title: Changes in the crystallinity of hydroxyapatite powder and structure of enamel treated with several concentrations of ammonium hexafluorosilicate.
abstract: OBJECTIVE
  To evaluate the effects of changing concentrations of ammonium hexafluorosilicate [SiF: (NH4)2SiF6] solution on the crystallinity of hydroxyapatite powder (HAP) and structure of human enamel in order to overcome the tooth discoloration caused by diamine silver fluoride [AgF: (NH3)2AgF] application.
  
  
  METHODS
  HAP was treated with several concentrations of SiF solution (from 10 to 19,400 ppm) for 5 minutes. The crystallinity of the HAP before and after SiF treatment was then measured by powder X-ray diffraction (XRD) analysis. The angular width (beta) of the 002 diffraction peak was measured at 1/2 the height of the maximum intensity. Also, enamel specimens were prepared from a human extracted tooth. Several concentrations of SiF solution were applied to polished or phosphoric acid etched enamel specimens. The enamel surface was then observed using scanning electron microscopy (SEM).
  
  
  RESULTS
  XRD peaks became sharper after SiF treatment indicating that the crystallinity of apatite powder was increased. The 1/beta value was increased from 2.8 +/- 0.1 to 4.3 +/- 0.1 after treatment with 1,000 ppm SiF solution. The amount of CaF2 formed in HAP was gradually increased with increasing concentrations of SiF solution. TheXRD pattern was consistent with CaF2 in case of over 9,000 ppm SiF solution. SEM photographs demonstrated that exposed enamel rods with acid etching were filled with CaF2-like precipitate after SiF treatment regardless of the concentration of SiF solution.
authors.affiliation: Department of Conservative Dentistry, Institute of Health Biosciences, University of Tokushima Graduate School, 3-18-15 Kuramoto, Tokushima 770-8504, Japan. suge@tokushima-u.ac.jp
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Suge
authors.forename: Kunio
authors.initials: K
authors.lastname: Ishikawa
authors.forename: Takashi
authors.initials: T
authors.lastname: Matsuo
mesh_terms: D000328:Adult; D003460:Crystallization; D003743:Dental Enamel / Q000737:chemistry*; D017886:Durapatite / Q000737:chemistry*; D005459:Fluorides / Q000737:chemistry*; D006801:Humans; D011208:Powders; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012824:Silicic Acid / Q000737:chemistry*
chemical_list: D011208:Powders; D000644:Quaternary Ammonium Compounds; D012824:Silicic Acid; C004832:hexafluorosilicate; D017886:Durapatite; D005459:Fluorides