6. Morphology of the tooth enamel. Morphological units of mature enamel. Characteristics of the enamel of primary and permanent teeth in childhood.

MORPHOLOGY AND PHYSIOLOGY OF ENAMEL

Morphology of Enamel

Enamel is the epithelial derived protecting covering for teeth. It is hardest of the mineralized tissues and covers the crown of tooth

• Non vital and non sensitive and cannot be repaired once lost
• Cells responsible for enamel formation are ameloblasts which are lost as tooth erupts
• As a result, has higher degree of mineralization and complex structural organisation to be resistant for a longer period of time
• Morphological unit of enamel is the enamel rod and structural unit is apatite crystal

1. Enamel Rods
2. Enamel Interrod Space
3. Rod Sheath
4. Striae of Retzius
5. Neonatal Line
6. Bands of Hunter Schreger
7. Cross Striation of Rods
8. Gnarled Enamel
9. Enamel Tufts and Lamellae
10. Dentino-Enamel Junction and Enamel Spindles
11. Enamel Surface
12. Perikymata

Enamel Rods

Enamel is composed of rods that extend from DEJ to the enamel outer surface, each rod is formed by 4 ameloblasts:

• 1 ameloblast forms the head
• 2 ameloblasts forms the neck
• 4 ameloblasts form the tail
• Crystal Orientation in the rods is longitudinal whilst in the tail, its diagonally or perpendicular
• To prevent tooth fracture and splitting of tooth, enamel rods are intertwined giving it additional support
• Rod’s surface is the rod sheath, centre is the core and contains less organic matter than the rod sheath
• Rod is perpendicular to the DEJ and curves towards the cusp tip

Enamel Interrod Space

• Areas between adjacent prisms called interprismatic. Made up of crystals but arranged at a different angle from those in the prism. Have larger inter-crystal spaces
• Amount of non-apatite impurities, mainly carbonates, is higher
• More organic matter in the crystal and amount of non-apatite impurities is higher

Rod Sheaths

• Surface of each rod is known as the rod sheath
• Is the least mineralized place as the crystals meet in different directions there
• Rod sheath contains slightly more organic matter than the rod core

Striae of Retzius

• Series of dark lines extending from the DEJ towards the tooth surface which reflect appositional or incremental growth of enamel layer
• In longitudinal section of tooth, series of dark lines. In Cross Section, appear as concentric rings

Neonatal Line

Neonatal lines are an enlarged stria of retzius that reflects the physiologic changes occurring at birth

• Accentuated incremental line that are produced by systematic disturbances that affect amelogenesis

Bands of Hunter and Schreger/ Hunter Schreger Lines

• Optical phenomena produced by changes in direction between adjacent groups of rods