Overall, the majority of the questions were answered correctly, independently to the imaging modality. The percentages of correct answers given by OS were 66.3% for OPG, 83.4% for CBCT and 76.4% for 3D model; and differed slightly to those given by ORTH with 63.7% for OPG, 78.0% for CBCT and 78.7% for 3D model (Figs. 1 and 2). Both OS and ORTH alike answered to around 20% of the questions that the OPG provided insufficient data in order to answer the question.

Assessing a CBCT increased the percentage of correct answers after OPG assessment, both for OS and ORTH. When given a printed 3D model after CBCT, an additional increase in correct answers could be observed for ORTH, but not for OS (Fig. 2 versus Fig. 1).

Evaluating the different questions independently, only three questions were answered significantly different between OS and ORTH (Table 3). The evaluation of a contact between tooth/tooth structure and nerve, the appraisal of root maturation and the diagnosis of a resorption reached in the case of this study higher percentage for the OS group, with odds ratios varying between 1.7 and 3.8. Otherwise, no apparent differences could be detected in the correctness of the answers.

When comparing the diagnostic accuracy based on OPG and CBCT (following OPG), no differences could be observed for any of the nine questions (Table 4). The same was true when assessing impact of age, gender and years of experience as a dentist on the accuracy of the answers.

At the end of every OPG evaluation, residents were asked whether further imaging was deemed necessary in order to improve diagnostic accuracy. In 81.6% of the cases, further imaging was requested after the OPG. When asked whether the image assessed provided sufficient information to enable a treatment, the ORTH considered the information content of OPGs significantly more often as sufficient compared to the OS group (p < 0.05) (Fig. 3). This decision was highly influenced by the residents’ background. The odds to request a CBCT were far greater if the OPG assessment was done by a OS (OR 6.3), by a female dentist (OR 3.8) or dentists with only 0 to 4 year of experience (OR 3.0) (Table 5).