Cyclic Fatigue of Reciproc and WaveOne

Cyclic fatigue of Reciproc and WaveOnereciprocating instruments

G. Plotino, N. M. Grande, L. Testarelli & G. GambariniDepartment of Endodontics, ‘Sapienza’ University of Rome, Rome, Italy

Abstract

Plotino G, Grande NM, Testarelli L, Gambarini G. Cyclic

fatigue of Reciproc and WaveOne reciprocating instruments.

International Endodontic Journal.

Aim To evaluate the cyclic fatigue resistance of

Reciproc� and WaveOne� instruments in simulated

root canals.

Methodology Two groups of 15 NiTi endodontic

instruments of identical tip size of 0.25 mm were

tested, group A; Reciproc� R25 and group B: Wave-

One� primary. Cyclic fatigue testing was performed in a

stainless steel artificial canal manufactured by repro-

ducing the instrument’s size and taper. A simulated

root canal with a 60� angle of curvature and 5-mm

radius of curvature was constructed for both the

instruments tested. The centre of the curvature was

5 mm from the tip of the instrument and the curved

segment of the canal was approximately 5 mm in

length. The Reciproc� instruments were activated

using the preset programme specific for the Reciproc�

instruments, whilst the WaveOne� instruments were

activated using the preset programme specific for the

WaveOne� instruments. All instruments were rotated

until fracture occurred and the time to fracture (TtF)

and the length of the fractured tip were recorded and

registered. Means and standard deviations of TtF and

fragment length were calculated for each system and

data were subjected to Student’s t-test (P < 0.05).

Results A statistically significant difference (P < 0.05)

was noted between Reciproc� and WaveOne� instru-

ments. Reciproc� R25 instruments were associated with

a significant increase in the mean time to fracture when

compared with primary WaveOne� instruments

(130.8 ± 18.4 vs. 97.8 ± 15.9 s). There was no signif-

icant difference (P > 0.05) in the mean length of the

fractured fragments between the instruments.

Conclusions Reciproc� instruments were associated

with a significantly higher cyclic fatigue resistance

than WaveOne� instruments.

Keywords: cyclic fatigue, nickel–titanium, recipro-

cation.

Received 28 October 2011; accepted 30 December 2011

Introduction

The fracture of instruments used in rotary motion

occurs through two different mechanisms: fracture

caused by torsion and fracture caused by flexural

fatigue (Serene et al. 1995, Ullmann & Peters 2005,

Plotino et al. 2009a). Torsional fracture occurs when

an instrument tip or another part of the instrument

becomes locked in a canal whilst the shank continues

to rotate. The tip fractures when handpiece torque

exceeds the elastic limit of the metal (Martın et al.

2003). Instruments fractured through excess torsional

loads often display signs of plastic deformation (Satta-

pan et al. 2000). The cyclic fatigue resistance of nickel–

titanium rotary (NTR) files has been studied using

artificial root canals with a variety of features, for

example, the angle and radius of curvature, the

localization of the point of maximum curvature and

the type of artificial root canal (Pruett et al. 1997).

Subsequently, a new approach using only a ProTa-

per F2 instrument (Dentsply Maillefer, Ballaigues,

Correspondence: Dr Gianluca Plotino, Department of End-

odontics, ‘Sapienza’ University of Rome, Via Tommaso Salvini,

57 – 00197 Rome, Italy (Tel.: +393396910098; e-mail:

[email protected]).

doi:10.1111/j.1365-2591.2012.02015.x

ª 2012 International Endodontic Journal International Endodontic Journal 1

Switzerland) in a reciprocating movement was intro-

duced (Yared 2008), thereby presenting a new per-

spective for NiTi files. The employment of reciprocating

motion instead of the conventional continuous rotation

method was suggested as an advantage for the prep-

aration of curved canals with the use of one single NiTi

file (De-Deus et al. 2010a, Franco et al. 2011, Paque

et al. 2011, You et al. 2011). The concept of using a

single NiTi instrument to prepare the entire root canal

is interesting, because the learning curve is consider-

ably reduced as a result of technique simplification and

reduction of the endodontic armamentarium. More-

over, the use of a single NiTi instrument is likely to be

more cost-effective than the conventional multifile NiTi

rotary systems.

Recently, two different reciprocating systems were

introduced: Reciproc� (VDW, Munich, Germany) and

WaveOne� (Dentsply Maillefer, Ballaigues, Switzer-

land). The Reciproc� clinical sequence, as suggested

by the manufacturer, is a single instrument technique

using one of the three files: R25 (tip size 25 with a taper

of 0.08 over the first apical millimitres), R40 (tip size 40

with a taper of 0.06 over the first apical millimitres),

R50 (tip size 50 with a taper of 0.05 over the first apical

millimitres). WaveOne� NiTi files are available in three

sizes: small (tip size 21 with a taper of 0.06), primary

(tip size 25 with a taper of 0.08) and large (tip size 40

with a taper of 0.08). Both instruments are produced

with M-wire nickel–titanium, a new alloy produced in

an innovative thermal treatment process (Gambarini

et al. 2008). Reciproc� and WaveOne� instruments

have been designed specifically for use in reciprocation.

Both instruments have a left-handed angulation of the

blades, which means they cut in the counterclockwise

(CCW) direction. The values of clockwise (CW) and

CCW rotations are different. A large rotating angle in

the cutting direction (CCW) determines the instrument

advances in the canal and engages dentine to cut it,

whereas a smaller angle in the opposite direction (CW)

allows the file to be immediately disengaged and safely

progress along the canal path, whilst reducing the

effect of a screwing effect and file breakage. These

angles are specific for the different instruments and

they were determined using the torsional properties of

the instruments.

The reciprocating movement aims to minimize the

risk of instrument fracture caused by torsional stress:

the angle of CCW rotation is designed to be smaller

than the elastic limit of the instrument. On the other

hand, although those instruments complete one rota-

tion of 360� in several reciprocating movements,

accumulation of metal fatigue remains a concern.

The aim of this study was to evaluate the cyclic fatigue

resistance of new Reciproc� and WaveOne� instru-

ments in simulated root canals. The null hypothesis

tested is that no differences are present in the cyclic

fatigue resistance between the two instruments.

Materials and methods

Two groups of 15 NiTi endodontic instruments of

identical tip size of 0.25 mm were tested, Reciproc�

R25 and WaveOne� primary. All instruments were

inspected using an optical stereomicroscope with 20·magnification for morphologic analysis and for any

signs of visible deformation. All defective instruments

were discarded.

The cyclic fatigue testing device used in this study

has been described previously (Plotino et al. 2009b,

2010a,b,c). The device consists of a main frame to

which a mobile plastic support is connected for the

electric handpiece and a stainless steel block containing

the artificial canals. The electric handpiece is mounted

on a mobile device to allow precise and reproducible

placement of each instrument inside the artificial canal.

This ensured three-dimensional alignment and posi-

tioning of the instruments to the same depth. The

artificial canal was manufactured by reproducing the

instrument’s size and taper, thus providing the instru-

ment with a suitable trajectory that conforms to the

parameters of the curvature chosen. A simulated root

canal with a 60� angle of curvature and 5-mm radius

of curvature was constructed for both the instruments

tested. The centre of the curvature was 5 mm from the

tip of the instrument and the curved segment of the

canal was approximately 5 mm in length.

The instruments were activated by using a 6 : 1

reduction handpiece (Sirona Dental Systems GmbH,

Bensheim, Germany) powered by a torque-controlled

motor (Silver Reciproc; VDW, Munich, Germany) using

the preset programme Reciproc ALL specific for the

Reciproc� instruments and the preset programme

WaveOne ALL specific for the WaveOne� instruments.

To reduce the friction of the file as it contacted the

artificial canal walls, a special high-flow synthetic oil

designed for lubrication of mechanical parts (Super Oil;

Singer Co Ltd, Elizabethport, NJ, USA) was applied. All

instruments were rotated until fracture occurred; the

time to fracture (TtF) was recorded visually using a 1/

100-s chronometer and registered to the nearest whole

number. The length of the fractured tip was also recorded

for each instrument. Means and standard deviations of

Cyclic fatigue of reciprocating instruments Plotino et al.

International Endodontic Journal ª 2012 International Endodontic Journal2

TtF and fragment length were calculated for each system

and data were subjected to Student’s t-test with the

significance set at the 95% confidence level.

Results

Mean values and standard deviation expressed as TtF

are displayed in Table 1. A greater time to fracture is

caused by an enhanced resistance to cyclic fatigue. A

statistically significant difference (P < 0.05) was noted

between Reciproc� and WaveOne� instruments (Ta-

ble 1). Reciproc� R25 instruments were associated

with a significant increase in the mean time to fracture

when compared with primary WaveOne� instruments

(130.8 ± 18.4 vs. 97.8 ± 15.9 s).

The mean length of the fractured segment was also

recorded to evaluate the correct positioning of the

tested instrument inside the canal curvature and

whether similar stresses were being induced. No

statistically significant difference (P > 0.05) in the

mean length of the fractured fragments was evident

for the instruments (Table 1).

Discussion

The two instruments used in the present study were

selected because they are to date the only commercially

available instruments designed specifically to be used in

reciprocating motion. The instruments have the same

nominal size, tip size 25 with 0.08 taper. Taper is

constant in the apical 3 mm of the instruments but

reduces in the middle and coronal portion of the

working part of the instrument.

The null hypothesis can be rejected, as Reciproc�

instruments demonstrated a significantly higher cyclic

fatigue resistance than WaveOne� instruments under

the conditions of the present study. It is well known that

cyclic fatigue is influenced by the dimensions of the

instruments (Plotino et al. 2006, 2007); in the present

study, the similar dimensions of the instruments tested

should have reduced this possible variability. Cyclic

fatigue can be also influenced by the alloy and/or the

manufacturing process of the instruments (Gambarini

et al. 2008, 2011); in the present study, both instruments

were made by the same alloy produced with the same

proprietary thermal treatment (M-wire). Thus, even in

this case, different results between the instruments

should not be related to their metallurgical behaviour.

A possible difference between the two tested instru-

ments can be the reciprocating movement, which is not

clearly disclosed by the manufacturers. It has been

shown that a reciprocating movement can affect and

improve cyclic fatigue resistance of NiTi instruments,

both ex vivo and in vivo (De-Deus et al. 2010b, Varela-

Patino et al. 2010, You et al. 2010). According to the

manufacturer, Reciproc� instruments are used at 10

cycles of reciprocation per second, the equivalent of

approximately 300 rpm, whilst no information is

available for WaveOne� instruments. The authors

attempted to obtain more information about the two

different reciprocating movements, which are available

on the digital display of the motors used for Reciproc�

and WaveOne� (Silver Reciproc; VDW, Munich, Ger-

many and WaveOne Motor, Dentsply Maillefer, Ballai-

gues, Switzerland). The two movements were filmed

and recorded with a digital videocamera and analysed

using a digital imaging software. Some variations in the

speed and in the angles between Reciproc� and Wave-

One� instruments were obvious. It was not easy to

precisely determine the characteristics of the recipro-

cating movements of the motors and to exactly calcu-

late the angles of CCW and CW movements of each

instrument using a digital videocamera. More sophisti-

cated equipment is probably required to better visualize

and analyse these movements. However, because some

differences have been noted, it can be speculated that

these differences could play a role in the results obtained

in the present study. As this is a new research field, with

little or no data available in the dental literature, further

studies are needed to understand and evaluate the

angles and speed of reciprocation and their influence on

the cyclic fatigue resistance of these instruments.

Another possible explanation of the different results

obtained in the present study can be related to the

different cross-sectional design of the instruments

tested. Reciproc instruments have an S-shaped cross-

section with two cutting blades that is similar to the

cross-section of the Mtwo� NiTi rotary instruments

(Plotino et al. 2006). WaveOne� instruments have a

modified convex triangular cross-section at the tip and

a convex triangular cross-section in the middle and

coronal portion of the instrument that is similar to the

cross-section of ProTaper� instruments (Grande et al.

Table 1 Mean time to fracture (TtF) ± standard deviation

(seconds) and mean fragment length ± SD (mm) of the

instruments tested

Reciproc R25 WaveOne primary

TtF 130.8 ± 18.4a 97.8 ± 15.9b

Fragment length 5.8 ± 0.2 6.1 ± 0.1

Different superscript letters represent statistical significance.

Plotino et al. Cyclic fatigue of reciprocating instruments


2006). The influence of the cross-sectional design of a

NiTi instrument on its cyclic fatigue resistance is

controversial and has been the subject of a number of

recent investigations (Turpin et al. 2001, Biz & Figuei-

redo 2004, Diemer & Calas 2004, Chow et al. 2005).

However, how and why the design of the instrument

could influence their behaviour under cyclic fatigue

stress remains unclear. In fact, some studies found that

the fatigue life of various instruments did not seem to

be affected by the instrument design, suggesting that

the cross-sectional area or shape of the instrument is

not the main determinant of fatigue life (Melo et al.

2002, Cheung & Darvell 2007). Yet, other studies on

cyclic fatigue suggested that a different cross-sectional

design appeared to be an important determinant of

cyclic fatigue resistance of different files (Haikel et al.

1999, Grande et al. 2006, Tripi et al. 2006, Ray et al.

2007). However, in a previous study, Grande et al.

(2006) demonstrated that the metal mass at the point

of maximum stress influenced the lifespan of NiTi

rotary instruments during a cyclic fatigue test. The

authors compared the cyclic fatigue resistance of

Mtwo� instruments, with a lower cross-sectional metal

mass, and ProTaper� instruments, with a larger cross-

sectional metal mass, and reported that the bigger the

metal mass, the lower the fatigue resistance. These

results are consistent with those of the present study,

which showed that Reciproc� instruments, with a

design similar to Mtwo�, are more resistant than

WaveOne� which has a cross-sectional design similar

to ProTaper�.

It must be explained that the reciprocating move-

ment is mainly aimed at reducing torsional loads and

consequently torsional failure, whilst the effect on

flexural stresses is probably less evident. To date, the

tested instruments are sold as a single use instrument,

avoiding metal weakening owing to prolonged clinical

use; however, single use means that the same

instrument can be used in 3–4 root canals, which

could be complex and tortuous. Therefore, single use

reduces but not eliminates the risk of accumulation of

metal fatigue and failure. Hence, it may be concluded

that testing cyclic fatigue of reciprocating instruments

is as valuable as testing cyclic fatigue of rotary

instruments.

Conclusions

Reciproc� instruments resisted cyclic fatigue signifi-

cantly more than WaveOne� instruments; these differ-

ences could be related to the different cross-sectional

design and/or the different reciprocating movement of

the two instruments.

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