Impact of Case Difficulty on Endodontic Mishaps in an Undergraduate Student Clinic Sivakami Rethnam Haug, BDS, DrOdont,* Ane F. Solfjeld, DDS, MS, † Line E. Ranheim, DDS, MS, ‡ and Asgeir B  ardsen, DDS, DrOdont* Abstract Introduction: The aim of this study was to identify the effect of case difficulty on the number of endodontic mishaps and the number of treatment visits using 2 different instrumentation methods, hand files, and reciprocating engine-driven WaveOne files (Dentsply Maillefer, Ballaigues, Switzerland) in an undergraduate student clinic. Methods: Endodontic treatment performed by fourth-year dental students using 2 different instrumentation methods was evaluated: hand files and reciprocating engine-driven WaveOne files. All cases were categorized according to the American Association of Endodontists case difficulty assessment form. Endodontic mishaps related to instrumentation and treatment visits needed to complete the treatment were recorded. Results: Of the 257 teeth included in the study, 141 were instrumented with hand files and 116 with WaveOne files. Eighty-two teeth (31.9%) were registered with at least 1 endodontic mishap. The most frequent endodontic mishap was overinstrumenta- tion (17.5%). This was followed by loss of working length (8.56%), obturation more than 2 mm from the radio- graphic apex (8.56%), overfill with gutta-percha (6.61%), canal transportation (4.28%), instrument sepa- ration (2.33%), and lateral or strip perforation (1.56%). Several endodontic mishaps were significantly correlated. Cases in the high difficulty category had significantly more endodontic mishaps (P < .001) and required more treatment visits (P < .01). There were no significant differences in endodontic mishaps or the number of treat- ment visits between the hand and engine-driven groups. Several endodontic mishaps were associated with signi- ficantly more treatment visits (P < .05). Conclusions: Case difficulty rather than the instrumentation method was the main determinant of endodontic mishaps in the undergraduate clinic. The American Association of Endodontists case difficulty assessment form is an important and valuable tool in undergraduate dental education to predict potential endodontic mishaps and the number of treatment visits. (J Endod 2018;-:1–8) Key Words American Association of Endodontists case difficulty assessment, endodontic mishaps, hand files, procedural errors, reciprocating WaveOne file system, root canal instrumentation I nstrumentation of the root canal system is a difficult task for reasons such as anatomic complexity, accessibility to the root ca- nal orifices, and limitation of the instruments available to obtain optimal results (1). These difficulties often lead to endodontic mishaps that eventually may have an impact on treatment outcome (2–6). To overcome problems associated with instrumentation, nickel-titanium (NiTi) was introduced to endodontic files to improve flexibility (7). This has provided clinicians with flexible hand files and has led to the development of engine-driven rotary and reciprocating instrumentation systems. A newly graduated dentist today is faced with a complex decision when choosing an engine-driven file system from the wide range that is available in the market. Therefore, it is imperative that educational professionals teach instrumentation techniques that prepare students to be competent clinicians and are critical to what is available. Undergraduate students ought to be taught at least 1 engine-driven instrumentation system that is comprehensive, is easy to use, and gives predictable results. It has been claimed that the reciprocating file system provides faster and superior results compared with hand files. Studies have shown that files under reciprocation show significantly higher cyclic fatigue and torsional resistance when compared with NiTi rotary instrumentation, thereby reducing the risk of instrument fracture (8–10). WaveOne (Dentsply Maillefer, Ballaigues, Switzerland) was first introduced as a single-file instrumentation technique with corresponding color-coded paper points and gutta-percha points, which appeared to be easy to use both for students and instructors. In a student clinic, even under clinical supervision of instructors, the occurrence of endodontic mishaps cannot be avoided. It is important that endodontic mishaps are kept to a minimum because they may reflect on the technical quality of root filling, which may eventually have an impact on treatment outcome. On the other hand, patients who require endodontic treatment at the student clinic present with variable levels of difficulties. The American Association of Endodontists (AAE) issued a case difficulty From the *Department of Clinical Dentistry, Faculty of Medicine, University of Bergen, Bergen, Norway; † Public Dental Health Service, Risør, Norway; and ‡ Private practice,  Alesund, Norway. Address requests for reprints to Dr Sivakami Rethnam Haug, Department of Clinical Dentistry, Faculty of Medicine, University of Bergen, Aarstadveien 19, 5009 Bergen, Norway. E-mail address: sivakami.haug@uib.no 0099-2399/$ - see front matter Copyright ª 2018 American Association of Endodontists. https://doi.org/10.1016/j.joen.2018.03.012 Significance This study accentuates the importance and rele- vance of case difficulty assessment. Our results show that the AAE case difficulty assessment form is a valuable tool in undergraduate dental ed- ucation to predict potential endodontic mishaps and the number of treatment visits. Clinical Research JOE — Volume -, Number -, - 2018 Endodontic Mishaps in a Student Clinic 1