Introduction

In an endodontic treatment, the root canal system is

our road map to success. In the past, we have been

thinking only vertically. Many students were taught

that the first concern in root canal preparation was

“working length”. Now, we understand that the critical

issue is three-dimensionality.

Root canals exist as multiple inter-relationships. Root

canal systems are not cylinders but ribbons, sheets and

banners. Eccentrically and abnormality are “normal”.

Almost 30 years ago, Schilder introduced the concept

“cleaning and shaping”.

These 2 concepts are inseparable. The secret to successful

clinical endodontics is proper shaping.

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Cleaning:

Refers to the removal of all contents of the root canal

system before and during shaping.

Substrates, microflora, bacterial products, foods, caries etc.

Shaping

Refers to a specific cavity form with particular design

objectives. The shape permits vertical pluggers to fit

freely within the root canal system and to general

hydraulics required to transform and capture a

maximum cushion of gutta-percha and sealer into all

foramina.

The purpose of this seminar is to provide the rationale and

techniques for proper cleaning and shaping of the root canal

system, which will enable the clinician to obturate the system.

As with many aspects of dental profession, such as a

denture being no better than the initial impression, or

an inlay being no better than the tooth preparation, it

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follows that canal obturation will be no better than the

cleaning and shaping of the entire system.

Generally speaking, the 2 main objectives in canal cleaning and shaping

are:

Biologic Mechanical

Biologically, the

goal of intracanal

procedures is to remove all

pulp tissue remnants and

micro-organism and their

substrates along with

infected dentin.

Mechanically 3-D

shaping of the canal is the

objective which must be

accomplished to achieve

biologic cleaning.

BIOLOGIC OBJECTIVES

1. Confine all instrumentation within the root canal space to

maintain its spatial integrity.

Repeated instrumentation extending beyond the

constriction is unwarranted. It causes peri-radicular

inflammation and often destroys the normal biologic

constriction of the root apex.

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2. Avoid pushing contaminated debris past the confines of the

apical constriction.

Many instances of post treatment pain and swelling can

be attributed to necrotic tissue and micro-organism and

their toxins being inoculated into the peri-radicular

tissues as a result of indescriminate cleaning

procedures. This induces a rapid immunologic

response.

3. Remove all the potential irritants from the entire canal

system.

This avoids recurrent peri-radicular inflammatory and

creates a condition that permits prompt, uneventful

healing.

4. Establish the exact W.L and completely clean and shape the

canal system during the first treatment visit.

5. Create sufficient width in the coronal half of the canal system

to allow for copious flushing and debridement.

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MECHANICAL OBJECTIVES

1. Develop a continuously tapering conical form in the root

canal preparation.

The final preparation of this system should be an exact

replica of the original canal configuration in shape,

taper, and flow only larger. Only too often, canals are

simply “bored out” with the clinician failing to

consider the spatial relationship of the canal to the

overall root anatomy.

2. Prepare a sound apical dentine matrix at the DC junction.

This provides the resistance form to the intraradicular

cavity preparation. This also prevents the over-

extension of instruments and controls the apical

movement of gutta-percha sealer during obturation.

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3. Prepare the canal to taper apically, with the narrowest cross-

sectional diameter at the apical termination (apical dentin

matrix).

The apical third of the canal preparation must provide

a tapering / parallel, spatial configuration in order to

ensure a firm seating of the gutta-percha and sealer.

The three-dimensional shape of the preparation,

especially of the apical 1/3 rd, must provide a retentive

cavity to enhance condensation procedures.

4. Confine cleaning and shaping procedures to the canal system,

thereby maintaining the spatial integrity of the apical

foramen.

Adherence to this principle prevents violation of the

peri-radicular tissues. This principle is evident when

foramina are transported (moved) during excessive

apical instructions.

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External transportations takes 2

forms and may occur when

instrumentation is carried

beyond the apical matrix.

Internal transportation occurs

when the foramen becomes

clogged with dentin mud /

denticles

Ripping of the

apical end of

the foramen

resulting in a

tendrop /

hourglass shape

Direct

perforation

begins with a

ledge or apical

blockage

External transmission is caused

by failing to precurve files, or

being too heavy handed

5. Remove all residue of cleaning and shaping procedures that

could prevent patency of the apical foramen i.e. dentin

shavings and tissue debris.

Recapitulation is essential to all cleaning procedures

ignoring this important step will often lead to ledges,

loss of canal length, dev of false canals etc.

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Preparatory procedures

1) MAF-Master apical file

Is the largest file that binds slightly at correct WL after

straight line assess. It is determined by passively

placing the successively larger files at the C.W.L. until

correct size is reached which binds at the tip.

2) Pre curving of instruments

A precurved file is a valuable tool for feeling canal

passages and for moving around calcification, ledges

and around curved foramina.

It is used also in an attempt to alleviate the diverse

effects of canal curvature.

The primary difficulty is limited areas coronal to the

curvature.

May be done with a cotton wool roll, commercial

devices.

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Methods of Cleaning and Shaping

Cleaning and shaping are dynamically delicate

motions, flowing, rhythmic, and energetic. In order to

use files and reamers efficiently, the movements

require distinction. There are 6 distinctive motions of

files and reamers.

A) Follow:

Usually performed with files.

Are used initially during cleaning and shaping or any

time an obstruction blocks the foramen.

Irrigating, precurving different kinds of curves,

curving al the way to the tip of the instrument, and

multiple curves in multiple directions of the instrument

are all part of follow.

B) Follow-withdraw

Files are used.

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This motion is used once the foramen has been reched

and the next step is to create the path from access

cavity to foramen.

The motion is follow, then withdraw or “follow and

pull” or “follow and remove”. It is simply an in – or –

out, passive motion that makes no attempt to shape the

canal.

C) Cart

Refers to the extension of a reamer, to or near the

radiographic terminus.

The reamer should gently and randomly touch the

dentinal walls and “cart” away debris.

D) Carve

Is for shaping.

Reamers are used.

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The key is not to press the instrument apically but

simply and to touch the dentin with a precurves reamer

and shape on withdrawal randomly.

E) Smooth

Is accomplished with files.

In the past, most endo procedures were performed with

a smoothing or circumferential filing motion.

If the previous four motions are followed smoothing is

rarely required.

F) Patency

Is achieved with files/ reamers.

It means that the portal of exit has been cleared of any

debris in the path.

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Motion of instrumentation / envelopes of motion:

A) Filing:

Indicates a push-pull action with the instrument. The

inward passage of the file is powered by the hand and

the rigidity of the file. A canal wall can be damaged

very quickly by this motion (use of passive insertion

and pulling withdrawal from canal).

This is an effective technique with H-file since they do

not engage during the insertion action and cut

efficiently during the withdrawal motion.

Disadvantages:

With H-file that it can easily cut three middle of a

curvature and cause strip perforation.

B) Reaming

Indicates clockwise / right-hand rotation of an

instrument. The instrument must be restrained from

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insertion to generate a cutting effect. Instrument # is

increased when this motion is employed.

C) Turn-and-pull

Is a combination of reaming and filling, the file is

inserted with a ¼ turn clockwise and inwardly directed

hand pressure (i.e. reaming) positioned into the canal

by this action, the file is subsequently withdrawn (i.e.

filling).

The rotation during placement sets the cutting edges of

the file into dentin and the non-rotating withdrawal breaks

local the dentin that has been engaged.

Disadvantages:

Hourglass canal shapes were observed by Weine.

According to Schilder

Clockwise rotation of a half-revolution followed by

withdrawal. The file is not inserted towards the apex,

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rather, he gradually allows the preparation to progress

out of the canal.

¼ turn to right followed by straight pull out

D) Watch-winding

Is the back-and-forth oscilation of a file (30-60°) right

and (30-60°) left as the instrument is pushed into the

canal.

It is an expanded use of the insertion technique

described by Ingle as “Vaiven”.

This back-and-forth movement causes the files and

reamers to plane the walls efficiently.

In a way, this is a predecessor to the balanced force

technique, as the 30-60° of clockwise rotation pushes

the file tip and working edges into the canal and the

30-60° of counter clockwise motion partially cuts away

the engaged dentin.

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E) Watch-winding and pull

When used with H-files, watch winding cannot cut

dentin with the backstroke. It can only wiggle and

wedge the edges tightly into the wall.

With each clockwise turn, the instrument moves

apically until it meets resistance and must be freed with a

pull stroke.

F) Balanced force technique

This calls for oscillation of the preparation instruments

right and left with different arcs in either direction.

To insert an instrument, it is rotated to the right

(clockwise) a quarter turn. This pulls the instrument

into the canal and positions the cutting edges into the

walls.

Next, it is rotated left (counterclockwise) at least 1/3 rd

of the revolution to unthread the instrument and drive

it from the canal.

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Advantages:

Simultaneous apical and counter-clockwise rotation of

file strikes a balance between the tooth structure and

instrument elastic memory. This balance locates the

instrument very near the canal axis, even in severely

curved canals, so this technique avoids transportation.

It works effectively without pre-curving.

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Techniques for preparing root canals:

Apical coronal technique Coronal-apical technique

In which the WL is established

and the full length of the canal is

then prepared.

In which the coronal portion of

the canal is prepared before

determining the WL

e.g.

- Standardized.

- Step-back.

- Roane (balanced force)

Advantages:

Allows early

debridement of the coronal

part of canal which may

contain bulk of organic

debris.

Enables better and

deeper penetration of irrigant

early in the preparation.

Tends to shorten the

effective WL and determining

the WL after such

enlargement will reduce the

problem of its alteration

during preparation.

Allows better control

over apical instrumentation.

e.g. :

- Step-down.

- Double-flare.

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- Crown-down pressureless.

- Canal-master

Apical coronal

1) Standardized preparation:

- Done in narrow canals with circular cross-sections.

WL determined.

Smallest instrument adjusted to WL.

Sequentially enlarged entire canal.

Obturation with silver cone.

Disadvantages:

- Risk of extrusion of debris.

- Alteration of WL.

- Vertical root # is overinstrumentation is carried out.

2) Step back preparation:

WL determined.

Instrument that fills to correct WL is chosen.

Enlarge 3 No’s larger at the apex.

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Reduce the WL length by 1mm and continue to enlarge canal / flaring.

Recapitulate, irrigate for patency.

Coronal preparation done using GGD.

Disadvantages:

- Extrusion of debris.

- Apical blockage.

- Alteration of W.L.

- Tendency for canal deviations.

3) Roane Technique (Balanced Force)

Three of its main features are:

- Canals are prepared to predesigned dimensions of which 3

are recognized and are 45, 60 and 80 according to the size of

apical preparation.

- These dimensions refer to the size of the file used at the third

step back.

- Each step-back from the master apical file at the PDL is

0.5mm shorter than the previous one. This is termed as the

“apical control zone”.

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- Flex R files are used.

- WL determined to the radiographic apex with the largest file

placed without force. This helps in determining the selection

of predesigned preparation (45, 60, 80).

Coronal apical technique

1) Step down technique:

- Is a modification of the step-back technique.

Prepare the coronal portion to 16-18 mm /beginning of the curve with anti-curvature filling.

GGD’s are used to refine the coronal part.

Determine WL.

Using step-back, complete the apical preparation.

Disadvantages:

- Ledge formation.

- Apical blockage.

- Perforation.

Through this technique overcomes most of the disadvantages

of the step-back technique.

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2) Double Flared Technique:

Determine W.L.

Prepare till 14 mm / coronal to the curve.

Irrigate and clean.

Go 1mm deeper, maintaining instrumentation coronal to the curve and file.

Again 1mm deeper.

Continue till WL is achieved.

Prepare using step-back

Indications:

- For straight canals or

- For straight portions of curved canals.

Contra indications:

- In calcified canals.

- In young permanent teeth with open apices.

3) Crown-down pressureless technique:

- For curved canals without causing deviations. Rotary action

is used to cut dentine with the apical part of files.

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Determine WL and prepare till # 35 till 16mm (widen the canal with smaller files first)

Reduce size + go down and enlarge till apex.

Change to #40 + repeat.

4) Canal master technique:

- Its aim is to aid the maintenance of curves using a rotary

instrument designed so that only the apical 1-2mm is engaged

in dentine removal.

Advantages:

- Avoids the need for recapitulation.

- The apical 0.75mm of the hand instrument is safe-ended to

facilitate maintenance of canal curvature.

Determine WL

Prepare to the beginning of the curve

Use canal master in step-back fashion.

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Hybrid-technique

- Consists of reaming the apical third and filing the coronal

two-thirds.

- The coronal preparation is obturated using gutta-percha.

CURVATURE-THE ENGINE OF COMPLICATIONS

- As an instrument is curved, elastic forces develop internally.

These forces attempt to return the instrument to its original

shape and are responsible for straightening of the final canal

shape and location.

- These internal elastic forces (i.e. restoring forces) act on the

canal wall during preparation and influence the amount of

dentin removed. They are particularly influential at the

junction of the instrument tip and its cutting edges. This

region is the most efficient cutting surface along an

instrument, and when activated by the restoring forces, it

removes more tissue. This phenomenon is responsible for

apical transportation and its consequences.

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1) Pre-curving of instruments.

2) Anti-curvature filing

- Is the controlled and directed preparation into the

bulky/safety zones and away from the thinner portions or

danger zones of the root structure, where perforation or

stripping of the canal walls can occur.

Need:

- It is a method of applying instrument pressure so that shaping

will occur away from the inside of the root curvature in the

coronal and middle 1/3 rd of a canal.

- Was described by Abou-Rose, Frank and Glick. They

emphasized that during shaping procedures, files should be

pulled from canals as pressure is applied to the outside canal

wall. This dimensionally applied pressure, prevents

dangerous midcurvature straightening in curved canals.

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Advantages:

- It maintains the integrity of canal walls at their thin portion

and reduces the possibility of root perforation / stripping.

- Maintains digital control over the instrument and the

preparation of the curved canal is used.

Top of the handle is pulled

into the curvature while the

shank is pulled away (anti-

curvature)

3) Radicular access

- Was first promoted by Schilder.

- This creates space in the more coronal regions of the canal

which enhances placing and manipulating subsequent files as

it increases the depth and effectiveness of irrigation.

- May be accompanied by rotary instrument / circumferential

filing.

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4) Reversible Flaring / Pre-flaring

- Is the presently preferred development of flaring whereby the

coronal portion of the preparation is flared before the

completion of the apical portion.

- In the standard flaring technique, the apical portion of the

tooth is completed before any filling is performed.

- In the reverse flaring and aspects of preparations are carried

out.

- Minimal filling at the tip enlargement of the coronal part

apex is completed apical flaring.

Advantages:

- Irrigants are allowed to get down the canal earlier and farther

to produce cleaning.

- In curved canals, more effective preparation of the apical

area is provided when the file has fewer obstructions in the

coronal part.

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- Files, pluggers, filling material can penetrate to the apex

more easily three a larger orifice.

Instruments used for Reverse Flaring

- 0.4 taper instruments (Ni-Ti).

- MeXIM

Available in 5 instruments – 25.0.25 at Do (0.03, 0.04,

0.045, 0.05, 0.055 /mm – tapers).

Used in gear reduction handpieces at 340 rpm.

Made from Ni-Ti in H-style.

Designed by MacSpadden.

Ritano Files.

Hand instrument with H-configuration with several

tapers.

Made in lengths shorter than 21mm.

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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:

I) 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.

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II) 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.

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- 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.

III) 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

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3 instrument K-file with a safe ended tip.

H-file.

Universal file (flexible H-file with a safe-ended tip).

IV) Random

- E.g. Excalibur.

- K-files.

- 20,000-25,000rpm.

V) Sonics

- Endostar 5

- Endosonic Air 3000

Advantages:

- Reduces fatigue and stress during preparation.

VI) Ultrasonics

Magnetostrictive Peizoelectric

- Requires H2O cooling - Most common

- No H2O cooling

- May produce apical widening

and ledges in curved canals.

Advantages:

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- Cleaning effect is by acoustic streaming.

BIOMECHANICAL PREPARATION

Contents

Introduction

Mechanical & Biological Objectives

Methods of Cleaning & Shaping

Methods of Instrumentation

Techniques for Preparing Root canal

Hand Automated

Apical coronal Coronal Apical

Cleaning & Shaping in curved canals

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