Embryology Flashcards
From what embryonic layer is enamel derived?
Ectoderm
What are all parts of teeth and supporting tissues (except enamel) derived from?
Ectomesenchyme
From what do teeth develop?
‘Tooth germs’
Where is the neural crest located?
Between the ectoderm and neural tube
What is mandibulo facial dysostosis
Failure of ectomesenchymal cells to migrate (into the developing face and jaws)
What is the first stage of tooth development and what 2 features develop?
Tooth initiation:
Primary epithelial band (PEB) develops at approx 6 weeks IUL
Appears as thickening in epithelium of embryonic mouth (stomodaeum)
Dental lamina develops at approx 7 weeks
The PEB has grown into the jaw and divided into 2 parts:
- vestibular lamina (will break down to form buccal sulcus)
- dental lamina (from which enamel organ develops)
Describe the ‘bud’ stage of tooth development
Approx 8-10 weeks
Dental lamina thickens into a ‘bud’ stage enamel organ
An ectomesenchymal condensation appears (dental papilla)
Describe the ‘cap’ stage of tooth development
Approx 11 weeks
The enamel organ forms a ‘cap’ over the papilla
The cells of the enamel organ differentiate into the external enamel epithelium (EEE) and internal enamel epithelium (IEE)
The EEE and IEE meet at the cervical loop
Describe the ‘bell’ stage of tooth development
Approx 14 weeks
More cell layers differentiated
Tooth shape being defined
‘Bell’ stage enamel organ has 4 layers
- IEE
- EEE
- stellate reticulum (between the IEE and EEE)
- stratum intermedium (lies adjacent to IEE)
Describe the late ‘bell’ stage of tooth development
Approx 18 weeks
Crown shape is well defined
Apposition of enamel and dentine begins
Describe the formation of dentine during tooth development
Dental papilla cells adjacent to IEE differentiate into odontoblasts, which lay down dentine matrix (mainly collagen), which is later mineralised.
The unmineralised dentine is predentine
Describe the formation of enamel in tooth development
Two stages:
1. Protein matrix deposited by ameloblasts
Matrix is partially mineralised (30%)
- Once this framework is established, the organic part is removed and mineralisation is completed (96%)
Describe the ameloblast differentiation stage of amelogenesis
Dentine induces IEE cells to differentiate into ameloblasts
They elongate, becoming columnar
The nucleus migrates to basal end of cell
Describe secretory phase of amelogenesjs
Ameloblasts become secretory cells
They synthesise and secrete the enamel matrix proteins (amelogenins)
The matrix is then partially mineralised (30% mineral)
Describe the maturation phase of amelogenesis
Most of matrix proteins removed
Mineral content of enamel increased
Mature enamel is 95% mineral
Describe the protection phase of amelogenesis
Ameloblasts regress to form protective layer- the reduced enamel epithelium
Involved in eruption
Formation of epithelial attachment
How is root shape defined?
Defined by apical growth of cervical loop
What is the new name of the cervical loop during root formation?
Hertwig’s epithelial root sheath (HERS)
What does HERS induce?
Induces formation of root dentine
What is the fate of Hertwig’s epithelial root sheath once the root dentine is formed?
HERS breaks up
Some remains may persist as ‘debris of Malasiez’, which may develop into a cyst
Describe the final steps of root formation once root dentine has been placed
Mesenchymal cells from the follicle contact dentine and differentiate into cementoblasts, which form cementum
Fibres from developing PDL are embedding in the cementum (Sharpey’s fibres)
Name the type of tissue, origin and product(s) of the enamel organ
Epithelium, ectoderm, enamel
Name the type of tissue, origin and product(s) of the dental papilla
Ectomesenchyme
Neural crest
Dentine, pulp
Name the type of tissue, origin and product(s) of the dental follicle
Ectomesenchyme
Neural crest
Cementum, PDL, alveolar bone
