3D-accuracy of conventional and intraoral-optical (CEREC®) impression procedures

Objectives: Digitizing of prepared teeth for crowns and FPDs can be performed indirectly after impression taking and fabricating casts as well as directly chairside (CEREC-3®-Camera). Goal of the "optical impression" procedure applied by the CEREC®-system is to overcome the clinical errors caused by impression taking and fabricating casts. The aim of this study was to determine the three-dimensional errors of the "optical impression" procedure compared with the most accurate conventional dental impression technique (one-stage-putty and wash-technique). Methods: The method applied based on a CAD-surface model of a prepared upper canine as well as a metal-master-die, which was NC-milled as a high-precision physical copy. Ten optical impressions (CEREC®) of the powdered master die as well as ten one-stage putty and wash impressions were taken from the metal master die. For the conventional procedure, the casts were poured with a type IV die stone and optically digitized. The digitized data sets were compared with the CAD-surface model using Surfacer (Imageware Inc., USA). Differences between the CAD-surface-model and the digitized data sets were analyzed quantitatively and qualitatively. The statistical analysis was performed by one-way ANOVA. Results: The mean positive/ negative deviations were 12/ -10 µm for the conventional and 50/ -15 µm for the optical impression. Significant differences (p < 0.05) were found between both procedures. Conclusion: The optical impression procedure (CEREC®) showed significantly reduced accuracy compared with the conventional technique. This study was supported in part by the ESPE Dental AG, Seefeld, Germany. Ralph.Luthardt@mailbox.tu-dresden.de