for endodontic therapy

a

Notch

! 27.12 After the radiographic control of the cone fit, the cone must be slightly shorter than the preparation. A notch is made by cotton pliers at the level of the reference point. b

! 27.13 a, b) The gutta-percha cone is cut off using a special gauge (Dentsply Sirona, USA) for gutta-percha points. This gauge is very useful to cut off the gutta-percha cones to the desired diameter.

! 27.14 The relation between the gutta-percha cone and the reference instrument (NiTiflex file correspondent to the diameter of the foramen) informs the operator how short the cone is relative to the canal preparation.

not be loose in the root canal, but must bind apically and oppose a certain resistance to withdrawal: this is an index of retention, which opposes the cone’s removal from the root canal when heated with the heat carrier.

At this point, two questions may arise: 1 How much must the cone be shortened with respect to the canal preparation? The cone must be shortened by the length, by which one expects that it will rise during the compaction phase. In other words, in wide, straight root canals, where pluggers descend easily in the apical portion and where it will therefore

be easy to move the gutta-percha apically, it is better to shorten it more, by at least 1-2 mm (! 27.15). In contrast, in narrower, more curved canals, in which the pluggers descend less and it will be more difficult to move the gutta-percha apically, one must shorten the cone by only a few fractions of a millimeter, so as not to risk a short obturation (! 27.16). 2 How does one know whether the “tug-back” of the cone is due to the binding in the most apical portion or to binding laterally, somewhere short of the apical foramen? Obviously, if one is confronted by the

a b ! 27.15 a) Intraoperative radiograph of the cone fit in an upper central incisor: the canal is wide and straight; therefore, the cone is shortened by about 2 mm. b) Postoperative radiograph: during the vertical compaction, the cone has moved to the end of the preparation. A lateral canal has been filled, with a good apical control of the obturating material.

! 27.16 a) Intraoperative radiograph of the cone fit in a lower third molar: the canals are narrow and slightly curved; therefore, the cones are shortened by a fraction of a millimeter. b) Postoperative radiograph.

a b