OE L1 Early Tooth Development Flashcards
What is the 1st pharyngeal arch divided into?
The maxillary process
The mandibular process
Which process is more developmently ahead?
The mandible. Develops slightly sooner than the maxilla, and so do the resulting teeth.
What structure begins to form at 6 weeks?
The primary epithelial band.
What tissue begins to form underneath the primary epithelial band around 6 weeks iu?
Ectomesenchyme.
Epithelial cells of OE thicken and invaginate into underlying mesenchymal cells to form this ectomesenchyme.
How is the presumptive lip seperated from the presumptive jaw?
A cleft forms.
The primary epithelial band invaginates to seperate lip from jaw, and create a vestibule for teeth.
What 2 layers form from the invagination of the primary epithelial band?
- Vestibular lamina (anterior)
- Dental lamina (posterior)
NB: also called dental process
What are the localised thickenings of the denal lamina called?
Dental placodes. These placodes are the sites of future decidous tooth development.
What are the 3 stages of tooth development?
- Bud
- Cap
- Bell
Describe bud stage
- Dental lamina extends further into mesenchyme forming an epithelial bud (lots of energy required, cells have high mRNA conent as actively producing signalling components needed)
- Increased oxidative activity as mitochondria are producing lots of ATP
- Low glycogen as constantly being used up
- Mesenchymal cells pack tightly around epithelial bud
- Condesnation of mesenchyme
Describe late bud stage
- Condensation of mesenchyme continues
NB: mesenchymal cells form furture dental papilla (which goes on to form dentine and pulp). Epithelial cells of dental lamina form future enamel organ.
Describe early cap stage
- Bud flattens (cap appearance)
- Cells histo-differnetiate to form different cell layers that ultimately form inside enamel organ (stellate reticulum, stratum intermedium etc)
- Epithelial cells (future enamel organ) change: outer lining cells become cuboidal, inner cells become rounded and sparse
- Mesenchymal cells continue condensing to form dental papilla
Describe late cap stage
- Enamel organ grows larger
- Appearance of enamel organ (cap) sat on top of condensed mesenchyme (papilla)
- Cells surrounding papilla encapsulate enamel organ in a sac called dental follicle (made of condensed ectomesenchyme, forms supporting structures of tooth)
What does the term tooth germ describe?
Tooth germ = enamel organ + dental papilla + dental follicle
Describe late cap/early bell stage
- Full histo-differentiation of epithelial cells of enamel organ into functionally and morpholpgically distinct components
- Instructions for these changes controlled by temporary structure called enamel knot
Describe the enamel knot
A transient localised thickening of non-dividing epithelial cells around the cusp.
Enamel knot expresses a range of signalling molecules key to crown development.
Describe bell stage
- Continued proliferation of epithelial cells causes epithelial processes to grow downwards and surround dental papilla (primitive roots)- tooth now resembles bell shape
- Dental lamina still attached to oral epithelium
- Histo-differentiation of distinct cell layers (4)
What are the 4 distinct layers of the enamel organ at bell stage?
- Outer enamel epithelium
- Stellate reticulum
- Stratum intermedium
- Inner enamel epithelium
Describe the outer enamel epithelium
- Cuboidal shaped cells
- One cell layer thick
- High nuclear : cytoplasm ratio
- Non-secretory protective role
- Becomes part of dentogingival junction
Describe the stellate reticulum
- Star shaped cells
- Secrete hydrophillic glycosaminoglycans
- Produces jelly-like ECM
- Cells connected via desmosomes
Describe the stratum intermedium
- Just above the IEE
- 2-3 cells thick
- Flattened cells
- Rich in alkaline phosphotase
- Potential signalling function
- Criticial for enamel formation
Describe the inner enamel epithelium
- Just above the dental papilla
- 1 cell layer thick
- Columnar shaped cells
- Later differentiate into ameloblasts
What are the cervical loops?
The point where the OEE meets the IEE, 2 cells thick, site of root formation.
Describe late bell stage
- Dental lamina begins fragmenting and disintegrating, so developing tooth seperates from OE
- Some fragments remain as discrete islands of cells called Glands of Serres or epithelial pearls
- IEE growth is complete, shape of future cusp can be seen
Describe late bell/early crown stage
- Hard tissue formation begins
- Mesenchymal cells of dental papilla differentiate into odontoblasts
- Odontoblasts secrete pre-dentine matrix which is then mineralised to dentine
- Pre-dentine secretion begins at cusp tip and progresses down to apex of roots
Describe crown stage
- Enamel deposition begins
- As first predentine is secreted, the basement membrane breaks down and there is contact between IEE cells and predentine
- This contact triggers cells of IEE to undergo terminal differentiation into ameloblasts, which secrete enamel next to the dentine matrix
Describe the morphology of ameloblasts
- Low to tall columnar cells
- Nucleus polarises to base of cell away from the dental papilla
Describe the morphology of odontoblasts
- Tall columnar cells
- Basal polarised nucleus
- Large increase in synthetic organelles
When does blood vessel formation begin in tooth development?
Begins in cap stage, and continues to increase during bell stage.
Decreases after hard tissue formation.
Where do the blood vessels enter?
Enter the dental papilla at the sites where future roots form.
The enamel organ is avascular, and nutrients are supplied by the dental papilla.
When does nerve supply begin during tooth development?
Between bud and cap stage.
Describe the nerve supply to the developing tooth
- Pioneer nerve fibres approach the follicle and form a rich plexus around the tooth germ
- Nerve fibres do not penetrate the dental papilla until dentine formaiton begins
Does permanent dentition development occur during the deciduous tooth development?
Yes.
The permanent dentition arises from the dental lamina.
There is an extension of the dental lamina called the successional lamina from which the permanent tooth will form.
The bud in the successional lamina can stay dormant and remain at the bud stage until it is required.
