Fig. 2

X-ray images of three typical samples. The tooth profile was outlined by a yellow dotted line. The root filling was outlined by a green dotted line. And the void was outlined by a red dotted line. A A root canal filled by a student from LG in test was considered unaccepted in terms of filling length. B A root canal filled by a student from LG in test was considered unaccepted due to void presence. C A root canal filled by a student from WFG in test was considered to have adequate root length and no void