Tooth Development Flashcards
Which embryonic germ layer is enamel derived from?
Ectoderm
Which embryonic germ layer are dental and periodontal structures derived from? (but NOT enamel)
The ectomesenchyme
Which structure is the ectomesenchyme part of?
Neural crest
What do teeth develop from?
Tooth germs
Where does the neural crest form?
Between the ectoderm and the neural tube
Where does neural crest tissue migrate to?
Into the developing face and jaws
What is the primitive mouth called?
Stomodaeum
When does tooth development begin in embryonic development?
5-6 week old embryo
When does the primary epithelial band develop?
Approximately 6 weeks in utero
What is the primary epithelial band?
A thickening of the ectodermal epithelium of the embryonic mouth (stomadaeum)
Describe what happens to the primary epithelial band at 7 weeks in utero
- The PEB grows into the jaw and divides into 2 parts: vestibular lamina and dental lamina
The primary epithelial band divides into the vestibular lamina and the dental lamina. What do each of these give rise to?
- Vestibular lamina: forms the buccal sulcus
- Dental lamina: forms the enamel organ
What does the enamel organ develop from?
The dental lamina (which originates from the primary epithelial band - a thickening of the ectodermal epithelium of the mouth)
What shape is the dental lamina?
Horse-shoe shaped structure
What are the stages in tooth development?
- Bud stage
- Cap stage
- Bell stage
- Late bell stage
- Erupting tooth
Describe the ‘bud’ stage in tooth development
- Occurs approx 8-10 weeks IUL
- Dental lamina thickens into a bud stage enamel organ
- An ectomesenchymal condensation appears and this is the dental papilla
Describe the ‘cap’ stage in tooth development
- Approx 11 weeks IUL
- The enamel organ forms a cap over the papilla
- External enamel epithelium and internal enamel epithelium form. EEE and IEE meet at the cervical loop
Describe the ‘bell’ stage in tooth development
- Approx 14 weeks IUL
- Tooth shape is being defined
- Enamel organ has 4 cell layers: stratum intermedium, stellate reticulum, external enamel epithelium, internal enamel epithelium
Describe tooth development at 12 weeks
An extension appears on the lingual side of the dental lamina
This is the dental lamina for the permanent successor
At what stage does the 1st permanent molar germ develop and how does it do so?
At 16 weeks IUL, the 1st permanent molar germ develops as a backwards extension of the dental lamina
Describe the ‘late bell stage’ of the enamel organ
- Approx 18 weeks IUL
- Crown shape is well defined
- Apposition of enamel and dentine begin
Describe the formation of dentine and 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
Describe the process of dentinogenesis
- Odontoblast differentiation from dental papilla cells adjacent to IEE
- Deposition of dentine matrix (mainly collagen)
- The unmineralised dentine is termed predentine
- Mineralisation of dentine (hydroxyapatite)
Enamel is made in 2 stages. Describe these stages.
- Protein matrix deposited - matrix is partially mineralised
- Once this framework is established, the organic part is removed and mineralisation is completed (maturation)
Ameloblasts change form and function several times during amelogenesis. Describe these stages
- Differentiation
- Secretion
- Maturation
- Regression
Describe the ‘differentiation’ stage of amelogenesis
- Dentine induces IEE cells to differentiate into ameloblasts
- They elongate, becoming columnar
- The nucleus migrates to the basal end of the cell
Describe the ‘secretory’ stage of amelogenesis
- Ameloblasts become secretory cells
- The synthesise and secrete the enamel matrix proteins (amelogenins)
- The matrix is then partially mineralised (30% mineral)
Describe the ‘maturation’ stage of amelogenesis
- Most of the matrix proteins are removed
- Mineral content of enamel is increased
- Mature enamel is 95% mineral
Describe the ‘regression’ stage of amelogenesis
- Ameloblasts regress to form a protective layer (the reduced enamel epithelium)
- Involved in eruption
- Formation of epithelial attachment
When does root formation begin?
After crown formation is complete
How is the root shape defined?
The root shape is defined by apical growth of the cervical loop, which is now called Hertwig’s epithelial root sheath (HERS)
What is HERS?
Hertwig’s Epithelial Root Sheath
Formed by apical growth of the cervical loop
Which structure induces formation of root dentine?
Hertwig’s Epithelial Root Sheath
What happens to HERS once the initial layer of root dentine is formed?
HERS breaks up but persists as ‘debris of Malassez’ which may develop into a cyst
Which cells give rise to cementoblasts?
Mesenchymal cells from the dental follicle contact the dentine and differentiate into cementoblasts
What are the 3 parts of the tooth germ and what do they give rise to?
- Enamel organ: enamel
- Dental papilla: dentine, pulp
- Dental follicle: cementum, PDL, alveolar bone
Where is the enamel organ derived from?
Ectoderm
Where is the dental papilla derived from?
Neural crest
Where is the dental follicle derived from?
Neural crest
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
