DESIGN FEATURES OF ROTARY INSTRUMENTS
IN ENDODONTICS
Review Article
ZARNA SANGHVI* , KUNJAL MISTRY**
ABSTRACT
The last decade has been witness to phenomenal growth in endodontic technology. The introduction of these new
technologies has resulted in endodontics becoming easier, faster and most importantly, better. Principal among these is
Nickel Titanium (NiTi) rotary instrumentation that results in consistent, predictable, and reproducible shaping. The
purpose of this article is to review the design features of different rotary instruments used for pulp space preparation.
Individual design features affect the performance of NiTi rotary instruments. Important mechanical features include the
variability of taper, rake angle, cross-sectional geometry, tip configuration, design of blades, helical angle and pitch.
These design features influence flexibility, cutting efficiency and safety. In this review design features of commonly
used NiTi rotary systems are summarized.
Key Words: Rotary Instruments, NiTi Files, Taper, Rake Angle, Radial Land.
INTRODUCTION
The fundamental aim of endodontic treatment is to
prevent or cure apical periodontitis. One of the main
objectives of root canal preparation is to shape and
clean the root canal system effectively whilst
maintaining the original configuration without
creating any iatrogenic events such as instrument
fracture, external transportation, ledge, or
perforation. Preparation of the root canal system is
recognized as being one of the most important
stages in root canal treatment which includes both
enlargement and shaping of the complex
endodontic space together with its disinfection1,2. A
variety of instruments and techniques have been
developed and described for this critical stage of
root canal treatment.
Over the last few years, endodontics has undergone
a complete revolution with the introduction of the
Nickel Titanium alloy for the manufacture of
manual instruments initially and then rotary
endodontic instruments 3 . The extraordinary
characteristics of super-elasticity and strength of
the NiTi alloy have made it possible to manufacture
rotary instruments with double, triple and
quadruplet taper compared to the traditional
standard .02 taper of the stainless steel hand manual
instruments4,5,6. This has made it possible to achieve
perfect shaping with the use of very few instruments
in a short period of time and without the need for
above average skills on the part of the operator. The
super-elasticity has furthermore made it possible to
carry out extremely conservative shapes, better
centered, with less canal transportation and
therefore with more respect of the original anatomy.
In order to improve working safety, shorten
preparation time and create a continuously tapered,
conical flare of preparations advanced instrument
designs with non-cutting tips, radial lands, different
cross-sections, superior resistance to torsional
7,8,9
fracture and varying tapers have been developed .
Truly, NiTi rotary instrumentation has been one of
the most significant changes in dentistry in the past
10
25 years . All endodontic companies are trying to
produce files that will work more efficiently and
safely. Some of the areas though, where file design
*READER (DEPT . OF CONSERVATIVE DENTISTRY AND ENDODONTICS ) **READER (DEPT . OF CONSERVATIVE DENTISTRY AND ENDODONTICS
*AHMEDABAD DENTAL COLLEGE & HOSPITAL, BHADAJ-RANCHHODPURA ROAD, TA:- KALOL DIST:-GANDHINAGAR.
ADDRESS FOR AUTHOR CORROSPONDENCE : DR. ZARNA SANGHVI, PHONE:- (98795 34526)
** DHARAMSINH DESAI UNIVERSITY, FACULTY OF DENTAL SCIENCE, NADIAD.
The Journal of Ahmedabad Dental College and Hospital; 2(1), March 2011 - August 2011
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ZARNA SANGHVI et. al. : Rotary Instruments in Endodontics
continues to differ is in tip and taper design,
presence of radial lands, rake angles, helical angles,
11
and pitch .
The intention of this article is to compare the
various rotary endodontic instruments, based upon
clinical performance, as dictated by their design
feature.
Tip Design
A rotary cutting instrument may have a cutting or
non-cutting tip. Cutting tips on rotary files make
them too aggressive. An advantage of cutting tip is
that it has the ability to enter narrow, somewhat
calcified canals, but it also has disadvantage, if it
accidentally go long (past the end of the tooth),
upon retraction of the file, it will generally create an
elliptical tear which is very difficult to repair and
obturate and it also has the distinct possibility of
transportation if the file is held at length for any
period of time. Going long with a non-cutting tip
will create a concentric circle at the end of the root.
These are easily filled with a non-standardized
cone. Files such as the Profile and the Greater
3
Taper(GT), along with the new K , Hero 642 and
RaCe employ a non-cutting tip. ProTaper System
has Shaping files with partially active tips while the
finishing files have non-cutting tips.
Taper
Taper is another feature of file design and it is
particularly important concerning “system
concepts.” There are two ways to shape a canal
First, instrumentation of a root canal by using files
of the same taper but with varying apical tip
diameters. An example for this would be files that
all have a consistent taper (.02) but with various tip
diameters. A rotary file of constant taper would be
the .04 taper Profile that has a constant taper (.04)
but has varying apical tip diameters. Secondly,
instrumentation of root canal by varying or
12,13
graduating tapers . These files have the constant
apical tip size but their taper varies from .04 to .12.
The idea behind variable or graduating tapers is that
each successive file is only engaging a minimal
aspect of the canal wall. Therefore, frictional
resistance is reduced and requires less torque to
properly run the file. The popular GT Series of files
consist of three different instrument sequences,
GT20, GT30 and GT40, according to ISO size and
employs a varying taper (10%, 8%, 6%, 4%) while
the Quantec files use a graduated increase in
taper14,15. RaCe instruments are available in sizes
from ISO 15-60 with various tapers of 2%, 4%, 6%,
8%, 10% while K3 files are available in different
sequence, each including six files in sizes 15 to 60
with three different tapers (2%, 4% and 6%) along
with two orifice openers of 8% and 10% for coronal
pre-flaring. The Protaper System features a
progressive taper along its shank. One of the
benefits of such a design, according to the
manufacturer, is reduced torsional loading16. Hero
642 system compiles a complete set of 12 files with
varying ISO sizes, tapers and length of cutting
17
segments . Flex Master instruments are 2% tapered
files used to finish apical area and to blend the apical
18
with the coronal preparations . ISO sizes 20, 25 and
30 instruments have three different tapers (2%, 4%
and 6%). ISO sizes 35 to 70 are only available as a
2% taper.
Rake Angle
Rake angles are also important and affect the cutting
efficiency of the instrument. There remains
confusion over what constitutes a rake angle and
what is the cutting angle. The rake angle is the angle
formed by the cutting edge and a cross section taken
perpendicular to the long axis of the instrument. The
cutting angle, on the other hand, is the angle formed
by the cutting edge and a radius when the file is
sectioned perpendicular to the cutting edge.
Positive rake angles will cut more efficiently than
neutral rake angles, which scrap the inside of the
canal. Most conventional endodontic files utilize a
negative or “substantially neutral” rake angle. An
overly positive rake angle will result in digging and
gouging of the dentin. This can lead to separation.
The Journal of Ahmedabad Dental College and Hospital; 2(1), March 2011 - August 2011
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ZARNA SANGHVI et. al. : Rotary Instruments in Endodontics
Profile has negative rake angle. The K3, ProTaper,
Hero 642, RaCe and Flex Master systems exhibit
positive rake angle resulting in their optimum
cutting efficiency. Light Speed and GT rotary
system have neutral rake angle.
Fig.-1: Rake Angles
Fig.-2: Negative Rake Angle
the instrument. This part of the file is called the
radial land. This design feature is critical to the
instrument. The less blade support (the amount of
metal behind the cutting edge) the less resistant the
19
instrument is to torsional or rotary stresses . It is the
combination of a non-cutting tip and radial land that
keeps a file centered in the canal. Most rotary files
derive their strength from the mass of material in the
core. Peripheral strength can also be added to a file
by extending the width of the radial land. This
feature has been incorporated into the K3 file.
Previously, rotary files either had full radial lands
(Profile, GT) or their lands were recessed
3
(Quantec). The K , like the Profile, is a three fluted
file with three lands. Superior peripheral strength is
achieved in the K3 by adding more mass behind the
cutting blade. The increase in the K3's peripheral
mass prevents the propagation of cracks and
reduces the chances of separations and deformation
from torsional stresses. The K3 blade relief areas, in
addition to reducing frictional resistance also play
another role. Many files have no means to control
the depth at which the flutes engage the dentin. The
harder one pushes apically, the deeper the blades
will engage the canal walls. The K3 peripheral blade
relief helps to control the depth of cut. This aids in
protecting the file from over-engagement, and
separations (breakage). The chance of transporting
a root canal with a rotary file that has a non-cutting
tip and radial lands is minimal.
Fig.-3: Positive Rake Angle
Radial Land
Another critical design feature is the concept of
radial lands. A radial land is a surface that projects
axially from the central axis, between flutes, as far
as the cutting edge. The best way to explain this is
blade support. Blade support is defined as the
amount of material supporting the cutting blades of
Fig.-4: Profile/GT Radial Land
Fig.-5: K3 Radial Land
There is an important concept of rotary
instrumentation that should be remembered. The
concept is not of “drilling” a hole in a root. Rather, it
is one of taking a small hole, planning the inside,
The Journal of Ahmedabad Dental College and Hospital; 2(1), March 2011 - August 2011
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ZARNA SANGHVI et. al. : Rotary Instruments in Endodontics
and making it larger. The concept of radial lands is
reassuring in rotary endodontics. However,
ProTaper, Hero 642, Endo Sequence and RaCe do
not have radial lands.
Helical Angle
The helical angle is the angle that the cutting edge
makes with the long axis of the file. As a rotary file
works in a canal, the dentinal debris needs to be
removed quickly and effectively. Files with a
constant helical flute angle allow debris to
accumulate, particularly in the coronal part of the
file. Additionally, files that maintain the same
helical angle along the entire working length will be
more susceptible to the effect of “screwing in”
forces. By varying the flute angles, debris will be
removed in a more efficient manner and the file will
be less likely to screw into the canal. In the K 3, the
helical angle increases from the tip to the handle.
The result of this design is more successful
channeling that allows for superior debris removal.
The RaCe file is unique and utilizes an “alternating
helical design” that reduces rotational torque by
using spiraled and non spiraled portions along the
working length. This design feature also reduces the
tendency of the file to get “sucked into” the canal20.
Pitch
Pitch is the number of spirals or threads per unit
length. Screws historically have had a constant
pitch. The result of a constant pitch and constant
helical angles is a “pulling down” or “sucking down
into” the canal. This is particularly significant in
rotary instrumentation when using files with a
constant taper. K3 file has been designed with
constant tapers, but with variable pitch and helical
angles. The result is a dramatic reduction in the
sense of being “sucked down into” the canal. Profile
has a constant pitch throughout its cutting shank.
The GT has variable helical angles and a variable
pitch. Their variable pitched flutes provide a reamer
like efficiency at the shank and K-file strength at the
tip21. ProTaper has continuously changing pitch and
helical angle which reduces the screwing effect.
RaCe features one set of cutting edges that
alternates with a second set, pitched at a different
angle. Consequently, there are two different cutting
edges on one file. The cutting shank employs an
alternating spiral design. Naturally, this results in
22
variable helical angles along with a variable pitch.
Fig.-6: Variable Helical Angle
Fig.-7: Various Degrees of Helical Angle
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Table 1- Design Features of Current Rotary NiTi file Systems
Instrument system
Cross-sectional
Design
Tip Design
Taper
Rotation
speed(rpm)
Other Features
Triple U shape with radial Non-cutting
Profile
(Dentsply Maillefer) lands. Neutral rake angle
planes dentin walls
Fixed Taper 2%,4%, 150-300
and 6%
20 o Helix Angle and
constant pitch
Triple-U shape with radial Non-cutting
GT Files
(Dentsply Maillefer) lands
Fixed Taper 4%,6%, 150-300
8%,10% & 12%
Files have a short cutting
portion. Variable pitch
Specific instrument 750-2000
sequence produces a
tapered shape
Thin flexible non-cutting
shaft and short cutting
head
Convex triangular sharp Non-cutting
ProTaper
(Dentsply Maillefer) cutting edge, No radial
land.F3, F4, F5 have U flutes
for increased flexibility
Variable taper along 250-350
the length of each
instrument
Pitch and helical angle
balanced to prevent
instruments screwing into
canals
HERO 642
(Micromega)
Triangular shape with Non-cutting
positive rake angle for
cutting efficiency. No radial
land
Fixed Taper 2%,4%, 300-600
and 6%
Variable pitch. File have
short cutting portion (1216mm)
K3
(Sybron Endo)
Positive rake angle for Non-cutting
cutting efficiency, three
radial lands and peripheral
blade relief for reduced
friction
Fixed Taper 2%,4%, 200-300
and 6%
Variable pitch and variable
core diameter
Flex Master
(VDW Munich
Germany)
Convex triangular shape Non-cutting
with sharp cutting edge and
no radial land
Fixed Taper 2%,4%, 150-300
and 6%
Intro file has 11% taper
Individual helical angle for
each instrument size to
reduce screw in effect.
RaCe
(FKG Switzerland)
Triangular shape (except Non-cutting
RaCe 15/0.02 and 20/0.02
which have a square shape),
two alternating cutting
edges, no radial lands
Fixed Taper 2%,4%, 300-600
6%,8% and 10%
Alternating cutting edge
along the file length due to
alternating twisted and
untwisted segments to
reduce screw-in effect.
Qauntec SC, LX
(Sybron Endo)
S-Shape design with double Cutting (SC)
Fixed Taper 2%,3%, 300-350
helical flute, positive rake
4%,5%,6%,8%,10%
angle and two wide radial Non-cutting(LX) and 12%
lands
Flutes space progressively
becomes larger distal to
cutting blade.
Light Speed
Instruments
(Lightspeed, San
Antonio TX)
Triple-U shape with radial Non-cutting
lands
CONCLUSION
The choice of a specific rotary system for daily use
requires consideration of the combined evaluation
of all described parameters. The question arises
that what is the best design and which is the superior
file. It really depends upon the working condition
like position of tooth in the arch, number of roots
and root canals, size of pulp space, degree and level
of curvatures of root canal. If you want a file that
cuts quickly, then a file such as the ProTaper or
RaCe may fulfill your needs. However, with a fast
file, you must understand the limitations and
potential complications. The progressive nature of
the taper does seem to put the file at greater risk for
separation, if there is any deviation from the
recommended technique. Additionally, the lack of
radial lands must be fully appreciated. If efficiency
3
with safety is more of an issue, perhaps the K
3
should be your choice. The K combines a noncutting tip, along with a positive rake angle with
variable pitch, and radial lands. If you prefer to
instrument your canals through a series of varying
tapers, then a system such as the GT or Quantec may
satisfy your needs. One thing we can say with
confidence is that before you choose a rotary file,
you must try it. Extracted teeth are of a big help in
this case. Understanding the fundamentals of file
design and combining that with your pre-clinical
The Journal of Ahmedabad Dental College and Hospital; 2(1), March 2011 - August 2011
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ZARNA SANGHVI et. al. : Rotary Instruments in Endodontics
trial will facilitate making the correct choice in
rotary files. Keep in mind, that as you become more
experienced your expectations of rotary files will
change. Eventually, you will realize there is a place
in the endodontic armamentarium for many of these
file designs. The ultimate goal is to be able to
confidently offer patient a root canal procedure,
which will hold up long term and be of equal or
greater longevity than that of an implant.
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