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14 ◊Page 13 indicated the type of cement used has comparatively little impact.28 In contemporary practice, heat gen- erators are used to plasticize gutta- percha. Additionally, cordless heat- ing devices are available. Another recent addition is a carrier-based material, Guttacore® (Dentsply Si- rona), which uses modified gutta- percha materials instead of plastic as its base. Early data indicate that obturation with this new material is similar to warm vertical compaction or lateral compaction.29 Practical aspects of obturation The main steps in the sequence of root canal obturation are: • Choosing a technique and timing the obturation. • Selecting master cones. • Canal drying, sealer application. • Filling the apical portion (lateral and vertical compaction). • Completing the fill. • Assessing the quality of the fill. The root canal system should be as- sessed before choosing an obtura- tion technique. In the presence of open apices or procedural errors such as apical zipping and also for teeth with apices in close proxim- ity to the mandibular canal, there is significant potential for overfills. In order to avoid such mishaps, these cases may be better obturated with cold lateral condensation to avoid overfilling, or in some cases, MTA may be placed as a barrier. In general, canals should be filled only when there are no symptoms of acute apical periodontitis or an api- cal abscess, such as significant pain on percussion or not dryable due to secretion into the canal. Gutta-per- cha cones first should be disinfected by submerging them in an NaOCl so- lution for about 60 seconds. In addition to a solid filler such as gutta-percha, a sealer or cement should be used. Most sealers are toxic in the freshly mixed state, but this toxicity is reduced after setting. When in contact with tissues and tissue fluids, zinc oxide eugenol- based sealers are absorbable while resin-based materials typically are not absorbed.30 Some by-products of sealers may adversely affect and de- lay healing. Therefore, sealers should not be routinely extruded into the periradicular tissues. The appropriate amount of sealer is then deposited into the canal system. This may be done using a lentulo spiral, a K-file or the master cones themselves; each method is acceptable, provided that an appro- priate amount of sealer is deposited. If the master cones are the carrier for the sealer, they should be removed and inspected for a complete coating with sealer and then replaced in the canal. The master cones are placed close to working length using a slight pump- ing motion to allow trapped air and the excess sealer to flow in a coronal direction. The marking on the cone should be close to the coronal refer- ence point for working length deter- mination. For lateral compaction, a preselected finger spreader is then slowly inserted alongside the master cone to the marked length and held with measured apical pressure for about 10 seconds. During this proce- dure, the master cone is pushed lat- erally and vertically as the clinician feels the compression of the gutta- percha. Rotation of the spreader around its axis will disengage it from the gutta-percha mass and facilitate removal from the canal. mCME Dental Tribune Middle East & Africa Edition | 2/2018 The space created by the spreader is filled by inserting a small, lightly sealer-coated accessory gutta-percha cone. Using auxiliary cones larger than the taper of the spreader will produce voids or sealer pools in the filling and should be avoided. The procedure is repeated by inserting several gutta-percha cones until the entire canal is filled. For vertical com- paction, electrically heated pluggers are used to melt a master cone fit- ted to length. Tapered gutta-percha cones optimize the hydraulic forces that arise during compaction of sof- tened gutta-percha with pluggers of a similar taper. After fitting the mas- ter cone as before, different hand pluggers and heated pluggers are placed into the root canal to verify a fit to within 5 to 7 mm of the apical constriction. For both lateral and vertical compac- tion the gutta-percha mass in each canal should end about 1 mm be- low the pulpal floor, leaving a small dimple. In cases where placement of a post is planned, guttapercha is confined to the apical 5 mm.31 All root canals that do not receive a post may be protected with an orifice bar- rier (Fig. 3) to protect from leakage prior to placement of a definitive restoration.32 This has been shown to promote healing of apical periodon- titis.33 Materials that are suitable for such a barrier include light-curing glass ionomers, flowable composites or fissure sealants. In order to facili- tate retreatment if necessary, such a barrier should be thin so that the gutta-percha fill is just visible. Radiographic appearance of filled root canal systems Prepared and filled canals should demonstrate a homogenous ra- diopaque appearance, free of voids and filled to working length. The fill should approximate canal walls and extend as much as possible into ca- nal irregularities such as an isthmus or a c-shaped; canal system. This is difficult to achieve clinically and frequently requires the clinician to use a thermoplastic obturation tech- nique. This complicated procedure may benefit from the use of the den- tal 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 lo- cations such as the furcation. It has been well established that accessory anatomy may contribute to periapi- cal periodontitis34 but clinical experi- ence suggests the role of accessory anatomy in causing bone resorption is comparatively small. Indeed, it ap- pears that filling accessory canals is not predictable and not per se a pre- requisite for success.35 In order to avoid overextension of root filling material into the peri- apical tissue, specifically in the man- dibular 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 anat- omy is often difficult. It may be ap- propriate 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 gen- eral, undesirable and uncorrectable outcomes of root canal treatment, identifiable on the final radiograph, include: • Excessive dentin removal during access and instrumentation. • Preparation errors such as perfora- tion, ledge formation and apical zip- ping. • Presence of an instrument frag- ment in not fully disinfected canals. • Obturation material overfill and overextension. Each of these outcomes must be doc- umented 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 con- temporary instruments is a predict- able 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 suc- cessfully in routine practice, the ad- ditional training, expertise and tech- nology of endodontists is necessary in cases that are beyond the typical spectrum. The best long-term out- comes 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 methods, 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 perma- nently harm a patient. The absence of gross errors that are associated with persistent presence of bacterial infection and excessive dentin re- moval during access and canal prep- aration have the greatest impact on outcomes. References 1. Karabucak B, Bunes A, Chehoud C, Kohli MR, Setzer F. Prevalence of api- cal periodontitis in endodontically treated premolars and molars with untreated canal: A cone-beam com- puted tomography study. J Endod 2016;42:538-41. 2. Walia H, Brantley WA, Gerstein H. An initial investigation of the bending and torsional properties of nitinol root canal files. J Endod 1988;14:346-51. 3. Gluskin AH, Peters CI, Peters OA. Minimally invasive endodontics: challenging prevailing paradigms. Br Dent J 2014;216:347-53. 4. Thompson SA. An overview of nickel-titanium alloys used in den- tistry. Int Endod J 2000;33:297-310. 5. Shen Y, Zhou HM, Zheng YF, Peng B, Haapasalo M. Current challenges and concepts of the thermomechan- ical treatment of nickel-titanium instruments. 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Reprinted with permission from the American Association of Endodontists Dr Ove A. Peters Dr Peters was award- ed a degree in den- tistry (Dr med dent) from the University of Kiel, Germany, in 1990. After two years in the Department of Neurophysiology at the University of Kiel, he served as an as- sistant professor of prosthodontics at the University of Heidelberg, Germany, from 1993 to 1996. Peters received post-grad- uate endodontic training at Zurich Uni- versity Dental School (1997-2001) and at the University of California, San Francisco (2004-2006). He was an associate pro- fessor and head of the faculty practice in restorative dentistry at the University of Zurich from 1996 to 2001. Peters also earned a certificate in endo- dontics and MS certificate in oral biol- ogy 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 Fran- cisco, and the director of the Advanced Euducation Program in Endodontology. His main scientific interests are the perfor- mance 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 interna- tionally. He has written multiple chapters in leading textbooks and serves on the re- view panels and editorial boards of high- impact endodontic journals. He may be contacted at opeters@pacific.edu.