MINERAL DISTRIBUTION AND DIMENSIONAL CHANGES IN HUMAN DENTIN DURING DEMINERALIZATION

Many bonding agents require the dentin surface to be acid-etched prior to being bonded. Understanding the stability and morphology of the et ched dentin surface is important for improving bond strength and relia bility in these systems. In this study, the atomic force microscope wa s used to quantify dimensional changes that occur to fully hydrated de ntin during demineralization with a pH 4.0 lactic acid gel. A high-res olution microtomography instrument, the x-ray tomographic microscope, was also used to quantify the mineral density distribution in the dent in as a function of etching time. The intertubular dentin surface shra nk by less than 0.5 Fun during etching, while the peritubular dentin r eceded at an initially rapid linear rate. The dentin surface retained its initial morphology, although it was more porous with the removal o f the peritubular dentin. Beneath the etched surface, there were three major zones characterized by mineral density differences. The first z one was a fully demineralized collagen layer, subjacent to which was a partially demineralized zone of roughly constant mineral density. Imm ediately following the partially mineralized layer was normal dentin. The presence of the partially mineralized layer could be explained in terms of different transport rates in the peritubular and intertubular dentin.