Dimensional stability of silicone-based impression materials.

This study attempts to demonstrate that the polymerization reaction is not the only factor that affects the shrinkage of silicone-based impression materials because evaporation of the constituents also contributes to the shrinkage. These factors can be evaluated by the study of time-dependent dimensional changes. This is shown both by chemical kinetics and by experimental testing of condensation and addition polymerizing impression materials with different viscosities. Comparison of the different materials shows that the two contributions, polymerization shrinkage, and evaporation shrinkage, can be assessed separately by analysis of the time-dependent shrinkage diagrams. The instability due to the polymerization reaction is complete after a few hours, but the contribution of the constituent evaporation, if present, can have a significant long-term role.