Dimensional changes of dental impression materials by thermal changes

Dental impression materials for prosthodontic treatment must be easy to use, precisely replicate of oral tissue, be dimensionally stable, and be compatible with gypsum materials. The dimensional accuracy of all materials is affected by thermal changes; impression materials shrink during cooling from mouth temperature (37°C)to room temperature (23°C). Five kinds of light body addition-reaction silicone impression materials [Contrast (CT), Voco Co., Germany; Examix (EM), GC Co., Japan; Extrude (EX), Kerr Co., USA; Imprint II (IM), 3M Co., USA; Perfect (PF), Handae Chemical, Korea] were tested by making cylindrical specimens (6 mm diameter and 12 mm height). The thermal expansion of the impression materials was measured with a thermomechanical analyzer (TMA 2940, TA Instruments, USA) between 23-37°C. Data were analyzed via the Mann-Whitney Usage Test. To simulate actual dental impressions, tooth and tray shapes were modeled to measure the linear shrinkage of impression materials at anterior and posterior locations. The thermal expansion of impression materials tested decreased as follows: CT ≥ PF ≥ EM ≥ EX ≥ IM (p < 0.05). The anterior region changed more than the posterior region for the same impression materials. The dimensional changes averaged more than 40 μm in the anterior region, but less than 40 μm in the posterior region for all materials. Thermal expansion coefficients of some impression materials were significantly different from each other (p < 0.05), and the anterior region had more dimensional change than the posterior region for the same impression materials.