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C.E. article_ instrumentation and obturation I canal system. This is difficult to achieve clinically and frequently requires the clinician to use a thermoplas- tic obturation technique. This complicated procedure may benefit from the use of the dental operating microscope. Other anatomical spaces that may be filled include accessory canals that are most common in the apical root third (Fig. 3, mesial and distal root) but may be found in other locations such as the furcation. It has been well established that accessory anatomy may contribute to periapical periodontitis34 but clinical experience suggests the role of accessory anatomy in causing bone resorption is comparatively small. Indeed, it appears that filling accessory canals is not predictable and not per se a prerequisite for success.35 In order to avoid overextension of root filling material into the periapical tissue, specifically in the mandibular canal, it is recommended to accurately determine working length to prevent destruction of the apical constriction. For infected root canal systems, it seems that the best healing results are achieved when the working length is slightly short of the tip of the root, as visible on a radiograph.25, 36 Determination of apical canal anatomy is often difficult. It may be appropriate for second mandibular molars that are in close proximity to the mandibular canal to be referred to a specialist. Overfills are not only an impediment to healing but in the worst case can be associated with permanent nerve damage. In general, undesirable and uncorrectable outcomes of root canal treatment, identifiable on the final radio- graph, include: • Excessive dentin removal during access and instrumentation. •Preparationerrorssuchasperforation,ledge formation and apical zipping. •Presenceofaninstrumentfragmentinnotfully disinfected canals. •Obturationmaterialoverfillandoverextension. Each of these outcomes must be documented and the patient notified as they may reduce the likelihood of a successful outcome. In cases such as par- or dysesthesia after an overfill, immediate referral to a surgeon is indicated. _Summary and conclusions Root canal preparation with contemporary in- struments is a predictable procedure in most cases for a well-trained clinician following established guidelines. Cases with a recognized high degree of difficulty are best referred to an endodontist. While many cases can be treated successfully in routine practice, the additional training, expertise and tech- nology of endodontists is necessary in cases that are beyond the typical spectrum. The best long-term outcomes are obtained when a correctly planned final restoration is placed as soon as possible after root canal treatment is completed (Fig. 4). Root canals may be filled through various meth- ods, typically using a combination of a cement and a solid filling material such as gutta-percha. The specific obturation material used appears to have a smaller role on outcomes. Overfills, particularly into the area of the inferior alveolar nerve, have the potential to permanently harm a patient. The absence of gross errors that are associated with persistent presence of bacterial infection and excessive dentin removal during access and canal preparation have the greatest impact on outcomes._ This article originally appeared in ENDODONTICS: Colleagues for Excellence, Fall 2016. Reprinted with permission from the American Association of Endo- dontists, ©2016. The AAE clinical newsletter is avail- able at www.aae.org/colleagues. A complete list of references is available from the publisher and also at www.aae.org/colleagues. _about the author roots Dr. Ove A. Peters was awarded a degree in den- tistry (Dr. med dent) from the University of Kiel, Germany, in 1990. After two years in the Department of Neuro- physiology at the University of Kiel, he served as an assistant professor of pros- thodontics at the University of Heidelberg, Germany, from 1993 to 1996. Peters received post-graduate endodontic training at Zurich Uni- versity Dental School (1997-2001) and at the University of California, San Francisco (2004-2006). He was an associ- ate professor and head of the faculty practice in restorative dentistry at the University of Zurich from 1996 to 2001. Peters also earned a certificate in endodontics and MS certificate in oral biology from UCSF and was board certified in endodontics in 2010. He received the Louis I. Grossman Award in 2012. Peters is currently a tenured professor and co-chair of the Department of Endodontics at the Arthur A. Dugoni School of Dentistry at the University of the Pacific, San Francisco, and the director of the Advanced Euducation Program in Endodontology. His main scientific interests are the performance of root canal instruments assessed by mechanical testing methods, three-dimensional imaging and the efficacy of antimicrobial regimes in root canal treat- ment. More recently, he became involved in endodontic biology and now runs a dental stem cell biology laboratory. Peters has published more than 100 papers in peer-reviewed journals and has lectured extensively both nationally and internationally. He has written multiple chapters in leading textbooks and serves on the review panels and editorial boards of high-impact endodontic journals. He may be contacted at opeters@pacific.edu. roots 1_ 2017 I 11