High resolution electron microscopy of the initial mineral deposition on enamel surface.

The human partially impacted third molar was used to investigate the initial stage of dental calculus on enamel surface. The thin layer of mineral deposition consisted of needle-like crystals. High resolution electron microscopy (HREM) revealed that these crystals directly contacted each other. Electron diffraction represented that needle-like crystals of calculus consisted of hydroxyapatite (OH-AP). These findings indicate that the high calcium (Ca) x inorganic phosphate (Pi) ion-product condition in an extremely narrow and closed environment produces the stable OH-AP precipitates and that the growth of calculus crystals is thought to advance through the additional mineralization.