Development of enamel is an unique process

1. Amelogenesis

2. Objectives of studying amelogenesis
1. Understand the nature of enamel.
2. Appreciate how this dental tissue is unique.
3. Appreciate how the enamel protect the underlying dentin.
4. Appreciate the physical properties of enamel.
5. Know the chemical composition of enamel.

3. 1. Morphogenic stage.
2. Differentiating stage (Organizing stage).
3. Secretory stage (Formative stage).
4. Maturative stage (Calcifying stage).
5. Protective stage.
6. Desmolytic stage.
Life cycle of ameloblasts

4. 1-Morphogenic stage of IEE at cap stage
Structure of inner enamel epithelium :
1.Columnar cells separated from dental papilla
by basement membrane.
2.Large centrally located nucleus.
3.Proximal end: The end of IEE facing stellate
reticulum.
4.Distal end: The end of the Inner dental
epithelium facing dental papilla.
5.Active cells contain RER,GC, ribosomes and
mitochondria.
IEE
proximal end
Distal end
BM

5. 2-Differentiating stage of IEE at early bell stage
• Differentiation:
1. The cell become tall columnar leading to
disappearance of cell free zone.
2. Nucleus move toward proximal end.
3. Mitochondria move toward proximal end.
4. GC & RER move toward the distal end.
5. Ameloblast begin to secrete the organic matrix of
enamel.
6. Ameloblast cells are attached together by desmosome
termed web which are two types:
(A) Proximal terminal web at the proximal end.
(B) Distal terminal web at the distal end.
DTW
PTW

6. 3-Secretory stage of ameloblasts
Enamel matrix
Odontoblast cells
Dentin matrix
Ameloblast cells
PTW
Enamel matrix formation and secretion
1. Ribosomes out from the nucleus to RER in
the cytoplasm.
2. protein is formed inside RER according to
the amino code of ribosomes.
3. RER form small granule contain protein.
4. This small granule go to GC to add CHO
and form secretory granules contain
enamel matrix and out to the cytoplasm.
5. This granule go toward the distal end of
the ameloblast and get out from the cell in
the front of newly formed dentin.

7. • Tome’s process
1. After formation of the first layer of enamel matrix,
the ameloblast move away from the dentin to allow
for further enamel matrix deposition.
2. By this movement , each ameloblast develop conical
process termed tomes process.
3. Tom's process are demarcated from cell body by
distal terminal web.
4. Tom's process contain secretory granules.
5. The rest of enamel are secreted from tom's process.
Tome’s process

8. .

9. Pulp
Dentin and enamel firstly formed at cusp tip or incisal edge and then
sweep down the slopes toward cervical line.

10. 4- Maturative stage (calcification stage)
striated border
1.Ameloblast reduced in length.
2.Decrease of number of cell organelles.
3.Disappearance of tom's processes.
4.Distal end of the cells become ruffled and termed
ruffled border.
5.The become ruffled engulf the enamel matrix with
secretion of calcium and phosphorus for enamel
calcification, so, enamel become mature.

11. 5- Protective stage
Primary enamel cuticle
After complete maturation of enamel , ameloblast lose
their ruffled border and secrete thin organic layer on the
crown termed primary enamel cuticle.
Reduced Enamel Epithelium
• Ameloblast become flat and lose their regular
arrangement and can not be differentiated from the other
cells of dental organ.
• All cells of dental organ form a layer cover the crown
termed reduced dental epithelium which protect the
crown from the surrounding connective tissue.
• If the reduced dental epithelium destroyed from above the
crown, the enamel may be resorbed by the action of
connective tissue cells.

12. • During process of tooth eruption to the oral cavity, the reduced dental epithelium
proliferate by cell division and secrete enzyme for destruction of connective tissue
separating it from oral epithelium.
• This enzyme is termed desmolytic enzyme. Then, the reduced enamel epithelium fused
with the oral epithelium and become part of gingiva during tooth erupt.
6- Desmolytic stage

13. Amelogenesis
Stage of enamel formation
1. Stage of organic matrix formation of enamel.
2. Stage of mineralization and maturation of enamel.
(A) Immediate partial mineralization up to 25-30%.
(B) Maturation up to 96%.

14. Finish