Solid-state NMR spectroscopy measurement of fluoride reaction by bovine enamel and dentin treated with silver diammine fluoride

Objectives: The aim of this study was to investigate the formation of fluoride compounds in bovine enamel and dentin treated with silver diammine fluoride (SDF) using F-19 and P-31 solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Methods: Enamel and dentin powder, obtained from bovine teeth, were treated with 38% SDF for four minutes and then washed thoroughly with Milli-Q water. The dehydrated SDF-treated samples were then examined. F-19 solid-state MAS NMR spectra were acquired and H-1-P-31 cross-polarization (CP) experiments were performed on SDF-treated enamel and dentin powder. The surfaces of SDF-treated enamel and dentin blocks were observed by Scanning Electron Microscope (SEM). Results: F-19 MAS NMR detected a more pronounced signal intensity for the dentin sample than the enamel, indicating an increased reactivity of SDF for dentin, compared with enamel. F-19 NMR spectra for the SDF-treated samples showed fluorhydroxyapatite (FHAp), and other fluoride com-pounds such as CaF2 and the fluoride-substituted carbonate. The H-1-P-31 CP intensities of prominent peaks were lower for the SDF-treated samples than the non-treated sample, indicating that the F- ion replaced the OH- ion in the lattice tunnel. SEM observations on the SDF-treated samples showed pronounced multiple precipitation and particles in dentin compared with enamel. Significance: The solid-state MAS NMR revealed the reaction of fluoride on enamel and dentin and the identification of fluoride compounds. In particular, the formation of FHAp indicates that SDF is effective in reducing the risk of tooth decay. (C) 2022 Published by Elsevier Inc. on behalf of The Academy of Dental Materials.