Dental development Flashcards
what is enamel derived from
ectoderm
apart from enamel, where are the other parts of the teeth derived from
ectomesenchyme
what is the ectomesenchyme
part of the ‘neural crest’ that develops beside the primitive nervous system
where do teeth develop from
tooth germs
What are the stages of tooth development
- initiation
- morphogenesis
- cytodifferentiation
- matrix secretion
what happens at the initiation stage of tooth development
- occurs at dental lamina
- a space develops (‘stomodaeum’) in between maxillary process and mandibular process
- primary epithelial band develops 5-6 weeks IUL
- PEB divides into 2 parts (vestibular lamina and dental lamina)
when does the primary epithelial band develop
5-6 weeks IUL
what does the vestibular lamina breakdown to form
buccal sulcus
what is formed from the dental lamina
enamel organ
What happens during morphogenesis
Bud stage
- thickening of dental lamina forms enamel organ
- reorganisation of cells around enamel organ forming the dental papilla
- enamel organ = enamel
- dental papilla = all other structures
Cap stage
- 11wks IUL
- bud organises into a cap
- External enamel epithelium (EEE) and Internal enamel epithelium (IEE) form cap over dental papilla
- EEE and IEE meet at the cervical loop
What happens during the cytodifferentiation stage
Bell stage
- 14 wks IUL
- 4 cell layers in enamel organ:
1. IEE
2. EEE
3. stratum intermedium
4. stellate reticulus
permanent tooth germ takes shape
What happens in the matrix secretion stage
Late bell stage
- 18 wks IUL
- crown shape defined
- dentine formation established
- enamel formation beginning
How does the formation of dentine and enamel begin
- dental papilla cells adjacent to IEE differentiate into odontoblasts
- they lay down dentine matrix which is later mineralised (predentine)
- once dentine formation has begun, IEE cells differentiate into ameloblasts, which form enamel
what is unmineralised dentine called
predentine
what is mineralised dentine made of
hydroxyapatite
During dentinogenesis, some ectomesenchyme cells differentiate at an early stage and keep themselves dormant, why?
they will make tertiary dentine if the odontoblast cells die
what happens as the cells differentiate into odontoblasts/ ameloblasts
- polarisation of cells
- increase in organelles in cells
how is the enamel matrix different from the dentine matrix
enamel doesn’t have collagen
How is enamel formed
- Differentiation
- Dentine induces IEE cells to differentiate into ameloblasts - Secretory phase
- ‘tongue’ process
- ameloblasts synthesise and secrete the enamel matrix proteins
- crystallites laid down in organised way to create structure of enamel rods (matrix mineralised to 30%) - Maturation phase
- removal of organic content of matrix to get 96% mineralisation
4. Protection phase 'regression stage' - ameloblasts regress to form a protective layer - ready for eruption - formation of the epithelial attachment
when is the root formed
after the crown is completed
how is the root formed
- EEE and IEE meet at cervical loop
- root shape defined by apical growth of the cervical loop = “hertwig’s epithelial root sheath”
- HERS induces formation of root dentine by growing downwards
- HERS breaks up after initial layer of root dentine formed
- remains of HERS persist as ‘debris of Malassez’
- Mesenchymal cells from the follicle contact the dentine, and differentiate into cementoblasts. These form cementum
What are the remains of hertwigs root sheath called when it breaks down
what can they develop into
debris of Malassez
odontic cyst
what is hypodontia
less teeth than there should be and strange shape
what are supernumeray ‘mesio-dens’
lateral conoid tooth in between central incisors
what is gemination
2 laterals on top of each other, growing together
what is fusion
2 central and lateral incisors growing together
what is dentinogenesis imperfecta
dentine not formed properly
What is the part of the tooth germ that gives rise to cementum, PDL and alv. bone
dental follicle
What is the part of the tooth germ that gives rise to dentine and pulp
dental papilla
What is the part of the tooth germ that gives rise to enamel
enamel organ
what is the condition called when the ectomesenchymal cells fail to migrate
mandibulofacial dysostosis
what causes amelogenesis imperfecta
- autosomal recessibe hypoplastic hypomaturation amelogenesis imperfecta
- MMP 20 gene
- located on long arm of chromosome 11 at position 22.3
- provides instructions for making enamelysin
- enamelysin cleaves other proteins, such as amelogenin and ameloblastin, into smaller pieces (easier to remove)
