Management of Severe Curvatures in Root Canal Treatment with the New Generation of Rotating Files Using a Safe and Predictable Protocol

2.1. Selected Cases

In the first case, a 65 years old female patient was presented with pain associated with the third mandibular molar 3.8. After clinical and radiographic examination, the diagnosis was a non-vital tooth associated with symptomatic apical periodontitis. The patient was unfit for extraction due to her medical condition, therefore, root canal treatment was recommended. In the radiograph, it was possible to see a 90° severe curvature in the mesial root.

In the second case, a 35 years old female patient presented with irreversible pulpitis in the second mandibular molar 4.7. The radiograph showed a severe double curvature in the mesial root.

In the third case, a 50 years old male patient presented with pain in the mandibular left side. There was a fixed bridge 6x8; the bridge was removed and the clinical diagnosis confirmed irreversible pulpitis in tooth number 3.8. Radiographic examination showed 45° severe curvatures in the mesial roots and a 90° severe curvature in the distal root.

2.2. Root Canal Preparation Protocol

The protocol for shaping, in a safe and predictable way, with a severe curve was as follows:

Predominantly, it is essential to perform a correct pre-operative radiograph and to assess the presence and degree of curvature present in the tooth to be treated. Obviously, the traditional intraoral radiograph (2D) was used, which can only be useful for detecting curvatures on the Mesio-Distal projection. In the case of a curvature on the Bucco-Palatal direction, this common radiograph is not effective in identifying it; therefore, its existence was detected only through manual scouting.

In case of a severe curvature at 120°, 90° or more, through intraoral radiograph, the distance from the occlusal surface to the beginning of the curvature was calculated and 0.5 - 1 mm was subtracted.

Once the operative field was isolated and a correct access cavity was performed, the orifices were probed in the first mms using a small hand file that was not pre-bent.

2.3. Pre-Flaring

When the pre-flaring of the first mm of the coronal third was performed, during this phase, the HyFlex EDM 25.12 opener (Coltene/Whaledent, Langenau, Germany) was utilized.

2.4. Scouting

At this stage, it was necessary to use a pre-bent 0.08 K-File (Coltene/Whaledent, Langenau, Germany) adjusted with a rubber stopper at the length measured before the curvature.

The scouting took place by applying little pressure with the balanced force motion. In this phase, the file must always be connected to the apex locator. The scouting ended when the 0.08 file reached the point before the curvature.

2.5. Glide-Path

A pre-bent K-File 0.10 (Coltene/Whaledent, Langenau, Germany) was brought to the point before the curvature.

At this point, the glide-path was finished, always at the same point, using HyFlex EDM 10.05(Coltene/Whaledent, Langenau, Germany) designed specifically for the glide-path.

2.6. Shaping

HyFlex EDM 20.05 (Coltene/Whaledent, Langenau, Germany) was used up to the same point before the curvature.

2.7. Scouting

The small pre-curved K-File 0.08 was again inserted beyond the curvature that reached the correct working length as confirmed by the apex locator.

2.8. Glide-Path

A pre-bent 0.10 K-File was brought to the working length.

Following that, a pre-bent K-File 0.15 was delivered 2 mm before the working length.

Then, HyFlex EDM 10.05 was used up to the working length. (This file should be inserted in the canal pre-bent and without rotation. After it reaches beyond the curvature, the rotation should be activated).

2.9. Scouting

Using HyFlex EDM 20.05, the working length was reached (This file should be inserted in the canal pre-bent and without rotation. After it reaches beyond the curvature, the rotation should be activated).

Then, the shaping phase was finalized using EDM 20.05 (Coltene/Whaledent, Langenau, Germany). According to the difficulty of the case, the shaping is continued using the HyFlex EDM 25 One File which has 0.8 taper in the first mm and then the taper decreases (This file should be inserted in the canal pre-bent and without rotation. After it reaches beyond the curvature, the rotation should be activated).

During the glide-path and shaping phase, it was fundamental to exploit the martensitic alloy of these modern rotating files. Both the HyFlex EDM 10.05 and 20.05 and the 25 one file must be pre-curved before being inserted into the root canal. Owing to their modern alloy, this was possible, without causing a risk of fracture of the instrument, and with the help of pre-curving, the rotating file easily passed the curvature regardless of its severity.

All the files, manual or rotating, must always work in the presence of an irrigant and between one file. Additionally, it was necessary to check the patency by a small K-File.

Both manual and rotary files must work within the root canal only for a few mms; the working length should not be reached instantly. Therefore, after every 2-4 mm of work, the files were removed from the root canal to be cleaned. The canal was then irrigated, and shaping was continued.

During scouting, pre-flaring, glide-path and shaping the files must always be carefully observed to note if the flutes are intact or have been damaged due to stress.

Another great advantage of the new rotating files, HyFlex EDM, is that in case of the opening of the flutes due to stress, they can be regenerated using heat, and the files return as new and can be reused without risk.

HyFlex EDM must be used with continuous rotation. HyFlex 10.05 must be used at 300 rpm with a torque of 1.6 N cm. HyFlex EDM 20.05 and 25 one file must be used at 400 rpm with a torque of 3 N cm.

The HyFlex, due to their special alloy, can tolerate severe bends without the risk of fractures and without altering the original anatomy of the root canal.