title: Fine structure of tooth enamel in the yellowing human teeth: SEM and HRTEM studies.
abstract: OBJECTIVE
  The aim of this study was to clarify an influence of the fine structure of human tooth enamel to the yellowing teeth.
  
  
  METHODS
  Sound maxillary first premolars of 15-50-year-old females that were extracted for the orthodontic treatment were used as the test samples. The tooth enamel sections of these teeth that prepared by ion polishing were observed by scanning electron microscopy (SEM). Furthermore, the fine structure of substance filling the inter-rod spaces was analyzed by high resolution transmission electron microscopy (HRTEM).
  
  
  RESULTS
  In white tooth, the inter-rod spaces were observed at the width of about 0.1 μm, while in yellow tooth, the inter-rod spaces were not clearly observed by SEM. HRTEM observations revealed for the first time that the inter-rod spaces were filled with fine particles of poorly crystallized hydroxyapatite in the yellow tooth. In yellow tooth, it was considered that the color of the inner dentin was recognized due to the decrease of light scattering by filling the tooth enamel inter-rod spaces. The generation of particles in the tooth enamel inter-rod spaces was considered to be caused by the long-time progression of calcification.
  
  
  CONCLUSIONS
  These results suggested that the change in fine structure, filling in inter-rod spaces of tooth enamel, was related to progression of calcification in the inter-rod spaces with advancing age and one of the factors of yellowness of human tooth.
authors.affiliation: Analytical Science Research, Kao Corporation, 1334 Minato, Wakayama, Wakayama Prefecture, 640-8580, Japan.
authors.forename: Masanobu
authors.initials: M
authors.lastname: Wakasa
authors.affiliation: Analytical Science Research, Kao Corporation, 1334 Minato, Wakayama, Wakayama Prefecture, 640-8580, Japan.
authors.forename: Kuniyuki
authors.initials: K
authors.lastname: Nakanishi
authors.affiliation: Analytical Science Research, Kao Corporation, 1334 Minato, Wakayama, Wakayama Prefecture, 640-8580, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Manago
authors.affiliation: Personal Health Care Products Research, Kao Corporation, 2-1-3 Bunka, Sumida-Ku, Tokyo, 131-8501, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Isobe
authors.affiliation: Personal Health Care Products Research, Kao Corporation, 2-1-3 Bunka, Sumida-Ku, Tokyo, 131-8501, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Eshita
authors.affiliation: Analytical Science Research, Kao Corporation, 1334 Minato, Wakayama, Wakayama Prefecture, 640-8580, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Okamoto
authors.affiliation: Department of Mathematical and Physical Sciences, Kyoto Institute of Technology, Matsugasaki, Sakyo-Ku, Kyoto 606-8585, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Isshiki
mesh_terms: D000293:Adolescent; D000328:Adult; D003743:Dental Enamel / Q000648:ultrastructure*; D003804:Dentin / Q000648:ultrastructure; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D008875:Middle Aged; D010858:Pigmentation; D013499:Surface Properties; D055815:Young Adult
keywords: calcification; hydroxyapatite; inter-rod spaces; ion polishing