Three-dimensional analysis of dual-arch impression trays.

Objective: The objective of this investigation was to measure and compare the dimensions of casts made using four types of impression trays and two impression materials to the dimensions of the original master model. Thisstudy differed from previous studies by using three-dimensional measurement. Method and materials: Vinyl polysiloxane and polyether impressions were made of two crown preparations of ivorine teeth cemented into an acrylic master model. Two grooves were placed into each of the preparations. In addition, six points were placed on each occlusal surface and six were placed on each finish line. Impressions were poured with a Type IV dental stone at 48 hours. A three-dimensional measuring system was used to determine coordinates of 32 points on the master model and resulting casts. Inter- and intratooth dimensions were calculated from the measured coordinates. Results: The accuracy and precision of the impression techniques were assessed using analysis of variance (ANOVA) and Dunnett's t test. The ANOVA and Dunnett's ttest indicated that only the custom tray did not detect any inaccuracies and was as reproducible as the master model. Conclusion: This study suggests that the custom tray technique is most accurate, even though all other techniques evaluated apparently produce clinically acceptable results.