amelogenesis

Question 1

what are the stages of amelogenesis?

Answer 1

1. induction
2. enamel secretion
3. enamel maturation & mineralisation

Question 2

where does ameloblast differentiation begin?

Answer 2

begins at the cusps and goes down slopes

Question 3

what happens during the induction stage of amelogenesis?

Answer 3

• occurs after dentinogenesis
• signal sent from odontoblasts across ADJ to inner enamel epithelium cells to induce differentiation into secretory ameloblasts
  
  • reciprocal induction

Question 4

what happens during enamel secretion stage of amelogenesis?

Answer 4

• 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

Question 5

structure of ameloblasts

Answer 5

• 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

Question 6

what is the tomes process? what is its role

Answer 6

• Specialised organ
• Allows directional secretion of the tissue being formed
  
  • Secretes perpendicular to the cell surface
• Will secrete enamel in a structured form

Question 7

role of the stratum intermedium in amelogenesis

Answer 7

• SI cells are involved in transport of organic and inorganic material to and from ameloblasts
• Involved in ion transport
  
  • Relevant for mineralisation process

Question 8

why does enamel formation occur when distant from the pulp? how is this achieved?

Answer 8

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

Question 9

what occurs during the enamel maturation stage of amelogenesis?

Answer 9

• 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
• 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

Question 10

how does the appearance of the ameloblasts change during the maturation stage of amelogenesis?

Answer 10

• 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)

Question 11

how does reduced enamel epithelium form?

Answer 11

• during maturation stage of amelogenesis
• ameloblasts differentiate into flattened epithelial cells which form the REE

Question 12

what occurs during the mineralisation stage of amelogenesis?

Answer 12

4 stages

1. deposition of enamel template
   * formation of partially mineralised enamel matrix during enamel deposition
2. increase in mineralisation
   * starts at surface of enamel and goes into deeper layers
3. increase in mineral rebounding from innermost layer out to enamel surface
4. complete mineralisation of outer layer

Question 13

where is enamel most highly mineralised?

Answer 13

at the surface

Question 14

how do ameloblasts change during their life cycle?

Answer 14

1. differentiate into secretory ameloblasts from inner enamel epithelium cells
   * secrete structureless enamel matrix
2. ameloblasts migrate from ADJ and form Tomes processes
   * secrete structured enamel matrix
3. 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)

4. ameloblasts either undergo apoptosis or differentiate into cells of reduced enamel epithelium

Question 15

what is the role of the reduced enamel epithelium?

Answer 15

protects enamel surface during eruption

Question 16

functions of the internal enamel epithelium

Answer 16

• 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

Question 17

what makes up the cervical loop area?

Answer 17

Question 18

what occurs during assymetric cell division?

Answer 18

• One daughter cell will go on to become a stem cell
• One cell develops into a differentiated cell type

Question 19

what is a niche?

Answer 19

environment that

• houses stem cells
• allows for self renewal of stem cells
• instructive in generation of differentiating progeny

Question 20

what is the epithelial stem cell niche

where is it

what are its roles

Answer 20

located at the apical end of the tooth

its descendent gives rise to the ameloblasts that form the hard enamel

Question 21

what regulates epithelial stem cell niche?

Answer 21

FGF10

• Stimulates lunatic fringe expression in epithelium
  
  • Leads to differentiation of the cell

Question 22

where is FGF10 expressed?

Answer 22

dental mesenchyme near the cervical loop at the time of crown development

Question 23

what happens to the stem cell progenies?

Answer 23

• 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

Question 24

fate of the cervical loop

Answer 24

two options

• can remain ‘crown’ and continue enamel production
• adopt ‘root’ fate
  
  • irreversible

Question 25

when does HERS form and what is its role

Answer 25

* after crown formation, the stellate reticulum is lost * this leads double layer of epithelium - HERS * HERS directs root formation