Each resident was shown the region of interest to which the questions related to

Allowed setup change of OPG: zoom

Allowed setup change of CBCT: brightness, contrast, zoom, scroll in all three levels (coronal, axial and sagittal

3D model: no restrictions

The OPGs of this study were taken either in-house (CRANEX D, Kw73, 10 mA) or extramural. All CBCTs were taken at the Centre of Dental Medicine of the University of Zurich (CBCT: 3D-Accuitomo 170). In order to produce printed 3D models, DICOM data of the region of interest were cropped and STL-files produced using dedicated software (Slicer 4.5.0.) The STL file was printed with a 3D printer (Objet Eden 260 V) in a resolution of 600 dpi with a horizontal layering of 16 μm, using a semi-translucent material (synthetic material, Med610 Stratasys).

For each case and image, the following nine categorical items had to be answered (yes; no; available information not sufficient):

Is there a direct contact between teeth/tooth structures and nerve structures?

Is the tooth displaced?

Is there more than one root?

Is there a direct non-physiological contact between the tooth/tooth structure and the adjacent teeth?

Is there a pericoronal cyst formation, respectively a cystic formation originating from the tooth/tooth structure?

Has more than a third of the root maturation been completed?

Is a resorption in the bone or tooth structure visible?

Is an ankylosis visible?

Is the tooth/tooth structure worth being preserved?

Following questions relating to the treatability were asked after the OPG evaluation:

Is this case treatable with this amount of information?

Would you request further imaging to improve your diagnostic accuracy?

Even if in the resident’s opinion the OPG provided sufficient information to answer all questions, the resident was nevertheless requested to assess the CBCT. The same applied to the 3D model. After every imaging modality assessment, the questionnaires were collected to avoid retrospect changes.