###### Abstract  
This study aimed to assess the errors that happened during root canal treatment (RCT) and compare the quality of root canal fillings (RCTs) performed by different academic grades of dental students at Jouf University. Materials and Methods: a retrospective audit study was conducted to check the errors that occurred during RCT performed by seniors and undergraduates. The quality of the RCTs were evaluated, using digital peripacial radiographs depending on previously validated criteria. Data analyses were performed using Statistical Package for the Social Sciences. Descriptive statistics were used for expressing the frequencies of variables and the Chi-square test was used for comparing different variables with a 0.05 level of significance. Results: overall, 332 endodonically treated teeth (566 root canals) were finally chosen for the study. Out of these treated cases, 156 teeth (47%) had a total of 287 recorded errors, mainly in posterior teeth. From the total number of errors, short obturation was the highest error occurred (29%), followed by lack of apical seal (25.1%). Root perforation was the least reported error (2.8%), proceeded by broken instruments (5.6%). A total of 13.2% of the errors were teeth left with unfilled canals, while 7.7% were for an overextended filling. There were no significant differences between the quality of RCF performed by different academic grades. Conclusion: depending on the current study, the quality of RCTs performed by seniors and undergraduate students was 53% acceptable. A clear plan should be applied to improve the quality of treatment outcomes of undergraduate students by implementing more effective preclinical training courses, increasing the ration of supervisor-to-students, and using more advanced modalities during treatment. d 2022 2  
uniformly tapered canal from the coronal part to the apex of the root, obturation with no voids, and the presence of homogenous filling materials 0.5-2 mm before the radiographic apex [4; 5]. Many iatrogenic factors can compromise the prognosis of RCT, such as inadequacy of the preparation, ledge formation, perforation, overfilling, underfilling, breaking of the instrument within the canals, inadequate coronal seal, and inadequate apical seal [6; 7; 8]. It was found that each 1 mm loss of length of the root canal after 2 mm in teeth with apical periodontitis increases the RCT failure rate by 14% [9; 10]. Dental students at Jouf University take a five-year Bachelor Dental Surgery course following the problem-based learning (PBL) system [11; 12; 13]. This Bachelor's course is preceded by a preliminary year and followed by a one-year internship. The students undertake a full-year course in preclinical endodontics in the third academic year. This course involves 28 didactic hours and 56 training hours in a laboratory during which the students perform all the basic technical procedures of RCT on natural teeth. The clinical endodontic course starts in the fourth academic year and involves 5 h of theoretical lectures and 84 h of clinical sessions, during which students endodontically treat single- and multi-rooted teeth using hand root canal instruments and cold Gutta Percha condensation techniques with aid of digital periapical radiographs. The followed protocol during RCT includes identification of the working length using the conventional parallel and/or bisecting angle periapical radiographs, use of step-back preparation techniques, and, finally, the obturation is performed using the cold lateral compaction technique. To finish the clinical course in the fourth year, the student should accomplish a minimum of 12 cases that are equally distributed among anterior, premolars, and first molar teeth. During the fifth academic year, the student performs RCTs as part of the comprehensive management of four patients who need, at least, three disciplines among which, RCT must be. Fifth-year students perform the RCTs following the same protocol as the fourth academic year.