AMELOGENESIS TWO-PHASE CONCEPT
ORGANIC MATRIX FORMATION Secretion of ENAMEL PROTIENS
MINERALIZATION MATURATION & Deposition of HYDROXY-APATITE CRYSTALS
:CHEMICAL COMPOSITION INORGANIC CONTENT
ORGANIC CONTENT
By weight
96% CRYSTALLINE CALCIUM PHOSPHATE
“HYDROXYAPATITE” Ca 10(PO4)6 (OH)2
4% AMELOGENINS ENAMELINS
Life history of
Ameloblast
Tooth development
AMELOGENESIS STAGES: Life History of Ameloblast 1- MORPHOGENIC 2- ORGANIZING (DIFFERENTIATION)
3- SECRETORY (Initial) (Tomes process) 4- MATURATIVE (ruffle ended) (smooth ended) 5- PROTECTIVE 6- DESMOLYTIC
MORPHOGENIC
SECRETORY
ORGANIZING MATURATIVE PROTECTIVE
DESMOLYTIC
Differentiation Gradient From cusp tip
cervically
Morphogenic Stage :Crown 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
IEE cells
Organizing 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
dental papilla cells
IEE cells
induction
differentiation of odontoblasts
MORPHOGENIC ORGANIZING
SECRETORY
induction
odontoblast
Reciprocal induction
Secretory Stage Formation of dentin → reciprocal induction histodifferentiation of IEE into ameloblasts with all criteria of protein secreting cells
appearance of distal terminal bars
Secretory Stage Criteria for all
Protein Synthesizing and Secreting Cells Large open-faced nucleus Abundant cytoplasm in no. of mitochondria in rough endoplasmic reticulum RER in size of Golgi apparatus
Presence of secretory granules
Enamel Matrix Secretion :Cellular pathway m RNA RER Golgi apparatus Secretion granules Liberation at the apical cell surface
SECRETORY AMELOBLAST
’Tomes process
Responsible for rod and inter-rod configeation
Rod and inter-rod substance
Maturative Stage (with the help of stratum intermedium cells)
2. Introduction of minerals 3. Reabsorption of enamel proteins & water
starts after all enamel matrix at incisal edge or cusp tip is formed Ameloblasts →reduced in size organells of secretion become enclosed in Selective function of ameloblast during maturation autophagic vacuoles
MATURATIVE AMELOBLAST
• Folding of distal cell membrane → striated boredr • Increase of surface area for transport of materials
number of mitochondria, shifted to distal end of cell Smooth-Ruffled • Transitory stage: ended
smooth-ended
ended
Mineralization of Enamel Matrix
Initial partial mineralization of of total mineral content
Reabsorption of enamel proteins & water
Crystal growth
30%
96% APATITE CONTENT
Protective Stage:
After maturation of enamel Ameloblasts → reduced form with other layers of dental organ → reduced dental epithelium protects mature enamel from surrounding C.T.
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