amelogenesis Flashcards
what are the stages of amelogenesis?
- induction
- enamel secretion
- enamel maturation & mineralisation
where does ameloblast differentiation begin?
begins at the cusps and goes down slopes
what happens during the induction stage of amelogenesis?
- occurs after dentinogenesis
- signal sent from odontoblasts across ADJ to inner enamel epithelium cells to induce differentiation into secretory ameloblasts
- reciprocal induction
what happens during enamel secretion stage of amelogenesis?
- after dentine formation
- ameloblasts secrete enamel matrix
- structureless enamel layer first
- ameloblasts migrate away from ADJ - results in formation of Tomes process
- can deposit prismatic structured enamel
structure of ameloblasts
- Large columnar cells
- Deposit structured enamel
- Each cell deposits one unit of enamel
- Very large cells - larger than other cells
- Nuclei are arranged proximally
- Have terminal bar apparatus
- Formed from desmosomes
- Links the cells together
- Forms seal between cells
- No exchange of ions occurs
- Important for mineralisation process
- Rich in endoplasmic reticulum
what is the tomes process? what is its role
- Specialised organ
- Allows directional secretion of the tissue being formed
- Secretes perpendicular to the cell surface
- Will secrete enamel in a structured form
role of the stratum intermedium in amelogenesis
- SI cells are involved in transport of organic and inorganic material to and from ameloblasts
- Involved in ion transport
- Relevant for mineralisation process
why does enamel formation occur when distant from the pulp? how is this achieved?
Enamel formation is initiated in presence of poor nutritive support as distant from pulp
Compensation for this is achieved by internal enamel epithelial cells accumulating glycogen
what occurs during the enamel maturation stage of amelogenesis?
- after enamel matrix has reached full thickness
- further differentiation of ameloblasts
- lose tomes processes
- cyclical process
- water and organic material are selectively removed from the enamel while additional inorganic material is introduced
- aim to increase level of mineralisation
- water and organic material are selectively removed from the enamel while additional inorganic material is introduced
- ameloblasts reduce in number -
- apoptosis
- basement membrane re-synthesised
- remaining ameloblasts differentiation into flattened epithelial cells
- form the reduced enamel epithelium
- enamel organ becomes vascularised
- cells from EEE, SR, SI because contiguous with dental follicle tissue
how does the appearance of the ameloblasts change during the maturation stage of amelogenesis?
- further differentiation
- lose their tomes processes
- Ameloblasts alternate between possessing a ruffled border (introduction of inorganic material) and a smooth border (removal of protein and water)
how does reduced enamel epithelium form?
- during maturation stage of amelogenesis
- ameloblasts differentiate into flattened epithelial cells which form the REE
what occurs during the mineralisation stage of amelogenesis?
4 stages
- deposition of enamel template
* formation of partially mineralised enamel matrix during enamel deposition - increase in mineralisation
* starts at surface of enamel and goes into deeper layers - increase in mineral rebounding from innermost layer out to enamel surface
- complete mineralisation of outer layer
where is enamel most highly mineralised?
at the surface
how do ameloblasts change during their life cycle?
- differentiate into secretory ameloblasts from inner enamel epithelium cells
* secrete structureless enamel matrix - ameloblasts migrate from ADJ and form Tomes processes
* secrete structured enamel matrix - undergo further differentiation - when thickness of enamel matrix has been secreted
- lose tomes processes
- Ameloblasts alternate between
- a ruffled border (introduction of inorganic material)
- a smooth border (removal of protein and water)
- ameloblasts either undergo apoptosis or differentiate into cells of reduced enamel epithelium
what is the role of the reduced enamel epithelium?
protects enamel surface during eruption
functions of the internal enamel epithelium
- Determining crown pattern of tooth
- Induction of odontoblasts differentiation
- Differentiation into ameloblasts through reciprocal induction
- Secretion of enamel matrix
- Maturation/mineralisation of enamel
- Protection of newly formed enamel surface
what makes up the cervical loop area?
what occurs during assymetric cell division?
- One daughter cell will go on to become a stem cell
- One cell develops into a differentiated cell type
what is a niche?
environment that
- houses stem cells
- allows for self renewal of stem cells
- instructive in generation of differentiating progeny
what is the epithelial stem cell niche
where is it
what are its roles
located at the apical end of the tooth
its descendent gives rise to the ameloblasts that form the hard enamel
what regulates epithelial stem cell niche?
FGF10
- Stimulates lunatic fringe expression in epithelium
- Leads to differentiation of the cell
where is FGF10 expressed?
dental mesenchyme near the cervical loop at the time of crown development
what happens to the stem cell progenies?
- If progenies remains in stellate reticulum which is notch 1 positive then it remains a stem cells
- If daughter cell comes into close proximity to the epithelium then it will experience lunatic fringe
- Leads to differentiation of the cell
fate of the cervical loop
two options
- can remain ‘crown’ and continue enamel production
- adopt ‘root’ fate
- irreversible
when does HERS form and what is its role
- after crown formation, the stellate reticulum is lost
- this leads double layer of epithelium - HERS
- HERS directs root formation
