Crystal precipitation on dentin by poly(acrylic acid) solutions containing SO4(2-) ions

The ability of four different 40% poly(acrylic acid) (PAA) solutions, containing 4 or 6 wt-% of either Na2SO4 or (NH4)2SO4, to cause precipitation of CaSO4 on dentin surfaces was investigated. Each treatment consisted of exposing the dentin to one of the four solutions for either 1 or 2 min and was followed by a water rinse (1 min) and air drying (30 sec). The treated dentin surfaces were then evaluated in a scanning electron microscope (SEM), which showed that crystals precipitated on the dentin with these solutions. Of the four investigated PAAs, one performed better than the others with regard to crystal precipitation and blockage of the tubules. This solution was selected for additional studies of the effects of different PAA concentrations (10%, 20%, 30%, 40%, and 50%). In these solutions, 4 and 6 wt-% of either Na2SO4 or (NH4)2SO4 were dissolved. Additional dentin surfaces were then treated with these solutions as described earlier and evaluated in an SEM. This evaluation showed that solutions containing 30-50% PAA resulted in optimized crystal formation for all the different sulfate solutions and that the optimization occurred within 1 min. Besides optimizing crystal precipitation, these mixtures also minimized the frequency of open dentinal tubules.