Accuracy of conventional impression taking compared to intraoral digitizing

Objectives: For the production of indirect restorations, the shape of the prepared teeth has to be transferred to a real or virtual model. Using CAD/CAM-technologies, conventional impression taking as well as intraoral digitizing can be applied. Aim of the study was to investigate the accuracy of the multi-step intraoral digitizing (CEREC 3D, Sirona, Bensheim, Germany) compared to the one-step putty and wash technique (Dimension penta H; Dimension Garant L; 3M ESPE, Seefeld, Germany) with subsequent extroral digitizing of master casts regarding data quality, matching accuracy and inter-procedure agreement. Methods: The procedures applied are fixed in a study protocol approved by the Medical Faculties Ethics Board. After gathering informed consent, from 10 volunteers data of one upper jaw quadrant was acquired using in a random order (1) multi-step intraoral digitizing, subsequently matching the data-sets and (2) conventional impression taking with subsequent extraoral digitizing of the entire master casts. Master-casts were manufactured according to the Zeiser-technique using a type IV die stone and then optically digitized. For the intraoral data-acquisition the teeth were coated with CEREC Liquid and CEREC Powder (Vita, Bad Säckingen, Germany). The data sets acquired intraorally were matched beginning in the premolar region and moving to the anterior and posterior teeth. After matching, the complete data sets were compared to the CAD-surface models of the one-stage putty and wash impression, that was chosen as reference (Surfacer, Imageware Inc., USA). Results: The mean deviations between the data sets acquired intraorally and the reference ranged between + 28 µm/ -21 µm and +48 µm/ -85 µm. The best inter-procedure agreement was found in the premolar region. Conclusion: While matching of data sets acquired intraorally seems to be a reliable procedure for short ranges, the accuracy after matching multiple data-sets proved to be inferior compared to conventional impression taking.