Observations on the elastic behavior of a synthetic orthodontic elastomer.

The study focused on changes in elasticity that accompany water storage of a synthetic orthodontic elastomer. We plotted loading and unloading curves to permit the direct measurement of instantaneous elastic recovery (IER) and permanent set (PS) and the calculation of delayed recovery (DR). We obtained baseline data by testing dry as received material. Comparable tests were performed on material that had been stored in water at 37 degrees C for one, seven, 14, 42, and 70 days. Gas chromatography-mass spectrometry was used for analysis of organic substances leached from the elastomer by water. A two-way ANOVA revealed that extension distance and water storage duration affected load requirement, IER, PS, and DR. The presence of leachable organic substances in 14-, 42-, and 70-day storage water was evidence of time-dependent matrix decomposition. Findings from tests of elastic performance and analysis of specimen storage water indicate that exposure of the elastomer to water leads first to weakening of noncovalent forces and subsequently to degradation.