The dimensional changes of elastomeric impression materials under various conditions of humidity.

The dimensional changes of four modern elastomeric impression materials have been investigated under three different relative humidity conditions.It was found that the dimensional changes of these materials could be markedly affected by their storage conditions. Although no material was found to be completely stable, under particular conditions some materials were superior to others. It was also found that the curing system used for polysulphide materials profoundly affects their behaviour, whilst the presence of a thinner in a polyether material also has a strong influence on its behaviour.Recommendations are given on the optimum conditions for the different materials.