EFFECT OF CITRIC-ACID CONCENTRATION ON DENTIN DEMINERALIZATION, DEHYDRATION, AND REHYDRATION - ATOMIC-FORCE MICROSCOPY STUDY

Most current dentin bonding procedures use acid etchants to partially demineralize the dentin structure and provide pathways for resin infil tration. This study determined the recession rates of peritubular dent in and intertubular dentin as a function of pH during demineralization in citric acid solutions (0.0005-2.5M) and the effects of dehydration and rehydration on the partially demineralized dentin. Polished denti n disks were prepared with an internal reference layer and were studie d at specific intervals for citric acid etching between pH 1 and 3.4 i n an atomic force microscope. Peritubular dentin etched rapidly and Li nearly with time until it could no longer be measured. The intertubula r surface began etching at nearly the same rate, hut then recession sl owed for all concentrations and stabilized after recession of less tha n 1 mu m for all but the pH 1 solution. The decrease in recession was attributed to the Limitation of contraction of the demineralized colla gen scaffold as long as it remained hydrated. Dehydration following et ching resulted in significant collapse of the surface, changes in roug hness, and a slight decrease in tubule diameter for samples etched for 30 min. Measurements could not be made of the collapse for low pH sam ples, because shrinkage stresses disrupted the integrity of the refere nce layer. On rehydration, the dehydrated surfaces underwent an expans ion up to the level seen after etching and tubule diameters returned t o the etched values. These results indicate that the collapse of demin eralized matrix is almost totally recoverable on rehydration. (C) 1998 John Wiley & Sons, Inc.