Tooth Development Flashcards
What are the 3 primary embryonic layers?
- Ectoderm
- Mesoderm
- Endoderm
Which one of the 3 primary embryonic layers 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 Ectomesenchyme?
- Part of the ‘neural crest’ that develops beside the primitive nervous system
What do teeth develop from?
Tooth germs
What is another name for Ectomesenchyme?
Neural crest tissue
What is the first stage of tooth development?
Initiation
What is the stomodaeum in a 5-6 week human embryo?
The space of the mouth
Approximately when does the primary epithelial band develop?
Approximately 6 weeks
What does the primary epithelial band appear as?
A thickening in epithelium f embryonic mouth (stomodaeum)
Approximately when does the dental lamina develop?
Approximately 7 weeks
What 2 parts does the primary epithelial band divide into?
- Vestibular lamina, which will break down to form the buccal sulcus
- The dental lamina, from which the enamel organ develops
What shape is the dental lamina?
A horseshoe shaped structure
What is the second stage in tooth development?
Morphogenesis
What does morphogenesis mean?
The generation of shape
When does the enamel organ - ‘bud’ stage occur?
At approximately 8-10 weeks
What is the ‘bud’ stage of dental development?
- Dental lamina thickens into a ‘bud’ stage enamel organ
- An Ectomesenchymeal condensation appears and this is the dental papilla
When does the enamel organ - ‘cap’ stage occur?
At approximately 11 weeks
What 2 epitheliums are present in the enamel ‘cap stage’?
- External enamel epithelium
- Internal enamel epithelium
- EEE and IEE meet at the cervical loop
What is the third stage of tooth development?
Cytodifferentiation
When does the enamel organ - ‘bell’ stage occur?
At approximately 14 weeks
At what stage is the tooth shape starting to be defined?
The ‘bell’ stage
What are the 4 cell layers present in the ‘bell’ stage enamel organ?
- Stratum intermedium
- Internal enamel epithelium
- External enamel epithelium
- Stellate reticulum
What is the function of stellate reticulum in the ‘bell’ stage enamel organ?
Support tissue during the formation of enamel
At what time does an extension appear on the lingual side of the dental lamina - this is the dental lamina for the permanent successor?
At approximately 12 weeks
At what time does the 1st permanent molar germ develop as a backwards extension of the dental lamina?
At approximately 16 weeks
What is the fourth stage of tooth development?
Matrix secretion
At what time does matrix secretion occur?
Approximately 18 weeks
In what stage does the apposition of enamel and dentine begin?
The late ‘bell’ stage
What do dental papilla cells adjacent to the internal enamel epithelium differentiate into?
Odontoblasts
What do odontoblasts do?
They lay down dentine matrix, which is later mineralised (pre-dentine)
What do ameloblasts do?
Form enamel
What is the process of dentinogenesis?
- Odontoblast differentiation from IEE
- Deposition of dentin matrix
- mineralisation of dentine
What are the 2 stages of formation of enamel?
- Protein matrix deposited
- Matrix is partially mineralised - Once this framework is established, the organic part is removed, and mineralisation is complete
- The ameloblasts change form and function several times during amelogenesis
What happens during the differentiation stage of amelogenesis?
- Dentine induces IEE cells to differentiate into ameloblasts
- They elongate, become columnar
- The nucleus migrates to the basal end of the cell
What happens during the secretory stage of amelogenesis?
- Ameloblasts become secretory cells
- They synthesise and secrete the enamel matrix proteins (amelogenins)
- The matrix is then partially mineralised
What happens during the maturation stage of amelogenesis?
- Most of the matrix proteins are removed
- Mineral content of enamel is increased
- Mature enamel is 95% mineralised
What happens during the protection stage of amelogenesis?
- Ameloblasts regress to form a protective layer - the reduced enamel epithelium
- Involved in eruption
- Formation of epithelial attachment
What is the 5th stage in tooth development?
Root formation
What has to be completed before root formation begins?
Crown formation
Where do the EEE and IEE meet?
At the cervical loop
What does migration of the cervical loop map out?
The crown shape
What is the root shape defined by in root formation?
By apical growth of the cervical loop, which is now called the Hertwig’s epithelial root sheath
What is the Hertwig’s epithelial root sheath?
- The apical growth of the cervical loop
- 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
- Once the initial layer of root dentine is formed, Hertwig’s sheath breaks up (no enamel in root)
What is ‘debris of Malassez’?
Remains of Hertwig’s epithelial root sheath which may develop into a cyst
What are cementoblasts?
Produce cementum
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, alveolar bone (part)
What are the possible characteristics of dental development disorders?
- Presence
- Number
- Size
- Shape
- Structure
- Eruption
What is hypodontia?
Lacking teeth and not formed properly
What is supernumerary ‘mesio-dens’?
Extra tooth in the middle
What is germination?
2 laterals glued together
What is fusion?
Central and lateral joined together
What is dentinogenesis imperfecta?
Dentine has not been formed properly
