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