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Dental Tribune Middle East & Africa Edition | 5/2017 ◊Page 8 while maintaining apical sizes o support antimicrobial effica- cy. There currently is no direct clinical evidence to support this strategy but it is clear that root fractures pose problems in the long-term outcomes of our patients. Another recent development is the emer- gence of certain specialized rotaries, such as dedicated ori- fice shapers and so-called glide path files. The orifice shapers have larger tapers, such as .08, which means that they are not flexible and can overpre- pare at the canal orifice level. Glide path files, for example PathFiles® and ProGlider® (Dentsply Sirona), are delicate instruments and may fracture when used incorrectly. It is recommended to use a small K-file (size #10) before any rotary instrumentation and to use a delicate touch. Clinical results While results from in vitro studies on rotary systems are abundant, clinical studies on these instruments are sparse. Comparing NiTi and stain- less steel K-files, Pettiette et al.7 found less canal transportation and fewer gross preparation errors such as strip perforations. Subsequently, using radiographic evaluation of the same patient group, they demonstrated better healing in the NiTi group.22 An earlier outcome study with three rotary preparation paradigms did not show any difference between the three systems with an overall favorable outcome rate of about 87 percent.23 The most consistent clinical results are obtained when the manufactur- er’s directions are followed. While these vary by instrument, a set of common rules applies to root ca- nal preparation. Root canal systems are best prepared in the following sequence: • Analysis of the specific anatomy of the case. • Canal scouting. • Coronal modifications. • Negotiation to patency. • Determination of working length. • Glide path preparation. • Root canal shaping to desired size. • Gauging the foramen, apical ad- justment. Obturation of the endodontic space A well-shaped and cleaned canal sys- tem should create the conditions for intact periapical tissues. On the other hand, this root canal system is inac- cessible to the body’s immune sys- tem and therefore it cannot combat coronal leakage. Accordingly, best practices dictate that root canals should be filled as completely as pos- sible to prevent ingress of nutrients or oral microorganism. None of the established techniques for root canal filling provides a defin- itive coronal, lateral and apical seal.24 Basic strategies in root canal obturation Ideally, root canal fillings should seal all foramina leading to the periodon- tium, be without voids, adapt to the instrumented canal walls and end at working length. There are various ac- ceptable materials and techniques to obturate root canal systems, includ- ing: • Sealer (cement/paste/resin) only. • Sealer and a single cone of a stiff or flexible core material. • Sealer coating combined with cold compaction of core materials. • Sealer coating combined with warm compaction of core materials. • Sealer coating combined with carri- er-based core materials. Several of these techniques have shown comparable success rates re- Fig. 4: Root canal treatment of tooth #15 with four ca- nals, diagnosed with irreversible pulpitis and acute api- cal periodontitis. The tooth was restored with a crown immediately after finalizing the root canal treatment. Case courtesy of Dr. Reza Hamid the more coronal is more vulnerable to file fracture. Instrument handling has been shown to be associated with file frac- ture. For example, a lower rotational speed (~250 rpm) results in delayed build-up of fatigue12 and reduced in- cidence of taper lock.13 Material imperfections such as mi- crofractures and milling marks are believed to act as fracture initiation sites.14 Such surface imperfections af- ter manufacturing can be removed by electropolishing but it is unclear if this process extends fatigue life.15 Manufacturers’ recommendations stress that rotaries should be ad- vanced with very light pressure; however, recommendations differ with regard to the way the instruments are moved. A typical recommendation is to move the in- strument into the canal gently in an in-and-out motion for three to four cycles, directed away from the fur- cation, then withdraw to clean the flutes. It is difficult to determine exactly the apically exerted force in the clinical setting; experiments have suggested that forces start at about 1 Newton (N) and range up to 5 N.16 Precise torque limits have been discussed as a means to reduce failure. Most clinicians use torque-controlled mo- tors, which are based on presetting a maximum current for a DC electric motor. To reduce friction, manufacturers often recommend the use of gel- based lubricants in dentin; how- ever, such lubricants have not been shown to be beneficial and actually did increase torque for radial-landed ProFile® instruments.17 Therefore, it is recommended to flood the canal system with sodium hypochlorite (NaOCl) during the use of rotaries. The best way to do this is to create an access cavity that can act as a reser- voir (Fig. 3). There are several concerns about reusing NiTi instruments. The effec- tiveness of disinfection procedures is not clear. It has been shown that protein particles cannot completely be removed from machined nickel- titanium surfaces.18 Moreover, it is clear that with additional usage, the chance for instrument fracture in- creases. Current recommendations advise that clinicians are judicious when reusing rotary instruments as there is no conclusive evidence of disease transmission occurring. Recently, the term minimally inva- sive endodontics has been used to describe smaller-than-usual apical sizes and, perhaps more important- ly, an understanding that the long- term success of root canal-treated teeth will improve by retaining as much dentin structure as feasible.3 The thought process for this was the finding that most root-canal treated teeth survive 10 years and longer.19 In studies, the reasons cited for the extraction vary but in many cases teeth are either fractured or non-re- storable for other reasons.20,21 In consequence, a smaller coronal dimension of rotaries is considered mCME garding apical bone fill or healing of periradicular lesions, so a clinician may choose from a variety of tech- niques and approaches that works best for him or her. Existing research directs clinicians toward preparation and disinfection of the root canal as the single most important factor in the treatment of endodontic patho- sis, and no particular sealing tech- nique can claim superior healing success.25 Current developments in root canal obturation materials After the introduction of MTA (min- eral trioxide aggregate) as a mate- rial for perforation repair and api- cal surgery more than two decades ago, materials with similar bioactive properties now are available as root canal sealers. Bioceramic root canal cement (BC Sealer™, Brasseler) has clinically acceptable radiopacity and flow.26 Moreover, it is well-tolerated in cell culture experiments.27 How- ever, there is no clinical evidence that using this cement leads to bet- ter outcomes. In fact, most research has indicated the type of cement used has com- paratively 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 9 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. Editorial note: A complete list of refer- ences is available from the publisher and also at www.aae.org/colleagues. This article originally appeared in ENDODONTICS: Colleagues for Ex- cellence, Fall 2016. Reprinted with permission from the American Asso- ciation of Endodontists, ©2016. The AAE clinical newsletter is available at www.aae.org/colleagues. 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. 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 compaction, electrically heated pluggers are used to melt a master cone fitted to length. Tapered gutta-percha cones opti- mize the hydraulic forces that arise during compaction of softened gut- ta-percha with pluggers of a similar taper. After fitting the master 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 below the pulpal floor, leaving a small dim- ple. 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 protect- ed with an orifice barrier (Fig. 3) to protect from leakage prior to place- ment of a definitive restoration.32 This has been shown to promote healing of apical periodontitis.33 Materials that are suitable for such a barrier include light-curing glass ionomers, flowable composites or fissure sealants. In order to facilitate retreatment if necessary, such a bar- rier 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 appears that filling acces- sory canals is not predictable and not per se a prerequisite 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