## 4 Discussion  
At Jouf University, RCT is started by an initial identification of root length, using the conventional parallel and/or bisecting angle technique (for the 4 th and 5 th academic grades) with help of an electronic apex locator (that can be used by interns). The preparation of the canals is performed following the protocol of step-back instrumentation technique using conventional hand stainless-steel K-files (for the 4 th and 5 th academic years) and hand protapers (for interns) and irrigation with normal saline and sodium hypochlorite. Finally, the obturation is performed using the conventional Gutta Percha lateral compaction technique followed by direct restoration (such as composite or amalgam) or indirect restoration (such as inlay, onlay, post and core, and crown). For treatment of each tooth, at least 4 periapical radiographs must be taken before, during, and after treatment using a digital radiographic machine (Minray; Soredex; Tuusula, Finland) controlled by the radiograph software program (Digora for windows 2.8.109.465 network client: Strasbourg; France). Generally, the average academic staff-to-student ratio was 1:5, 1:8, and 1:10 for 4 th and 5 th academic years and interns, respectively, at the time of the study. Iatrogenic errors during restorative treatments have a major role in poor prognosis and lack of durability of those treatments. Continuous assessment of the performance of students is critical for continuous improvement of the quality of treatment outcomes. The current study was conducted from the data of 72.8% of known subjects who received RCT by senior and undergraduate dental students at the College of Dentistry, Jouf University, from 2014 (the first clinical year of the College) to October 2021. Most of the excluded cases were due to a lack of or inadequate periapical radiographs, especially those cases being finished before the digital periapical radiographic machines become available in the College. The technical quality of RCT depended on the criteria that were approved by the European Society of endodontology in scoring the technical quality of RCT [43]. To reduce bias during evaluation to the minimum, specific categories, as mentioned in the methodology, were mutually distributed to the examiners by file number without identifying the academic grade of the students. Errors such as perforation, ledges, and breaking of files were evaluated by one consultant. Errors that happened during sealing of the canal/s and lack of coronal seal and canal recognition were evaluated by the second consultant [25]. Most of the known iatrogenic errors that may happen during RCT were covered in the present study. This study revealed that the quality of 53% of examined RCTs that were performed by seniors and undergraduates was adequate, while 47% of these cases showed one or more iatrogenic errors happened during treatment. These results were very close to studies that showed the adequacy of RCT performed by undergraduate students as ranging between 50% and 55% [14; 15; 16; 29; 37]. However, the results were contrary to other works that showed that RCT by undergraduates was adequate in more than 70% of cases [18; 21; 22; 23], and those who reported that less than 30% were adequate [27; 38]. This conflict can be explained by the variation in the criteria of evaluation, educational system, methodology, students' hand skills, and sampling size calculation. Adequate length (0-2 mm from the apex of the root) and homogeneity of the RC filling were proven to have a tremendous effect on the success and durability of RCT [5; 44]. The current study showed that deficiency in the length of RCT (short length) was the highest among studied groups (29.6%). This result was highly comparable to other studies that showed the deficiency in the length of RCT was the highest among other errors, ranging from 25% to 30% [17; 27]. However, these percentages were very high compared to different studies that showed 5-20% deficiency [14; 26; 32; 45].