5. Mineralization of the enamel matrix. Mechanisms of enamel mineralization. Theories of mineralization. Physiology of tooth enamel. Crystalline structure. Ionic exchange in enamel.

HISTOGENESIS OF ENAMEL (AMELOGENESIS)

Enamel is the epithelial derived protecting that covers the teeth. It is the hardest of the mineralized tissues and covers the crown of the tooth. It is non-vital and non-sensitive and cannot be repaired once lost.

Cells responsible for formation of enamel are ameloblasts

• Ameloblasts lost as tooth erupts hence why enamel cannot renew itself
• To compensate for lack of regeneration, enamel has an acquired complex structural organisation and high degree of mineralisation
• Starts in early bell stage

Amelogenesis begins after final differentiation of ameloblasts

• Amelogenesis is the two-step process of enamel formation
• First Step: enamel matric formation which gives 20-30% mineral content
• Second Step: process of mineralization and maturation when the full width of enamel has been deposited
• Differentiation is a result of several changes in the enamel organ and dental papilla, they stimulate the differentiation of preameloblasts into ameloblasts
• Preameloblasts begin to grow in height and turn into cylindrical cells
• Mitotic activity stops its division but instead intracellular differentiation occurs
• Endoplasmic reticulum, Golgi Apparatus, Mitochondria change are developing
• Preameloblasts receive signal stimulation from the dental papilla
• Until now, source of nutrition for preameloblasts has been dental papilla, since mesodermal tissue has blood vessels
• This transport occurs through the basal lamina between the enamel organ and dental papilla
• Ameloblasts are ectodermally derived cells which secrete matric proteins and are responsible for creating an extracellular environment favourable for mineral deposition

Functional Stages of Life Cycle of Ameloblasts:

1. Initiation

• Proliferation
• Morphogenesis
• Organization and Differentiation
• Secretion (Tome's processes appear)
• Maturation
• Protection

Enamel Matrix Produced by ameloblasts during secretory phase

Phases of Ameloblast’s Life 3 main functional phases

1. Presecretory Stage

• Differentiating ameloblasts acquire their phenotype, change polarity, develop an extensive protein synthetic apparatus and prepare to secrete the organic matrix of enamel

2. Secretory Stage
3. Maturation Stage

Presecretory Stage

Morphogenetic Phase of Presecretory Stage

• During Bell Stage, shape of crown is determined. Cells of inner epithelium are separated from dental papilla by a basement membrane
• Cells are cuboidal or low columnar with a large, central nucleus and poorly develop Golgi elements in the proximal portion of cells (Facing stratum intermedium)

Differentiation Phase of Presecretory Stage

• As cells of inner epithelium differentiate into ameloblasts, they elongate and their nuclei shift proximally towards the stratum intermedium