Enamel composition and structure

Enamel composition and structure

1. Physical properties

   • Hardest substance in the human body
   • Brittle - underlying dentine supports the enamel
   • Regional variations - surface enamel is the hardest and thickest. Vertical orientation of enamel near surface therefore more resistant to masticatory forces.
   • Age variations - enamel translucency increases with age, shows underlying dentin

2. Chemical properties

   • 96% by weight inorganic matrix - Hap crystals; long crystallites. F- substitution increases stability against acid dissolution.
   • Remaining weight is organic matrix, consisting of...
     • Amelogenins - 90% of the organic content, facilitates crystal growth during maturation
     • Non-amelogenins
       • Ameloblastin
       • Enamelin
       • Also involved in crystal growth
     • In immature enamel, nearly 30% wt is organic content

3. Structure and structural features

   • Basic unit - prism
     • Reflects path of ameloblast from ADJ to surface - 1:1 ratio
     • T/F - are prisms present in enamel close to ADJ and surface? F because aprismatic enamel found here due to lack of PTP + DTP when it was secreted therefore aprismatic (reflects start and end of secretory stage)
   • Apperance in microscopy
     • LM - fish scales, key hole, etc
     • SEM - interrod / rod orientations apparent
   • Hunter-Schreger bands - cause by changes in direction of adjacent groups of rods = light reflects differentially as dark+light bands
   • Enamel lamellae - linear structure going into various depths of enamel - filled with organic material
   • Enamel spindles - odontoblast process embedded in enamel after enamel matrix is mineralised
   • Enamel tufts - branches structures going into enamel at ADJ
   • ADJ appearance - scalloped = increase SA for
   • Striae of Retzius - incremental growth lines, successive aposition of layers of enamel. Appears at surface of enamel as perikymata.
   • Gnarled enamel - rod "twisting" due to difference in orientation of groups of rods/prisms - undulations near cusp region

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