Abstract
Comparative properties have been determined for some commonly used ear impression materials (condensation reaction silicones) and some recently developed dental products (addition reaction silicones). Experiments have included measurement of dimensional stability, weight change on storage, viscosity, syringing characteristics, the energy required to tear the material and the stress relaxation characteristics. The major finding is that of the superb dimensional stability of the addition-cured silicones, which show no significant shrinkage over time. This is in contrast to a linear shrinkage of the order of 0.5% over a 48-hour period for the condensation silicones.