Enamel

• Tooth enamel is the hardest calcified matrix of the body consisting of 96% hydroxyapatite
• Organic matrix makes up 1% of tooth enamel
• Water makes up 3% of tooth enamel
• Tooth enamel is semitranslucent and appears yellow to grayish white
• Hydroxyapatite is made up of calcium and phosphate
• Enamel formation involves the differentiation of cells of the inner enamel epithelium in 3 functional stages: presecretory, secretory, and maturation
• Enamel formation begins at the early crown stage of tooth development
• Ameloblasts are enamel-forming cells
• Amelogenin is a major component of enamel matrix proteins, making up 90%
• Tomes' processes are short extensions towards the dentinoenamel junction
• During the maturation phase of enamel formation, ameloblasts remove water and organic material from the enamel to introduce additional inorganic material
• Enamel rods are the fundamental morphologic unit of enamel, covered by prism sheath or rod sheath with interprismatic substance between prisms
• Enamel rods are oriented at right angles to the dentin surface, built up of segments separated by dark lines giving a striated appearance
• Incremental lines of Retzius illustrate the incremental pattern of enamel formation with brownish bands in ground sections
• Perikymata are transverse, wave-like grooves on the tooth surface, believed to be external manifestations of the striae of Retzius
• Neonatal line marks the division between enamel formed before and after birth, found in deciduous teeth and cusps of permanent first molars
• Hunter-Schreger bands are alternating light and dark lines in dental enamel, seen in longitudinal ground sections under oblique reflected light
• Enamel tufts are fan-shaped, hypocalcified structures of enamel rods projecting from the dentinoenamel junction into the enamel proper
• Enamel lamellae are defects in enamel resembling cracks containing mostly organic material, providing an area for bacteria to enter
• Enamel spindles are elongated odontoblastic processes that traverse the dentinoenamel junction from the underlying odontoblast, possibly serving as pain receptors
• The dentinoenamel junction has a scalloped line where the enamel fits into shallow depressions of the dentin
• Enamel has no power of regeneration, no nerve supply, is a good thermal insulator, and its acid solubility is reduced by fluoride