Determination of chemical species of fluoride during uptake mechanism of glass-ionomer cements with NMR spectroscopy

摘要

Objective. The aim of the present study was to determine the chemical species formed inside glass ionomer cements after fluoride uptake and to investigate the depth of penetration of fluoride ions within the cement matrix.Methods. An experimental fluoride-free glass with composition 2SiO(2)-AlO3-CaO was produced. The glass powder was mixed with aqueous poly(acrylic acid) (PAA), and allowed to set. The resulting specimens were stored in 20 ml KF solution with 1000 ppm fluorine for 24 hand then placed into the same amount of water as for 24 h. A fluoride selective electrode was used to give the F concentration of the respective solutions. F-19 MAS-NMR spectra were recorded on powdered cement specimens using a Bruker AVANCE-NEO 600 spectrometer. In addition, SEM observation and EDX chemical analysis were conducted on the cross-section of a carefully fractured specimen.Results. Fluoride was shown to be mainly present in the surface layers of the specimen after placement in the KF solution, and only a small fraction was re-released into water. F-19 NMR spectroscopy showed that AlF complexes were formed within the cement.Significance. The fluoride taken up by a free-fluoride glass ionomer cement mostly occupies surface layers and is retained because it bonds to aluminum within the matrix. This finding explains why the majority of fluoride taken up by conventional glass ionomer cements is retained. (C) 2021 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.