Accuracy of digital and conventional impression techniques and workflow

Digital impression techniques are advertised as an alternative to conventional impressioning. The purpose of this in vitro study was to compare the accuracy of full ceramic crowns obtained from intraoral scans with Lava C.O.S. (3M ESPE), CEREC (Sirona), and iTero (Straumann) with conventional impression techniques. A model of a simplified molar was fabricated. Ten 2-step and 10 single-step putty-wash impressions were taken using silicone impression material and poured with type IV plaster. For both techniques 10 crowns were made of two materials (Lava zirconia, Cera E cast crowns). Then, 10 digital impressions (Lava C.O.S.) were taken and Lava zirconia crowns manufactured, 10 full ceramic crowns were fabricated with CEREC (Empress CAD) and 10 full ceramic crowns were made with iTero (Copran Zr-i). The accessible marginal inaccuracy (AMI) and the internal fit (IF) were measured. For AMI, the following results were obtained (mean +/- SD): overall groups, 44 +/- 26 mu m; single-step putty-wash impression (Lava zirconia), 33 +/- 19 mu m; single-step putty-wash impression (Cera-E), 38 +/- 25 mu m; two-step putty-wash impression (Lava zirconia), 60 +/- 30 mu m; two-step putty-wash impression (Cera-E), 68 +/- 29 mu m; Lava C.O.S., 48 +/- 25 mu m; CEREC, 30 +/- 17 mu m; and iTero, 41 +/- 16 mu m. With regard to IF, errors were assessed as follows (mean +/- SD): overall groups, 49 +/- 25 mu m; single-step putty-wash impression (Lava zirconia), 36 +/- 5 mu m; single-step putty-wash impression (Cera-E), 44 +/- 22 mu m; two-step putty-wash impression (Lava zirconia), 35 +/- 7 mu m; two-step putty-wash impression (Cera-E), 56 +/- 36 mu m; Lava C.O.S., 29 +/- 7 mu m; CEREC, 88 +/- 20 mu m; and iTero, 50 +/- 2 mu m. Within the limitations of this in vitro study, it can be stated that digital impression systems allow the fabrication of fixed prosthetic restorations with similar accuracy as conventional impression methods. Digital impression techniques can be regarded as a clinical alternative to conventional impressions for fixed dental restorations.