Biomechanical preparation / dental implant courses

BIOMECHANICALBIOMECHANICAL
PREPARATIONPREPARATION
OF ROOT CANALOF ROOT CANAL
PART IIPART II
INDIAN DENTAL ACADEMYINDIAN DENTAL ACADEMY
Leader in continuing Dental EducationLeader in continuing Dental Education
www.indiandentalacademy.comwww.indiandentalacademy.com

 Cleaning and shaping technical issuesCleaning and shaping technical issues
 Hand and engine driven instrumentsHand and engine driven instruments
 Stress on protaperStress on protaper
 Steps for radicular preparation—cohenSteps for radicular preparation—cohen
 Iej 2001 articlesIej 2001 articles

CLEANING AND SHAPING:TECHNICAL ISSUES
Because several technical issues arise with the instruments and devices
used for cleaning and shaping.
A vast array of instruments, both hand-held and engine-driven, is
available for root canal preparation.Up to the last decade of the past
century, endodontic instruments were manufactured from stainless steel.
With the advent of nickel-titanium, instrument designs began to vary in
terms of taper, length of cutting blades, and tip design. Files traditionally
have been produced according to empiric designs, and most instruments
still are devised by individual clinicians rather than developed through
an evidence-based approach.

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Similar to the development of composite resins in restorative
dentistry, the development of new files is a fast and market-driven
process. With new versions rapidly becoming available, the
clinician may find it difficult to pick the file and technique most
suitable for an individual case.
Practitioners must always bear in mind that all file systems have
benefits and weaknesses. Ultimately, clinical experience, handling
properties, usage safety, and case outcomes, rather than
marketing or the inventor’s name, should decide the fate of a
particular
design.

Hand and Engine-Driven Instruments
Hand instruments have been in clinical use for almost
100 years, and they still are an integral part of cleaning
and shaping procedures. A norm established by the
American Dental Association (ADA) and the International
Standards Organization (ISO)13,131 sets the standards for broaches, K-
type files and reamers, Hedström
files, and paste carries; however, the term ISO-normed
instruments currently is used mainly for K-files. One important feature
of these instruments is a
defined increase in diameter of 0.05mm or 0.1mm,
depending on the instrument size

Broaches
Barbed broaches produced in variety of sizes and color codes.
manufactured by cutting sharp,coronally angulated barbs into metal wire
blanks.
Broaches are intended to remove vital pulp
in cases of mild inflammation, they work well for severing pulp at the
constriction level
in toto.
The use of broaches has declined since the advent of NiTi rotary shaping
instruments, but broaching
occasionally may be useful for expediting procedures and for removing
materials (e.g., cotton pellets)
from canals

K-Files
K-files manufactured by twisting square or triangular metal blanks along
their long axis, producing partly horizontal cutting blades.
Noncutting tips, also called Batt tips, are created by grinding and
smoothing the apical end of the instrument .
Roane and Powell introduced a modified shape, the Flex-R file, which
was manufactured fully by grinding so that the transitional angles were
smoothed laterally between the tip and the instrument’s working parts.
Similar techniques are required to manufacture NiTi K-files, such as the
NiTi-Flex (Dentsply Maillefer, Ballaigues, Switzerland). NiTi K-files
are extremely flexible and are especially useful for apical enlargement in
severe apical curves.

They can be precurved but only
with strong overbending; this subjects the file to excess strain and
should be done carefully. Because of their flexibility, the smaller
NiTi files (sizes up to #25) are of limited use.
Cross-sectional analysis of a K-file reveals why this design allows
careful application of clockwise and counterclockwise rotational
and translational working strokes. ISO-normed K- and Hedström
files are available in different lengths (21, 25, and 31 mm), but all
have a 16mm long section of cutting flutes

Hedström Files
Hedström files are milled from round, stainless steel blanks.
They are very efficient for translational strokes but rotational working
movements are strongly discouraged
because of the possibility of fracture.
Hedström files up to size #25 can be efficiently used to relocate canal
orifices and, with adequate filing strokes, to remove overhangs.
Similarly, wide oval canals can be instrumented with Hedström files as
well as with rotary instruments.
On the other hand, overzealous filing can lead to considerable thinning
of the radicular wall and
strip perforations.
As with stainless steel K-
files, Hedström files should be single-use instruments

Gates-Glidden Drills
Gates-Glidden (GG) drills are important instruments that have been used for more than
100 years without noteworthy design changes.
These instruments, especially the nickel-titanium FlexoGates model (Dentsply
Maillefer), usually work well for preenlargement of coronal canal areas.77,174
However, when misused, GG drills can dramatically reduce radicular wall thickness.
GG 1 to 6 (with corresponding diameters of 0.5 to 1.5 mm); the number of rings on the
shank identifies the specific drill size. GG instruments are available in various lengths.
Each instrument has a long, thin shaft with parallel walls and a short cutting head.
Because of their design and physical properties, GG drills are side-cutting instruments
with safety tips; they can be used to cut dentin as they are withdrawn from the canal
(i.e., on the outstroke).
Used this way, their cutting action can deliberately be directed away from external root
concavities in single-rooted and furcated teeth
GG instruments should be used only in the straight portions of the canal, and they
should be used serially and passively

Two procedural sequences have been proposed: with
the step-down technique, the clinician starts with a large Shaping of the
Root Canal System orifice and progression for about 1 mm. The
subsequent
smaller instruments progress deeper into the canal until the coronal third
has been preenlarged.
This technique efficiently opens root canal orifices and works best when
canals exit the access cavity without severe angulations.
Opened orifices simplify subsequent cleaning and shaping procedures
and help to establish a smooth glide path from the access cavity into the
root canal system.

With the step-back approach, a small GG instrument is introduced into
the canal and dentin is removed on the outstroke.
This process is repeated with the next larger GG instrument, which is
again worked shorter
than the preceding smaller one. In this way, the coronal third of the root
canal is enlarged and dentin overhangs are removed.
As stated earlier, when used adequately GG instruments are inexpensive,
safe, and clinically beneficial tools.
High revolutions per minute (rpm), excessive pressure, an incorrect
angle of insertion, and the use of GG instruments to aggressively drill
into canals have resulted in mishaps, such as strip perforation.

Also, GG instruments may fracture when used in curved canal
areas because of cyclic fatigue, and the short cutting heads may
fracture with high torsional loads.
Gates-Glidden drills may be used safely and to their fullest
potential at 750 to 1500 rpm.
As with nickel-titanium rotary instruments, GG drills work best
when used in electric gear reduction handpieces rather than with
air motors.

Nickel-Titanium Rotary Instruments
Since the early 1990s, several instrument systems manufactured from nickel-titanium
have been introduced into endodontic practice.
The specific design characteristics vary, such as tip sizing, taper, cross section, helix
angle, and pitch
Some of the early systems have been removed from the market or play only minor
roles;
others, such as LightSpeed (LightSpeed Technologies,San Antonio, TX) and ProFile
(Dentsply–Tulsa,Dentsply Maillefer), are still widely used.
manufactured by a grinding process, although some are produced by laser etching.
Precision at the surface quality is not really at a high level, whereas the tolerances are.
Surface quality also is an important detail , because cracks that arise from superficial
defects play a role in instrument fracture.
Superficial defects such as metal flash and rollover are common in unused NiTi
instruments
Attempts have been made to improve surface quality by electropolishing the surface
and by coating it with titanium nitride
The latter process also seems to have a beneficial effect on cutting efficiency.

In essence, two properties of the NiTi alloy are of particular interest in
endodontics: superelasticity and high resistance to cyclic fatigue
These two properties allow continuously rotating instruments to be used
successfully in curved root canals. Many variables and physical
properties influence the clinical performance of NiTi rotaries
Much of what is known about NiTi instruments,including reasons for
instrument fracture18 and instrument
sequences, has been gleaned from clinical practice.
In vitro research continues to clarify the relationship between NiTi
metallurgy and instrument performance, but already
NiTi rotary instruments have become an important adjunct in
endodontics.
NiTi rotary instruments have substantially reduced the incidence of
several clinical problems, such as
blocks, ledges, transportation, and perforation.
However, they also have a tendency to fracture more easily than hand
instrumentswww.indiandentalacademy.comwww.indiandentalacademy.com

LightSpeed Instruments
The LightSpeed file, developed by Dr. Steve Senia and Dr. William Wildey in the early
1990s, was introduced as an instrument different from all others because of its long,
thin, noncutting shaft and 0.25 to
2mm anterior cutting part.
A full set consists of 25 instruments in sizes #20 to #100, including half sizes
The recommended working speed for LightSpeed instruments is 1500 to 2000 rpm, and
they should be
used with minimal torque
The cross sections of the LightSpeed’s cutting part show three round excavations, the
U-shape design
common to many earlier NiTi instruments.
Because of the relatively thin noncutting shaft, LightSpeed instruments are
considerably more
flexible than any other instrument on the market.
In addition, cyclic fatigue is lower than with all other instruments, allowing the use of
higher rpm speeds. All LightSpeed instruments feature a noncutting round tip; tip
length increases with instrument size to compensate for decreasing flexibility.

The LightSpeed’s predecessor, the Canal Master-U,had the same general
design but was used as a hand instrument.
LightSpeed’s manufacturer still recommends some hand use of its
instruments, specifically for
determining canal diameter.
In general, the LightSpeedsystem requires a specific instrument
sequence to produce a tapered shape that facilitates obturation with a
gutta-percha cone or with LightSpeed’s proprietary obturation system.
The LightSpeed is a widely researched NiTi rotary instrument, and most
reports have found that the system has a low incidence of canal
transportation and preparation errors.* Loss of working length was
minimal in most of these studies.

ProFile
The ProFile system was introduced by Dr. Ben Johnson in 1994.
In contrast to the LightSpeed, with its thin, flexible shaft, the ProFile has an increased
taper compare with conventional hand instruments.
The ProFile first was sold as a series of 29 hand instruments in #.02 taper,but it soon
became available in #.04 and #.06 conicity
The tips of the ProFile Series 29 rotary instruments (Dentsply–Tulsa) had a constant
proportion of diameter increments (29%).
Because of the nonstandardized diameters, obturation was performed with
nonstandardized gutta-percha cones, using either lateral compaction or thermoplastic
obturation of gutta-percha
Later, another ProFile series (Dentsply Maillefer) was developed and marketed in
Europe.
This version featured tip sizes similar to those of ISOnormed instruments.
This set was believed to better accommodate standardized gutta-percha cones, which
are predominantly used in Europe.
Subsequently,instruments with even greater tapers and 19mm lengths were introduced,
and recently a #.02 variant was added

Cross sections of a ProFile instrument show a U-shape design with radial
lands and a parallel central core.
Lateral views show a 20-degree helix angle, a constant pitch, and bullet-
shaped, noncutting tips. Together with a neutral or slightly negative rake
angle, this configuration ensures a reaming or scraping action on dentin
rather than cutting.
Also, debris is transported coronally and is effectively removed from the
root canals.
The recommended rotational speed for ProFile instruments is 150 to 300
rpm, and to ensure a constant rpm level, the preferred means is electrical
motors with gear reduction rather than air-driven motors.
ProFile instruments shaped canals without major preparation errors in a
number of in vitro investigations.*
A slight improvement in canal shape was noted when size #.04 and #.06
tapered instruments were used in an alternating fashion
Loss of working length did not exceed 0.5 mm and was not affected by
the use of size #.06 instruments.www.indiandentalacademy.comwww.indiandentalacademy.com

GT Files
The Greater Taper file, or GT file (Fig. 9-25), was introduced by Dr.
Buchanan in 1994.
This instrument also incorporates the U-file design.
The GT system was first produced as a set of four hand-operated files
and later as engine-driven files. The instruments came in four tapers
(#.06, #.08, #.10, and #.12), and the maximum diameter of the working
part was 1 mm
. This decreased the length of the cutting flutes and increased the taper.
The instruments had a variable pitch and an increasing number of flutes
in progression to the tip; the apical instrument diameter was 0.2 mm.
Instrument tips were noncutting and rounded.
The GT set subsequently was modified to accommodate
a wider range of apical sizes.
Compared with ProFile and LightSpeed preparations These walls were
homogeneously machined and smoothwww.indiandentalacademy.comwww.indiandentalacademy.com

HERO 642
First-generation rotary systems had neutral or slightly negative rake
angles.
Second-generation systems were designed with positive rake angles,
which gave them greater cutting efficiency.
HERO instruments (MicroMega, Besançon, France) are an example of a
second-generation system.
Cross sections of a HERO instrument show geometries similar to those
of an H-file without radial lands
Tapers of #.02, #.04, and #.06 are available in sizes ranging from #20 to
#45
The instruments are relatively flexible (the acronym HERO stands for
high elasticity in rotation) but maintain an even distribution of force into
the cutting areas
HERO instruments have a progressive flute pitch and a noncutting,
passive tip, similar to other NiTi rotary systems.

ProTaper
The ProTaper system is based on a unique concept and comprises just
six instruments, three shaping files and three finishing files.
These instruments were designed by Dr. Cliff Ruddle, Dr. John West,
and Dr. Pierre Machtou.
The cross section of the ProTaper shows a modified Ktype file with
sharp cutting edges and no radial lands
This creates a stable core and sufficient flexibility for the smaller files.
The cross section of finishing file F3 is slightly relieved for increased
flexibility.
The unique design factor is the varying tapers along the instruments’
long axes.
The three shaping files have tapers that increase coronally, and the
reverse pattern is seen in the three finishing files.

Shaping files #1 and #2 have tip diameters of 0.185mm and 0.2mm,
respectively, 14 mm long cutting blades, and partially active tips.
The diameters of these files at D14 are 1.2 and 1.1 mm, respectively. The
finishing files (F1, F2, and F3) have tip diameters of 0.2, 0.25, and 0.3
mm, respectively, between D0 and D3, and the tapers are 0.07, 0.08, and
0.09, respectively.
The finishing files have noncutting tips.
The convex triangular cross section of ProTaper instruments reduces the
contact areas between the file and the dentin.
The greater cutting efficiency inherent in this design has been safely
improved by balancing the pitch and helix angle, preventing the
instruments from inadvertently screwing into the canal.
The instruments are coded by colored rings on the handles.
ProTaper instruments can be used in gear reduction electrical
handpieces at 300 rpm in accordance with universally recognized
guidelineswww.indiandentalacademy.comwww.indiandentalacademy.com

ProTaper Benefits.
1. The progressive (multiple) taper design improves
flexibility and “carving” efficiency, an important
asset in curved and restrictive canals
2. The balanced pitch and helical angles of the instrument
optimize cutting action while effectively augering debris coronally,
as well as preventing the instrument from screwing into the canal.
3. Both the “shapers” and the “finishers” remove the debris and
soft tissue from the canal and finish the preparation with a smooth
continuous taper.
4. The triangular cross-section of the instruments increases
safety, cutting action, and tactile sense while reducing the lateral
contact area between the file and the dentin
5. The modified guiding instrument tip can easily follow
a prepared glide path without gouging side walls.www.indiandentalacademy.comwww.indiandentalacademy.com

Canal Preparation.
ProTaper System: Guidelines for Use
1. Prepare a straight-line access cavity with no restrictions in the
entry path into the chamber.
2. Fill the access cavity brimful with sodium hypochlorite and/or
ProLube.
3. Establish a smooth glide path with No. 10 and No.15 stainless
steel hand files.
4. Use maximum magnification to observe the movement of the
rotary instrument. “Seeing” rotary apical movement is safer than
simply “feeling” such movement.
5. Use a torque- and speed-controlled electric motor,powering the
handpiece at 200 to 300 rpm.
6. Be much gentler than with hand instruments.Always treat in a
moist canal. Irrigate frequently!
7. Slow down! Each instrument should do minimal shaping. Only
two, three, or four passes may be required for the file to engage
restrictive dentin and carve the shape to the proper depth.www.indiandentalacademy.comwww.indiandentalacademy.com

8. Instruments break when flutes become loaded or when
instruments are forced. Check the flutes frequently under
magnification and clean them. Cyclic fatigue from overuse, or if
the glide path is not well established, also leads to breakage.
9. ProTaper instruments are disposable and, like all endodontic
files and reamers, are designed for single-patient use. Sometimes
instruments are even changed within the same treatment (eg, in
the case of a four-canal molar).
10. Irrigate with 17% EDTA or a viscous chelator during
the ProTaper shaping.

ProTaper System: Directions for Use
1. Establish proper access and a glide path with No. 10 and No. 15 stainless
steel files to the working length or the apical constriction exit.
2. Flood the canal and chamber with sodium hypochlorite and begin shaping
with the Shaper S-1 using multiple, passive-pressure passes. Go no
deeper than three-quarters of the estimated canal length.Irrigate and
recapitulate with a No. 10 hand file,establishing patency to full working
length. Now,with S-1, extend the preparation to full working length. Again
irrigate and recapitulate.
3. “Brush” with the Shaper S-X to improve the straight-line access in short
teeth or to relocate canal access away from furcations in posterior teeth.
4. Shaping file S-2 is now used to full working length.Irrigate, recapitulate,
and reirrigate.
5. Confirm and maintain working length with a hand file. (Remember, as curves
are straightened, canals are shortened.)
6. With Finisher F-1, passively extend the preparation to within 0.5 mm of the
working length. Withdraw after one second! And only one second!
The F-1 has a tip size of 0.20 mm, and if a No. 20 hand instrument is found
to be snug, the preparation is finished.With the instrument in place,
radiographically verify the exact length before final irrigation.

7. If the F-1 and the No. 20 hand file are loose, continue the
preparation with the Finisher F-2, which is 0.25 mm diameter at
the tip. Confirm with a No. 25 hand instrument and, if snug,
confirm the length radiographically, irrigate, and complete.
8. If the F-2 instrument and the No. 25 hand file are loose,
continue the preparation to just short of the working length with
the Finisher F-3 file, which has a 0.30 mm tip diameter, and
follow with the confirming No. 30 instrument. If the No. 30 is found
to be snug, the preparation is finished . If this is loose, there are a
number of techniques to enlarge the apical third to larger sizes.
9. Frequent irrigation and file cleansing are imperative—
irrigation and recapitulation!

K3
In a sequence of constant development by their inventor,Dr. McSpadden,
the Quantec 2000 files were followed by the Quantec SC, the Quantec
LX, and the current K3 system (all by SybronEndo).
The overall design of the K3 is similar to that of the ProFile and
theHERO in that it includes size #.02, #.04, and #.06 instruments.
Research with the K3 is limited because of its recent introduction, but
thus far its shaping ability seems to be similar to that of the ProTaper30
and superior to that achieved with hand instruments

FlexMaster
The FlexMaster file system currently is not available in the United
States. It also features #.02, #.04, and #.06 tapers.
The cross sections have a triangular shape with sharp cutting
edges and no radial lands.
This makes for a relatively solid instrument core and excellent
cutting ability.
RaCe
The RaCe was manufactured since 1999 by FKG and was later
distributed in the United States by Brasseler (Savannah, GA).
The name, which stands for reamer with alternating cutting edges,
describes just one design feature of this instrument .

Preparation using Automated Devices
Disadvantages:
Loss of tactile sense and lack of control of where and how
much dentine is removed from the root canal wall.
Classification:
Rotary
Used in slow running standard handpiece e.g., GGD, Peeso, Canal
master – used only in the structure part.
Latest deviation is the new 16:1 gear reduction handpiece NiTi matic at
300rpm.
Ni-Ti files are used.
Used for preparation of severely curved canals.
Files are manufactured with an off-centre tip that facilitates negotiating
around curvatures and ledges.

Reciprocal quarter turn:
This uses a special handpiece that contrarotates the instrument three 90°.
E.g. Giromatic (1964).
Endocursor.
Endolift – has a vertical component in addition to the rotation.

Disadvantages of Automated
Hand instrument requires the same amount of time as automated.
Flare preparation with hand instrument tends to remove debris from within
the canal system than automated.
Automated is difficult to use in the most post regions of the oral cavity.
There is greater propensity for the automated system to produce zipped
canals, ledges etc.
A controlled power-assisted system designed to eliminate the original
problems encountered by Giromatic appeared in 1981.
Dynatrak
Uses stainless steel instruments with increased flexibility consist flute
depth and curved canals and rounded tip to minimize and control ledges,
zips, etc.

Vertical
Canal finder.
Has a vertical movement of 3-1 mm and free rotational
movement.
Instrument used is canal master (H-file with a safe ended tip).
Canal Lender.
Vertical movement of 0.4-0.8 mm
3 instrument K-file with a safe ended tip.
H-file.
Universal file (flexible H-file with a safe-ended tip).

Random
E.g. Excalibur.
K-files.
20,000-25,000rpm.
Sonics
Endostar 5
Endosonic Air 3000
Advantages:
Reduces fatigue and stress during preparation.
Ultrasonics
Magnetostrictive Peizoelectric
- Requires H2O cooling - Most common
- No H2O cooling
- May produce apical widening
and ledges in curved canals.
Advantages:
Cleaning effect is by acoustic streaming.

LASER-ASSISTED CANAL PREPARATION
After the development of the ruby laser by Maiman in 1960, Stern
and Sognnaes (1964) were the first investigators to look at the
effects of ruby laser irradiation on hard dental tissues.
Early studies of the effects of lasers on hard dental tissues were
based simply on theempirical use of available lasers and an
examination of the tissue modified by various techniques.
Laser stands for Light Amplification by Stimulated Emission of
Radiation, and it is characterized by being monochromatic (one
color/one wavelength), coherent, and unidirectional. These are
specific qualities that differentiate the laser light from, say, an
incandescent light bulb.

 Some steps for preparation From cohenSome steps for preparation From cohen

Abstract
Buchanan LS.
The standardized-taper root canal preparation – Part 1. Concepts
for variably tapered shaping instruments.
International Endodontic Journal 33 , 516–529, 2000.
Aim
To introduce the concept of variable taper instruments for
predictable and ergonomic root canal preparation, and
demonstrate the design features of Greater Taper files.

Key learning points
• Canal preparation is difficult to practice and teach with traditional
K-files and Gates Glidden drills.
• Variable Taper files are designed to offer the optimal preparation
features of adequate (not excessive) coronal enlargement, full
deep shape, and apical resistance form in a
simple instrument sequence.
• Variable Taper technique is simple to master, and offers
predictable cleaning and obturation outcomes, even in
inexperienced hands.

Problems with traditional preparations
Once a root canal has been negotiated to its terminus and its
length determined, the only thing standing in the way of thoroughly
cleaning and filling it is the need for ideal shape.
Without adequate shape, the irrigation devices available at this
time cannot adequately clean complex root canals to their full
apical and lateral extents (Coffae & Brilliant 1975).
Likewise, our obturation results, regardless of the filling technique
used, are almost wholly dependent upon the shape into which the
filling materials are placed (Schilder 1974).

Unfortunately, shaping root canals has been dangerous, difficult,
and time-consuming
Ccoronal enlargement has often been excessive, resultingin strip
perforations
Any iatrogenic result in the apical third of a root can be repaired
predictably.
This is not so in the cervical third of roots . Even with the
phenomenal new perforation repair material, MTA,strip
perforation of a molar root dramatically lowers that tooth’s long-
term prognosis.
This, in fact, is the worst possible outcome for conventional
endodontic treatment and must be avoided at any cost.

The more common, but less noticed, failures are long-term losses due to
vertical fracture
when roots are not perforated but unduly weakened.
Endodontists say,‘The root is mine!’ meaning that the shapes we create in root
canals the roots are not ours. They are the patients’ roots, and they may have
to function for 50 or 60 years.
Aside from coronal leakage, root fractures are the competent endodontist’s
greatest threat to long-term clinical success.
Shapes achieved by the use of relatively nontapered coronal enlargement
tools, such as Gates Glidden or Peezo burs, are at best, irregular.
Whilst experienced clinicians can learn how to use these cutting instruments
safely, neophytes are destined for painful learning experiences

A less disastrous but frequent outcome is the inadequate cleaning and filling
that
routinely results from ineffective shaping in the apical half of the canal. Two
classic
preparation deficits are seen in this region:
• ‘Anaemic’ enlargement in the middle third (not enough deep shape), and
• Over-enlargement of the apical preparation (Fig. 4).
Inadequate shape in the middle third of canals is a setup for poor cleaning, as
irrigating solutions cannot be introduced to the full apical and lateral extents of
root canal systems.
Obturation results degraded, especially in the apical third.
More than half of all cone-fitting and condensation problems caused by
‘anaemic’ deep shape due to premature binding of cones and condensation
devices (including Thermafil carriers).
Apically, the classic error is to over-enlarge the terminal diameter of the canal.
Taking successively larger files to the same length in a root canal is a setup for
apical lacerations, even when using the Balanced Force technique (Roane et al
. 1985). If the working length is too short (1–2 mm), the canal is often ledged,
causing poor apical cleaning and a short fill. If the working length is even
slightly in error beyond the terminus, all working length has been lost.

Abstract
Buchanan LS.
The standardized-taper root canal preparation – Part 2.
GT file selection and safe handpiece-driven file use.
Aim
To present guidelines on GT file selection, and safe operation.
Summary
It is not necessary to remove excessive dentine for effective root canal
preparation. GT files allow safe, standardized preparation, and should be
selected to fit the case in hand.
Small Root canals should be prepared with 0.06 and 0.08 taper GT files
Large Root canals should be prepared with 0.10 GT or 0.12 Accessory GT
files. The greatest challenge is un-learning habits acquired from traditional
instrumentation methods.
GT files should be used with light touch, and without up–down pumping
motions. Spin speeds should be controlled below 300 r.p.m. for routine
preparation. GT files are subject to fatigue and should be tracked to avoid
overuse. It is recommended that GT files are discarded after the equivalent of
five root canal preparations.
For severe curvatures, GT files should be single-case tools.www.indiandentalacademy.comwww.indiandentalacademy.com

Key learning points
• The standard GT file set comprises three instruments of 0.06,
0.08 and 0.10 taper. All are size 20 at the tip, and have a
maximum diameter of 1 mm.
• Accessory GT files have a standard taper 0.12, and maximum
diameter of 1.5 mm. They are available in tip sizes 35, 50 and 70.
• Large Roots are lower canines, upper anteriors, upper and lower
single-rooted premolars, palatal roots of upper molars and distal
roots of lower molars. They should be prepared
with 0.10 GT or 0.12 Accessory GT files.
• Small Roots are lower incisors, multirooted premolars, buccal
roots of upper molars and mesial roots of lower molars. They
should be prepared with 0.06 or 0.08 GT files.
• All GT files should be used with light force and at the correct spin
speed.
• GT files should be discarded after the equivalent of five root
canal uses.

Abstract
Buchanan LS.
The standardized-taper root canal preparation – Part 3. GT file technique in
Large Root canals with small apical diameters.
Aim
To describe the preparation of Large Root canals with small apical diameters
by the GT file technique.
Summary
One to three GT files; one to nine clinical steps, and one to five minutes of
clinical time.
Following proper access, pulp tissue should be removed, and lubricant applied
to prevent pulp compaction and blockage.
Initial crown-down enlargement is accomplished with up to three standard GT
rotary files 0.10, 0.08 and 0.06 taper, running at 300 r.p.m.,and with light touch.
Care taken not to overload instruments, and they should be withdrawn, cleaned
and inspected whenever they bind.
Prior to cone-fit, the apical resistance form is confirmed with conventional files,
employed as feeler gauges of the tapering form created at the canal terminus.
Regardless of the shaping time, canals should be soaked with sodium
hypochlorite solution for at least 30 min for effective cleaning.www.indiandentalacademy.comwww.indiandentalacademy.com

Key learning points
• Large Root canals with small apical diameters should be
prepared to shaping objectives 0.08 or 0.10 taper.
• Compacted pulp tissue causes many canal blockages. It should
be removed early, and canals should be well lubricated.
• Large Root canals with small apical diameters should be
prepared in crown-down sequence, with recapitulation of steps
until the shaping objective is achieved.
• Apical resistance form should always be confirmed before cone-
fit.
• Canals should be exposed to sodium hypochlorite for at least 30
min for effective cleaning.

Abstract
Buchanan LS.
Large
Root canals with large apical diameters.
International Endodontic Journal34, 157–164, 2001.
Aim
To describe the GT file shaping steps required to create apical resistance in the
presence of a wide root apex.
Summary
Canals are occasionally encountered with apices wider than 0.25 mm.
These can be some of the most difficult to manage with conventional
instruments, and
overfills are common. Shaping such canals with GT files requires a paradigm
shift of
thinking, extending tapered files through the apex to create linear resistance in
the apical few mm of the canal. GT standard and accessory files allow canals
with apices up to around 0.7 mm to be prepared for tapered gutta percha cone-
fit. Apices larger than this should be considered too large for further shaping,
and repaired with MTA before filling.www.indiandentalacademy.comwww.indiandentalacademy.com

. Key learning points
•
Tapered apical preparations offer optimal resistance form for
obturation.
•
Tapered apical preparations can be prepared in most roots with
wide apices by
extending GT files and GT accessory files to or through the apex.
•
Apices wider than 0.7 mm should be repaired with MTA prior to
filling

Shaping canals with wide apices
The GT method of shaping canals with larger apical diameters is
to cut one of the 0.12 accessory GT files to length and to gauge
again.
Be certain that the root in question is large enough in diameter to
safely accept the 1.5 mm maximum flute diameters (MFD)
of the 0.12 accessory GT files. If you are in a distal root of a lower
molar, which is long, thin and curved, and you find out the terminal
diameter of the canal is 0.35 mm,
Take the 0.10 GT file 1.5 mm long rather than risk perforation with
the size35-0.12 accessory GT file in that particular root.

Abstract
Buchanan LS.
The standardized-taper root canal preparation – Part 5. GT file
technique in Small Root
canals.
International Endodontic Journal34 , 244–249, 2001.
Aim
To describe the shaping of Small Root canals with GT files.
Summary
Small Roots are lower incisors, two and three canal bicuspids,
buccal roots of upper molars, and mesial roots of lower molars.
The Shaping Objective instrument for such cases is usually a 0.08
or 0.06 taper GT file.
After proper access, pulp tissue should be removed to prevent its
compaction and canal blockage. Orifice shaping and smoothing is
then achieved with a 35-0.12 accessory GT File, running at full
slow-speed r.p.m.(5–20K).

Crown-down preparation commences with the 0.10 GT file,
followed by the 0.08 and 0.06 tapers as needed.
Occasionally, a 20-0.04 Profile is required to reach length. Files
are rotated at 300 r.p.m. with steady, light pressure, and
withdrawn frequently for cleaning and inspection.
Once one of these files has cut to length, the canal terminus is
enlarged to Shaping Objective.
If difficulty is encountered, be willing to accept a 0.06 instead of
the original 0.08 taper Shaping Objective.
If the terminal diameter is 0.2 mm you will have plenty of apical
resistance form in a tortuous canal with the 0.06 taper
preparation.
It is definitely better to end up with a smaller shape than originally
planned, than to experience the heartache of separation.

Key learning points
• Small Root canals should be prepared to a Shaping Objective
0.08 or 0.06 taper.
• Pulp tissue should be removed before preparation to prevent
compaction and blockage.
• Preparation follows in a crown-down sequence, and may
occasionally require the use of small Profiles.
• Final apical shaping is easily achieved when root length is
reached.

Abstract
Buchanan LS.
abruptly curvey canals.
Aim
To describe the application of GT files in roots with abrupt curvatures.
Summary
Most dentists interpret obstructions to instrument progress as calcification,
rather than abrupt curvature.
Basically, there are not any apically calcified canals, only clinicians who are
not clever enough or patient enough to sneak to patency.
Dentists should be on their guard and sensitive to the ‘rubber band’ sensation
of residual pulp tissue, and the ‘loose resistance’ sensation of the curved or
ledged canal. Residual pulp tissue should be removed and the canal lubricated.
The ledged or curved canal will only be helped by file bending. The size 10 file
test is the key to identify canals requiring pre-bent instruments.
The canal should first be flared short of the obstruction, before shaping the
canal after it with regular, pre-bent K-files. Pre-bent GT hand-files can then be
used with care to blend the apical and more coronal regions for final shape.
Cone-fit may then require chilling and pre-bending GP cones (pre-bend more
than one), before packing the canal.

Key learning points
•
Root canals do not calcify apically.
•
File progress is prevented by pulp tissue, abrupt curvatures or
ledging.
•
Loose resistance to the passage of a size 10 file shows the canals
that require instrument
pre-bending. This test should be repeated at intervals during the
preparation.
•
Even NiTi GT files can be pre-bent for use in abrupt curves.
•
Gutta percha cones can be pre-bent after chilling.

Conclusions
Shaping root canals, for the experienced, discriminating dentist,
has traditionally taken 30–45 min per canal, depending on the
canal and the clinician.
Variably tapered nickel titanium rotary GT files have absolutely
revolutionized that process, and because this system is a more
than 10X improvement over previous methods, it is here to stay .
GT files, in the hands of dental students in their first experience
with the instruments cut ideal preparation shapes in every case. It
took them an average of 22 min to create an inconsistently
tapered preparation with K-files and Gates-Glidden burs. It took
an average of 4 min to create consistently ideal root canal
preparations with rotary GT files (Buchanan 2000).
In addition, they are a system of files designed specifically (for the
first time) to address every anatomic challenge presented to the
practising clinician.

THANK YOUwww.indiandentalacademy.comwww.indiandentalacademy.com

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