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ePaper created 2016-03-11, 23:13:06 | version 1.38.0
issue 2016 — 63 Endodontics Article Fig. 1 Comparison of instruments and cones with uniform and nonuniform tapers. standardized GP cones with feathered tips. For this reason, specific calipers and instruments to cut GP cones precisely were developed. With the introduction of GP cones of greater tapers, a problem related also to the taper arose. These new GP cones can be grouped into two categories: uniform and nonuniform taper. The former cones are usually marketed as 0.04- or 0.06- tapered cones, while the latter are usually marketedinassociationwithabrandname relatedtoaspecificinstrumentationtech- nique (e.g., ProTaper cones, DENTSPLY; and TF Adaptive [TFA] cones, Kerr). De- velopment of these cones was necessary, since nowadays more NiTi rotary instru- ments have a nonuniform taper (e.g., Pro- Taper; and HyFlex EDM, Coltène/Whale- dent)oraworkingpartsmallerthan16 mm (e.g., Twisted Files [TF], Kerr; and TFA). Tip sizes and tapers of NiTi instruments While some instruments have a nonuni- form taper, the majority of endodontic NiTirotaryinstrumentshaveauniformta- per, and the associated techniques are in- tended to create at least a 0.04- or 0.06- tapered preparation. For this reason, GP cones of greater tapers are usually sold in 0.04 and 0.06 tapers. However, NiTi instruments with the same nominal size and taper may not have the same dimensions and consequently not create an identical root canal prepa- ration,sincethelengthoftheworkingpart may be different (Fig. 1). For example, in a 25.06 K3XF instrument (Kerr; or other instruments, including Revo-S, MICRO- MEGA; ProFile, DENTSPLY; and Race, FKG Dentaire), the working part is 16 mm, whileina25.06TFinstrument,itis10 mm. Evenifthetaperandtipsizesarethesame, a 25.06 K3XF instrument will enlarge the root canal to 1.21 mm. This calculation can be made as follows: 0.06 mm increase for each millimeter, multiplied for 16 mm = 0.96 mm + 0.25 mm tip size = 1.21 mm. In contrast,a25.06TFinstrument(afilewith a reduced working part) will enlarge the canal to a lesser extent: 0.85 mm (0.06 mm × 10 mm = 0.60 mm + 0.25 mm tip size = 0.85 mm). Similar differences can be found be- tween any NiTi instrument with a conven- tional 16 mm working part compared with anyotherinstrumentwithareducedwork- ing part. NiTi instruments with a shorter working part are widely used because a shorter working part creates less stress during instrumentation by reducing taper lock and torsional stress in the coronal part,thelargestsectionoftheinstrument. With a lower operative torque, efficiency and safety are more easily improved. For Fig.1 25.06 GP cone 16 mm long; 0.06 taper SM2 TFA GP cone 25.06 K3 SM2 25.06 TFA 10 mm long; 0.06 taper 16 mm working part 10 mm Article_Gambarini_00-00.qxp_Layout 1 02.03.16 20:48 Seite 2 Article_Gambarini_00-00.qxp_Layout 102.03.1620:48 Seite 2