Demineralization of caries-affected transparent dentin by citric acid: an atomic force microscopy study

Objectives: This study determined recession rates of peritubular dentin and intertubular dentin in citric acid solution (0.018 M, pH=2.5) for caries-affected transparent dentin, one of the major components of dentin substrate as altered by caries, with comparisons made with non-carious dentin. Methods: Transparent dentin was identified by sagittally sectioning five obviously carious teeth. Sections were then cut through the transparent dentin area perpendicular to the course of the dentinal tubules. Polished dentin samples of the transparent dentin and non-carious dentin were prepared with an internal reference layer and studied at specific intervals for citric acid etching in an atomic force microscope (AFM). Results: At baseline, transparent dentin was identified by dentinal tubules that were largely occluded with mineral deposits that on etching proved to be acid resistant. Peritubular dentin etched rapidly and linearly over time until it could no longer be measured, yielding etching rates for transparent dentin that could not be distinguished from normal dentin. The normal and transparent intertubular dentin surfaces began etching at nearly the same rate, but then surface recession stabilized after less than 1 μm depth change for both dentin types. Significance: Most previous studies have focused on demineralization and bonding to normal dentin, although many bonding procedures involve altered dentin substrates, such as those modified by caries. In this study, peritubular and intertubular dentin from normal and caries-affected dentin exhibited similar behavior. The major difference was the presence of acid resistant mineral in most of tubule lumens in the transparent dentin.