Thermal expansion of addition polymerization (Type II) silicone impression materials.

— The coefficients of thermal expansion and contraction of several dental addition silicone impression materials have been measured and their importance for precision of impressions recorded. Dies were made from impressions following: (1) cooling to 22 °C for 15 min, (2) cooling to 22 °C for 15 min and heating to 37 °C for 15 min, (3) holding for 24 hr at 22°C, and (4) storing for 24 hr and then heating to 37 °C for 15 min. The results show that a reheating of the impressions to mouth temperature before die casting reduces their inaccuracy significantly.