New approach to root canal preparation: The in–out technique

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A deep carious lesion in tooth #27. (All images: Grzegorz Witkowski)

Tue. 22. August 2023


Much has changed in endodontics during the last 20 years, except the anatomy, which is still just as complex. We can improve our protocols and techniques, but the complexity of the anatomical structures can be very problematic, especially for instrumentation. Despite the continuous development of instruments regarding their cross sections, the alloy they are manufactured from and the heat treatment they undergo, for example, we still do not have a perfect solution regarding instrumentation protocols. The greatest problem is that standard instrumentation techniques, commonly recommended in many file system manuals—note that I am not referring to file working motion—do not respect the natural anatomy and its complexity.

Fig.: 1

Fig.: 1

Fig.: 2

Fig.: 2

It is important to understand that when dentists work with rotary files, which typically rotates at approximately 300 rpm in the canal space, the flutes of the instrument are totally blocked just after the start of the motion. Therefore, most of the debris and cut dentine are packed into the lateral anatomy. This creates problems from the very beginning because of this blocking of already tight and narrow spaces, which are difficult to clean later. Improper instrumentation performed too fast with multiple strokes in one movement followed by lack of proper irrigation and activation leads to failures even when the radiograph shows beautiful white lines. We must not forget that anatomy is 3D (Fig. 1).

Most technical instructions advise dental practitioners to use files in three to four continuous pecking motions, every move advancing a little bit more without removing the file, and then to remove the file from the canal, clean the instrument, irrigate the canal and repeat, until the operator reaches the apical area. This kind of approach creates a pumping motion and pushes all the debris laterally and towards the apical area, respectively. Then the final irrigation protocol is performed. It is much more difficult from the beginning because of all the blockages in the lateral anatomies and ramifications created with the preparation (Fig. 2).

In this article, I would like to propose a novel approach to mechanical preparation, the in–out technique. The protocol suggested is valid for any file on the market as well as any available file working motion. It is also future-proof, as you will be able to work with this technique with any new file that is developed.

The protocol

If you prepare a manual glide path, do it before mechanical instrumentation. Remember to irrigate also during this step. After creating the access cavity and locating all the orifices in the pulp chamber floor, introduce the file into each canal space with one insertion only (Fig. 3) until the file starts to cut the dentine. As soon as the file starts to cut, remove the file (typically after engaging 2–3 mm of the instrument; Fig. 4). Repeat in every canal with a single stroke to approximately the same level. Remember to clean the file flutes after each insertion. Next, irrigate and activate the irrigants with heat if possible (you can use a heated plugger for this, one to three applications of heat of 1 second per canal) and follow with an ultrasonic or sonic device for 20 seconds in each canal. Then rinse again with fresh sodium hypochlorite. This is round one. Repeat for as many rounds as necessary to reach the apical area. After reaching the apical area, start the final disinfection protocol (Figs. 5a & b).

The benefit of this protocol is a cleaner space from the beginning of the preparation and during canal preparation. You do not push as much debris inside the root canal space and its ramifications as well as lateral anatomy. When implementing this in–out technique, more irrigant is used, helping ensure proper canal disinfection. This approach also helps avoid file breakage in many cases, as files are not forced beyond their limits.

Fig.: 6

Fig.: 6

Case 1

A 43-year-old patient came to our office having been referred for endodontic treatment. During oral examination, a deep carious lesion in tooth #27 was visible. Radiographic examination confirmed the diagnosis (Fig. 6). After gingivectomy with a gingiva trimmer bur (JOTA), which was necessary in order to create space for proper isolation (Figs. 7–9), the cavity was cleaned and prepared for build-up.

After restoring the missing wall, the access cavity was prepared. Next, instrumentation with manual files was performed in order to check the patency and create a glide path for mechanical preparation (Fig. 10). During this part, copious irrigation with sodium hypochlorite was also introduced. Four orifices to root canals were located: two mesiobuccal canals, a distobuccal canal and a palatal canal. Patency was achieved in all the canals (Fig. 11).

Mechanical preparation was performed with VDW.ROTATE files (VDW) with a standard sequence: 15/0.04, 20/0.05, 25/0.06. During instrumentation with every instrument, the in–out technique was used (Fig. 12). Between every file introduction, the root canal space was irrigated and activated with EDDY tips (VDW) powered at a high frequency by an air scaler according to the  manufacturer’s protocol (Figs. 13 & 14).

Final obturation was performed after the final irrigation protocol (part of the “safe endo concept”). For obturation, the VDW.1Seal bioceramic sealer (VDW) was used with the single-cone technique (Figs. 15–17). The final radiograph showed that the anatomy had been successfully obturated, from which it can be concluded that the proper preparation technique, together with the optimal irrigation protocol, can help clinicians to perform successful treatment (Fig. 18).

Fig.: 19

Fig.: 19

Case 2

A 56-year-old patient was referred to our clinic for endodontic treatment of tooth #15. The initial radiograph showed a complex anatomy with abrupt curvatures (Fig. 19). In such cases, our main goal is to avoid breaking the instrument. The in–out technique is a good choice in these situations too. After isolation, the access cavity was created (Fig. 20). Owing to abrupt curvatures in both canals located, a glide path was achieved with manual ISO #8, 10 and 12 K-files (VDW; Fig. 21). During manual instrumentation, small adjustments to the access cavity were made with an ultrasonic tip (Fig. 22).

After manual glide path preparation, final instrumentation with VDW.ROTATE files was performed using the in–out technique (Fig. 23). After preparation and final irrigation, obturation was performed with the continuous wave compaction technique and 2Seal, a root canal sealer on an epoxy–amine resin basis (VDW; Fig. 24). The final radiograph showed the fully obturated root canal complex (Fig. 25).

Fig.: 26

Fig.: 26

Case 3

A 34-year-old patient was referred to our clinic for endodontic primary treatment. The patient had acute pain and was treated during an emergency visit. The initial radiograph (Fig. 26) and intra-oral examination demonstrated the need for endodontic intervention for tooth #16. The access cavity was created with the use of the ED3D ultrasonic scaler tip (Woodpecker) and adapted in order to visualise all of the pulp chamber floor (Fig. 27). A pulp stone was located and removed also with the ED3D tip (Figs. 28 & 29). Before instrumentation, initial irrigation of the cavity with 5.25% sodium hypochlorite and activation with EDDY tips was performed in order to remove remnants of the pulp from the pulp chamber (Fig. 30). The initial glide path was then created using manual ISO #8–10 K-files (VDW). Mechanical instrumentation with VDW.ROTATE files in the second mesiobuccal, first and second distobuccal, and palatal canals and the R25 RECIPROC blue file (VDW) was used in the first mesiobuccal canal (Fig. 31). All instruments were used in the in–out technique with copious irrigation with activation in between instruments. Owing to the very long and curved canals, the IrriFlex needle (PD) was used for the final irrigation protocol (Fig. 32). Obturation was done with VDW.1Seal using the cavit piston technique (Fig. 33). The final radiograph was taken and examined regarding the clinical outcome (Fig. 34). From the visible lateral anatomy obturation, it can be concluded that the in–out technique for use during preparation is a promising solution for clinical success in canal preparation.


Endodontic treatment is very complex and prone to many mistakes during the process. When performing canal preparation, dental practitioners need to follow certain rules. The most important is not to push debris inside the canal space and lateral anatomy but mostly inside the apical area. Shilder’s shaping for cleaning has become shaping and cleaning. With new technologies, we are able to clean and disinfect root canal systems efficiently. The in–out technique appears to be a promising solution for that problem and can help clinicians to obtain successful treatment results.

Editorial note:

This article was published in roots—international magazine of endodontics vol. 19issue 1/2023. A list of references is available from the publisher.

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