## 4 Discussion
The reasons for this controversy between the current study and the studies that showed a very low incidence of inadequate length were mentioned in one of these studies [19]. This may be attributed to the strict protocol followed during RCT, such as judging the cases before the start of the treatment (if appropriate for undergraduate level or not), teaching principles, intimate supervision during every step of RCT, and considering redoing the suspected cases by the consultants, which is difficult to follow in every case due to a low consultant-to-student ratio at Jouf University [19]. Root perforation was the least reported error among all seniors and undergraduates (2.8%), preceded by broken instruments (5.6%). This agreed with other studies that reported root perforation as the least-common mishap during RCT [27; 28; 30]. However, this disagreed with the studies performed by other authors who reported the broken instrument as the least reported error preceded by the root perforation [23; 34]. Generally, the errors were mostly associated with posterior teeth compared to anterior teeth (71.8%), with a slightly higher number in maxillary than mandibular teeth. This was consistent with several studies that expressed that the posterior teeth were more associated with accidents during RCT [15; 20; 29]. However, these findings contradicted some studies that showed the mandibular molars were more frequent in recording errors comparing maxillary molars [16; 30], and the studies that showed no significant differences between anterior and posterior teeth [17; 32]. The maxillary molars were the teeth most associated with errors in respect of overextension of RC filling, unfilled canals, and lack of coronal seal. The reason for the increase in the incidence of errors during treatment of posterior teeth may be attributed to the form and shape of the roots, the accessibility to the treated tooth, and students' hand skills. Grade-wise, there were no significant differences in the quality of endodontically treated teeth by different examined academic grades (12.5, 12.6, and 11.3% for intern, 5 th, and 4 th academic years). Although there is no study, as per our knowledge, to compare the quality of performed RCT between different grades collectively like the current study, some studies compared two variables. One of these studies found no significant differences in the quality of RCF performed by final year dental students and interns for all types of examined teeth, which was in agreement with the current study [24]. Other findings showed less encountered errors with advanced training (after 2 years of training) which is contrary to our study [25]. From the authors' point of view, the reason for the lack of differences between different grades may be attributed to the application of the same techniques and protocols followed during RCT with no introduction of advanced modalities for higher grades, a decrease in the number of requirements in 5 th year students and interns, types and complexity of the referred cases to interns, the cases needing re-treatment in interns which had lower success rate compared to initial cases, and a decrease in the number of the cases by interns compared to those in the 4 th and 5 th academic year. The decrease in the number of reported cases treated by seniors compared to undergraduates was mainly due to the limited number of seniors who work within the College during the internship year, as up to 50% of seniors can be assigned to work in Dental Specialty centers of the Ministry of Health of Saudi Arabia for no more than 6 months. The principal aim of the present study was to evaluate the performance of seniors and undergraduate students when performing adequate RCT depending on available digital periapical radiographs. It is clear that the quality of RCT performed after graduation is dependent on how students have been taught during the undergraduate stage. The relatively lower percentage of acceptable RCT assessed in this study could be attributable to many reasons.