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8 mCME Dental Tribune Middle East & Africa Edition | 5/2017 Canal preparation and obturation: An updated view of the two pillars of nonsurgical endodontics mCME articles in Dental Tribune have been approved by: HAAD as having educational content for 1 CME Credit Hour DHA awarded this program for 1 CPD Credit Point CAPP designates this activity for 1 CE Credit By Ove A. Peters, USA The ultimate goal of endodontic treatment is the long-term retention in function of teeth with pulpal or periapical pathosis. Depending on the diagnosis, this therapy typically involves the preparation and obtura- tion of all root canals. Both steps are critical to an optimal long-term outcome. This article is intended to update clinicians on the current understanding of best prac- tices in the two pillars of nonsurgical endodontics, canal preparation and obturation, and to highlight strate- gies for decision making in both uncomplicated and more diffi cult endodontic cases. Prior to initiating therapy, a clini- cian must establish a diagnosis, take a thorough patient history and conduct clinical tests. Recently, judi- cious use of cone-beam computed tomography (CBCT) has augmented the clinically available imaging mo- dalities. Verifying the mental image of canal anatomy goes a long way to promote success in canal prepa- ration. For example, a missed canal frequently is associated with endo- dontic failures.1 As most maxillary molars have two canals in the mesiobuccal root, case referral to an endodontist for microscope-supported treatment should be considered. Endodontists are increasingly using CBCT and the operating microscope to diagnose and treat anatomically challenging teeth, such as those with unusual root anatomies, congenital variants or iatrogenic alteration. The endo- dontic specialist, using appropriate strategies, can achieve good out- comes even in cases with signifi cant challenges (Fig. 1). Preparation of the endodontic space The goal of canal preparation is to provide adequate access for disin- fecting solutions without making major preparation errors such as perforations, canal transportations, instrument fractures or unnecessary removal of tooth structure. The in- troduction of nickel-titanium (NiTi) instruments to endodontics almost two decades ago2 has resulted in dramatic improvements for success- ful canal preparation for generalists and specialists. Today there are more than 50 canal preparation systems; however, not every instrument sys- tem is suitable for every clinician and not all cases lend themselves to rotary preparation. Several key factors have added versa- tility in this regard, for example, the emergence of special designs such as orifi ce shapers and mechanized glide path fi les. Another recent de- velopment is the application of heat mCME SELF INSTRUCTION PROGRAM CAPPmea together with Dental Tribune provides the opportunity with its mCME - Self Instruction Program a quick and simple way to meet your continuing education needs. mCME offers you the fl exibility to work at your own pace through the material from any location at any time. The content is international, drawn from the upper echelon of dental medicine, but also presents a regional outlook in terms of perspective and subject matter. Membership Yearly membership subscription for mCME: 1,100 AED One Time article newspaper subscription: 250 AED per issue. After the payment, you will receive your membership number and allowing you to start the program. Completion of mCME • • • • • • • • mCME participants are required to read the continuing medical education (CME) articles published in each issue. Each article offers 2 CME Credit and are followed by a quiz Questionnaire online, which is available on www.cappmea.com/ mCME/questionnaires.html. Each quiz has to be returned to events@cappmea.com or faxed to: +97143686883 in three months from the publication date. A minimum passing score of 80% must be achieved in order to claim credit. No more than two answered questions can be submitted at the same time Validity of the article – 3 months Validity of the subscription – 1 year Collection of Credit hours: You will receive the summary report with Certifi cate, maximum one month after the expiry date of your membership. For single subscription certifi cates and summary reports will be sent one month after the publication of the article. The answers and critiques published herein have been checked carefully and represent authoritative opinions about the questions concerned. Articles are available on www.cappmea.com after the publication. For more information please contact events@cappmea.com or +971 4 3616174 FOR INTERACTION WITH THE AUTHORS FIND THE CONTACT DETAILS AT THE END OF EACH ARTICLE. treatment to NiTi alloy, both before and after the fi le is manufactured. Deeper knowledge of metallurgical properties is desirable for clinicians who want to capitalize on these new alloys. Finally, more recent strategies such as minimally invasive endo- dontics have emerged.3 Basic nickel titanium metallurgy What makes NiTi so special? It is highly resistant to corrosion and, more importantly, it is highly elastic and fracture-resistant. NiTi exists re- versibly in two conformations, mar- tensite and austenite, depending on external tension and ambient tem- perature. While steel allows 3 per- cent elastic deformation, NiTi in the austenitic form can withstand defor- mations of up to 7 percent without permanent damage or plastic defor- mation.4 Knowing this is critical for rotary endodontic instruments for two reasons. First, during prepara- tion of curved canals, forces between the canal wall and abrading instru- ments are smaller with more elastic instruments, hence less preparation errors are likely to occur. Second, rotation in curved canals will bend instruments once per rotation, which ultimately will lead to work hardening and brittle fracture, also known as cyclic fatigue. Steel can withstand up to 20 complete bend- ing cycles, while NiTi can endure up to 1,000 cycles.4 Recently manufacturers have learned to produce NiTi instruments that are in the martensitic state and even more fl exible than previous fi les. Figure 2 shows how instrument conditions (austenite vs. martensite) are determined in the testing labora- tory, using prescribed heating and cooling cycles.5 Heat-treated fi les with high martensite content typi- cally do not have a silver metallic shade but are colored due to an ox- ide layer, such as gold or blue. It is important to note that CM fi les frequently deform; however, with a delicate touch, cutting is adequate and often even superior to con- ventional NiTi instruments.6 It is imperative for clinicians to retrain themselves prior to using these new instruments to avoid excessive de- formation and subsequent instru- ment fracture. in Preparation strategies Experimental and clinical evidence suggests that the use of NiTi in- struments combined with rotary movement results improved preparation quality. Specifi cally, the incidence of gross preparation errors is greatly reduced.7 Canals with wide oval or ribbon-shaped cross-sections present diffi culties for rotary instru- ments and strategies such as cir- cumferential fi ling and ultrasonics should be used in those canals. Studies found that oscillating instru- ments recommended for these canal types did not perform as well,8 par- ticularly in curved canals. Specifi c instruments developed to address these challenges include the Self-Adjusting File (SAF) System (ReDent- NOVA, Raana), TRUShape® (Dentsply Sirona, Tulsa, Okla.) and XP Endo® (Bras- seler, Savannah, Ga.). How- ever, there is no direct clinical evidence that these instruments lead to better outcomes. Canal transportation with contemporary NiTi ro- taries, measured as un- desirable changes of the canal center seen in cross- sections of natural teeth, is usually very small. This indicates that canal walls are not excessively thinned and apical canal paths are only minimally straight- ened (Fig. 1), even when pre- paring curved root canals. While preparation usually removes dentin somewhat preferentially toward the outside of the curvature,9 current NiTi instruments, including reciprocating fi les, can enlarge the canal path safely while minimiz- ing procedural errors. Almost all current rotaries are non-landed, meaning they have sharp cutting edges, and they can be used in lateral action toward a specifi c point on the perim- eter. This “brushing” action allows the clinician to ac- tively change canal paths away from the furcation in the coronal and middle thirds of the root canal10 but may create apical ca- nal straightening when taken beyond the apical constriction. Circumferen- tial engagement of canal walls by active instruments may lead to a threading-in effect, but contemporary rotaries are designed with variable pitch and helical angle to counteract this tendency. An important design ele- ment for all contemporary rotaries is a passive, non- cutting tip that guides the cutting planes to allow for more evenly distributed dentin removal. Rotaries with cutting, active tips such as dedicated retreat- ment fi les should be used with caution to avoid prep- aration errors. NiTi instrument usage As a general rule, fl exible instruments are not very resistant to torsional load but are resistant to cyclic fa- tigue. Conversely, more rig- id fi les can withstand more torque but are susceptible to fatigue. The greater the amount and the more pe- Fig. 1: Root canal treatment of tooth #3 diagnosed with pulp necrosis and acute apical periodontitis. The me- siobuccal root has a signifi cant curve and two canals with separate apical foramina. Case courtesy of Dr. Jeffrey Kawilarang. (Photos/Provided by American Association of Endodontists) Fig. 2: Behavior of controlledmemory nickel-titanium ro- taries compared with standard instruments. Shown are data from Typhoon Differential scanning calorimetry, which document the transition between austenite and martensite at about 5 degrees C for standard NiTi and at about 25 degrees C for controlled-memory (CM) alloy (A). At room temperature, this results in a drastically increased fatigue lifespan (B). Image A modifi ed and reprinted with permission from Shen et al.J Endod 2011; 37:1566-1571 Fig. 3: Root canal treatment of tooth #19 with four canals diagnosed with irreversible pulpitis and acute apical peri- odontitis. A second canal in the distal root of a mandibular molar is not infrequent. Note multiple apical foramina in both the mesial and the distal apices. Prior to temporiza- tion, the orifi ces were protected with a barrier of lightcur- ing glass ionomer. Case courtesy of Dr. Paymon Bahrami. ripheral the distribution of metal in the cross sec- tion, the stiffer the fi le.11 Therefore, a fi le with greater taper and larger diameter is more susceptible to fatigue failure; moreover, a canal curvature that is ÿPage 9