Basic Research—Technology
Incidence of Dentinal Cracks after Root Canal
Preparation with Twisted File Adaptive Instruments
Using Different Kinematics
Ertugrul Karataş, DDS, PhD,* Hakan Arslan, DDS, PhD,* Meltem Alsancak, DDS,*
€
Damla Ozsu
Kırıcı, DDS,* and I_ brahim Ersoy, DDS, PhD†
Abstract
Introduction: The purpose of the present study was to
assess the effect of root canal instrumentation using
Twisted File Adaptive instruments (Axis/SybronEndo,
Orange, CA) with different kinematics (adaptive motion,
90 clockwise [CW]–30 counterclockwise [CCW], 150
CW–30 CCW, 210 CW–30 CCW, and continuous
rotation) on crack formation. Methods: One hundred
five mandibular central incisor teeth were selected.
Fifteen teeth were left unprepared (control group),
and the remaining 90 teeth were assigned to the 5
root canal shaping groups as follows (n = 15): adaptive
motion, 90 CW–30 CCW, 150 CW–30 CCW, 210
CW–30 CCW, continuous rotation, and hand file. All
the roots were sectioned horizontally at 3, 6, and
9 mm from the apex with a low-speed saw under water
cooling, and the slices were then viewed through a stereomicroscope at 25 magnification. Digital images of
each slice were captured using a camera to determine
the presence of dentinal cracks. Results: No cracks
were observed in the control group, and the continuous
rotation group had more cracks than the reciprocation
groups (90 CW–30 CCW, 150 CW–30 CCW, and
210 CW–30 CCW) (P < .05). Both the continuous rotation and adaptive motion groups had significantly more
dentinal cracks than the hand file group (P < .05).
Regarding the different sections (3, 6, and 9 mm), there
was a significant difference between the experimental
groups at the 9-mm level (P < .05). Conclusions: The
incidence of dentinal cracks is less with TF Adaptive instruments working in 210 CW–30 CCW reciprocating
motion compared with working in continuous rotation
and adaptive motion. (J Endod 2015;41:1130–1133)
Key Words
Cracks, kinematics, root canal instrumentation, Twisted
File Adaptive system
I
nstrumentation with nickel-titanium instruments could result in some complications
such as perforations (1), canal transportation, ledge and zip formation (2), separation of instruments (3), and dentinal cracks (4–10). Vertical root fracture, which might
occur as a result of a dentinal crack (11), can lead to extraction of the tooth (12).
Recently, a new system has been introduced called Twisted File Adaptive (TF Adaptive) (Axis/SybronEndo, Orange, CA) that uses continuous rotation when it is exposed to
minimal or no applied load. The TF Adaptive instrument can change to a reciprocation
mode, with specifically designed clockwise and counterclockwise angles, which vary
from 600 –0 up to 370 –50 when it engages dentin and a load is applied.
Because the incidence of dentinal cracks after root canal instrumentation may
differ according to the preparation technique (13), design (9) and taper (14) of the
file, and instrumentation length (15), it might be speculated that the root canal instrumentation with different movement kinematics (continuous rotation, reciprocation with
different angles, and adaptive motion) may change the incidence of dentinal defects. To
date, no studies have determined the incidence of dentinal microcracks resulting from
the use of the TF Adaptive instruments with different kinematics. Therefore, the purpose
of the present study was to assess the effect of root canal instrumentation using TF Adaptive system instruments with different kinematics (adaptive motion, 90 clockwise
[CW]–30 counterclockwise [CCW], 150 CW–30 CCW, 210 CW–30 CCW, and
continuous rotation) on crack formation. The null hypothesis was that there would
be no differences in crack formation among the groups.
Materials and Methods
Extracted human mandibular central incisors with single canals and similar
lengths were selected and kept in purified filtered water. The soft tissue remnants
and calculi on the external root surface were removed mechanically, and the coronal
portions of all the teeth were removed using an Isomet low-speed saw (Isomet 1000;
Buehler, Lake Bluff, IL) under water cooling to achieve a final 13-mm length for each
tooth. All the roots were observed with a stereomicroscope (Novex, Arnhem, Holland)
with 15 magnification to detect any pre-existing external defects or cracks. Proximal
radiographs were taken, and a tooth having more than a single root canal and apical
foramen, root canal treatment, internal/external resorption, immature root apices,
caries/cracks/fractures on the root surface, and/or root canal curvature more than
10 was excluded from the study. In all the teeth, the canal width near the minor apical
foramen was compatible with a size 10 K-file (Dentsply Maillefer, Ballaigues,
Switzerland).
From the *Department of Endodontics, Faculty of Dentistry, Ataturk University, Erzurum, Turkey; and †Department of Endodontics, Faculty of Dentistry, Şifa
University, _Izmir, Turkey.
Address requests for reprints to Dr Ertugrul Karataş, Department of Restorative Dentistry and Endodontics, Faculty of Dentistry, Ataturk University, Erzurum 25240,
Turkey. E-mail address: dtertu@windowslive.com
0099-2399/$ - see front matter
Copyright ª 2015 American Association of Endodontists.
http://dx.doi.org/10.1016/j.joen.2015.02.029
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Karataş et al.
JOE — Volume 41, Number 7, July 2015
Basic Research—Technology
According to these criteria, 105 mandibular central incisor teeth
were selected, and the teeth were randomly divided into 6 groups (n =
15). The root width was measured buccolingually and mesiodistally
5 mm from the apex, and the homogeneity of the 6 groups was assessed
using an analysis of variance (P = 1.000). A size 10 K-file was introduced into the canals of all samples until the tip of the file became visible
at the apical foramen. The distance between the tip of the file and the
reference plane was defined as the canal length, and the working length
(WL) was established by subtracting 1 mm from this length. A silicone
impression material was used for coating the surface of the roots to
simulate the periodontal ligament, and all the roots were then
embedded in acrylic blocks. Fifteen teeth were left unprepared (control
group). Seventy-five teeth were instrumented using TF Adaptive instruments (SM1 [20/.04], SM2 [25/.06], and SM3 [35/.04]) at the full WL.
The remaining 15 teeth were instrumented with hand files. The irrigation was performed using a syringe and a 27-G needle (Hayat, Istanbul,
Turkey) placed 1 mm from the WL. After each instrument change, 2 mL
sodium hypochlorite was used for irrigation and a total of 10 mL sodium
hypochlorite was used for each canal.
Group 1 (Adaptive Motion)
The root canals were instrumented using the TF Adaptive instruments (SM1 [20/.04], SM2 [25/.06], and SM3 [35/.04]) with an Elements Motor (SybronEndo, Glendora, CA).
Group 2 (90 CW–30 CCW)
In this group, root canal preparation was performed using an electric motor (Satelec Endodual; Acteon, Merignac, France) that allows the
user to modify and set the reciprocating angles in both CW and CCW directions. The angle of reciprocation was set at CW = 90 and CCW = 30
for root canal preparation.
Group 3 (150 CW–30 CCW)
The root canals were instrumented using a motor (Acteon) at a
reciprocation range of 150 CW and 30 CCW (angle of progression
for each reciprocation was 120 ).
Group 4 (210 CW–30 CCW)
The root canals were instrumented using an Acteon motor at a
reciprocation range of 210 CW and 30 CCW (angle of progression
for each reciprocation was 180 ).
Figure 1. A representative image of the slice with a dentinal crack.
All the root canal preparations were performed by 1 operator and
the assessments of the cross sections were performed by 2 other examiners who were blinded to all the experimental groups.
All the roots were sectioned horizontally at 3, 6, and 9 mm from the
apex with a low-speed saw under water cooling. The slices were stained
with a dye (VOCO Caries Marker, Cuxhaven, Germany) to enhance the
detection of cracks. The slices were then viewed through a stereomicroscope at 25 magnification. Digital images of each slice were captured
using a camera (Coolpix 4500; Nikon, Tokyo, Japan) to determine the
presence of dentinal cracks. A ‘‘crack’’ was defined if an incomplete
crack (a line extending from the canal wall into the dentin without
reaching the outer surface of the root), a complete crack (a line extending from the root canal wall to the outer surface of the root) (Fig. 1), or
a craze line (other lines that did not reach any surface of the root or
extend from the outer surface into the dentin but did not reach the canal
wall) were present in the root dentin. ‘‘No crack’’ was defined as root
dentin devoid of craze lines, complete cracks, and incomplete cracks
(Fig. 2). More than 1 crack per slice was possible. However, the data
were collected as present/absent of a crack. The chi-square test was
used for statistical analysis of differences among the experimental
groups (P = .05).
Group 5 (Continuous Rotation)
In this group, the root canals were prepared using an Acteon
motor at continuous rotation.
Group 6 (Hand File)
The coronal flaring was performed with #2 and #1 Gates Glidden
drills (Mani Inc, Tachigiken, Japan). K-files were used in a crown-down
sequence by using #35 .02 taper, #30 .02 taper, #25 .02 taper, and #20
.02 file until 1 mm short of the WL. Thereafter, each root canal was prepared to the WL according to the following sequence: #20 .02 taper, #25
.02 taper, #30.02 taper, and #35 .02 taper (15).
Group 7 (Control)
In this group, the teeth were left unprepared.
In all groups, the root canals were instrumented at a speed of
250 rpm using an 8:1 reduction handpiece except for the TF Adaptive
group. (In this group, the instruments were used with the TF Adaptive
program of their motor.)
JOE — Volume 41, Number 7, July 2015
Figure 2. A representative image of the slice without any dentinal cracks.
Dentinal Cracks
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Basic Research—Technology
TABLE 1. Number of Cracks in the Different Cross-section Slices
Absolute number of cracks
9 mm (%)
6 mm (%)
3 mm (%)
Total cracked
roots per group (%)
7 (47)a
3 (20)abc
3 (20)abc
0 (0)c
6 (40)a
3 (20)abc
0 (0)bc
.008
4 (27)
3 (20)
3 (20)
3 (20)
6 (40)
1 (7)
0 (0)
.130
2 (13)
0 (0)
1 (7)
0 (0)
3 (20)
1 (7)
0 (0)
.199
13 (29)ab
6 (13)bc
7 (16)bc
3 (7)cd
15 (33)a
5 (11)c
0 (0)d
.000
TF Adaptive
90 CW–30 CCW
150 CW–30 CCW
210 CW–30 CCW
Continuous rotation
Hand files
Control
P value
CCW, counterclockwise; CW, clockwise; TF Adaptive, Twisted File Adaptive.
Values with the same letters were not statistically different at P = .05. Note that >1 crack per slice was possible.
Results
Table 1 summarize the results. No cracks were observed in the
control group, and the difference between the control group and the
experimental groups was statistically significant (P < .001). The continuous rotation group had more cracks than the reciprocation groups
(90 CW–30 CCW, 150 CW–30 CCW, and 210 CW–30 CCW)
(P < .05). The adaptive motion group was associated with significantly
more cracks compared with the 210 CW–30 CCW group. Both the
continuous rotation and adaptive motion groups had significantly
more dentinal cracks than the hand file group (P < .05). There was
no statistically significant difference among the reciprocation groups
(P > .05).
Regarding the different sections (3, 6, and 9 mm), there was a significant difference between the experimental groups at the 9-mm level
(P < .05). The continuous rotation and adaptive motion groups had
significantly more cracks than the 210 CW–30 CCW and control
groups in the coronal section (P < .05). There was no significant
difference among the reciprocation, hand file, and control groups at
the 9-mm level in terms of crack formation. In the 6-mm and 3-mm
sections, there was no significant difference in the crack formation
among the groups (P > .05).
In all reciprocation groups, especially in the 90 CW–30 CCW,
some of the TF Adaptive files were distorted after a single use. In
contrast, in the continuous rotation and adaptive motion groups,
none of the TF Adaptive files were distorted.
Discussion
In the present study, the effect of the TF Adaptive instruments with
different movement kinematics on crack development was evaluated.
According to the results, all of the kinematics compared in the current
study was associated with dentinal cracks. In addition, because the
different movement kinematics produced different amounts of dentinal
crack, the null hypothesis was rejected.
Saber Sel and Abu El Sadat (16) have evaluated the effect of
altering the reciprocation range of the WaveOne instrument (Dentsply
Maillefer) on its fatigue life and shaping ability. They concluded that
decreasing the reciprocation range of WaveOne instruments resulted
in an increased cyclic fatigue resistance with less canal transportation.
It might be speculated that the root canal instrumentation with different
progression ranges may change the incidence of dentinal defects. Thus,
the present study compared 90 CW–30 CCW, 150 CW–30 CCW, and
210 CW–30 CCW reciprocation angles with adaptive and continuous
rotation motion in terms of crack formation. These angles were selected
because of their different progression range (60 , 120 , and 180 in
the 90 CW–30 CCW, 150 CW–30 CCW, and 210 CW–30 CCW
groups, respectively).
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Karataş et al.
According to the results of the present study, the adaptive motion
group produced more cracks than the 210 CW–30 CCW group. However, there was no significant difference among the TF Adaptive, 90
CW–30 CCW, and 150 CW–30 CCW groups. The TF Adaptive instrument uses continuous rotation when it is exposed to minimal or no
applied load. When the file engages dentin or a load is applied,
it changes to a reciprocation mode, with the angles of 600 CW–0
CCW up to 370 CW–50 CCW. However, it is unclear whether the
kinematic of adaptive movement was reciprocation or the continuous
rotation during root canal preparation. Therefore, there is a lack of
clarity on the progression range of adaptive movement. On the other
hand, the reciprocation groups had certain progression ranges. The
progression range of 210 CW–30 CCW group was 180 , whereas it
was 60 and 120 in the 90 CW–30 CCW and 150 CW–30 CCW
groups, respectively. Thus, it can be speculated that decreasing the
reciprocation range of TF Adaptive instruments might have resulted
in an increased incidence of dentinal crack formation.
In the present study, continuous rotation caused more cracks than
reciprocation. Applying a rotational force to the root canal wall can
create microcracks and craze lines in root dentin (5). Continuous rotation might have increased the stress concentration on the root canal wall
because of applying more rotational forces to the root canal wall, resulting in more crack formation.
In addition, it has been reported that the dentinal cracks can be
related to instrumentation techniques (13). Adorno et al (13) evaluated
the effect of preparation techniques on crack development in the apical
root canal wall, and they found that the crown-down technique was
associated with more cracks than the step-back technique at a level
of 1 mm short of the apical foramen. Although most nickel-titanium systems work in a crown-down manner, reciprocal systems simulate the
balanced force technique (17). Liu et al (7) evaluated the incidence
of dentinal cracks after root canal instrumentation with different file systems and reported that reciprocating motion caused less dentinal damage than continuous rotation motion. Although a direct comparison
cannot be performed, this finding may be assumed to be similar to
our results.
Abou El Nasr and Abd El Kader (18) evaluated dentinal damage
with single-file systems (WaveOne and ProTaper) using different
kinematics and concluded that the alloy from which the material is
manufactured is a more important factor in determining the dentin
damaging potential of single-file instruments than the motion of
instrumentation. Similarly, Kansal et al (19) assessed dentinal damage during root canal instrumentation using reciprocating and rotary
files (WaveOne and ProTaper) and concluded that dentinal cracks
are produced irrespective of motion kinematics. However, in the present study, all the roots were prepared with the same type of instrument; thus, a direct comparison could not be performed between the
JOE — Volume 41, Number 7, July 2015
Basic Research—Technology
results of the previous studies and the present study. Moreover,
different instruments with alloys and designs may produce different
amounts of dentinal cracks (16, 18).
According to the result of the present study, the TF adaptive motion
and continuous rotation groups produced more dentinal cracks than
the hand file group. This is in agreement with Liu et al (15), who
concluded that rotary instruments caused more dentinal defects than
hand instruments. There was no significant difference among the
hand file and reciprocation groups in terms of dentinal crack formation. However, all the reciprocation groups, except the 210 CW–30
CCW group, produced more dentinal cracks than the control group.
The tapered files may generate an increased stress on the dentin
wall (14). Wilcox et al (11) concluded that the likelihood of root fracture increases with the amount of tooth structure removed. It was found
that the amount of dentin removed by tapered files at the coronal part of
the root canal is more than at the apical part of the root canal (20).
Regarding the different sections, there was no significant difference
among the groups at the 3- and 6-mm levels. However, at the 9-mm
level, the continuous rotation and adaptive motion groups produced
significantly more cracks than the 210 CW–30 CCW and control
groups. The taper of the files might have led to more crack formation
at the 9-mm level in the continuous rotation and adaptive motion
groups.
In the present study, the TF Adaptive system was selected for root
canal preparation in all groups. To our knowledge, there are no data
about dentinal crack formation after using these instruments with
different kinematics. Moreover, the TF Adaptive system instrument
can work in both continuous rotation and reciprocating motion. However, there was no significant difference between the adaptive motion
and continuous rotation groups (P > .05).
There are conflicting reports about the use of the dyeing method in
the assessment of cracks. Wright et al (21) reported that methylene blue
provides discrimination between cracked and noncracked resected
roots. In contrast, Von Arx et al (22) reported that staining alone
may not necessarily enhance the detection of cracks because the dye
cannot flow into craze lines unless there is a break in the surface. In
the present study, a dye was used to enhance the detection of cracks
as used previously (23).
Conclusion
Within the limitations of this in vitro study, it can be concluded
that all the kinematics used in the present study caused dentinal crack
formation. The incidence of dentinal cracks is less with TF Adaptive instruments working in 210 CW–30 CCW reciprocating motion
compared with working in continuous rotation and adaptive motion.
Acknowledgments
The authors deny any conflicts of interest related to this study.
JOE — Volume 41, Number 7, July 2015
References
1. Tsesis I, Rosenberg E, Faivishevsky V, et al. Prevalence and associated periodontal
status of teeth with root perforation: a retrospective study of 2,002 patients’ medical
records. J Endod 2010;36:797–800.
2. Aydin B, Kose T, Caliskan MK. Effectiveness of HERO 642 versus Hedstrom files for
removing gutta-percha fillings in curved root canals: an ex vivo study. Int Endod J
2009;42:1050–6.
3. Cuje J, Bargholz C, Hulsmann M. The outcome of retained instrument removal in a
specialist practice. Int Endod J 2010;43:545–54.
4. Capar ID, Arslan H, Akcay M, et al. Effects of ProTaper Universal, ProTaper Next, and
HyFlex instruments on crack formation in dentin. J Endod 2014;40:1482–4.
5. Yoldas O, Yilmaz S, Atakan G, et al. Dentinal microcrack formation during root canal
preparations by different NiTi rotary instruments and the self-adjusting file. J Endod
2012;38:232–5.
6. Topcuoglu HS, Demirbuga S, Tuncay O, et al. The effects of Mtwo, R-Endo, and
D-RaCe retreatment instruments on the incidence of dentinal defects during the
removal of root canal filling material. J Endod 2014;40:266–70.
7. Liu R, Hou BX, Wesselink PR, et al. The incidence of root microcracks caused by 3
different single-file systems versus the ProTaper system. J Endod 2013;39:1054–6.
8. Hin ES, Wu MK, Wesselink PR, et al. Effects of self-adjusting file, Mtwo, and
ProTaper on the root canal wall. J Endod 2013;39:262–4.
9. Burklein S, Tsotsis P, Schafer E. Incidence of dentinal defects after root canal preparation: reciprocating versus rotary instrumentation. J Endod 2013;39:501–4.
10. Karatas E, Gunduz HA, Kirici DO, et al. Dentinal crack formation during root canal
preparations by the Twisted File Adaptive, ProTaper Next, ProTaper Universal, and
WaveOne instruments. J Endod 2015;41:261–4.
11. Wilcox LR, Roskelley C, Sutton T. The relationship of root canal enlargement to
finger-spreader induced vertical root fracture. J Endod 1997;23:533–4.
12. Tamse A, Fuss Z, Lustig J, et al. An evaluation of endodontically treated vertically
fractured teeth. J Endod 1999;25:506–8.
13. Adorno CG, Yoshioka T, Suda H. The effect of working length and root canal preparation technique on crack development in the apical root canal wall. Int Endod J
2010;43:321–7.
14. Bier CA, Shemesh H, Tanomaru-Filho M, et al. The ability of different nickel-titanium
rotary instruments to induce dentinal damage during canal preparation. J Endod
2009;35:236–8.
15. Liu R, Kaiwar A, Shemesh H, et al. Incidence of apical root cracks and apical
dentinal detachments after canal preparation with hand and rotary files at different
instrumentation lengths. J Endod 2013;39:129–32.
16. Saber Sel D, Abu El Sadat SM. Effect of altering the reciprocation range on the fatigue
life and the shaping ability of WaveOne nickel-titanium instruments. J Endod 2013;
39:685–8.
17. Kocak S, Kocak MM, Saglam BC, et al. Apical extrusion of debris using self-adjusting
file, reciprocating single-file, and 2 rotary instrumentation systems. J Endod 2013;
39:1278–80.
18. Abou El Nasr HM, Abd El Kader KG. Dentinal damage and fracture resistance of oval
roots prepared with single-file systems using different kinematics. J Endod 2014;40:
849–51.
19. Kansal R, Rajput A, Talwar S, et al. Assessment of dentinal damage during canal
preparation using reciprocating and rotary files. J Endod 2014;40:1443–6.
20. Akhlaghi NM, Kahali R, Abtahi A, et al. Comparison of dentine removal using V-taper
and K-Flexofile instruments. Int Endod J 2010;43:1029–36.
21. Wright HM Jr, Loushine RJ, Weller RN, et al. Identification of resected root-end
dentinal cracks: a comparative study of transillumination and dyes. J Endod
2004;30:712–5.
22. von Arx T, Kunz R, Schneider AC, et al. Detection of dentinal cracks after root-end
resection: an ex vivo study comparing microscopy and endoscopy with scanning
electron microscopy. J Endod 2010;36:1563–8.
23. Arslan H, Karatas E, Capar ID, et al. Effect of ProTaper Universal, Endoflare, Revo-S,
HyFlex coronal flaring instruments, and Gates Glidden drills on crack formation.
J Endod 2014;40:1681–3.
Dentinal Cracks
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