enamel

• Enamel, also known as substantia adamantia, is the hardest tissue in the body, covering the entire anatomical crown of a tooth and providing contour and shape to it
• Enamel is a brittle, acellular, and permeable substance with a thickness ranging from 10 microns to 2.5 mm and a color that can vary from yellowish white to grayish white, appearing translucent
• Chemically, enamel is composed of 96% inorganic material, mainly hydroxyapatite, along with trace minerals like strontium, magnesium, lead, and fluoride, and 4% organic material including water, amelogenins, and enamelins
• The main structures of enamel include enamel rods, rod sheath, and interrod substance, with enamel rods having three parts: the body or head, the neck, and the tail, and following a wavy course from the DEJ to the surface of enamel
• Enamel rods may vary in number from 5 to 12m, and in cross-section, they may appear as fish scale, paddle-shaped, or with a keyhole pattern
• Hunter-Schreger bands are a series of alternating dark and light bands in the enamel, caused by changes in the direction of the enamel rods, with dark bands known as diazones and light bands as parazones
• Incremental lines of Retzius are brownish bands illustrating the incremental pattern of laying down enamel, comparable to growth rings of a tree
• Enamel tufts are narrow ribbon-like structures that project into the enamel, originating from the DEJ to at least 1/3 of the enamel, and are less mineralized, creating weakened planes
• Perikymata are wavelike transverse grooves, an external manifestation of incremental lines of Retzius, present only in postnatal enamel
• Enamel cuticle, also known as Nasmyth's membrane, is a delicate membrane derived from ameloblasts that covers the entire crown of a newly erupted tooth
• Enamel pearls, also called enamel droplets, are formed when HERS becomes detached and differentiates into ameloblasts, forming enamel in the bifurcation or trifurcation of teeth
• Enamel is incapable of repair and replacement, undergoing attrition, abrasion, and erosion as it ages, with changes including loss of rod ends, flattening of perikymata, darkening in color, and becoming less permeable
• Clinical considerations regarding enamel include the importance of the course or direction of enamel rods in cavity preparation, the brittleness of enamel requiring support by sound dentin, and the predisposition of deep pits and fissures to dental caries
• Enamel is permeable to fluoride and other substances, and keeping the cervical surface of enamel well polished and smooth is essential in dental care
• The process of etching, using phosphoric acid, aids in microretention of restorations by dissolving the organic portion of enamel, creating micromechanical retention