5. Mineralisation of enamel matrix. Mechanisms of enamel mineralisation. Theories of mineralisation. Physiology of tooth enamel. Crystalline structure. Ionic exchange in enamel

Mechanisms of enamel mineralisation

Primary mechanisms

• Needle shaped crystals appear after deposition of 50 nm thick matrix. It’s initially thin widespread and dispersed

• Rapidly increases in size and becomes hexagonal

Secondary mechanism

• Occurs at DEJ 

• Rapid process and cannot easily distinguished from primary mineralisation 

• Enamel is transformed from soft to hard substance 

• Large quantities of inorganic material is deposited in the matrix 

Time between enamel matrix deposition and mineralisation.

• Time between enamel matrix deposition and mineralisation is short 

• First matrix deposited is the 1st enamel that is mineralised 

Localisation of matrix deposition and mineralisation

• Matrix formation and mineralisation begins peripherally to the tips of cusps

• then laterally to the sides of the crowns and finally the cervical region of the crown is mineralised 

Theories of mineralisation

• Booster mechanism: Enzymes like alkaline phosphatase increases calcium and phosphate ion concentrations, leading to precipitation 

• Seeding Mechanism (Epitaxy):  ‘seeds’ which are substances that act as templates for crystal nucleation and growth 

• Vesicle Concept: Vesicles originating in ameloblasts contain substances aiding calcification 

• Nanosphere Theory: Amelogenins self-assemble into nanosphere structures, creating a framework for crystal formation 

what is booster mechanism theory?

• Booster mechanism: Enzymes like alkaline phosphatase increases calcium and phosphate ion concentrations, leading to precipitation 

What is seeding mechanism (epitaxy) theory?

• Seeding Mechanism (Epitaxy):  ‘seeds’ which are substances that act as templates for crystal nucleation and growth 

what is vesicle concept theory?

• Vesicle Concept: Vesicles originating in ameloblasts contain substances aiding calcification 

What is nanosphere theory?

• Nanosphere Theory: Amelogenins self-assemble into nanosphere structures, creating a framework for crystal formation 

What is the physiology of tooth enamel

• Enamel is 96% mineralised, containing hydroxyapatite cyrstals and organic material and water.

• Enamel proteins include amelogenins, enamelin, ameloblastin and tuftelin

Describe the crystallin structure of enamel 

• Minerals - hydroxyapatite, carbonate apatite and fluorapatite 

• Intercrystalline spaces - amorphous calcium carbonate, Mg, Zn, Mn, Cu, Al etc 

• The apatite crystals can have different forms like pencil, ribbon, needle and hexagonal 

• Water can either be loosely or firmly attached to the crystal 

• Crystal rods are longitudinal while innterod crystals are oblique or perpendicular 

what is the difference between the crystal rods and innterod crystals of enamel?

• Crystal rods are longitudinal

• innterod crystals are oblique or perpendicular

can water be attached to the crystalline structure of enamel?

• Water can either be loosely or firmly attached to the crystal 

what are the different forms of apatite crystals?

• can have different forms like pencil, ribbon, needle and hexagonal 

what minerals are found in crystalline structure of enamel 

• Minerals - hydroxyapatite, carbonate apatite and fluorapatite 

what is in the intercrystalline spaces of the crystalline structure of enamel?

• Intercrystalline spaces - amorphous calcium carbonate, Mg, Zn, Mn, Cu, Al etc 

Ion exchange and its process

• Weak and slow

• Ions in crystal may undergo ionic exchange w ions in environment

1. First stage - reversible ion diffusion into the superficial hydrate layer

2. Second stage - reversible neutralisation of charges in the subsurface absorbed ion layer

3. Third stage - difficult to reverse; ions integrate into the crystal surface

4. Fourth stage - irreversible; ions replace defects within the crystal lattice