Dental Tribune Middle East & Africa Edition | 4/2019 ENDO TRIBUNE A2 Strategies for the treatment of extremely curved root canals By Dr Bernard Bengs, Germany One of the major challenges in endo- dontics is the enormous complexity of root canals. Among other things, a large number of difficulties must be overcome in terms of the num- ber, position, possible branches and curvatures of the canals. Case stud- ies are used to demonstrate how predictable treatment results can be achieved in adverse anatomies too. The aim of root canal preparation is the complete removal of all vital and necrotic tissue, infected canal wall dentine, foreign matter and root filling material. Adequate chemical disinfection should be made possi- ble and shaping should allow wall-to- wall obturation of the canal system. As early as 1974, Herbert Schilder published guidelines on this topic, which have virtually remained un- changed, including the creation of a continuously conical canal shape from the access cavity to the apex, respecting the course of the root ca- nal and maintaining the position of the apical foramen at a size as small as practicable.1 In the presence of very pronounced curvatures, espeially abrupt or even S-shaped (i.e. double) curvatures, it can prove extremely difficult to im- plement these guidelines. The angle of curvature is not the only factor here; the length of the distance af- ter the curvature is also decisive for the demands on the instruments. As the degree of difficulty increases, the risk of step formation, splinting and instrument fracture quite naturally increases. Treatment planning Initial information is provided by the preoperative radiographic image. In complex anatomies, such as those that often occur in the posterior re- gion, a CBCT scan provides valuable information on 3-D curvatures and the confluence of canals.2 This infor- mation is extremely important for treatment planning, as it allows the clinician to determine a strategy re- garding the instruments to be used and canal preparation in advance. For example, very narrow, strongly curved roots should, if applicable, be prepared with a smaller ISO size or a slimmer taper, since even very flexi- ble nickel-titanium (NiTi) file systems become significantly stiffer with in- creasing dimensions, which entails unwanted transportation or even strip perforations as risks. Each case should be considered individually to allow sufficient removal of infected tissue without risking unwanted ex- cessive removal of dentine. Fig. 1: Pre-op radiograph of tooth #25 Fig. 2: Trepanation Fig. 3: The untwisted PathFile after use in the canal. In vital cases, the size of the prepara- tion may be more moderate than in cases of pulp necroses or revisions, as less removal of dentine will be required here. Ultimately, of course, the treatment size should be de- termined by apical gauging (apical measurement). As this is only practi- cable to a limited extent in the case of very extreme, even opposing curvatures, even more attention should be paid to tactile feedback during instrumental canal prepara- tion. Sufficient preparation is always required for root canal irrigation and subsequent obturation so that a shape of at least size 30.04, or better of size 30.06 or 35.06 (rarely larger in the case of strong curvatures), which is usually required in extreme cases, must be prepared manually using the step-back technique. Otherwise, it will not be possible to achieve suf- ficient disinfection and filling of the root canal. Notes on preparation The preparation of an optimal pri- mary and secondary access cavity is extremely important, particularly in the case of strong curvatures. There- fore, a most straightline access to the canal system is very important, as otherwise steps or blockages are cre- ated right at the beginning of treat- ment that can only be corrected with great difficulty. First, the course of the canal should be probed with an ISO size 6, 8 or 10 scouting file, if necessary, after coro- nal pre-flaring with an orifice shaper or Gates–Glidden drill. Irrespective of the file system used, the prepara- tion of a glide path is essential for safe canal preparation. Particularly in the case of strongly curved, nar- row canals, the use of rotary NiTi glide path files is not only less prone to complications than with manual instruments, but also more comfort- able. The gliding space created allows Fig. 4: Radiographic measurement Fig. 5: The HyFlex CM file sequence a significantly lower-risk use of the following rotary NiTi files for canal preparation.3 The point of confluence of canals represents a special case of curva- ture, as this often occurs particularly abruptly. It, therefore, makes sense, for example in the case of two canals in the mesial root of a mandibular first molar, to initially prepare only one canal fully to its working length. This will often be the mesiolingual canal. To determine the confluence, a gutta-percha point is then posi- tioned in the prepared canal and a Kerr file is inserted into the other canal. The marking of the instru- ment tip in the gutta-percha point determines the length up to which the second canal must now be pre- pared. This avoids risky stressing of the instruments, as well as the un- necessary removal of dentine. Fur- thermore, the chemical preparation of the canal system is an indispen- sable part of the preparation, since only part of the canal wall surface is addressed during mechanical prepa- ration. Case 1: Pulp necrosis in an S-shaped canal In November 2013, a 46-year-old emergency patient with acute symp- toms of tooth #25 presented. The tooth had been restored with a ce- ramic inlay, the sensitivity test for cold was negative, and the tooth was sensitive to percussion and pressure. The preoperative radiograph re- vealed periapical periodontitis (Fig. 1). The diagnosis was pulp necrosis after a previous preparation close to the pulp. The inlay was removed and an adhesive pre-endodontic build- up was fabricated from composite. During trepanation, pus drained from the canal entrances. Working length was then determined, fol- lowed by initial preparation with Kerr files up to only ISO size 8, for time reasons, together with inter- mittent irrigation with heated 6% sodium hypochlorite (NaOCl). Sub- sequently, a drug deposit was insert- ed by rotating in Ledermix. Owing to the small preparation size, the use of calcium hydroxide would only have been possible to a limited extent. Root canal therapy was continued approximately six weeks later: after anaesthesia and placement of a rub- ber dam, tooth #25 was trepanned under the microscope (Fig. 2). The glide path was first prepared manu- ally with C+ Files of ISO sizes 6 and 8 (Dentsply Maillefer), then mechani- cally with PathFiles of size 13, 16 and 19 (Dentsply Maillefer). The more flexible HyFlex Glidepath files (COL- TENE) were not yet available at the time of treatment. A detailed image of the brand-new PathFile illustrated how extremely the S-shaped canal configuration had stressed the rota- ry NiTi instruments after a single use (Fig. 3). It depicted the plastic defor- mation of the instrument, a clear in- dication that this instrument could only withstand the requirements with good fortune. A fractured in- strument would certainly have been within the realms of possibility. After radiographic confirmation of the working length, the canals were prepared with the HyFlex CM (con- trolled memory) NiTi files (COLTENE; Figs. 4 & 5). The following sequence was used: 15.04, 20.04, 20.06, 25.04, 25.06, 30.04 and 30.06. Intermit- tent irrigation was again per- formed with heated 6% NaOCl. ÿPage A3 Fig. 6: The master point image Figs. 7 & 8: Root canal filling and check of tooth #25