode. What is this?
The enamel organ forming bud stage and forming tooth
What 3 organs other than teeth can placodes be seen?
- Nail
- Hair
- Mammary glands
What are the oral implications of hypohidrotic ectodermal dysplasia? (3 points)
- Not as many teeth as would expect
- Shape of teeth being formed is different
- Arrangement - some teeth are impacted
Apart from teeth, what else is affected by severe hypohidrotic ectodermal dysplasia? (3 points)
- Hair
- Nails
- Mammary glands
What is the third stage of dental development?
- Cytodifferentiation
bell stage
When is the ‘bell’ stage?
Approx. 14 weeks IUL
What happens in the bell stage of development? (2 points)
- More cell layers differentiated
- Tooth shape is being defined
The ‘bell’ stage enamel organ has 4 cell layers. What are these?
- Stratum intermedium
- Stellate reticulum
- Internal enamel epithelium
- External enamel epithelium
Are there nutrients present in the early bell stage?
- Yes
Explain the crown pattern formation of teeth?
- Process of forming a tooth doesn’t occur all the way through the structure
- Starts at the tooth cusp area
- Differentiated cell start to produce dentine then enamel
- This occurs from the cusps downwards
- When look at changes in the formation of the tooth - it occurs in layers from the cusp downwards to the cervical region
When approximately does an extension appear on the side of the dental lamina?
At approx. 12 weeks
What is the dental lamina produced for?
For the permanent successor
Approximately when doe the first permanent molar germ develop as a backwards extension of the dental lamina?
At approx. 16 weeks
What is the fourth stage of dental development?
- Matrix secretions
When does then late ‘bell’ stage occur?
At approx. 18 weeks IUL
What happens in the late ‘bell’ stage?
- Crown shape is well defined
- Apposition of enamel and dentine begins
- (dentine formation is established and then enamel formation begins)
How is dentine and enamel initially formed? (3 points)
- Dental papilla cells adjacent to the IEE differentiate into odontoblasts
- Odontoblasts lay down dentine matric, which is later mineralised
- Once dentine formation has begun, IEE cells differentiate into ameloblasts, which form enamel
What happens in the process of dentinogenesis? (4 points)
- Odontoblast differentiation from IEE
- Deposition of dentine matrix (mainly collagen)
- This unmineralised dentine is predentine
- Mineralisation of dentine (hydroxyapatite)
Enamel is very highly mineralised. What is it as a %?
96% mineralised
Enamel is made in 2 stages. What are these?
- Protein matrix deposited (matrix is partially mineralised - 30%)
- Once this framework is established, the organic part is removed and mineralisation is complete (maturation)
During amelogenesis what happens to the ameloblasts?
- They change form and function several times
What are the 4 main stages of ameloblast differentiation?
- Differentiation
- Secretion
- Maturation
- Regression
What are the 7 stages of ameloblast differentiation?
- Morphogenic
- Histodifferentiation
- Secretory (initial)
- Secretory (tomes process)
- Maturative (ruffle-end)
- Maturative (smooth)
- Protective
What happens to ameloblasts during the first stage of ameloblast differentiation? (3 points)
- Dentine induces IEE cells to differentiate into ameloblasts
- They elongate, becoming columnar
- The nucleus migrates to the basal end of the cell
What happens during the secretory phase of amelogenesis? (3 points)
- 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 during the maturation phase of amelogenesis? (3 points)
- Most of the matrix proteins are removed
- Mineral content of enamel is increased
- Mature enamel is 95% mineral
What happens during the protection phase of amelogenesis? (3 points)
- Ameloblasts regress to form a protective layer - the reduced enamel epithelium
- Involved in eruption
- Formation of epithelial attachment
An example of amelogenesis imperfecta is autosomal recessive hypoplastic hypomaturation amelogenesis imperfecta. What gene causes this type of AI and what chromosome is it located on?
- Matrix metallopeptidase 20 gene (MMP20)
- Located on the long (q) arm of chromosome 11 at position 22.3
What does the matrix metallopeptidase 20 (MMP20) gene provide instruction for making?
Provides instruction for making enamelysin
What does enamelysin do?
-It cleaves other proteins, such as amelogenin and ameloblastin, into smaller pieces (easier to remove)
What is the enamel like in people with amelogenesis imperfecta? (7 points)
- Yellow in colour
- Less translucent
- More opaque
- Rough
- Dull (not shiny)
- Irregularities
- Formation of tooth might not occur as it should so shape irregularities
What might you see on an x-ray of someone with amelogenesis imperfecta?
- Vertical bone loss
- Can’t see clear difference of where enamel is and where dentine is
What is dentinogenesis imperfecta?
- Enamel is properly formed but dentine doesn’t have the proper level of maturation
What can you not see in an x-ray of a patient with dentinogenesis imperfecta?
- Can’t see pulp chambers (can’t see root canal)
It can be difficult to give RCT to a patient with dentinogenesis imperfecta. Why is this? (2 points)
- Dentine is easy to manipulate but can be a problem on its own - if you deviate file to wrong direction it can cause a big mess
- Radiographs will not show shape and length of root (makes it more difficult)
What is the 5th stage in tooth development?
- Root formation
Does crown formation have to be complete for root formation to begin?
Yes
What happens during root formation?
- The enamel organ maps out the shape of the crown
- The EEE and IEE meet at the cervical loop
- Migration of the cervical loop maps the crown shape (migration downwards starts to create the root)
What is the root shape defined by and what is the name for this?
- Defined by the apical growth of the cervical loop
- This is called Hertwig’s epithelial root sheath
How many layers of cells are found in the Hertwig’s epithelial root sheath and the enamel organ? (2 points)
- HERS = 2 cell layer
- EO = 4 cell layer
What is the process of root formation in relation to the Hertwig’s epithelial root sheath? (5 points)
- HERS induces formation of root dentine
- Once the initial layer of root dentine is formed, HERS breaks up (no enamel in root)
- Remains of HERS persists as ‘debris of malassez’, which may develop into a cyst
- Mesenchymal cells from the follicle contact the dentine, and differentiate into cementoblasts - these form cementum
- Fibres from the developing PDL are embedded in the cementum (Sharpey’s fibres)
What type of tissue is associated with the enamel organ ?
Epithelium
What type of tissue is associated with the dental papilla ?
Ectomesenchyme
What type of tissue is associated with 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 follicle ?
Neural crest
What does the enamel organ produce ?
Enamel
What does the dental papilla produce?
Dentine & pulp
What does the dental follicle produce?
Cementum, PDL, alveolar bone (part)
What are 4 different types of teeth developmental abnormalities?
- Prenatal
- Post natal
- Inherited
- Acquired
What 5 things can teeth developmental abnormalities affect in relation to the tooth?
- Number
- Shape
- Size
- Structure
- Eruption
What does gemination mean?
From 1 tooth 2 have formed
What is meant by the term fusion?
Where 2 teeth have fused together (usually see 2 roots o n a radiograph)
What is meant by the term concrescence?
Connection is between cementum
