Temperature increases on the external root surface during endodontic treatment using single file systems

Abstract

The aim of this study is to evaluate increases in temperature on the external root surface during endodontic treatment with different rotary systems.
Fifty human mandibular incisors with a single root canal were selected. All root canals were instrumented using a size 20 Hedstrom file, and the canals were irrigated with 5% sodium hypochlorite solution. The samples were randomly divided into the following three groups of 15 teeth: Group 1: The OneShape Endodontic File no.: 25; Group 2: The Reciproc Endodontic File no.: 25; Group 3: The WaveOne Endodontic File no.: 25. During the preparation, the temperature changes were measured in the middle third of the roots using a noncontact infrared thermometer. The temperature data were transferred from the thermometer to the computer and were observed graphically. Statistical analysis was performed using the Kruskal-Wallis analysis of variance at a significance level of 0.05.
The increases in temperature caused by the OneShape file system were lower than those of the other files (P < 0.05). The WaveOne file showed the highest temperature increases. However, there were no significant differences between the Reciproc and WaveOne files.
The single file rotary systems used in this study may be recommended for clinical use.

Full text

676 Nigerian Journal of Clinical Practice • Sep-Oct 2015 • Vol 18 • Issue 5
Abstract
Aims: The aim of this study is to evaluate increases in temperature on the external root surface during endodontic
treatment with different rotary systems.
Materials and Methods: Fifty human mandibular incisors with a single root canal were selected. All root canals were
instrumented using a size 20 Hedstrom le, and the canals were irrigated with 5% sodium hypochlorite solution. The
samples were randomly divided into the following three groups of 15 teeth: Group 1: The OneShape Endodontic File
no.: 25; Group 2: The Reciproc Endodontic File no.: 25; Group 3: The WaveOne Endodontic File no.: 25. During the
preparation, the temperature changes were measured in the middle third of the roots using a noncontact infrared
thermometer. The temperature data were transferred from the thermometer to the computer and were observed
graphically. Statistical analysis was performed using the Kruskal–Wallis analysis of variance at a signicance level of 0.05.
Results: The increases in temperature caused by the OneShape le system were lower than those of the other
les (P < 0.05). The WaveOne le showed the highest temperature increases. However, there were no signicant
differences between the Reciproc and WaveOne les.
Conclusions: The single le rotary systems used in this study may be recommended for clinical use.
Key words: Infrared thermometer, one le systems, reciprocating motion, root canal preparation, rotational motion
Date of Acceptance: 25-Feb-2015
Address for correspondence:
Dr. Hakan Göktürk,
Department of Endodontics, Faculty of Dentistry,
Gaziosmanpaşa University, Tokat, Turkey.
E-mail: gokturk82@hotmail.com
Introduction
The aim of endodontic treatment is to clean all pulpal tissue
remnants, hermetically fill the root canal space and create
an area without inflammation.[1] The complexity of the root
canal system is due to the presence of accessory and lateral
canals, isthmuses and apical deltas.[2] Therefore, root canal
preparation is a difficult step, and many new file systems are
being developed to eliminate these problems.
The clinical use of rotary nickel‑titanium (NiTi) endodontic
instruments improves the efficiency of endodontic treatment
by reducing the time spent on treatment procedures,
sensitivity and complication risks.[3] Previous studies have
reported reduced intervention times, and there was little
to no canal transportation when using rotary NiTi files.[4,5]
During instrument use, frictional forces generate heat
along the root canal, and higher rotational speed causes
higher temperature increases.[6] Manufacturers have
developed instruments made from new alloys and new
working motions, such as reciprocation to improve the
fracture resistance of NiTi rotary files.[7] The reciprocating
motion is caused by special movements identified by
counterclockwise (cutting action) and clockwise (release
of the instrument) motions. It is reported that this
Temperature increases on the external root surface
during endodontic treatment using single file
systems
İ Özkoçak, MM Taşkan1, H Göktürk, F Aytaç2, EŞ Karaarslan2
Departments of Endodontics, 1Periodontology and 2Restorative Dentistry, Faculty of Dentistry, Gaziosmanpaşa University,
Tokat, Turkey
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Website: www.njcponline.com
DOI: 10.4103/1119-3077.158976
PMID: *******
Original Article
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Özkoçak, et al.: Temperature increases during endodontic treatment
677
Nigerian Journal of Clinical Practice • Sep-Oct 2015 • Vol 18 • Issue 5
movement reduces stress on the file and the risk of cyclical
fatigue caused by tension.[8] The Reciproc (VDW, Munich,
Germany) and WaveOne (Dentsply Maillefer, Ballaigues,
Switzerland) instruments are examples of instruments that
use this concept. Another new example of a single file
instrument (or preparation) using continuous clockwise
rotation is the OneShape (Micro Mega, Besancon, France).
During endodontic treatments, dental complications
may occur in tooth structure and adjacent tissues. These
complications include a tooth ankylosis, bone necrosis and
resorption.[9] The study by Eriksson and Albrektsson[9]
revealed the harmful effects of increased temperatures on
alveolar bone and periodontal ligament. They reported
that a temperature increase of 10°C on the outer root
surface caused bone resorption and tooth ankyloses.[9] The
authors indicated that the threshold temperature increase
for alveolar bone is 19°C because this temperature
increase results in alkaline phosphatase denaturation.[10]
However, other authors have shown that temperature
increases <19°C also cause alveolar bone necrosis.[9,11]
Another study indicated that exposing the bone to a
temperature of 53°C for 1 min interrupted the blood flow.[12]
Exposure to a temperature of 43°C may result in protein
denaturation in the periodontal ligament.[11]
There are several methods of measuring tissue
temperature.[13‑16] There are measurement instruments
based on contact such as subgingival thermometers and
thermocouples. These instruments may by inconvenient
because of the difficulties involved in surgery and
sterilization. Infrared thermometers can measure the tissue
surface and determine only the superficial temperature
without contact.
There are no studies in the literature examining the
temperature increases that occur on the external root
surface during endodontic treatment with a single file rotary
system. The aim of the study is to evaluate the temperature
changes on the external root surface during root canal
preparation with three different single file rotary systems
in vitro. The null hypothesis tested was that there are no
differences among the temperature increases for the single
file rotary systems examined.
Materials and Methods
The research proposal was submitted to review by the
Ethics in Tokat Clinical Research Ethics Committee of the
Gaziosmanpaşa University of Turkey (No. 14KAEK‑134),
and the study design was approved.
A total of 50 human mandibulary incisors with a single
root canal and with anatomically similar root lengths were
extracted for periodontal reasons. All teeth were stored
at 4°C in physiologic saline for no longer than 4 weeks
after extraction. Only teeth with fully formed apices were
selected. All calculus and other remnants were removed
completely from the surfaces of the teeth. An access cavity
was opened using high‑speed hand tools. The working
length was established as 1 mm short of the root canal.
The canal length was visually established by placing a
size‑15 K‑type file (VDW, Munchen, Germany) into each
root canal until the tip was visible at the apical foramen.
All root canals were instrumented using a size‑20 H‑type
file (VDW, Munchen, Germany) until the file moved
freely within the canal. The canals were irrigated with
5% sodium hypochlorite solution (Whitedentmed, Erhan
Kimya, Turkey). The teeth were mounted vertically into
self‑curing 4 mm acrylic resin blocks, and the root surfaces
were exposed. The acrylic blocks are placed into a vice to
prevent contact and heat exchange [Figure 1]. The samples
were randomly divided into three groups of 15 teeth each
according to the endodontic files used for root canal. The
groups were the following:
Group 1: OneShape Endodontic File no.: 25 (Micro Mega,
Besançon, France).
Group 2: Reciproc Endodontic File no.: 25 (VDW,
Munchen, Germany).
Group 3: WaveOne Endodontic File no.: 25 (Dentsply
Maillefer, Ballaigues, Switzerland).
Each instrument was used according to the manufacturers’
instructions, and file systems were used inside the root
canal for 60 sec in all groups. Before each canal preparation,
RC‑Prep (Stone Pharmaceuticals, Philadelphia, PA, USA)
was used as a lubricant. During the tooth preparations, the
temperature changes were measured using a noncontact
infrared thermometer (Optris LS LT, Berlin, Germany)
with a sensitivity of 0.1°C at the middle third of the roots.
Preparations were finished in nearly 45 sec but instruments
were used 60 sec in root canals to watch thermal changes
Figure 1: Experimental setup established for temperature rise in
this study
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Özkoçak, et al.: Temperature increases during endodontic treatment
678 Nigerian Journal of Clinical Practice • Sep-Oct 2015 • Vol 18 • Issue 5
after access to the apices. Five teeth were examined as
controls by measuring the temperature alterations for 60 sec
without any preparation. This was performed to determine
whether the infrared thermometer caused any temperature
change. The temperature alterations were transferred to a
computer and were observed graphically.
Statistical analysis
The data were not normally distributed, and the Kruskal–
Wallis analysis of variance was used for statistical analysis.
A Bonferroni correction was applied to the results. The
level of significance was 5% (P < 0.05).
Results
The mean temperature increases and standard deviations
for the experimental groups are shown in Table 1. Figure 2
shows the results obtained in this experiment.
There were significant differences between Group 1 and
Group 2 (P < 0.05, P = 0.006). There was also a difference
between Group 1 and Group 3 (P < 0.05, P = 0.001).
There were no significant differences between Group 2 and
Group 3 (P > 0.05, P = 0.202).
The temperature increases caused by the OneShape file
system were lower than those of the other files (P < 0.05).
An evaluation of all groups showed that the WaveOne file
caused the highest temperature increases. However, there
were no significant differences between the Reciproc and
WaveOne files.
Discussion
This in vitro study investigated the temperature changes
on the external root surface during preparation with
three different NiTi rotary systems. The results of this
study supported the hypothesis partially that there are
no differences among the temperature measurements of
the three rotary file systems. There were no significant
differences between the Reciproc and WaveOne files.
However, there were significant differences between the
OneShape file and the other single file systems. The
temperature increases caused by the OneShape file system
were lower than those caused by the other files.
The heat produced during a root canal preparation may
influence the root face and periodontal ligament. In
addition, the adjacent bone may be adversely affected.[17,18]
Therefore, in the thicker dentin, less heat is passed to the
outer root surface. It has been reported that a temperature
increase >10°C could be harmful for cementum, periodontal
ligament, and alveolar bone tissues.[9,19] The amount of
transmitted heat is affected by the following factors: the
anatomy of the root canal and the amount of residual dentin
thickness, the extent of contact between the instrument
and the canal wall, intermittent or continuous instrument
usage and the operator force.[9,18]
Due to its low thermal conductivity, residual dentin
thickness is important because it acts as a protective coating
against thermal damage. Periodontal tissue damage may
occur when the amount of remaining dentine is <1 mm.[20]
Thus, it is important to study tooth responses to protect
the periodontal ligament from high temperatures. Lipski[14]
stated that the temperature increase in mandibular incisor
teeth exceeded 10°C during root canal procedures. However,
the increase in temperature did not exceed the critical level
for the maxillary central incisors and maxillary canines.[14]
In the current study, mandibular incisor teeth were analyzed
because they are the most critical teeth in terms of heat
conduction.
Hardie[6] reported that the heat generated during the
root canal preparation is directly related to the speed
of the instruments. The recently developed single file
NiTi systems Reciproc (VDW, Munich, Germany) and
WaveOne (Dentsply Maillefer, Ballaigues, Switzerland) are
able to prepare root canals with only one instrument. These
instruments require less time for tooth preparation than
the rotary full‑sequence systems.[21] The main features of
these systems are their single‑use, reciprocating motion and
M‑wire alloys.[22] The M‑wire alloy increases flexibility and
improves resistance to cyclic fatigue of the instruments.[23]
Figure 2: Temperature rise during preparation performed with
(a) OneShape, (b) Reciproc, (c) WaveOne, and (d) Control
d
c
b
a
Table 1: Mean and SD of temperature rise (°C)
Groups nMean SD SE 95% CI for mean
Lower
bound
Upper
bound
OneShape system (G1) 15 5.8* 1.5 0.4 5.0 6.7
Resiproc system (G2) 15 8.6†2.7 0.7 7.1 10.1
WaveOne system (G3) 15 10.3†3.8 1.0 8.2 12.4
Total 45 8.2 3.3 0.5 7.2 9.2
There were no significant differences between the same symbols.
SD=Standard deviation; SE=Standard error; CI=Confidence interval
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Nigerian Journal of Clinical Practice • Sep-Oct 2015 • Vol 18 • Issue 5
The OneShape has a rotational speed of 400 rpm. The
Reciproc instruments work at approximately 282–300 rpm,
with a 150–158° counterclockwise rotation, followed by a
30–34° clockwise rotation.[24] The OneShape instrument
has a constant taper of 0.06. The Reciproc R25 and the
primary WaveOne instruments have a taper of 0.08 over the
first 3 mm that decreases to 4.3% and 5.5%, respectively.[25]
In the current study, two different single file NiTi rotary
systems that use reciprocating movement and continuous
clockwise rotation single file conventional NiTi rotary
system were used. While the lowest temperature increase
was shown in the OneShape file that is a conventional NiTi
rotary system, the highest temperature increase occurred
with the WaveOne file. The WaveOne file is a single file
rotary system, and it increased the temperature by more
than the critical level (10°C). The difference between the
OneShape and the Reciproc instruments may be attributed
to the different working motions and the different rotational
speeds.
Although the WaveOne and Reciproc instruments
have similar properties, such as tip size, alloy type
and movement, they have different cross‑sectional
designs.[26] The Reciproc size 25 taper 0.08 file has a sharp
double‑cutting edge S‑shaped geometry. However, the
WaveOne file is characterized by a modified triangular
cross‑section with radial lands at the tip and a convex
triangular cross‑section in the middle and coronal portion
of the instrument. The WaveOne modified cross‑section
results in lower cutting efficiency and less chip space.[27]
Both the OneShape and the Reciproc have a markedly
smaller core diameter than the WaveOne. Therefore,
the chip space of these instruments is greater than that
of the WaveOne.[25] Although there were no statistically
significant differences between the single file rotary
systems found in this study, the WaveOne file caused
higher temperature increases than the Reciproc file. We
hypothesize that because the WaveOne file system has a
greater taper and removes less material, it increases the
temperature more than the other systems do.
Several methods have been investigated to measure
temperature changes.[15,28,29] Noncontact infrared
thermometers measure the temperature in a short period
of time and do not require other instruments or contact
during the measurement. In addition, they do not cause
infection, are less costly and do not require any preparation
prior to the measurement.[30] Therefore, noncontact infrared
thermometers are highly advantageous devices. In the
study, the Optris LS LT thermometer was used, which is a
noncontact infrared thermometer, to measure temperature
alterations. According to the manufacturer’s instructions,
the portable infrared thermometer not only allows selection
of close focus and standard focus, but it is also equipped with
innovative sighting systems (double and cross laser) for exact
spot size marking at any distance. These devices can easily
measure the temperature of moving objects.
The present study was conducted using an extraoral
environment. Thus, it was impossible to properly simulate
the intraoral environment, periodontal status and patient
habits. The results may be different for data obtained in
an actual patient because periodontal and osseous blood
circulation may influence the heat increases. Thus, further
clinical studies are required to assess both the reciprocal
and conventional root canal instruments for their potential
risk factors.
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How to cite this article: Özkoçak I, Taşkan MM, Göktürk H, Aytaç F,
Karaarslan EŞ. Temperature increases on the external root surface
during endodontic treatment using single le systems. Niger J Clin Pract
2015;18:676-80.
Source of Support: Nil, Conict of Interest: None declared.
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