Enamel week 3

• Substantia adamantia:

  • Ectodermal derivative
  • Covers the entire anatomical crown of the tooth
  • Provides contour and shape to the crown
  • Hardest tissue in the body
  • Brittle
  • Acellular
  • Permeable
  • Thickness ranges from 10 microns to 2.5 mm
  • Color is yellowish white-grayish white
  • Translucent
  • 96% inorganic material (hydroxyapatite) and trace minerals (strontium, magnesium, lead, fluoride)
  • 4% organic material (water, amelogenins, enamelins)
• Enamel rods:

  • May vary from 5-12 million in number
  • Has three parts: the body or head, the neck, and the tail
  • Follows a wavy course from DEJ to the surface of enamel
  • In cross-section may appear as fish scale, paddle-shaped, or may have a keyhole pattern
• Boundary of enamel rod and interrod substance:

  • Less calcified area
  • Cements or holds together the enamel rods
• Intertwining or twisting of enamel rods at incisal or cuspal region:

  • Aids in resisting high masticatory loads without fracture
• Series of alternating dark and light bands in the enamel:

  • Due to a change in direction of the enamel rods
  • Dark bands are diazones
  • Light bands are parazones
• Brownish bands that illustrate the incremental pattern of laying down of enamel:

  • Comparable to growth rings of a tree
• Line of boundary of prenatal and postnatal enamel (in deciduous teeth only):

  • Accentuated incremental lines of Retzius
  • Prominent in cervical areas
• Thin, leaflike structures that extend from enamel surface towards DEJ and even towards dentin:

  • Organic in nature and hypomineralized
• Tufts of grass that project into the enamel:

  • Narrow ribbon-like structure
  • Hypocalcified enamel rods and interprismatic substances that originate from DEJ to at least 1/3 of the enamel
  • Less mineralized, weakened planes
• External manifestation of incremental lines of Retzius:

  • Wavelike transverse grooves
  • Present only in postnatal enamel
• Narrow fissure-like structures which are actually outer edges of the enamel lamellae
• Primary enamel cuticle (Nasmyth’s membrane):

  • Delicate membrane that covers the entire crown of a newly erupted tooth
  • Derived from the ameloblasts
• Membrana preformativa:

  • Junction between dentin and enamel
  • Scalloped or has a pitted appearance
  • Hypomineralized zone
• Thickened end of odontoblastic process that crosses the DEJ and is entrapped in the enamel:

  • Pain receptors
• Enamel droplets (HERS):

  • HERS becomes detached and differentiates into ameloblasts and forms enamel in the bifurcation or trifurcation of teeth
• Enamel characteristics:

  1. Enamel is incapable of repair and replacement.

  2. Enamel undergoes attrition, abrasion, and erosion.

  3. As the tooth ages, there is a loss of rod ends and flattening of perikymata.

  4. Enamel becomes darker in color.

  5. Enamel becomes less permeable with advancing age.
• Important considerations:

  1. The course or direction of enamel rods is important in cavity preparation.

  2. Enamel is brittle and must be supported by sound dentin.

  3. Presence of deep pits and fissures predispose teeth to dental caries.

  4. Dental lamellae and enamel tufts are predisposing locations for dental caries.

  5. Enamel is permeable to fluoride and other substances.

  6. Keep the cervical surface of enamel well polished and smooth.

  7. The process of etching produces pitting and irregularities that aid in microretention of the restoration.