## 4 Discussion
Previous studies have indicated that this method provides more consistent and accurate grading [25,26]; however, they require significant training before usage, standardization of variation among independent instructors now needing to alter individual variability in teaching habits, increased time needed to obtain digital feedback and high costs. Consequently, digital assessment should not replace conventional methods; rather, it can overlap these as a supplemental method of evaluation. The aim of developing the novel, multicolored 3D-printed teeth was to replace the conventional monochromatic plastic teeth in order to facilitate a more objective and accurate evaluation method, while still using the traditional assessment method by both students and instructors. Moreover, the conventional assessment method more closely follows actual clinical practice. Hence, the novel multicolored 3D-printed tooth analogs enable assessment in the same manner as with conventional plastic teeth, while providing more objective and accurate evaluation of cavity preparation. Intra-examiner reliability is determined by comparing the grades given by an examiner of the same object at one point in time with those given at another significantly separated point in time. In the present study, this was done 3 months apart. Furthermore, the examiners who participated in the present study were of different levels of expertise (Examiner 1 was considered to have more expertise), because previous studies have reported that experience improved intra-examiner reliability, and less experienced examiners have been shown to be more inconsistent [20]. Our findings are consistent with those previously reported, as Examiner 1 displayed more intra-examiner reliability (ICC = 0.716 on multicolored teeth and 0.612 on regular teeth) than Examiner 2 (ICC = 0.481 on multicolored teeth and 0.095 on regular teeth). Our findings suggest that examiner/instructor influence is the main factor correlated to the grades given to dental student cavity preparations. Furthermore, it was found that the novel, multicolored 3D-printed tooth analogs increase the level of consistency of the less experienced examiner. The explanation for the improvement by the less experienced examiner with the 3D model is that it provides an alternative means to assess student performance over the conventional method of assessment. The multicolored 3D-printed teeth provided additional visual feedback on performance success and errors according to the various color layers exposed inside the cavity. These make the dimensions, depth, and location of the tooth preparation more clear for both student and teacher, thus facilitating more objective and accurate evaluation of tooth preparation. Conceptualization, D.L. and T.B. ; methodology, D.L., T.B. and R.P. ; investigation, M.A. ; data curation, D.L., A.S. and M.A. ; writing--original draft preparation, M.A., D.L. and T.B. ; writing--review and editing, D.L., R.P., A.S., M.D. and T.B. ; visualization, M.D. ; supervision, T.B. and R.P. ; project administration, D.L. and A.S.; funding acquisition, T.B. and R.P. All authors have read and agreed to the published version of the manuscript. This study was partially supported by a grant provided by the Ministry of Science, Technology and Space, Israel, Grant number: 3-12439. **Institutional Review Board Statement:** The study was conducted according to the guidelines and approved by the Institutional Ethics Committee of Tel Aviv University (12 February 2018). **Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study. **Data Availability Statement:** Data available on request due to restrictions eg privacy or ethical. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy of the students' grades. **Acknowledgments:** This study was partially supported by a grant provided by the Ministry of Science, Technology, and Space, Israel, grant number: 3-12439.