Accuracy of impressions attainable with dual-arch trays

Dual-arch trays are recommended for impression taking especially for small restorations. Objective: Therefore the accuracy of impressions with dual-arch trays was evaluated. Material and Method: A stainless steel cast of a full lower arch with a partial crown, an mod-inlay and a full crown preparation was used as a master. With 3 materials (Impregum Penta (IP), ESPE; Dimension Penta H Quick/Garant (DP) (double-mixing technique), ESPE, Honigum Mixstar Mono (HM), DMG) impressions were made using Triple Trays (TT) (Premier) and Bite-Relator (BR) (Temrex). As a comparison custom trays (ct) were fabricated and IP and HM applied in a standard monophase technique. Additionally double-mix impressions were made with DP and Panasil putty soft/contact plus (PP) (Kettenbach) using a Schreinemakers (ST) stainless steel tray. With each material/tray combination 10 impressions were made. All the impressions were poured with type-IV Fuji-Rock plaster. The accuracy of the impressions was assessed indirectly from the change of 59 predefined transversal dimensions on the obtained casts in comparison to the master cast. The results were subjected to nonparametric statistical procedures (H-test). Results: The mean linear percentage change between the master model and the casts ranged from 0.19 (0.16/0.21)% [median (interquartil range)] for HM-TT to 0.43 (0.33/0.50)% (DP-BR) for the crown, from 0.38 (0.28/0.42)% (DP-ct) to 0.78 (0.37/1.01)% (HM-BR) for the inlay and from 0.50 (0.41/0.66)% (IP-ct) to 0.91 (0.80/1.31)% (Im-BR) for the partial crown preparation. The data for the ST-tray (PP) ranged from 0.25 (0.21/0.31)% for the crown to 57.8 (0.39/0.71)% for the inlay preparation. Overall the results obtained for TT were significantly better as for BR (p<0.01). Generally the dual arch trays performed better in the crown preparation. Conclusion: It can be concluded within the limits of this study that the accuracy obtainable with dual-arch trays is at least in impressions for single crowns not inferior to other impression techniques.