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AMELOGENESISAMELOGENESIS
ORGANIC MATRIX FORMATION
MINERALIZATION &MATURATION
Deposition of
HYDROXY-APATITE CRYSTALS
TWO-PHASE CONCEPT
Secretion of
ENAMEL PROTIENS
CHEMICAL COMPOSITIONCHEMICAL COMPOSITION::
CRYSTALLINE CALCIUM PHOSPHATE
“HYDROXYAPATITE” Ca 10(PO4)6 (OH)2
96%96%
By weight
4%4%
AMELOGENINS ENAMELINS
INORGANICINORGANIC CONTENTCONTENT
ORGANIC ORGANIC CONTENTCONTENT
Tooth
development
Life historyof
Ameloblast
1- MORPHOGENICMORPHOGENIC
2- ORGANIZINGORGANIZING (DIFFERENTIATION)
3- SECRETORY SECRETORY (Initial)(Tomes process)
4- MATURATIVE MATURATIVE (ruffle ended) (smooth ended)
5- PROTECTIVEPROTECTIVE
6- DESMOLYTICDESMOLYTIC
AMELOGENESIS STAGES:AMELOGENESIS STAGES:Life History of AmeloblastLife History of Ameloblast
MORPHOGENIC SECRETORYMORPHOGENIC SECRETORY
PROTECTIVEPROTECTIVE
MATURATIVE MATURATIVE
ORGANIZINGORGANIZING
DESMOLYTICDESMOLYTIC
DifferentiationDifferentiation GradientGradient
FromFromcusp tipcusp tip
cervicallycervically
Morphogenic StageMorphogenic StageCrown pattern determinationCrown pattern determination::
Inner Enamel Epithelial cells:•arrange themselves on B.M. determine future DEJ
• short columnar cells , large oval nucleus
•Golgi apparatus & centrioles in proximal end of the cells
•Mitochondria evenly distributed
•Proximal terminal bars
• Separated from dental papilla by: B.M. & cell free zone
Organizing StageOrganizing Stage
Inner Enamel Epithelial cells:
• Become tall columnar cells (40 microns) (cell free zone disappears)
• Reversal of polarity:o golgi app. & centrioles distally o nucleus & mitochondria proximmaly
IEE cells
inductioninduction
differentiation of odontoblasts
dental papilla cells
IEE cells
MORPHOGENIC SECRETORY MORPHOGENIC SECRETORY ORGANIZINGORGANIZING
Reciprocal induction
induction
odontoblasodontoblastt
Formation of dentinFormation of dentin reciprocal inductionreciprocal induction histodifferentiation of IEEhistodifferentiation of IEE
into into ameloblastsameloblasts with all criteria ofwith all criteria of protein secreting cellsprotein secreting cells
appearance of distal appearance of distal terminal barsterminal bars
Secretory StageSecretory Stage
Criteria for allCriteria for all Protein Synthesizing and Secreting Protein Synthesizing and Secreting CellsCells
Large open-faced nucleusLarge open-faced nucleus Abundant cytoplasmAbundant cytoplasm in no. of mitochondriain no. of mitochondria in rough endoplasmic in rough endoplasmic
reticulum RERreticulum RER in size of Golgi apparatusin size of Golgi apparatus
Presence of secretory Presence of secretory
granulesgranules
Secretory StageSecretory Stage
Enamel Matrix SecretionEnamel Matrix SecretionCellular pathway:
m RNAm RNA
RERRER
Golgi Golgi apparatusapparatus
Secretion Secretion granulesgranules
Liberation at Liberation at the apical cell the apical cell
surfacesurface
SECRETORY AMELOBLASTSECRETORY AMELOBLAST
Responsible for rod and inter-rod configeation
Tomes’process
Rod and inter-rod substance
Selective function of ameloblast during maturation
starts after all enamel starts after all enamel matrix at incisal edge matrix at incisal edge or cusp tip is formedor cusp tip is formed
Ameloblasts Ameloblasts
reduced in sizereduced in size organells of secretionorganells of secretion
become enclosed in become enclosed in
autophagic vacuolesautophagic vacuoles
Maturative StageMaturative Stage(with the help of stratum intermedium cells)cells)
1.1. Introduction of mineralsIntroduction of minerals2.2. Reabsorption of enamel proteins & waterReabsorption of enamel proteins & water
• Folding of distal cell membrane striated
boredr
• Increase of surface area for transport of materials
number of mitochondria, shifted to distal end of cell
• Transitory stage:
smooth-ended
MATURATIVE AMELOBLASTMATURATIVE AMELOBLAST
RuffledRuffled--endedended
Smooth- Smooth- endedended
Mineralization of Enamel MatrixMineralization of Enamel Matrix
Initial partial mineralization of 30%30%
of total mineral content
Reabsorption of enamel proteins & water
Crystal growth 96% APATITE CONTENT
Protective Stage:Protective Stage:
After maturation of enamelAfter maturation of enamel Ameloblasts Ameloblasts reduced reduced form with other layers of form with other layers of
dental organ dental organ reduced reduced dental epitheliumdental epithelium
protects mature enamel protects mature enamel
from surrounding C.T.from surrounding C.T.
Desmolytic Stage:Desmolytic Stage:
• reduced enamel epithelial cells
secrete
desmolytic enzymes
degenerate C.T.
separating
developing tooth &
oral epithelium:
a pathway for eruption
Relationship of Tomes’
process to the key hole pattern