This prospective cohort study involved all registered fifth-year (final) undergraduate students (n=46) at PNU, College of Dentistry, during the academic year 2019-2020. Half of these student (n=23) attended an elective endodontic preclinical course during the previous year. The study was exempt from ethical approval by the institutional review board at PNU (IRB#19-0165).
The undergraduate dental curriculum at PNU, College of Dentistry is a five-year program, composed of a mixture of the block (modules) and stream (longitudinal) courses. Undergraduate endodontic teaching starts with a preclinical block course in the third year composed of a theoretical component and hands-on preclinical sessions that run for seven weeks, culminating in a total of ninety contact hours. All preclinical training takes place in a simulated setting, on mannequin heads, on which students are expected to complete root canal treatment for plastic and natural anterior and posterior teeth. Upon passing this preclinical course, students can commence performing non-surgical root canal treatment on patients under close supervision as part of stream comprehensive clinical courses.
An elective advanced preclinical endodontic block course is also offered in the fourth year. This course runs for five weeks (a total of forty-five contact hours) and offers advanced theoretical knowledge along with simulated preclinical training sessions focused on molar teeth.
Case selection
All completed non-surgical root canal treatment cases performed by the fifth-year students during the academic year were evaluated. Students performed root canal treatment at the college of dentistry’s dental clinics under the supervision of endodontic specialists, with an average student to staff ratio of 1:7. An aseptic technique with rubber dam isolation was applied in all cases. Working length was established using electronic apex locator and periapical radiographs. Canal cleaning and shaping was done either using manual 0.02mm taper stainless-steel k-files (Medin, A.S. Czech Republic) with step-back technique or rotary instrumentation using nickel-titanium Protaper Universal files (Dentsply Maillefer, Ballaigues, Switzerland). Canals were irrigated with Sodium hypochlorite 2.25% for chemical disinfection, dried with paper points then filled with gutta-percha cones and AH plus sealer (Dentsply-Sirona, United States) using a lateral condensation technique. On completion, coronal restoration was performed, and a postoperative periapical radiograph was exposed using the paralleling technique.
The academic dental software system, AxiUm (Exan, BC, Canada) - employed at the dental clinics - was used to specify all non-surgical root canal treatment cases completed by fifth-year students from the start of the academic year on the first of September 2019 until work at the dental clinics was abruptly terminated on the eighth of March 2020 due to the COVID 19 pandemic. Retreatment cases were excluded. During evaluation, records with poor quality or missing periapical radiographs were also excluded.
The cases were divided into two groups: Group 1; (attendees), teeth treated by students who had attended both the preclinical endodontic block course in the third-year and the elective preclinical course in the fourth-year. Group 2; (non-attendees), teeth treated by students who had not attended the elective preclinical course.
Assessment of clinical performance
Root canal treatment quality and procedural errors
Clinical performance of the students was assessed by evaluating the technical quality of the performed root canal treatment and the presence of procedural errors. Technical quality was determined based on criteria for adequate root canal filling: distance between the end of the root canal filling and the radiographic apex, filling density and the detection of procedural errors, which had been adopted by Barriesh-Nusaair et al. [10] and Balto et al. [9]. and are summarized in Table 1 and Table 2. The tooth was considered as one unit, scored according to the presence of errors, and/or defects in obturation length and density in any of its canals, for clinical failure of one root will eventually lead to failure of the tooth [9].
Table 1: Criteria for evaluation of technical quality of root canal treatment
Criteria
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Definition
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Length of root canal filling
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Adequate
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End of root canal filling is either at or ≤ 2mm from radiographic apex.
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Inadequate
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Root canal filling is either short more than 2mm from the radiographic apex or extends beyond radiographic apex.
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Density of root canal filling
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Adequate
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No voids visible within the root canal filling or between the filling and the canal walls.
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Inadequate
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Voids are visible within the root canal filling or between the filling and the canal walls.
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Presence of procedural errors
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Present
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One or more procedural errors are detected.
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Non present
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No procedural errors detected.
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Table 2: Criteria for detection of procedural errors.
Procedural Error
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Criteria of Diagnosis
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Ledge formation
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The obturation was at least 1 mm shorter than the working length and deviated from the original canal shape in teeth where root canal curvature occurred.
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Apical transportation
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In the apical third, the obturation was located on the outside curve of the canal.
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Apical perforation
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The apical termination of the filled canal was different from the original canal terminus or when the obturation extruded through the apical foramen.
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Root perforation
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Extrusion of canal obturation in any other area of a root except the furcation area and the inner wall of the root
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Strip perforation
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Extrusion of canal obturation in the lateral (inner) wall of the root canal
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Presence of fractured instrument
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A fractured instrument was detected inside a root canal or with its tip extending into the periapical area
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Furcation perforation
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Extrusion of filling material through the furcation area in multi-rooted teeth
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Number of cases performed by each student was also recorded. Two endodontists with a minimum experience of three years, blinded to the treating students, evaluated independently, the technical quality of canal obturations, and presence of procedural errors by studying the preoperative, working length, and postoperative radiographs. Mesial and distal angulated radiographs were included for multi-rooted teeth. The periapical radiographic images were retrieved from the digital archives, viewed, and analyzed using Mipax (Microtek, Taiwan). All radiographs were examined at 1.5 magnification on the same 21-inch LCD monitor resolution (1920 × 1200 at 60 Hz) in a darkened room, and the same ambient conditions were sustained during all the radiographic evaluation. Each original digital image was manipulated by the investigator to enhance the contrast and brightness of the image to give the subjectively clearest image of the root canal and radiographic apex as recommended by Akdeniz and Soǧuon [17].
Prior to the actual study, intra- and inter-examiner reliability was determined by evaluating eighteen endodontically treated teeth randomly selected from AxiUm records, these were not included in the study. These cases were evaluated twice by the same examiners, four weeks apart. Inter- and intra- examiner agreement were measured by Cohen’s kappa (k). Values for inter-examiner agreement for obturation length, density, and procedural errors were k=0.702, k=0.667, and k=0.824 respectively, while intra-examiner reliability ranged from (k=0.77 -k=1). This indicated good to excellent agreement [18]. Therefore, as reported by previous studies [19–21], it seemed acceptable to randomly allocate the sample radiographs equally between both endodontists.
Undergraduate students’ confidence survey
All students completing the five-year dental program in 2019-2020 were invited to participate in an online questionnaire survey at the beginning of their internship year in July 2020. Prior to completing the questionnaire, the students were made aware of the objectives of the survey and how the results will be used. They were informed that participation is voluntary, their answers will remain entirely anonymous, and they can withdraw at any time during or after completing the questionnaire.
The questionnaire adapted from Davey et al. [14], and Murray and Chandler [22] contained thirteen multiple-choice format questions and three open-ended questions. The questionnaire indicated students’ attendance of the endodontic elective course, assessed their experiences, perceived competence performing root canal treatments, along with their self-rated levels of the confidence in carrying out various endodontic tasks and their views on their undergraduate endodontic training. Participants were asked to classify their perceived level of confidence over a five-point scale: very confident, confident, neutral, low confidence, or extremely low confidence.
Statistical analysis
Statistical analysis was performed using the Statistical Package for Social Sciences software (SPSS version 27.0 IBM Inc., Chicago; IL, USA), Descriptive data analysis was carried out and Person chi-square test, Fisher Freeman Halton exact test were conducted to analyze the categorical data: root canal filling quality, confidence level and satisfaction. Independent samples T- test was used to compare the number of teeth completed students in each group. A p-value <0.05 was considered statistically significant.