STATEMENT OF PROBLEM
The use of computer-aided design and computer-aided manufacturing (CAD-CAM) technologies is widely established, with single restorations or short fixed partial dentures having similar accuracy when generated from digital scans or conventional impressions. However, research on complete-arch scanning of edentulous jaws is sparse.
The purpose of this pilot in vitro study was to compare the accuracy of a digital scan with the conventional method in a workflow generating implant-supported complete-arch prostheses and to establish whether interference from flexible soft tissue segments affects accuracy.
MATERIAL AND METHODS
An edentulous maxillary master cast containing 6 angled implant analogs was used and digitized with mounted scan bodies by using a high-precision laboratory scanner. The master cast was then scanned 10 times with 4 different intraoral scanners: TRIOS 3 with a complete-arch scanning strategy (TRI1) or implant-scanning strategy (TRI2), TRIOS Color (TRC), CEREC Omnicam (CER), and CEREC Primescan (PS). The same procedure was repeated with 4 different levels of free gingiva (G0-G3). Ten conventional impressions were obtained. Differences in implant position and direction were evaluated at the implant shoulder as mean values for trueness and interquartile range (IQR) for precision. Statistical analysis was performed by using the Kruskal-Wallis and post hoc Conover tests (α=.05).
At G0, position deviations ranged from 34.8 μm (IQR 23.0 μm) (TRC) to 68.3 μm (12.2 μm) (CER). Direction deviations ranged from 0.34 degrees (IQR 0.18 degrees) (conventional) to 0.57 degrees (IQR 0.37 degrees) (TRI2). For digital systems, the position deviation ranged from 48.4 μm (IQR 5.9 μm) (PS) to 76.6 μm (IQR 8.1 μm) (TRC) at G1, from 36.3 μm (IQR 9.3 μm) (PS) to 79.9 μm (IQR 36.1 μm) (TRI1) at G2, and from 51.8 μm (IQR 14.3 μm) (PS) to 257.5 μm (IQR 106.3 μm) (TRC) at G3. The direction deviation ranged from 0.45 degrees (IQR 0.15 degrees) (CER) to 0.64 degrees (IQR 0.20 degrees) (TRC) at G1, from 0.38 degrees (IQR 0.05 degrees) (PS) to 0.925 degrees (IQR 0.09 degrees) (TRI) at G2, and from 0.44 degrees (IQR 0.07 degrees) (PS) to 1.634 degrees (IQR 1.08 degrees) (TRI) at G3. Statistical analysis revealed significant differences among the test groups for position (G0: P<.001; G1: P<.05; G2: P<.001; G3: P<.001) and direction (G0: P<.005; G1: P<.001; G2: P<.001; G3: P<.001).
Without soft tissue interference, the accuracy of certain digital scanning systems was comparable with that of the conventional impression technique. The amount of flexible soft tissue interference affected the accuracy of the digital scans.