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| CE article instrumentation and obturation Canal preparation and obturation: An updated view of the two pillars of nonsurgical endodontics Author: Dr Ove A. Peters, USA CE credit This article qualifies for CE credit. To take the CE quiz, log on to www. dtstudyclub.com. Click on ‘CE arti- cles’ and search for this edition of the magazine. If you are not regis- tered with the site, you will be asked to do so before taking the quiz. 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 obtu- ration 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 practices in the two pillars of non-surgical endodon- tics, canal preparation and obturation, and to high- light strategies for decision making in both uncompli- cated and more difficult endodontic cases. ing major preparation errors, such as perforations, canal transportations, instrument fractures or un- necessary removal of tooth structure. The introduc- tion of nickel-titanium (NiTi) instruments to endo- dontics almost two decades ago2 has resulted in dramatic improvements for successful canal prepa- ration for generalists and specialists. Today, there are more than 50 canal preparation systems; how- ever, not every instrument system is suitable for every clinician and not all cases lend themselves to rotary preparation. Prior to initiating therapy, a clinician must establish a diagnosis, take a thorough patient history and conduct clinical tests. Recently, judicious use of cone beam computed tomography (CBCT) has augmented the clin- ically available imaging modalities. Verifying the mental image of canal anatomy goes a long way to promote success in canal preparation. For example, a missed ca- nal is frequently associated with endodontic failures.1 As most maxillary molars have two canals in the mesiobuccal root, case referral to an endodontist for microscope-supported treatment should be consid- ered. Endodontists are increasingly using CBCT and the operating microscope to diagnose and treat ana- tomically challenging teeth, such as those with unu- sual root anatomies, congenital variants or iatrogenic alteration. The endodontic specialist, using appropri- ate strategies, can achieve good outcomes even in cases with significant challenges (Fig. 1). Preparation of the endodontic space The goal of canal preparation is to provide ade- quate access for disinfecting solutions without mak- Several key factors have added versatility in this regard, for example, the emergence of special designs such as orifice shapers and mechanised glide path files. Another recent development is the application of heat treatment to NiTi alloy, both before and after the file is manufactured. Deeper knowledge of met- allurgical properties is desirable for clinicians who want to capitalise 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 reversibly in two conformations, martensite and austenite, depending on external tension and ambient temperature. While steel allows 3 % elastic deformation, NiTi in the aus- tenitic form can withstand deformations of up to 7 % without permanent damage or plastic deformation.4 Knowing this is critical for rotary endodontic instru- ments for two reasons. First, during preparation of curved canals, forces between the canal wall and 16 roots 3 2017