Tooth development Flashcards
What alternative to implants and dentures is being researched?
Stem-cell research to develop tooth germs that can be implanted and grown in the mouth
Drawbacks of possible tooth germ technology to replace missing teeth
- might not be commercially viable
- might not be able to compete with dentures/implants
- method of implanting tooth bud
- alveolar bone resorbed, PDL lost, soft tissue lost, occlusion changes after extraction
What are the 3 primary embryonic layers that all body tissues develop from?
ectoderm, mesoderm, endoderm
What dental tissue is formed from the ectoderm?
Enamel
What are all parts of the teeth (except enamel) derived from?
ectomesenchyme / neural crest tissue that migrates into the developing face and jaw (forms dentine, pulp, cementum, PDL, jaw bones)
Where does the ectomesenchyme originate?
From the neural crest that develops between the ectoderm and neural tube. Migrates to developing head.
What is the cause of Treacher-Collins Syndrome phenotype?
Failure of ectomesenchyme / neural crest tissue to migrate into the developing face and jaw.
Name of the structure teeth develop from
tooth germs
What is the first stage in tooth development?
initiation
Name of the oral epithelial tissue covering the primitive mouth
stomodaeum
Appearance of primitive mouth at week 5-6
2 maxillary processes separated by a frontal nasal process. 2 mandibular processes. Covered by stomodaeum.
How is the maxilla formed?
Joining together of the frontal nasal process and the 2 maxillary processes
How is the mandible formed?
Joining together of the 2 mandibular processes
What is the congenital abnormality caused by the failure of the 2 maxillary processes and the frontal nasal process to fuse?
Cleft lip and palate
What is the first stage of tooth initiation?
At 6 weeks, the stomodaeum (oral epithelium) thickens and invaginates into the mesenchyme to form the primary epithelial band.
What is the primary epithelial band?
The thickening and invagination of the stomodaeum into the mesenchyme at 6 weeks IUL.
What happens by week 7?
The primary epithelial band divides into 2 processes: the vestibular lamina (buccally located) and the dental lamina (lingually located).
What does the vestibular lamina form?
Forms the vestibule / buccal sulcus
What is the vestibule?
Horse-shoe shaped space between the lips/cheeks and teeth/gingiva
What does the dental lamina form?
enamel organ
What shape is the dental lamina?
Horse-shoe shaped, following the line of the vestibular fold
How is the vestibule of the oral cavity formed?
Cells of the vestibular lamina proliferate followed by apoptosis of the central epithelial cells to produce the sulcus of the vestibule.
How do the early tooth germs appear by week 8?
as a series of swellings on the deep surface of the dental lamina.
What is the second stage of tooth development after initiation?
Morphogenesis
What is the first stage of morphogenesis?
Bud stage
What happens in the bud stage?
The dental lamina thickens to form the bud shaped enamel organ
What surrounds the bud shaped enamel organ?
ectomesenchymal condensation which is the dental papilla
What cells make up the dental papilla?
Ectomesenchymal cells that have migrated. (failure of migration will lead to an underdeveloped dental papilla)
When is the enamel organ at the bud stage?
8-10 weeks
What follows the bud stage of the enamel organ?
Cap stage
At which week does the enamel organ form the cap stage?
11 weeks
What structure is below the internal enamel epithelium in the cap stage?
dental papilla
What are the two layers of the cap stage enamel organ?
External enamel epithelium makes up the outside of the cap, the internal enamel epithelium makes up the inside of the cap.
Where do the external and internal enamel epithelia meet?
At the cervical loop
Which stage follows morphogenesis (bud and cap stages)?
Cytodifferentiation (cell specialisation) (bell stage)
When does the bell stage of the enamel organ occur?
Approx 14 weeks - depends on which tooth is being formed.
What happens during the bell stage enamel organ?
more cell layers differentiate and the internal enamel epithelium starts to define the occlusal shape of the crown.
What are the 4 cell layers at the bell stage of the enamel organ?
Stellate reticulum, stratum intermedium, internal enamel epithelium and external enamel epithelium.
Where is the stellate reticulum found?
star shaped cells at the centre of the bell stage of the enamel organ
Where is the stratum intermedium found?
Lies over the IEE (at the location of future cusps) between the IEE and the stellate reticulum in the bell stage enamel organ.
How does the permanent tooth germ form?
The dental lamina for the permanent tooth forms as an extension of the lingual side of the dental lamina for the deciduous tooth germ. Approx week 12
Which permanent teeth do not form from an extension of the dental lamina of their deciduous counterpart?
the 12 permanent molars because there are no previous deciduous teeth.
How do the enamel organs for the permanent molars form?
The dental lamina grows backwards to bud off successively (don’t have deciduous predecessor) at around week 16
What is the stage of tooth development after cytodifferentiation?
Matrix secretion (late bell stage)
What week is the late bell stage?
week 18
What happens during the late bell stage?
Apposition of dentine and enamel begins
Name of the junction between dentine and enamel
Amelo-dentinal junction
At which stage of tooth development is the crown shape well defined?
Late bell stage of the enamel organ
In which directions is enamel and dentine formed?
Dentine forms inwards while enamel forms outwards
Is enamel or dentine formed first?
Dentine is formed before enamel
How do odontoblasts differentiate?
Developing ameloblasts (preameloblasts) influence mesenchymal dental papilla cells adjacent to IEE to differentiate into odontoblasts.
Which cells differentiate into odontoblasts?
the dental papilla cells adjacent to the IEE
Which cells differentiate into ameloblasts?
IEE cells
Process of dentinogenesis
Odontoblasts deposit unmineralised dentine matrix (mainly collagen) which is predentine. This is then mineralised by the deposition of hydroxyapatite to form dentine.
Which cells produce dentine (predentine initially)?
odontoblasts
Which cells form enamel?
Ameloblasts
When do ameloblasts differentiate and secrete enamel?
Internal enamel epithelial (IEE) cells differentiate into ameloblasts once dentine formation has begun. The presence of dentine induces the ameloblasts to secrete enamel.
How do the IEE cells differentiate into ameloblasts?
they elongate, becoming columnar and the nucleus migrates to the basal end of the cell.
What is an enamel knot?
Cluster of cells associated with the stratum intermedium that form during the bud stage and establish the crown shape.
How many enamel knots would an incisor have?
4 - 3 form the mamelons on the incisal edge while 1 forms the cingulum.
How many enamel knots might a 16/26 have?
5 - 4 knots form the cusps while 1 forms the tubercle of Carabelli
Which disorder is associated with a mutation / lack of the Edgar gene?
Amelogenesis imperfecta - enamelins and amelogenins (enamel proteins) are not broken down during enamel maturation which leads to the enamel being softer.
Does the enamel organ or dental papilla define the shape of the tooth?
Enamel organ - although ameloblasts fully differentiate/secrete enamel later, they determine the conversion of mesenchymal cells into odontoblasts.
How do the dentinal tubules form?
As each odontoblast recedes, it grows a longer projection within the secreted matrix which becomes a dentinal tubule.
Similarity between ultrastructure of ameloblasts and odontoblasts
Both are polarised with their nuclei in the opposite end of the cell (basal end) to where matrix is secreted from.
Which structure secretes enamel crystals in ameloblasts?
Tomes process
What are the 2 stages of enamel formation?
- a protein matrix is deposited which partially mineralises enamel to 30%
- maturation - once this framework is formed, the organic part breaks down to complete mineralisation (96%)
Stages of ameloblast differentiation
Differentiation, Secretion, Maturation, Regression
Why is the regression stage of amelogenesis differentiation important?
As ameloblasts regress they form a group of cells that later develop into the junctional epithelium (periodontium)
What happens during the secretory phase of amelogenesis?
Ameloblasts become secretory cells which synthesise and secrete enamel matrix proteins (e.g. amelogenins)
What level of mineralisation is reached during the secretory phase of amelogenesis?
Partial mineralisation (30% - out of 95%)
What happens during the maturation phase of amelogenesis?
Most of the matrix proteins are removed and the mineral content of enamel is increased to 95%
What happens during the protection/regression phase of amelogenesis?
ameloblasts regress to form a protective layer called the reduced enamel epithelium
Function of the reduced enamel epithelium
involved in eruption and the formation of epithelial attachment (junctional epithelium)
What is the final stage of tooth development after matrix secretion?
Root formation
When does root formation begin?
After the crown formation is completed
What maps the root shape?
Apical growth / migration of the cervical loop.
What is the name of the cervical loop as it grows apically to create the root?
Hertwig’s epithelial root sheath (2-cell-layered structure as opposed to 4 layered enamel organ)
Function of Hertwig’s epithelial root sheath
induces the formation of root dentine
What happens to Hertwig’s epithelial root sheath once the initial layer of root dentine forms?
Hertwig’s epithelial root sheath breaks down to form cell rests / debris of Malassez and a connection now forms between the dental follicle and root dentine.
Which cells do cysts develop from?
cell rests / debris of Malassez
How is cementum formed?
When Hertwig’s epithelial root sheath breaks down, the mesenchymal cells from the dental follicle contact the dentine and differentiate into cementoblasts which form cementum.
Name of the PDL fibres that are embedded into cementum
Sharpey’s fibres
What type of tissue is the enamel organ formed from?
Epithelium originating from ectoderm
What tooth component does the enamel organ form?
Enamel
What type of tissue are the dental papilla and dental follicle formed from?
ectomesenchyme tissue originating from the neural crest
What tooth structures are formed by the dental papilla?
Dentine and pulp
What tooth structures are formed by the dental follicle?
Cementum, periodontal ligament, part of the alveolar bone
Name of dental developmental disorder in which patients may have fewer teeth and the teeth can appear conical and smaller
hypodontia
Name of dental developmental disorder in which an extra tooth is present between the 2 central incisors
supernumerary mesio-dens
What is gemination?
Dental developmental disorder in which 2 teeth develop from one tooth bud, creating an extra tooth
What is fusion?
dental developmental disorder in which 2 tooth germs unite creating a larger tooth with a single root
Name of dental developmental disorder of improper dentine formation
dentinogenesis imperfecta
