Late Tooth Development Flashcards
What is the primary enamel knot?
An epithelial thickening
Why does the primary enamel knot not increase in size?
The cells do not divide
Explain the primary enamel knot as a signalling centre
These molecules are cofactors that activate signalling pathways.
The knot does not contain receptors for these cofactors. The cells surrounding the knot have to response to these factors.
What are 2 points for the role of the primary enamel knot?
The juxtaposition of the non-proliferative cells of the PEK and the proliferative cells of the rest of the epithelial cap is believed to drive the bending of the inner enamel epithelium into a cap shape.
The PEK secrets signalling molecules that influence the proliferation and differentiation of the cells of the developing tooth germs.
What type of structure is the primary enamel knot? Where is is present and what eventually happens to it?
The PEK is a transient structure only present at the cap stage of tooth development. The PEK is later eliminates by programmed cells death (apoptosis).
How many PEK are there in a monocusp and a multipcuspid tooth at the cusp stage?
What does the PEK mark?
1
The position of the first buccal cusp of molars
Give some important anatomical features of a root
- Stratum intermedium
- Stellate reticulum
- Dental follicle
- Cervical loop
- Dental papilla
- Inner and outer enamel epithelium
What stage does the dental follice begin to change?
What are its 3 layers?
Bell stage
Inner layer, loose connective tissue, outer layer
What stage is the tooth-crown shape established?
Bell stage
What teeth and where does the secondary enamel knot form?
In multicuspid teeth only
(forms the cap which then leads to different stages of teeth development) Forms at the tip of the root
What does different rates of division within the inner enamel epithelium lead to?
Folding within this IEE
Everything proliferates except for the secondary enamel knot.
The non-proliferative areas buckle and form a cuspal outline.
What begins at the 20th week of tooth development?
What do the buds give rise to?
Tooth buds for the permanent teeth begin to form at the late bell stage.
The dental lamina for deciduous teeth is present and the successional lamina for permanent teeth.
The buds give rise to the permanent incisors, canines and premolars.
What happens to begin the bud of the molar teeth?
Once the jaw is formed enough, the dental lamina sends a projection backwards (for permanent molars).
What is the difference between a successional and accessional tooth?
Successional: permanent tooth with a tooth predecessor (a deciduous tooth before it)
Accessional: permanent tooth with no predecessor (no deciduous tooth)
What happens to the dental lamina at the late bell stage?
What is the name of a epithelial cluster that persists and what can this do?
It breaks down - the bells form into clusters.
Called epithelial pears of Serres. Can causes cysts, odontomas (tumours) or supernumerary teeth
What is the definitions of monophyodont, diphyodont and polyphyodont?
Monophydont = single generation, no replacement teeth
Diphyodont = second generation of teeth
Polyphyodont = multiple generations
Snakes are polyphyodont animals, what never breaks down for them due to this?
The dental lamina is permanent so new teeth can constantly be produced.
Why do humans only have two dentitions?
The secondary dental lamina breaks down so no more teeth can form after this.
A mutation in mice means continuous tooth generation by activating what signalling?
What happens when this signalling occurs?
Wnt/beta-catenin signalling
Tooth germ develop by budding off from the existing enamel epithelium, forming multiple small conical shaped teeth.
What signalling is concentrated in regenerating teeth in snakes and why?
What happens if there is overexpression of this?
Wnt signalling for constant regeneration.
Overexpression of this means an increase in tooth number.
What does terminal differentiation of specialised cells give rise to?
What in a tooth is mineralised? (2 things)
What one thing is non-mineralised?
Gives rise to fully formed dental tissues.
Enamel, dentine
Dental pulp
What stage does formation of hard tissues occur?
Where does it start?
The late bell stage.
Starts at the tip of the cusps.
What precursor cells are present in inner enamel epithelium and at the periphery of dental papilla?
What do the cells inside the bell shape differentiate to?
IEE - ameloblasts
Periphery of dental papilla - odontoblasts
To odontoblasts (these are the ones in the periphery)
What tissue do odontoblasts at the periphery of the tooth form? How?
Predentine which is mineralised to dentine.
All the nuclei align at one edge of the cell. Odontoblasts retreat towards the centre of the tooth.
What are the 5 steps under odontoblast and ameloblast differentiation?
Give some extra detail on this
- Elongation and polarisation of inner enamel epithelium
- Differentiation of odontoblasts
- Formation of dentine
- Ameloblasts become fully functional
- Formation of enamel
Preameloblasts send a signal to the periphery. This causes changes in the outer layer of cells (odontoblasts). This calls start forming predentine.
The predentine acts as a signal for preameloblasts which differentiate into ameloblasts.
What is the first thing to occur in amelogenesis?
Collapse of stellate reticulum.
They get their nutrients from blood vessels which are on the outside of the tooth.
Do premolars teeth form a primary enamel knot (PEK)?
Yes in all teeth
Does the PEK give rise to the SEKs?
No (two independent structures). Primary enamel knot dies and the secondary is produced.
Cite one molecule secreted by the PEK.
Bmp, sonic hedgehog, Wnt
The upper and lower permanent incisors bud from
which anatomical structure?
Lower = mandibular arch, upper = frontal nasal process
The 12 permanent molars bud from which anatomical
structure?
Appositional Lamina - extension of dental lamina backwards
What special cells are present in the dental lamina?
stratified squamous epithelium, putative stem cells
In which tooth tissue can forced activation of Wnt
signalling lead to the formation of dozens of teeth?
Successional lamina
Where do ameloblasts get their nutrients from?
Blood vessels on the outside of the tooth
What anatomical structure does the cervical loop give
rise to?
Where the inner enamel epithelium meets the outer enamel epithelium
Cite two animals with continuous tooth replacement.
Snakes and Crocodiles
What is the space outside the inner enamel epithelium called?
Dental follicle
Difference between accessional lamina and where they are found respectively?
The successional lamina gives rise to permanent teeth that replace the deciduous teeth. The accessional lamina gives rise to the permanent teeth that do not replace the deciduous teeth.
What causes the formation of the primary enamel knot?
Activation of Bmp4 signalling in the dental epithelium (via Bmp4 secreted by the dental mesenchyme) that causes the formation of the primary enamel knot (PEK). The inner enamel epithelium (IEE) folds because in the centre of the IEE, the PEK cells do not proliferate, while everywhere else in the IEE, epithelial cells do proliferate. As a result, the PEK cells buckle and are pushed upwards leading to the formation of the first cusp of the tooth crown.
Give information on the different tooth stages:
- number of dental epithelial cell populations
- enamel knots
- number of dental mesenchyme populations
Bud:
1 population of dental epithelial cells
1 inactive PEK
1 population of dental mesenchyme
Cap:
4 distinct populations of dental epithelial cells
1 active PEK
2 populations of dental mesenchyme
Bell:
4 distinct populations of dental epithelial cells
Several active SEK
2 populations of dental mesenchymal cells
