Physical and Chemical Characterization of the Surface Layers Formed on Dentin Following Treatment with an Experimental Anhydrous Stannous Fluoride Dentifrice

Purpose: To characterize, in vitro, the mode of action of stannous fluoride containing formulations in occluding dentin tubules, by means of high resolution microscopy techniques.

Methods: Focused ion beam scanning electron microscopy (FIB SEM) was used to site-specifically prepare cross sections for SEM and TEM imaging and analysis of dentin samples treated with either a stannous fluoride dispersion in glycerol or an experimental stannous fluoride dentifrice.

Results: An experimental stannous fluoride dentifrice formed a protective layer over the dentin surface and occluded dentin tubules. Additional supporting data derived from a stannous fluoride dispersion in glycerol suggest that stannous fluoride is a key component of this occluding system. Multiple SEM images obtained from sequential FIB cross-sections were reconstructed into 3-dimensional tomograms that showed a formed layer and tubule occlusion. Sections thinned by FIB techniques were observed by transmission electron microscopy (TEM) and related methods and showed that the coating, which was up to 3 microm-thick, consisted of a tin containing precipitate. Chemical analysis by energy dispersive x-ray spectroscopy (EDS) mapping that used scanning TEM (STEM) methods showed interdiffusion of tin up to 200 nm into the dentin structure.