Research ArticlePHYSICAL SCIENCE

Atomic-scale compositional mapping reveals Mg-rich amorphous calcium phosphate in human dental enamel

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Science Advances  07 Sep 2016:
Vol. 2, no. 9, e1601145
DOI: 10.1126/sciadv.1601145
  • Fig. 1 Human dental enamel from millimeter to nanometer.

    (A) Reflected optical bright-field image of the mature human tooth used in this study. Enamel is the outer layer of this cross section. (B) Transmitted optical dark-field image of human tooth enamel showing the junction between dentin and enamel as well as the inner and outer enamel. (C) Transmitted optical dark-field image showing outer enamel rods, each composed of thousands of HAP nanowires surrounded by a less dense interprismatic layer. (D) Higher-magnification TEM bright-field image of aligned HAP nanowires viewed edge on.

  • Fig. 2 APT reconstructed volumes of human dental enamel HAP nanowires showing intergranular Mg-rich ACP.

    (A to C) Mg atoms (A), Na atom distribution (B), and 0.7 atomic % (at %) Mg isosurface (C) revealing the Mg-rich ACP between HAP nanowires. (D) Cross-sectional view of 0.7 at % Mg isosurface that highlights the ribbon-like shape of the HAP nanowires. (E) Proximity histogram (proxigram) from Mg-rich ACP based on 0.7 at % Mg isosurface [based on the sum of interfaces shown in (D)].

  • Fig. 3 APT 3D reconstructed volumes of human dental enamel HAP nanowires containing a Mg-rich precipitate and organic matter.

    (A) 24Mg2+ (overlapping with 12C+) atom distribution. (B) Na isosurface (0.5 at %) showing Mg-ACP intergranular phase. (C) Isosurface 12C2+ (0.18 at %) (precipitate A), 1 at % 24Mg2+ isosurface (precipitate B), and 0.7 at % 24Mg2+ (Mg-ACP intergranular phase). (D) Proxigrams of precipitate A, precipitate B, and Mg-ACP (based on the sum of ACP interfaces).

  • Fig. 4 TEM image of human dental enamel HAP nanowires.

    TEM central bright-field image. Arrows show an intergranular layer (light contrast) between HAP nanowires and a triple point (circled) thought to be amorphous. The electron diffraction pattern is indexed as [2-1-13].

  • Fig. 5 APT 3D reconstructed volumes from sample 2 with isosurfaces from the main species that arise from organic regions, carbonates, or Mg-rich phases.

    (A) Isosurfaces of 12C2+, 14N2+, 42CNO+, and H (decomposed) highlighting the organic matter. (B) Isosurfaces of 44CO2+ highlighting the carbonates. (C) Isosurfaces of 25Mg2+ and 26Mg2+ highlighting the Mg-rich precipitate and ACP. (D) Isosurfaces of 28CO+ and 29COH+ highlighting both organic matter and carbonates.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/9/e1601145/DC1

    fig. S1. Typical APT mass spectrum of human dental enamel containing organic materials (sample 1, Fig. 2).

    fig. S2. Mass spectra from different regions of human tooth enamel.

    fig. S3. Mass spectrum from N-rich region (organic).

    fig. S4. APT 3D reconstructed volumes of sample 3.

    fig. S5. APT 3D reconstructed volumes of samples 4 and 5.

    fig. S6. APT 3D reconstructed volumes of sample 6.

    table S1. Theoretical isotope proportion for Mg, C, and C2 at 12, 12.5, and 13 daltons.

    table S2. Measured isotopic proportions at 12, 12.5, and 13 daltons in C-rich regions of enamel.

    table S3. Measured isotopic proportions at 12, 12.5, and 13 daltons in precipitate B.

    table S4. Measured isotopic proportions at 12, 12.5, and 13 daltons in intergranular ACP.

    table S5. Measured isotopic proportions at 12, 12.5, and 13 daltons in Mg-rich precipitate of sample 4.

    table S6. Typical composition of ACP, HAP, and Mg-rich precipitates in human dental enamel measured by APT.

    movie S1. Animation showing the 3D distribution of Mg and Na atoms in human dental enamel; APT sample 3.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Typical APT mass spectrum of human dental enamel containing organic materials (sample 1, Fig. 2).
    • fig. S2. Mass spectra from different regions of human tooth enamel.
    • fig. S3. Mass spectrum from N-rich region (organic).
    • fig. S4. APT 3D reconstructed volumes of sample 3.
    • fig. S5. APT 3D reconstructed volumes of samples 4 and 5.
    • fig. S6. APT 3D reconstructed volumes of sample 6.
    • table S1. Theoretical isotope proportion for Mg, C, and C2 at 12, 12.5, and 13 daltons.
    • table S2. Measured isotopic proportions at 12, 12.5, and 13 daltons in C-rich regions of enamel.
    • table S3. Measured isotopic proportions at 12, 12.5, and 13 daltons in precipitate B.
    • table S4. Measured isotopic proportions at 12, 12.5, and 13 daltons in intergranular ACP.
    • table S5. Measured isotopic proportions at 12, 12.5, and 13 daltons in Mg-rich precipitate of sample 4.
    • table S6. Typical composition of ACP, HAP, and Mg-rich precipitates in human dental enamel measured by APT.

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4 format). Animation showing the 3D distribution of Mg and Na atoms in human dental enamel; APT sample 3.

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