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ePaper created 2016-05-18, 11:28:18 | version 1.38.0
| technique canal preparation and filling 28 roots 2 2016 of the greater dimensions of the cone in the middle or coronal part. This could be considered GP taper lock. This is a different problem to that experienced by dentistsinthepast,whichwasmainlyrelatedtocone fitting in the apical part, and consequently requires a different approach. Choosing a cone with a smaller tip size may not solve the problem, while choosing a smaller-taperconemaysignificantlyincreasetherisk of iatrogenic errors such as underfilling and overex- tension of the cone through the apical foramen, be- causethetug-backinthecoronalpartdoesnotallow for correct fitting of the apical part of the cone. Therefore, the best and easiest solution is to choose brand-associated GP cones that precisely fit the root canal preparation achieved by the specific NiTi instruments and allow for ideal 3-D filling and good apical tug-back. However, with the K3XF sys- tem,clinicianscouldusebothtypesofcones(i.e.,the 0.04–0.06 cones or TF/TFA cones) because they will both fit the root canal preparation in the apical and middle thirds well, where tug-back and 3-D match- ing are more critical. More clinical hints Thus far, dimensions and sizes have been dis- cussed to help clinicians understand the difficulties in matching instruments and cones. However, there are also clinical ways to seek to solve problems en- counteredduringtheseprocedures.Thefollowingad- vicemaybeusefulforbothinstrumentswithnonuni- form tapers and many instrumentation techniques. Create greater coronal flaring If a GP cone does not perfectly match the root ca- nalpreparationandthusdoesnotreachtheworking length,onepossiblesolutionistoincreasethecoro- nalflaringbybrushingwiththelastinstrumentused. By doing so, the NiTi instrument will increase the di- mensions of the prepared canal in the coronal part, solving the problem of GP taper lock. Ensure correct apical fit Clinicians may experience two different clinical problems in the apical fit: the need for a better apical tug-back, which may require slightly cutting the tip of the master cone, and the fit related to the amount of canal transportation. The first situation may occur when, owing to the different dimensional tolerance, aGPconeisslightlysmallerthanthenominalsize,in- creasing the risk of overfilling during obturation. In such a case, the advice is to increase the dimensions of the master cone slightly by cutting 0.5–1 mm off the tip, or ideally to recalibrate the master cone pre- cisely using a tip-snip device. This can also occur if a canal is slightly overinstrumented (e.g., owing to an errorindeterminationoftheworkinglengthorinthe position of the rubber stop on the file). In such a sit- uation, the apical constriction would have been modifiedandtheconefitwouldhavetocompensate fortheerrorbyincreasingthetipsizeoftheGPmas- ter cone. Some NiTi instruments (HyFlex; TFA; TRUShape, DENTSPLY; NEONITI, NEOLIX; etc.) are significantly more flexible than the majority of competing NiTi ro- tary instruments. As a consequence, they tend to fol- low and maintain the original trajectory of the root canals more precisely, minimizing canal transporta- tion. Canal transportation frequently occurs when a rigid file is inserted into a curvature and tends to straighten it by cutting more in the inner part of the curvature coronally and in the outer part apically. However, this error, which can affect the quality of debridement, makes insertion of master GP cones easier, especially when complex, double or triple cur- vatures are present. For this reason, clinicians using suchflexibleNiTiinstrumentsmayexperienceslightly more difficult insertion of the master GP cone to the working length. If this problem occurs, once again slightly increasing flaring by circumferential filing can help. Conclusion Itmaybeconcludedthatclinicianswhouseinstru- mentswithnonuniformtapersorwithreducedwork- ing parts should preferably use brand associated GP cones that perfectly match with the prepared canals. Bydoingso,fittingthemasterGPconebecomesmuch easier and more predictable. In the very few cases in which problems still arise, the clinical hints provided may help practitioners to understand the problem and find a proper solution._ about Prof.Gianluca Gambarini is Professor of Endodontics at the Sapienza University of Rome’s dental school.He is an international lecturer and researcher,and actively collaborates with a number of manufacturers all over the world to develop new technolo- gies,operative procedures and materials for root canal treatment.Prof.Gambarini also works in a private endodontics practice in Rome. 22016