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 compa tible with gypsum materials. The dimensional accuracy of all materials is a ffected by thermal changes; impression materials shrink during cooling from mouth temperature (37 degreesC) to room temperature (23 degreesC). Five ki nds 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 th ermomechanical analyzer (TMA 2940, TA Instruments, USA) between 23-37 degre esC. Data were analyzed via the Mann-Whitney Usage Test. To simulate actual dental impressions, tooth and tray shapes were modeled to measure the line ar shrinkage of impression materials at anterior and posterior locations. T he thermal expansion of impression materials tested decreased as follows: C T greater than or equal to PF greater than or equal to EM greater than or e qual to EX greater than or equal to IM (p < 0.05). The anterior region chan ged more than the posterior region for the same impression materials. The d imensional changes averaged more than 40 <mu>m in the anterior region, but less than 40 mum in the posterior region for all materials. Thermal expansi on coefficients of some impression materials were significantly different f rom each other (p < 0.05), and the anterior region had more dimensional cha nge than the posterior region for the same impression materials. (C) 2001 J ohn Wiley & Sons, Inc.