ENAMEL

• Enamel is also known as Substantia adamantia
• Enamel is an ectodermal derivative that covers the entire anatomical crown of the tooth
• Enamel provides contour and shape to the crown
• The course or direction of enamel rods is important in cavity preparation
• Enamel is brittle and must be supported by sound dentin
• Presence of deep pits and fissures predispose teeth to dental caries
• Dental lamellae and enamel tufts are predisposing locations for dental caries
• Enamel is permeable to fluoride and other substances
• Keep the cervical surface of enamel well polished and smooth
• The process of etching produces pitting and irregularities that aid in microretention of the restoration
• Enamel cuticle consists of Primary enamel cuticle and Nasmyth's membrane
• Primary enamel cuticle is a delicate membrane that covers the entire crown of a newly erupted tooth and is derived from the ameloblasts
• Enamel rods (Enamel Prism) may vary from 5-12m in number and have three parts: the body or head, the neck, and the tail
• Enamel rods follow a wavy course from DEJ to the surface of enamel and may appear as fish scale, paddle-shaped, or have a keyhole pattern in cross-section
• Enamel tufts appear as tufts of grass projecting into the enamel and are narrow ribbon-like structures originating from DEJ to at least 1/3 of the enamel
• Enamel lamellae are thin, leaf-like structures that extend from the enamel surface towards DEJ and even towards dentin, they are organic in nature and hypomineralized
• Gnarled enamel consists of intertwining or twisting of enamel rods at the incisal or cuspal region, aiding in resisting high masticatory loads without fracture
• Enamel pearls, also known as Enamel droplets, are HERS that become detached and differentiate into ameloblasts, forming enamel in the bifurcation or trifurcation of teeth
• Enamel cracks are narrow fissure-like structures which are actually the outer edges of the enamel lamellae
• Enamel rods ends are concave and vary in depth and shape, contributing to adherence of plaque material
• Rod sheath is the boundary of enamel rod and interrod substance, a less calcified area
• Interrod substance cements or holds together the enamel rods
• Enamel spindle is the thickened end of the odontoplastic process that crosses the DEJ and is entrapped in the enamel, containing pain receptors
• Enamel structures layer consists of enamel rods, rod sheath, and interrod substance
• Enamel structures layer is present in all 1st teeth and 70% of 2nd teeth, with no prism outlines and being more heavily mineralized than underlying enamel
• Enamel lamellae are thin, leaf-like structures that extend from the enamel surface towards DEJ and even towards dentin, being organic in nature and hypomineralized
• Hunter-Schreger band is a series of alternating dark and light bands in the enamel due to changes in the direction of the enamel rods, with dark bands called diazones and light bands called parazones
• Dentinoenamel junction is the junction between dentin and enamel, having a scalloped or pitted appearance and being a hypomineralized zone
• Neonatal line is the boundary line of prenatal and postnatal enamel in deciduous teeth only, accentuated incremental lines of Retzius, prominent in cervical areas
• Enamel is incapable of repair and replacement
• Enamel undergoes attrition, abrasion, and erosion
• As the tooth ages, there is a loss of rod ends and flattening of perikymata
• Enamel becomes darker in color and less permeable with advancing age
• Perikymata are the external manifestations of incremental lines of Retzius, wavelike transverse grooves present only in postnatal enamel