Endo Tribune Middle East & Africa No.4, 2020
Torsional resistance of two nickel-titanium rotary instruments: A comparative study
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DTMEA_No.4. Vol.10_ET.indd
NL
Y
O
LS
NA
IO
SS
FE
O
PR
NT
AL
DE
www.dental-tribune.me
PUBLISHED IN DUBAI
July-August 2020 | No. 4, Vol. 10
Torsional resistance of two nickel-titanium
rotary instruments: A comparative study
By Prof. Gianluca Gambarini, Italy
Introduction
The main mechanisms of nickeltitanium (NiTi) endodontic instrument fracture have been revealed to
be two modes of failure, one being
torsional failure and the other cyclic
fatigue. The former contributes to a
significant pro- portion of failures.1
Cyclic fatigue fracture is caused by
repetitive compressive and tensile
stresses on the outermost fibres of
a file rotating in a curved root canal,
and torsional failure occurs when
the tip of the instrument binds to
the canal wall, even in a straight root
canal.1
Cyclic fatigue resistance of NiTi instruments has been2 assessed extensively. In contrast, there is less
information available on torsional
fracture resistance tests. The main
method of testing for static rotational fracture is the comparison of
the torsional resistance of the instruments as described by ISO 3630-1.
According to this specification, the
last 3 mm of the file tip must be fixed
with brass and a rotational speed of
2 rpm applied to create a continuous
torsional load until fracture occurs.3
Torsional load can be limited during
intra-canal rotary instrumentation
by the torque-controlled endodontic motor: torque settings can be selected to prevent excessive torsional
load on the instruments. It has been
shown that the correct preset torque
value for each instrument is very difficult to determine4. If too high (the
same happens when the clinician applies maximum torque), safety becomes dependent on the clinician’s
skill in avoiding over-engagement
and/or blockage of the file. If too low,
the rotary instrument will be loaded
by repeated locking and release
through use of the torque-controlled
motor or auto-reverse function.
How- ever, in narrow canals, where
instruments are subject to higher
torsional stresses than in wider canals, the chance of experiencing
these repetitive torsional loads is increased.
To this point, torque value at failure
according to the ISO test has not
been commonly used to determine
torque settings in torque-controlled
motors. In most cases, values are
higher than torque at failure. As a
consequence, the concept that the
use of a preset torque value is considered safe (i.e. capable of preventing
shear fracture of the instrument) is
not completely accurate. Therefore,
NiTi rotary instruments should ideally exhibit good resistance to torsion in all cases and in curved canals
should also be flexible and resistant
to cyclic fatigue.
study
File system
Maximum torque at failure in Ncm
Time to failure in seconds
(mean ± SD)
(mean ± SD)
EdgeFile X7
0.57 (± 0.10)
0.42 (± 3.50)
ProTaper Next
0.51 (± 0.10)
0.39 (± 2.90)
|
Table 1:
Table
1:Results.
Results
mass, the
more
resistant to staticprocesses
torsion the
in- and
17/.04 factors
instruments
repetitive
(alloys
5.5 Ncm.torThe torque
values
atrigid
fail-andmanufacturing
Many
can were
affectsubjected
resistanceto a to
7, 8
strument
sional
test.including
The test design,
was performed
a torqueIn the present
mass and According
dimensionsto the
heatstudy,
treatments).
ure were
recorded
by the is.
integrated
to
torsion,
dimen- using
were very
and torsional
resistanceEdgeFile
too was X7
simicontrolled
endodontic motor
(MASTERsurg,
Theof
momanufacturer,
files exsoftware
the motor
andsimilar
analysed
sions,
manufacturing
process
and KaVo).
5
lar,
showingThe
no statistically
significant
difference
between
tor allowed
recording
of torque
during
the
a higher
flexibility
and a greater
using
spreadsheet
software.
data hibit
motion
. Inprecise
the present
study,
two values
theone-way
two instruments.
null hypothesis
was
therefore
instruments’
use. The accuracy
andin
reliability
the de-using
to cyclic
fatigue
than comwas of
analysed
analysis Theresistance
NiTi
rotary instruments,
similar
6
vice had been
validated
a previous
To perform
of variance
and arejected.
Tukey test with a petitors’ instruments do. In stainlessdimension
and
design,inwere
testedstudy.
thecompare
test, the apical
3 mm
each file
was firmly
steel instruments, flexibility and
signifisecured,
cance level of a = 5%.
to
torque
at of
failure.
The
torsional
are usually innull
hypothesis
was block
that differences
Hence, the present study
showedresistance
that heat treatment
embedded
in a resin
produced with a mixed autoversely proportional.
This isinmainly
related
to theresin
different
manufacturdoes not significantly influence
torsional resistance,
polymerising
(DuraLay,
Reliance Dental
ManufacResults
due
to
the
mass
and/or
dimensions
ing
processes
would
found.
contrast
to
the
high
increase
in
flexibility
and
fatigue
returing).
Each file
was be
then
rotated clockwise
at
a
speed
Table 1 shows the results from the
oftreatment
the instruments.
The
greater the
sistance
derivedNext
from heat
as reported
in many
of 300 rpm until fracture occurred. The torque
limitstudy.
was The
present
ProTaper
9, 10
mass,
the
more
rigid
and
resistant to
published
articles.
set
at
5.5
Ncm,
to
ensure
recording
measurements
rangMethodology
files demonstrated no significantly
static
torsion
the
instrument
is.7,8 In
ing
from
0.1
to
5.5
Ncm.
The
torque
values
at
failure
were
Instruments from the following different resistance in terms of maxthe present
mass
and
recorded
by thesystems
integratedwere
software
of the imum
motor and
an- atEditorial
A list of references
is study,
available
from
thedimentwo
different
tested
torque
failure note:
compared
sions
were
very
similar
and
torsional
alysed
using
spreadsheet
software.
The
data
was
analpublisher.
and compared: ProTaper Next with the EdgeFile X7 files (p < 0.05).
ysed using one-way
analysis
variance and
a Tukey test
(Dentsply
Maillefer)
and of
EdgeFile
Similarly,
no statistically significant resistance too was similar, showing
with
a
significance
level
of
=
5
%.
X7 (EdgeEndo). For each system, ten differences were found between the no statistically significant difference
17/.04 instruments were subjected two instruments in terms of time to between the two instruments. The
null hypothesis was therefore reResults
to
a repetitive torsional test. The failure (p < 0.05).
jected.
test was performed using a torque-
Table 1 shows
the results
from(MASthe present study. The
controlled
endodontic
motor
Discussion
Hence, the present study showed
ProTaper
Next
files
demonstrated
no significantly difTERsurg, KaVo). The motor allowed
The ISO torsional resistance static that heat treatment does not sigferent resistance
terms
of maximum
at failure
precise
recordingin of
torque
values torque
test was developed more than 50 nificantly influence torsional resistcompared
with
the
EdgeFile
X7
files
(p
<
0.05).
Similarly,
during the instruments’ use. The ac- years ago to test manual stainlessance, in contrast to the high increase
no statistically
significantof
differences
were found between
curacy
and reliability
the device
steel instruments and is probably in flexibility and fatigue resistance
the two
instruments
terms
of time to failure (p < 0.05).
about
had
been
validatedin in
a previous
not ideal for testing rotary instru- derived from heat treatment as restudy. To perform the test, the apical ments that rotate at speeds much
9,10
ported
in many
published
articles.
Discussion
Gianluca
Gambarini
is head
of
3mm
of each file was firmly secured, higher than 2 rpm or for the spe- Prof.
embedded in a resin block produced cific motors with torque control and endodontics and restorative dentistry
at the Sapienza University of Rome in
The ISO
torsional
staticrestest was developed
with
a mixed
auto-resistance
polymerising
auto- reverse mode.5 Therefore, in
more
than
50
years
ago
to
test
manual
stainless-steel
inin (DuraLay, Reliance Dental Manu- the present study, torsional resist- Italy and director of the dental school’s
struments and
not rotated
ideal for testing rotary inmaster of endodontics programme. He
facturing).
Eachisfiprobably
le was then
ance was assessed by using a differ- Editorial note: A list of references is
strumentsat
that
rotateof
at300
speeds
than 2 rpm
maintains a private practice limited to
clockwise
a speed
rpmmuch
until higher
ent speed: the clinical one (300 rpm). available from the publisher.
or
for
the
specific
motors
with
torque
control
and
autofracture occurred. The torque limit The tested instruments were similar endodontics in Rome, where his focus
5
reverse
mode.
is on endodontic materials and clinical
Therefore,
in the
present study, torsional
was
set at
5.5 Ncm,
to ensure
recordin dimension and design, but had
resistance
was
assessed
by
using
a
different
speed:
the
ing measurements rang- ing from 0.1 been produced through different endodontics.
clinical one (300 rpm).
The tested instruments were similar in dimension and
design, but had been produced through different manufacturing processes (alloys and heat treatments). Ac-
As an international lecturer and researcher, Gambarini has held
more than 500 presentations at the world’s most renowned international congresses and universities. He has also received
several awards and led research projects funded by national and
About the author
Prof. Gianluca Gambarini
is head of endodontics and restorative
dentistry at the Sapienza University of
Rome in Italy and director of the dental school’s master of endodontics programme. He maintains a private practice
limited to endodontics in Rome, where
his focus is on endodontic materials and
clinical endodontics.
As an international lecturer and researcher, Gambarini has held more than
500 presentations at the world’s most
renowned international congresses and
universities. He has also received several
awards and led research projects funded
by national and international grants. In
addition to that, Gambarini is an active
consultant in the development of new
technologies, surgical procedures and
materials for root canal therapy. Furthermore, he holds patents concerning endodontic technologies he has developed.
Currently, Gambarini serves as Chairman
of the Clinical Practice Committee of the
European Society of Endodontology.
[2] =>
DTMEA_No.4. Vol.10_ET.indd
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