Tooth devlopment Flashcards
Wher does tooth devlopment come from
Interactions between the ectoderm of the oral cavity and the neural crest ectomesenchyme
What are the 4 stages
Bud
Cap
Bell (early)
Bell (late)
What happens at the 6/7th week
Ectoderm lining stomodeum give rise to the oral epithelium and the dental lamina adjacent to depper ectomesenchyme
What happens in the bud stage
It starts at 8th week with emergence of enamel organs which are swellings formed by the dental lamina under the influence of mesenchyme
The dental lamina penetrates the ectomesenchyme giving it the ‘bud’ shape
Ectomesenchyme condensation starts to happen
What happens in the cap stage
Involves growth and expansion of the enamel organ resulting in a concavity forming at the inner aspect giving it the ‘cap’ name
Near 12 weeks inner enamel epithelium forms from the inner cuboidal cells of enamel organ
The IEE are columnar and define the shape of the crown and they later differentiate into ameloblasts
Outer layer of the enamel organ form the outer enamel epithelium and stay cuboidal and maintains enamel organ shape
Condensed mesenchymal cells beneath the IEE form the dental papilla, the enamel also has a surrounding capule
At 14 weeks 2 new layers form of stratum reticulum and stratum intermedium, further growth occurs at IEE and OEE and they from the cervical loop
What gives rise to the pulp, PDL and hertwigs root sheath
dental papilla= pulp
dental follicle= PDL
Cervical loop= hertwigs root sheath
Where abouts is stellate reticulum and intermedium in the tooth germ
Stellate intermedium= lies over the inner enamel epithelium
stellate Reticulum= lies between the stellate intermedium and the outer enamel epithelium
What happens in the early bell stage
Enamel organ becomes more ‘bell’ shaped with cells on the periphery seperate into 4 layers
The Dental lamina disintergrates leaving teeth seperate from the epithelium of ht eoral cavity and leaving behind the rest of serres
Cells from the inner enamel epithelium induce cells of the dental papilla to form odontoblasts which will then eventually form dentine and as they continue they retreat towards the dental papilla forming a S-shape cure called the odontoblast process
What happens in the late bell stage
Otherwise called crown or maturation stage
Rapidly diving IEE cells stop at the location of where the cusps will form as the first mineralised hard tissue is formed
Adjacent cell layers in the dental papilla increase in size and differentitate to odontoblasts. After dentine formation IEE cells secrete an organic matrix which dentine mineralises
After 1st layer of dentine enamel formation happens soon after and IEE cells become ameloblasts
They form enamel and once done they loose the ‘Tomes process’ and flatten to become reduced enamel epithelium which protects the enamel during eruption and turn into junctional epithelium
How is the root formed
Once crown finished roots begin
Hertwigs root sheath formed by downwards growth of the I&OEE from the cervical loop as it grows in a apical direction as it encloses ther papilla and outlines root shape
The follicle lies external to this
How does cemetogenisis occur
After root forms fragmentation of hertwigs root sheath occurs enabling cells from adjacent dental follicle to contact root dentine which then differentiates to cementoblasts which are single layered cuboidal on surface of root dentine and secretes the cementum matrix
How is the PDL formed
Dental follicle cells differentiate to fibroblasts that secrete collagen
When cementum starts collagen secreted in follicle move into bundles perpendicular to root surface and form principle PDL fibres
One end is embedded into cementum and the other into alveolar bone (sharpeys fibers)
