Effect of ethanol on the hardness and relaxation modulus of experimental photo-activated soft lining materials stored in aqueous solutions.

We studied changes in the hardness, relaxation modulus [Er(t)], and weight change ratio (Wc) of experimental photo-activated acrylic soft lining materials (EPLs) stored in three aqueous solutions [distilled water (DW), physiological saline solution (PS), and artificial saliva (AS)] at 37 degrees C for 8 weeks. The hardness of the EPLs increased markedly during the first 4 days of storage, and subsequently changed little. The greatest hardness occurred in the EPL specimen containing the largest amount of ethanol (Et). The relaxation modulus [Er(8)] of the EPLs ranged from 1.35 to 1.66 MPa immediately before storage, and from 1.43 to 2.21 MPa after an 8-week immersion. Like hardness, the increase in [Er(t)] was greatest when the EPL contained large amounts of Et. The Wc ranged from 0.118 to 0.661% after storage for 8 weeks, and increased most for the EPL specimen containing the smallest amount of Et. Furthermore, 3-7 days after the start of immersion many hollows were observed in the surface of specimens with a high Et content. The results indicate that Wc and hollow formation are sensitive to the Et content of the EPL, and that Et content is closely tied to the change in hardness and relaxation modulus with time.