Quantitative Characterization of Demineralized Dentin in Its Natural Wet State

It has been hypothesized that differences in the structure and composition of dentin substrates, differences in smear layer, and type of acids would result in complex, nonuniform acid etched dentin demineralization. Objective: The purpose of this study is to determine the effect of the different dentin surfaces and acids on dentin demineralization measured in its natural wet state using Environmental SEM and micro-Raman imaging. Methods: The occlusal 1/3 of the crown was removed from 24 extracted, unerupted human third molars. Dentin surfaces were fractured or abraded with 600 grit SiC under water, carbide or diamond burs operating in a water-cooled high speed dental handpiece. The prepared dentin surfaces were randomly selected for treatment (15-30sec) with 10% citric acid, 35% H3PO4 or Self-etching bonding agent (Prompt L-Pop). Micro-Raman spectra and imaging were acquired at 1~1.5ìm spatial resolution at positions perpendicular to the treated surfaces; since this technique is non-destructive the same samples were also imaged with ESEM. Samples were kept wet throughout spectral acquisition and ESEM observations. Results: The mineral exists in the superficial layer of all etched dentin covered with smear layers. The degree of demineralization was determined from the ratios of the relative intensities of spectral features associated with the mineral and collagen. The depth, degree and profile of demineralization with H3PO4 are dramatically different from that with citric acid or Prompt. Different dentin surfaces have dramatic effect on the profile of dentin demineralization. Conclusions: Most current adhesives are applied using wet bonding techniques, in which the dentin is kept fully hydrated throughout the bonding. Our ability to fully characterize the hydrated, etched dentin substrates is very important for understanding bonding under in vivo conditions. Supported by NIH/NIDCR R0114392/K2515281/R0315735.