Amelogenesis Process of enamel formation inner enamel epithelium

Amelogenesis

• Process of enamel formation • inner enamel epithelium Ameloblasts • Late bell stage – cuspal region

• Secretory phase Synthesis of organic matrix Enamel Proteins Amelogenin Enamelin Sheathelin Amelin Enamelin Tuftelin • Maturation phase Final mineralisation

LIFE CYCLE OF AMELOBLAST Pre-secretory stage – Morphogenic / Morphogenetic stage – Organizing / Differentiating stage Secretory stage – Formative stage Post-secretory stages – Maturative stage – Protective stage – Desmolytic stage

1. Morphogenetic Stage • Bell stage • IEE Cuboidal / Low Columnar • Central Nucleus • Golgi Proximal • Others Scattered

Morphogenic stage • Shape of the DEJ & crown determined Cells of IEE interacts with Underlying connective tissue through differential growth Tooth Shape is determined

Reciprocal induction Ameloblast Enamel INNER ENAMEL EPITHELIUM Signaling molecules & GF Ectomesenchymal cells of dental papilla Odontoblast Dentin

2. Organising Stage • Differentiate into Ameloblasts • Elongate • N Proximal (RP) • Golgi Central • “Reversal of polarity”

Apical or proximal end Basal or distal end

Apical or proximal end Basal or distal end

Apical or proximal end “Reversal Of polarity” Basal or distal end

3. Secretory stage

Tome’s Process

Enamel Rod structure is determined by Tome’s Process

4. Maturation Stage • Ht – Ameloblast Ruffle end ameloblast Smooth end ameloblast

• Slight reduction in height • Decrease in organelle

5, Protective Stage • Flat Ameloblast • Enamel Cutilce • REE

6. Desmolytic Stage • REE Secretes • Collagenase • Hyaluronidase • Chondrotin sulfatase Disintegration of C T B/W oral epithelium & REE Fusion of Oral Epithelium & REE

IEE Tall columnar Nuclei shifted to proximal end (RP) GF from IEE Induction of differentiation of odontoblasts Odontoblasts secrete dentin Dentin crystals induce IEE Ameloblasts (“Reciprocal induction”)

Secrete Enamel Matrix Ameloblasts move away from the laid down enamel matrix Tome’s Process “Picket fence”/ “Saw tooth”appearance Enamel organ collapse ( B V becomes closer to Ameloblasts)

Enamel maturation Flat Ameloblasts + SI + SR + OEE REE Fuses with Oral epithelium Tooth erupts into the oral cavity

Amelogenesis • Two process 1. Organic matrix formation 2. Mineralization

Organic matrix formation • Enamel formation begins in the cusp tips and incisal edges → progresses outward and cervically. • In early stages of amelogenesis, the enamel matrix consists of 20 -30% proteins (amelogenin and non-amelogenin) and the proportion gradually decreases

Enamel proteins • Amelogenin – 80% • Non amelogenin 5 -20 % (crystal growth) – Enamelin – Tuftelin – Ameloblastin(ameilin & sheathlin) – Amelotin & enzymes like protienases

Mineralization • Mineralization takes place in two steps 1. Immediate partial mineralization 2. Maturation.

• Mineral deposition in enamel matrix occurs in four phases. – Primary mineralization corresponds to immediate partial mineralization (30 % of mineral deposition) – Secondary stage starts at the surface and proceeds toward DEJ – In tertiary stage, mineral rebounds from inner layer of enamel outward. – Fourth stage is responsible for further deposition of minerals in the surface enamel which makes it hypermineralized than the rest of enamel.

Maturation • This starts from the height of the crown and then gradually proceeds cervically. It begins at the dentinal end of the enamel rods. • Begins even before the matrix has formed to its full thickness. • Crystals grow in size rapidly, and the organic matrix becomes thin to make room for the growing crystals.