Dental enamel—a biological ceramic: regular substructures in enamel hydroxyapatite crystals revealed by atomic force microscopy

Hydroxyapatite crystals from developing rat incisor enamel and polished sections of mature human dental enamel were investigated using Atomic and Chemical Force Microscopy. Regular substructures were seen on crystals comprising ∼40 nm wide morphologically and chemically defined bands across the crystal long axes. Exposure to low pH resulted in selective dissolution between bands and the emergence of 2–3 spherical structures within each band. The spherical structures were chemically distinct exhibiting high friction in lateral force mode. Enamel crystals appear to comprise stacks of roughly hexagonal arrays of chemically or structurally distinct spherical subunits.