Suitability and accuracy of CBCT model scan: an in vitro study

Plaster casts can be digitized with desktop scanners, intraoral scanners, and recently also with cone beam computed tomography (CBCT). The aim of this study was to investigate the accuracy of five different CBCT devices digitizing a plaster cast. A study cast serving as a patient was made using the double mix impression technique, and the impression was poured out with plaster. On the resulting plaster cast, arch length (AL), intermolar width (IMW), and intercanine width (ICW) were measured by a coordinate measuring machine (CMM) (Zeiss O-Inspect 422). The patient cast was then scanned by five CBCT devices - CS 9300, CS 9300 Select, CS 8100 3D (all Carestream), Promax 3D Mid (Planmeca), and Whitefox (Acteon) - in eight scan modes. For each CBCT device, 37 scans were performed. The resulting DICOM data were exported as stereolithographic (STL) data and linearly measured using Convince Premium 2012 (3Shape) software. All measurements were compared to the reference master values of the patient cast. The accuracy measurements showed significant differences among the CBCT devices. The highest accuracy was achieved by Whitefox (IMW: mean ± standard deviation (SD): 5.5 ± 5.7 µm) and CS 9300 (IMW: -15 ± 7.4 µm). Comparable results with less accuracy were shown by CS 8100 3D (IMW: -81.2 ± 7.4 µm) and CS 300 Select (IMW: -82.2 ± 6.6 µm). Significantly lower accuracy was shown by Promax 3D Mid (IMW: -126.1 ± 4.8 µm). Some CBCT devices are suitable for the digitization of plaster casts and show very good clinical accuracy. Dental offices equipped with CBCT devices could digitize plaster casts without the need for additional devices. Keywords: CBCT devices, accuracy, indirect digitization, plaster cast, CAD/CAM, stereolithography