1 J. Mater. Chem., 2004, 14, 2242 – 2248 2004 Dental enamel - a biological ceramic: Regular substructures in enamel hydroxyapatite crystals revealed by atomic force microscopy Colin Robinson, Simon Connell, Jennifer Kirkham, Roger Shore, Alastair Smith. Leeds Dental Institute, University of Leeds, School of Physics and Astronomy, University of Leeds, Institute of Molecular Biophysics 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 ~40nm 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 subunits. Introduction Calcium hydroxyapatite is the primary mineral component of all mammalian skeletal and dental tissues, i.e. bone, dentine, cementum and enamel. The processes of apatite deposition and dissolution are thus of central importance to the development and pathology of the skeletal and dental tissues and thus to the development of techniques to engineer tissue repair and replacement. This is of particular interest where a biomimetic approach is adopted as the major strategy for tissue replacement or regeneration.