High-Resolution Characterization of Enamel Remineralization using Time-of-Flight Secondary Ion Mass Spectrometry and Electron Microscopy.

The aim of this in vitro study was to assess the suitability of high-resolution time-of-flight secondary-ion mass spectrometry (ToF-SIMS) for visualizing cross-sectional changes in human enamel microstructure and chemical composition during treatment and remineralization cycling of artificially generated caries lesions underneath an artificial plaque. Treatments consisted of exposure to twice daily toothpaste/water slurries prepared from 0, 1100, and 5000 µg/g fluoride (F) NaF/Silica toothpastes. In addition, treatments with slurries prepared from 1100 µg/g F SnF2/Silica toothpastes were done using 44Ca in the remineralization solution to allow for differentiation of newly formed mineral and exploration of incorporated metal dopants using ToF-SIMS. Complementary microhardness, scanning electron microscopy, and high-resolution transmission electron microscopy (HR-TEM) investigations were performed on enamel cross-sections. HR-TEM was used for the first time to determine the change in crystallinity during remineralization revealing distinct microstructural zones within one lesion. Chemical mapping using ToF-SIMS demonstrated that the distribution of F, while observed primarily in the new mineral phase, was widespread throughout the lesion with 44Ca substantially limited to the remineralizing mineral. Both penetrated the inter-rod spaces of the sound enamel illustrating how acid damage propagates into the native mineral as the caries lesion deepens. HR-TEM examination revealed different regions within the lesion characterized by distinct micro- and ultra-structures. Importantly, HR-TEM revealed a return of crystallinity following remineralization. Fluoride dose response observations verified the ability of these high-resolution techniques to differentiate remineralization efficacy. The collective results provided new insights such as the visualization of fluoride or calcium penetration pathways, as well as new tools to study the caries process.

Enamel Fluoride Uptake Determined Using the Microbiopsy Technique and Time-of-Flight Secondary Ion Mass Spectrometry: A Pilot Study.

This study evaluated the suitability of time-of-flight secondary ion mass spectrometry (ToF-SIMS) to assess enamel fluoride uptake (EFU) in comparison with the microbiopsy technique. Enamel specimens were exposed to equimolar solutions of fluoride prepared from sodium fluoride (NaF), stannous fluoride (SnF2), or amine fluoride (AmF). EFU was quantified by both techniques on the same specimens. EFU was found to be highest for samples treated with AmF, followed by SnF2 and NaF. Both methods yielded clearly interpretable, highly correlating (r = 0.95) data. ToF-SIMS can be considered a promising alternative to the microbiopsy technique for near-surface EFU assessment.