UCSF

INTRODUCTION: Permeabilities of enamel and dentin have implications on the symptoms and disease status of a patient with dentin caries and/or enamel hypomineralization. The purpose of the study is to investigate the effect of silver diamine fluoride (SDF) on physiochemical properties by correlating permeability with mineral density (MD) and elemental composition of hypomineralized enamel and carious dentin.

METHOD: Enamel and dentin from extracted carious primary teeth with (N=3;41 regions) and without (N=3;35 regions) SDF treatment in-vivo, and hypomineralized enamel from permanent molars with (N=4;10 regions) and without (N=7;41 regions) SDF treatment in-vitro were scanned using X-ray micro computed tomography. Spatial elemental maps of Zn2+ and Ca2+ were generated using X-ray fluorescence microprobe. Physicochemical properties were computed using Porous Microstructure Analysis, BoneJ, and RStudio software. Physicochemical effectors of tissue permeabilities were delineated using principal component analysis/regression.

RESULTS: Three dentin zones (carious; transparent; sound) of varying MD, diameter, and tubule occlusions were observed in carious primary teeth. Hypomineralized enamel exhibited variable severity and spacing between enamel rods. The intrinsic permeability of SDF-treated carious dentin (1.48e-14 +/- 7.11e-15 1/m2), but not SDF-treated transparent dentin (1.82e-15 +/- 1.46e-15 m2), was significantly lower than those of untreated carious dentin (1.48e-14 +/-7.11e-15 m2; P<0.0001) and transparent dentin (1.61e-15 +/-9.44e-16 m2; P=0.9293), respectively. Permeability of severely hypomineralized enamel (5.71e-15 +/- 2.04e-15 m2) was comparable to adjacent sound dentin (5.28e-15 +/- 1.30e-15 m2; P=0.1409), and was significantly higher than mildly hypomineralized enamel (1.39e-15 +/- 1.04e-15 m2; P<0.0001). Surprisingly, the permeability of SDF-treated severely hypomineralized enamel (5.00-15 +/- 2.04e-15 m2; P=0.0693) is not significantly different from that of untreated severely hypomineralized enamel. Principal component regression identified Zn2+ level (P<0.0001) and tissue anisotropy (P<0.0001) as significant effectors of tissue permeabilities. Principal component analysis and pairwise permutational multivariate analysis indicated that carious dentin with and without SDF and hypomineralized enamel are physiochemically distinct (P<0.0001).

CONCLUSION: Progression of caries is spatially and chemically dynamic. The physicochemical properties of SDF-treated carious dentin are likened to transparent dentin. Zn2+ localization can alter dentin and enamel permeability. Permeability of severely hypomineralized enamel is comparable to sound dentin. Permeability of non-carious hypomineralized enamel is unaffected by SDF treatment.