Title: 0218 - Effect of Fluoride on Dentin Remineralization Using 1H–31P Heteronuclear-correlation NMR
Noriko Hiraishi (Presenter)
Tokyo Medical and Dental University
Fumiaki Hayashi, RIKEN Center for Life Science Technologies
Masayuki Otsuki, Tokyo Medical & Dental University
Junji Tagami, Tokyo Medical and Dental University
Objectives: Fluoride action on minerals is based on ionic exchange of F– for OH– in apatite lattice or phosphate-containing CaF2-like mineral loosely bound on the surface. To investigate fluoride action and its reaction product, we demonstrated 2D 1H-31P heteronuclear-correlation (HETCOR) NMR spectroscopy.
Methods: Pulverized bovine dentin was used for NMR samples. Partially demineralized dentin was prepared with acetic acid (pH 5) (dem-dentin). NaF solution was used at 900 ppm and 100 ppm [F-]. The NMR samples were prepared:
(i) Dentin was treated 900 ppm [F-] for three hours
(ii) Dem-dentin was treated 900 ppm [F-] for three hours
(iii) Dem-dentin was immersed in artificial saliva (AS) for one week
(iv) The sample (ii) was immersed in artificial saliva (AS) for one week
(v) Dentin was treated with 100 ppm [F-] in pH 5 (50 mM acetic acid) for four weeks
(vi) Dentin was treated with 100 ppm [F-] in pH 7 (20mM HEPES) for 4 four weeks
AS contained 1.5 mM CaCl2, 0.9 mM KH2PO4,130 mM KCl, 20 mM HEPES (pH 7) and used at 37 °C. The samples were investigated by 1H–31P HETCOR NMR spectroscopy.
Results: When fluoride was applied, a minor OH– cross-peak was revealed as well as a major OH– cross-peak, a characteristic peaks of hydroxyapatite (Figure). Thus, the minor OH– peak was associated with fluoride-incorporation in apatite structure. The minor/major OH– ratio was increased most in (v), followed by (iv), meanwhile (iii) was the lowest. At [F-] (900 ppm), a minor OH– may not be readily shown. At [F-] (100 ppm), a better fluoride-incorporation was shown for (v) than (vi).
Conclusions: A high [F-] application could not produce the lattice-incorporation spontaneously. However, fluoride incorporation was possible by immersion of AS. Fluoridated apatite was formed when fluoride was applied on dentin in acid condition.
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