Softening of BISGMA-based polymers by ethanol and by organic acids of plaque.

The Wallace indentation hardness is a determinant for the abrasion resistance of smooth surface resins. It was the aim of the present study to investigate the softening effect of ethanol and of organic acids of plaque on BISGMA-based polymers. The hardness was measured before and after soaking for 1 day in ethanol, acetic acid, propionic acid, or lactic acid. The last three liquids were found to induce a softening of the polymers. The softening effect was more pronounced when the polymer originated from monomer mixtures with low content of diluting monomer. This finding reflects the extent of polymerization of the polymers.