Modified reciprocation > Feature article

Modified Reciprocation – Evolution of Revolution

Will McLean, University of Glasgow

Will McLean, University of Glasgow

by William McLean

One of the key goals of root canal treatment is the disinfection of the root canal system, this is achieved via chemomechanical means.1 This later term was coined to describe the process of mechanically preparing the root canal system to allow the introduction of irrigants enabling maximal effects over the largest surface area.

Due to the complexities of canal anatomy, we cannot achieve complete mechanical cleaning. Recent studies demonstrate even within the main canals, rotary instruments can achieve as little as 50% preparation of the canal walls.2 This ineffective mechanical debridement is compounded by the presence of fins, isthmuses and lateral canals making up the secondary anatomy of the root canal system.3 Effective irrigation with appropriate irrigants – Sodium Hypochlorite and EDTA – is essential to approximate the goal of canal disinfection.4

Having stated how ineffective mechanical preparation of the canal is, at present some preparation is still necessary in canals to allow us to deliver irrigant solutions. The earliest use of instruments designed specifically for use in the root canal system dates back to the late 18th Century.

Hand instrumentation has been the mainstay of root canal preparation and even today maintains a prominence. Mechanically driven instruments, although becoming a key tool over the last two decades in the endodontic armamentarium, are not new, the” revolution” is a development albeit a significant one of a concept that dates back to the earliest days of modern endodontics, the Gates Glidden drill we are all familiar with was introduced in 1885.5

The introduction of Nickel Titanium (NiTi) metallurgy to endodontic instrument manufacture offered many potential advantages over stainless steel instruments including greater flexibility and resistance to deformation.6 The market for NiTi Rotary instruments is significant, with multiple systems offered to the practitioner each claiming advantages over the competition.

The disadvantages of these systems have been in some cases complexity, and in many cost. It has been considered for some time that the “Holy Grail” in mechanically driven instrumentation is the single file system. This has proved elusive in rotary instruments due to the mechanics of rotary motion and the inherent risks associated with attempting to engineer a file that does all – instrument failure and failure to respect canal anatomy.

Rotary instruments fail via two mechanisms, flexural fatigue and torsional fatigue.7 The later occurs when the instrument engages the canal wall and continues to rotate. The instrument initially undergoes elastic deformation, a phase in which it will return to its original state if the torque applied is removed. If torque continues to be applied the instrument will undergo plastic deformation, a state in which it will not rebound to its original conformation.

If deformation continues failure will ensue. The point between elastic and plastic deformation is known as the elastic limit, if the instrument in use does not reach this critical point until later in use, deformation will be delayed and the instrument will have an extended working life. In his landmark paper Ghassan Yared described the use of reciprocation to delay taking a NiTi instrument to the elastic limit.8

Yared described the use of a ProTaper™ F2 file in a reciprocating handpiece. Previously, reciprocation in endodontics had described a motion with equal clockwise and anti-clockwise motion. In Yared’s paper, a Modified Reciprocation was described (originally outlined in an unpublished thesis by Thompson, 20069) in which clockwise and anti-clockwise motions were unequal, the effect of this is that after a number of reciprocations the file will undergo a complete revolution. It was concluded that reciprocation led to an increase in time to failure for the instrument and this movement/file combination was a genuine opportunity to realise a single file system for canal preparation.

Following this initial work, two systems have come to market. WaveOne™ developed by Dentsply and Reciproc™ developed by VDW. WaveOne is based upon the ProTaper file architecture and Reciproc on MTwo™ file architecture. One key difference from their rotary counterparts is that the principal movement is in an anti-clockwise direction and cut in a counter-clockwise direction. Both files are manufactured from M-Wire™ technology (thermomechanically treated NiTi) to improve strength and resistance to cyclic fatigue.

These files are sold with the promise of single file canal preparation, of course this is not essentially achievable as hand files are still required to establish the length of the canal using an apex locator and to gauge the apical diameter. Another occasion when multiple files (in this case WaveOne/Reciproc) are required is in the preparation of multi-rooted teeth, where canals of differing sizes are encountered.

There is a body of evidence developing to support the mechanical advantages of both WaveOne and Reciproc. Cyclic fatigue and torsional fatigue of WaveOne and Reciproc have been analysed.10 Reciproc demonstrated higher cyclic fatigue resistance and WaveOne higher torsional resistance. It was suggested that Reciproc and WaveOne may be suited to certain canal types. Reciproc may be best suited in curved canals due to its resistance to cyclic fatigue. WaveOne may be suited for use in constricted canals due to its ability to better resist torsional loads.

The evidence clearly indicates a mechanical advantage to the use of these files, but how well do they achieve what is required? A key aim of canal preparation is to respect the original canal anatomy. Both WaveOne and Reciproc have been shown in vitro to respect canal anatomy.11,12 There is evidence to support the use of a glidepath with WaveOne to minimise canal alterations.13 Both manufacturers highlight the reduced reliance on glidepath preparation at least in some situations. The fact that the use of hand instruments is limited in the protocols may well be a distinct disadvantage, as it does not allow the operator to develop an understanding of the anatomy of the canal system as they are robbed of the tactile sense afforded by hand instrumentation.

There is very little information regarding the cleaning efficacy of WaveOne and Reciproc. It has been found that WaveOne performed less favourably with regards to isthmus cleanliness than the K3™ file system and the Self-Adjusting File™.14 The authors suggested this may be related to the shortened time of preparation, leading to a diminished period over which irrigants were active.

Another study compared debris accumulation during use of Reciproc, WaveOne, Mtwo and ProTaper files.15 It was found that apically Reciproc performed better, with less debris accumulation. An in vitro study on the ability of Reciproc to effect bacterial elimination in oval-shaped canals demonstrated comparable results to other files systems studied.16 It was highlighted, that this ability was achievable provided apical preparation dimension and volume and time of irrigation were similar.

Reciprocation (both modified and true reciprocation) is part of my clinical practice. I find it a predictable and an efficient means of developing canal shape. I do not use modified reciprocation on every case and invariably develop a glide path and hence an appreciation of canal architecture.

Ultimately, I believe that practitioners should use a means of canal preparation that they are comfortable with and that they find predictable. Whatever is used, be it stainless steel handfiles, rotary NiTi or reciprocating NiTi, respect of canal anatomy during development of shape is paramount. If you decide to adopt reciprocation, remember, irrigation with sodium hypochlorite is essential. Any reduction in time taken to complete canal preparation should not lead to a shortened procedure time instead, an increase in time at which the irrigant is active apically within the root canal system.


1              Siqueira Jr JF, Rôças IN, Favieri A, Lima K. (2000) Chemomechanical Reduction of the Bacterial Population in the Root Canal after Instrumentation and Irrigation with 1%, 2.5%, and 5.25% Sodium Hypochlorite. Journal of Endodontics, 26, 331–334

2              Peters OA, Peters CI, Schönenberger K, Barbakow F. (2003) ProTaper rotary root canal preparation: effects of canal anatomy on final shape analysed by micro CT. Int Endod J. 36, 86-92.

3              Vertucci FJ. (1984) Root canal anatomy of the human permanent teeth. Oral Surgery, Oral Medicine, Oral Pathology, 58, 589-599.

4              Zehnder M. (2006) Root Canal Irrigants. Journal of Endodontics, 32, 389–398

5              Hülsmann M, Peters OA, Dummer PM. (2005). Mechanical preparation of root canals: shaping goals, techniques and means. Endodontic Topics, 10, 30-76.

6              Walia H, Brantley WA, Gerstein H. (1988) An initial investigation of the bending and torsional properties of Nitinol root canal files. Journal of Endodontics, 14, 346-351.

7              Parashos  P, Messer HH. (2006) Rotary NiTi instrument fracture and its consequences. Journal of Endodontics, 32, 1031-1043.

8              Yared G. (2008) Canal preparation using only one Ni‐Ti rotary instrument: preliminary observations. International Endodontic Journal, 41, 339-344.

9              Thompson NM. (2006) Development of a novel canal preparation technique using the torsional fatigue profile of the ProTaper F2 rotary instrument. Unpublished MSc Thesis, University of Toronto.

10           Kim HC, Kwak SW, Cheung GSP, Ko DH, Chung SM, Lee W. (2011) Cyclic fatigue and torsional resistance of two new nickel-titanium instruments used in reciprocation motion: Reciproc versus WaveOne. Journal of Endodontics, 38, 541-544.

11           Goldberg M, Dahan S, Machtou P. (2012) Centering Ability and Influence of Experience When Using WaveOne Single-File Technique in Simulated Canals. International Journal of Dentistry, 2012, 1-7.

12           Bürklein S, Benten S, Schäfer E. (2012) Shaping ability of different single‐file systems in severely curved root canals of extracted teeth. International Endodontic Journal, online view.

13           Berutti E, Salvatore Paolino D, Chiandussi G, Alovisi M, Cantatore G, Castellucci A, Pasqualini D. (2011) Root canal anatomy preservation of WaveOne reciprocating files with or without glide path. Journal of Endodontics, 38, 101-104

14           Dietrich MA, Kirkpatrick TC, Yaccino JM. (2012) In Vitro Canal and Isthmus Debris Removal of the Self-Adjusting File, K3, and WaveOne Files in the Mesial Root of Human Mandibular Molars. Journal of Endodontics, 38, 1140-1144.

15           Bürklein S, Hinschitza K, Dammaschke T, Scäfer E. (2012) Shaping ability and cleaning effectiveness of two single-file systems in severely curved root canals of extracted teeth: Reciproc and WaveOne versus Mtwo and ProTaper. International Endodontic Journal, 45, 449-461.

16           Alves FRF, Rôças IN, Almeida BM, Neves MAS, Zoffoli J, Siqueira Jr, JF. (2012) Quantitative molecular and culture analyses of bacterial elimination in oval‐shaped root canals by a single‐file instrumentation technique. International Endodontic Journal, 45, 871-877