cleaning & shaping

CONTENTS

• Introduction

• History

• Guidelines for S & C

• Schilder’s Objectives

• Principles

• Variations in Morphology

• Functional Motions

• RC working width

• Instrumentation Techniques

• Standardized

• Conventional Stepback

• Modified Stepback

• Passive Stepback

• Crown-down

• Crown-down Pressureless

• Double Flared

• Modified Double Flared

• Balanced Force

CONTENTS

• Instrumentation Techniques

• Modified Balanced Force

• Reverse Balanced Force

• Hybrid

• Canal Master Technique

• Non Instrumentation

• Laser Assisted Instrumentation

• Ultrasonic Instrumentation

• Sonic Instrumentation

• Special Anatomic Problems

• Curved Canals

• Calcified Canals

• C-shaped Canals

• S-shaped Canals

• Evaluation Criteria of Canal Preparation

• Iatrogenic Errors

• Conclusion

• References

Introduction

• Success – how well the canals are shaped and cleaned.

• S & C – important phase in endodontic treatment

• Root canal system must be:

• Cleaned of pulp tissue & debris

• Shaped to receive a 3-D filling of the entire RC space

Baumgartner & Madder We shape the canals with instruments and clean the canals with irrigants.

Instruments are sharp, dentin is soft, so at most cautious use of instruments are advised.

• Pulp Space :

• Organic Substances, Microflora, Bacterial Byproducts

• Food, Caries, Pulp Stones

• Previous RC fillings & Dentinal filings from RC Preparation

Of all the phases of anatomic study in the human system, one of the most complex is the pulp cavity morphology.

- M.T. Barrett

• Principle :

• To remove all organic debris & microorganisms from the root canal systems

• and to shape the walls of the canals to facilitate further cleaning

• and subsequent obturation of the entire RC space.

• Numerous Shaping Techniques – designed : produce a tapered preparation of the RC.

History

1733 Pierre Fauchard Trephination of teeth, preparation of root canals & cauterization of pulps -“ Le Chirurgien Dentiste “

1838 Edward Maynard Endodontic hand instruments

1852 Arthur Used small files for root canal enlargement

1885 Gates Glidden Gates Glidden drills

1889 William H Rollins First endodontic handpiece for automated RC preparation

1915 Kerr K-files

1957 Richmann Ultrasonics in endodontics

1967 Ingle Standardized Technique

1969 Clem First decribed Stepback Technique

1971 Weichmann & Johnson Lasers in endodontics

History

1974 Schilder Gave detailed description of Stepback Technique

1979 Mullaney Stepback Technique

1980 Georig Stepdown (Crown-down) Technique

1980 Marshall & Pappain Crown-down Pressureless Technique

1980 Abou Rass, Glick & Frank Anticurvature Filing

1983 Fava Double Flared Technique

1986 Roane & Sabala Balanced Force Technique

1993 Lussi Non Instrumentation Technique

1994 Torabinejad Passive Stepback Technique

2002 Sequeria Alternate Rotary Motion

Guidelines for Shaping of a RC (Grossman)

I. Preinstrumentation

• Direct access into root canals along a straight line

• Working length : accurately determined

II. Instrumentation

• Instruments : fitted with instrument stops

• Sequential order of instruments & recapitulation

• Sterile instruments in a wet canal only

• Cautious use of barbed broaches : only when wide canal

• Checked for deformation, discarded if strained

Guidelines for Shaping of a RC (Grossman)

III.Cleaning & Shaping

• Instruments : confined to the RC, prevent injury to periradicular tissues

• Don’t force an instrument if it binds

• Recapitualtion : prevent packing of debris

• Apical portion : enlarged to facilitate flow of irrigants

• Remainder of canal enlarged – maintain original tapered canal configuration

• Debris should not be forced through the apex

• Precurve file : curved canals – prevents ledging

Functional Motions of Instrumentation

• Reaming:

• Clockwise rotation – pushing motion

• Limited to quarter to half turn

• Disengaged with a mild pulling motion when bound

• Penetration – Rotation - Retraction

• Filing:

• Push-pull motion

• Passive insertion and active withdrawal of the instrument

• Combination of Reaming & Filing:

• File is inserted quarter turn clockwise and apically directed

pressure (reaming) and then subsequently withdrawn (filing).

• Files edges get engaged into dentin during withdrawal.

• By combination of these reaming and filing repeatedly, canal

enlargement takes place.

• Watch-winding:

• Aka, Twiddling motion

• Instrument reciprocated back and forth in counter-clockwise direction

• Then retracted to remove debris

• Movement with quarter turns using small K-files(#8 / #10) to reach till

working length before coronal flaring

Ingle

• Circumferential Filing:

• Instrument is inserted upto the apex

• Laterally pressed against one side of canal

• Withdrawn with a pulling motion to file the dentinal wall

• Procedure is repeated until the next file/reamer is used

• Narrow canals, reamer is used alternatively with files

• Anticurvature Filing:

• By Abou Rass et al

• Prevent perforation of the furcal wall of the mesial root of

molars. (Danger Zone)

• Top of Handle : pulled into the curvature

• Shank : pushed away from the inside of the curve

• Balances the cutting flutes against the safer part of the

root

• Serial Shaping Motion:

• Follow :

• Movement of smallest instrument to reach the apical foramen

• Negotiating any obstructions or curvatures

• Follow-withdraw :

• As apical foramen is reached, instrument is withdrawn or pulled coronally.

• Carting :

• Transporting dentinal debris & pulp remnants coronally

• Using reamer or F-flex files

• Carve :

• Shaping or sculpting the canal to form a continuously tapering cone

preparation without apical pressure using reamers

• Smoothening :

• Circumferential filing using K flex files

• Patency files :

• Smallest file that does not bind to the canal wall at the minor diameter

• Used to check the patency of the canal up to the apical foramen

• Scouting :

• Estimating the gauge and anatomy of root canal with help of instrument.

• Gauging :

• Knowing the cross sectional diameter of the foramen that is confirmed by thesize of the instruments that fits snugly at working length.

• Tuning:

• Ensuring that each sequentially larger instrument uniformly backs out of canal

by 0.5mm.

Schilders Objectives of Cleaning & Shaping

1. Continuously tapering canal from the apex to the access cavity

2. Maintain original anatomy

3. To leave as much radicular dentin(0.2mm-critical)

4. Maintain the position of apical foramen

5. Keep apical foramen as small as practically possible

Biological Objectives

• To confine the instrumentation within the apical foramen

• No extrusion of necrotic debris beyond the foramen

• Removal of all tissues and debris from the root canal space

• Creation of sufficient space for the placement of intra-canal medicament and

for irrigation purposes

Principles

I. Outline form

• Basic preparation throughout its length, dictated by the canalanatomy

• Initial anatomy must be maintained throughout the procedure

II. Convenience form

• Access has to be expanded if instruments starts to bind

III. Sanitation of the cavity

• Meticulous cleaning of the cavity walls until they feel glass-smooth

• Accompanied by continuous irrigation

Anil Kohli

Principles of Cleaning & Shaping

IV. Retention form

• Nearly parallel walls in the apical 2-3mm of the canal

• To ensure firm seating of the GP point

V. Resistance form

• Development of apical stop at the CDJ against which theobturation must terminate

VI. Extension for prevention

• Extension of cavity preparation throughout its entire length andbreadth

A. Radiographic Apex

B. Resistance Form: development of apical stop at CDJ

C. Retention Form: to retain primary filling point

D. Convenience Form

: subject to revision as needed to accommodatelarger, less flexible files

E. Outline Form

: basic preparation throughout its length dictated bycanal anatomy

Variations in Canal Morphology

Curved Canals


• Double curved canal

• Common : max. lateral incisors, canines & premolars, mand. molars

Bayonet / S-shaped Canals


• Due to failure of HERS to fuse on the lingual / buccal root surface

• Formed by coalescence of cementum deposition

• Common : Mand. 2nd molars > max. molars > mand. premolars

C-shaped Canals

Melton’s Classification:

• Category I

• Continuous C-shaped canal running from thepulp chamber to the apex.

• Category II

• Semicolon shaped (;) in which dentin separatesa main C-shaped canal from one mesial distinctcanal.

C-shaped Canals

• Category III

• 2 or more discrete and separate canals.

• Subdivision I

• C-shaped orifice in coronal 3rd that divides into 2 ormore discrete and separate canals that joinsapically.

• Subdivision II

• C-shaped orifice in coronal 3rd that divides into 2 ormore discrete and separate canals in the mid-rootto the apex.

• Category III

• Subdivision III

• C-shaped orifice in coronal 3rd that divides into 2 ormore discrete and separate canals in the coronal 3rd

to the apex.

• Category IV

• Only one round / oval canal in that cross-section

• Category V

• No canal / lumen can be observed.


• Narrow, ribbon-shaped communication between two root canals that

contains pulp or pulpally derived tissue.

• Classification ( Kim et al)

• Type I

Incomplete isthmus; faint communication between two canals.

• Type II

Characterized by two canals with definite connection between

them.

Isthmus

• Type III

Very short complete isthmus between two canals.

• Type IV

Complete or incomplete isthmus between two or more canals.

• Type V

Marked by two or three canal openings without visible

connections

Classification of Endodontic Instruments (Grossman)

Group 1

Hand Operated

A. Barbed Broaches & Rasps

B. K-type Reamers & Files

C. Hedstroem Files

Group 2Low speed instruments with latch type attachments

A. Gates-Glidden drills

B. Peeso Reamers

Group 3

Engine driven instruments

A. Rotary NiTi endo instruments

B. Reciprocating instruments

C. Self Adjusting File (SAF)

Group 4 Ultrasonics & Sonic Instruments

Instruments Used For Cleaning And Shaping

• Broaches

• Rasp

• K- files

• H –files

• GG drills

• NiTi rotary

• Light speed

• Profile

Root Canal Working Width

• RC should be widened for following reasons:

• To eliminate microorganism on the canal surface mechanically

• Completely removing the pulp tissue

• Increase the capacity of root canal to permit irrigation anddebridement of apical 3rd of root canal

• To shape the root canal to receive gutta-percha, wider canalare easy to fill particularly if its narrow initially

• Traditional Concept

• Enlarge the canal atleast 3 sizes beyond the size of the first instrument that binds.

• Enlarge the canal until clean, white dentinal shavings appear in the flute of theinstrument.

• NOT RECOMMENDED ANYMORE

• The color of the dentinal shaving is no indication of presence of infected dentin or organicdebris.

• Root canals should be enlarged regardless of initial width to remove irregularities of dentinand make smooth and tapering canal.

Grossman

• Current Concept

• Minimum size to which a root canal should be enlarged cannot be standardized and

varies from case to case.

• Factors affecting the size of canal while enlarging at working length

• Peri-apical pathology or resorption

• Narrow canals - initial canal width has to be assessed radiographically

• Whether root canal is vital / calcified / infected

• Radius of canal curvature which could make the canal preparation difficult

• Complex canal anatomy like C-shaped canals and the isthmus region

Grossman

• A study showed that molar tooth canals should be enlarged upto #40 for effective cleaning

• Canals shaped with greater taper NiTi allow irrigants to reach the apical third without much

enlargement of apex too much

• Study shown that canals shaped with 6% taper instruments upto #30 have cleaner canals

without smear layer or debris

Grossman

Narrow Apex

Benefits Drawbacks

• Minimal risk of Canal transportation • Little removal of infected dentin

• Minimal Extrusion of irrigants • Questionable rinsing effect in apical areas during irrigation

• Minimal Extrusion of filling material • Possibly compromised disinfection during inter appointment medication

• Can be combined with tapered preparation to counteract some drawbacks

• Not ideal for lateral condensation

Cohen

Wide Apex

Benefits Drawbacks

• Removal of infected dentin • Risk of preparation errors and extrusion of irrigants and filling material

• Access of irrigants and medications to apical third of root canal

• Not ideal for thermoplastic obturation

Cohen

Root Canal Shaping Techniques

Apico-Coronal Techniques Corono-Apical Techniques

• Standardized Technique • Crown-down Technique

• Stepback Preparation • Crown-down Pressureless

• Passive Stepback • Double Flared Technique

• Balanced Force Technique

• Hybrid Technique

Standardized Technique

• First formal RC preparation technique

• Ingle (1961)

• Canals prepared by enlarging sequentially to selected size.

• Final result : preparation similar in size, shape and taper of a standardized instrument

• Technique:

• Working length

• Canal negotiated with smallest size instrument, worked upto WL with sequentiallylarger file

• Finally a canal shape is produced which is similar to the last instrument used.

• Two factors of variations

• Canals shaped with standardized technique end up wider than the instrument size

would suggest.

• Production quality is insufficient, both for instruments and for gutta-percha cones,

leading to size variations.

Ingle

Conventional Stepback Preparation

• Telescopic / Flare / Serial RC preparation

• Mullaney, Walton, Weine & Martin : 1979

• Preparation : from the apex with fine instrument which is enlarged first to a size 25/30 andthen consecutively larger instruments are used for shaping the middle and coronal part ofthe canal.

• Technique:

Mullaney divided into 2 phases:

Phase I

Phase II A & B

• Phase I :

• Patency

• Working length

• Initial Apical File (IAF)

• Watch-winding motion with copious irrigation

• Recapitulation

• Canal enlarged upto No. 25 at the working length

• Phase II A :

• Next file size No.30 used 1mm short of WL

• Recapitulation (No. 25)

• Next file (No. 35) used 2mm short of WL

• Preparation steps back by 1mm till straight mid-canal is reached

• Phase II B :

• Coronal portion is prepared using GG/Orifice openers

: remove coronal constriction

• Phase II B (Refining Phase):

• For smoothing the canal walls

• To get taper from coronal portion till apex and will be larger

repilca of original canal

• Last apical instrument (No.25) used to smoothen the walls with

push-pull strokes with copious irrigation.

• This Preparation gives 5% taper to the canal.

• Serial Canal Preparation:

• By Walton & Torabinejad

• After apical preparation, preparation steps back by 0.5mm & one larger instrument

at a time.

• This Preparation gives 10% taper to the canal.

ADVANTAGES:

• Creates only small apical preparation with larger instruments used at

successively decreasing lengths to create a taper.

• Taper can be altered by changing the interval between consecutive

instruments.

DISADVANTAGES:

• Difficult to irrigate apical region

• More chances of apical extrusion of debris

• Time consuming

• It has tendency to straighten the curved canal

• Increased chances of iatrogenic errors

• Loss of working length

Modified Stepback Preparation

• After apical preparation, stepback preparation begins 2-3mm up the canal

• Provides short parallel retention form to the master GP point

ADVANTAGES :

• Reduced apical transportation

• Increases the percentage of canal walls being prepared

Nisha Garg

Modified Stepback Preparation

DISADVANTAGES :

• Passing a precurved instrument in a coronally tight canal straightens the

instrument leading to ledge formation.

• Holds only a minimal volume of irrigant and so accumulation of dentinal mud

leads to blockage of the foramen.

• WL is most likely to change as coronal constriction is removed.

• When GG drills and Peeso drills are advanced past the middle third of

root canal : Resulting shape is – “COKE BOTTLE”.

• GG drills and peeso drills - deep into the canal : risk of fracture as they

are not very resistant to fatigue occuring in curved canals.

• Strip perforations and over preparation

Ingle

• Coffae and Brilliant

• Use of #35 till working length, stepwise reduction of WL for subsequent

files upto #60.

• Then use of GG drills no. 2 and 3 approximately 16 and 14mm

approximately into the canal - showed superior debridement.

Ingle

Passive Stepback Technique

• Developed by Torabinejad

• Combination of hand and rotary files : to attain an adequate coronal flare before apical RC

preparation

• Provides gradual enlargement of root in an apical to coronal direction without applying

force, thereby reducing procedural errors.


• Technique:

• Access preparation and WL determination using No.15 file

• Additional files of 20, 25, 30, 35 and 40 are inserted passively into the canal :

removes debris and mildly flared preparation for insertion of GG.

• Copious irrigation

• No. 2 GG inserted to a point where it binds slightly, pulled back 1 – 1.5mm and then

activated – canals walls get flared.

• Similarly GG No. 3 and 4 are used coronally.


• Reconfirmation of WL

• No. 20 file is inserted upto WL and prepared by filing with instruments progressively

short of WL.


ADVANTAGES:

• Removal of debris and minor canal obstructions

• Knowledge of canal morphology

• Gradual passive enlargement of canal in apico-coronal direction

• Can be used with ultrasonic instruments

• Reduced incidence of procedural errors.

Crown-Down Technique (Step Down)

• Aka; Reverse flaring (Weine), Coronal 2/3rd enlargement (Cohen), Cervical Flaring (Goreig)

• Shaping of the coronal aspect of root canal first before apical instrumentation.

• Technique:

• Patency with No.8/10 K file

• Coronal 2/3rd prepared using H-files

(#15,20,25) to a WL depth of 16-18mm or to

a point where the file starts to bind.

• Flaring coronal segment with GG #2, #3 or #4, each drill being

sequentially shorter.

• WL determination

• Remaining canal prepared in step-down approach, using

descending file sequence, progressing by 1mm.

• Apical portion of canal is then enlarged to appropriate MAF which can vary from

canal to canal and from tooth to tooth.

• Final taper attained by the MAF is used in circumferential filing.

• Modifications:

• Crown-down pressureless technique

• Double flare technique

• Balanced force technique

Crown-Down Pressureless Technique

• By Marshall and Pappain

• Early coronal flare with GG drills followed by incremental removal of dentin from coronal toapical direction : hence termed “CROWN DOWN”

• Straight K-files are used in a large to small sequence with a reaming motion and no apicalpressure. : hence termed “PRESSURELESS”

• Morgan and Montgomery found this technique resulted in rounder shape when compared tousual stepback technique.

• Technique:

• After coronal access, provisional WL

• #35 K-file introduced into the canal with no apical pressure

• GG # 2 is used for coronal flaring upto or short of point where #35 file explored.

• Followed by GG # 3 & 4 : this shortens the WL.

• Crown-down preparation, #60 file used with no apical pressure & reaming action

is employed to enlarge the canal.

• Followed by use of sequentially smaller files, deeper into the canal

• Radiographs are taken when instrument penetrates the provisional WL

• Final step to enlarge the apical area to appropriate MAF at WL

Balanced Force Technique

• By Roane & Sabala (1985)

• Involves the use of instrument with non-cutting tip

• Flex-R files are recommended for this technique.

• Technique described as “Positioning and Preloading” an instrument through clockwise

rotation and then shaping the canal with a counter clockwise rotation.

• Technique:

• Coronal and middle thirds prepared using crown-down technique,

using GG.

• First file that binds short of WL is inserted into the canal

• Rotated clockwise (quarter turn) using only light pressure

• This movement causes flutes to engage a small amount of dentin

• Now file is rotated counter-clockwise with apical pressure to keep the

file at the same depth.

• This causes shearing off small amount of dentin engaged duringclockwise rotation.

• Dentinal shavings are removed with a characteristic “CLICKINGSOUND”

• After 2/3 cycles, file is loaded with dentinal shavings and isremoved from the canal with a prolonged clockwise rotation. (loadsdebris into the flutes)

• Sequential files are used in crown-down fashion before preparingthe apical third.

• Roane recommends minimum enlargement of size 45, 1.5mm short of apical

foramen in curved canals.

• Size 80 in single rooted teeth, carrying the preparation through full length of

the radiographic apex of the root.

• This technique has shown to reduce canal transportation and ledging.

Modified Balanced Force Technique

• Earlier called Alternated Rotary Movements

• Does not recommend withdrawal of instrument after each set of rotations

• Emphasized incremental apically directed movement and withdrawal when the file

has reached the working length.

Reverse Balanced Force Preparation

• NiTi greater Taper hand files are used.

• Flutes of Greater taper files are machined in a reverse direction unlike other files.

• Technique:

• File inserted and rotated 60° in anti-clockwise direction

• Then 120° in clockwise direction with apical pressure.

• Files are used in sequence from largest to smallest in crown-down sequenceupto the WL.


• Apical portion prepared using 2% taper ISO files in balanced force technique.

Double Flare Technique

• By Fava

• Canals prepared in crown-down manner using K-files in decreasing sizes.

• Followed by stepback technique in 1mm increments with increasing file sizes.

INDICATIONS:

• Straight root canals

• Straight portions of curved canals

CONTRAINDICATIONS:

• Calcified canals

• Young permanent teeth

• Open apex

• Technique:

• WL determination using small K-file

• Crown-down Preparation : Apical third is enlarged using larger to smaller K-files

until WL is reached.

• Apical enlargement done till MAF size

• Stepback preparation with descending files with frequent recapitulation with MAF.

ADVANTAGES:

• Greater taper in cervical and middle third such that the removal of canal contents

is more effective and RC is better cleaned.

• Improved quality of root canal filling compared to conventional technique.

• Flared technique maintains the RC shape and produces neither the hour glass

appearance nor apical zip.

• Facilitates irrigation procedure and easier placement of posts.

Modified Double Flare Technique

• By Saunders & Saunders

• Uses non cutting tipped instruments with stepback technique.

• Technique:

• Preparation starts in the coronal part of the canal

• #40 Flex R file with balanced force introduced into straight part of the canal

• Sequential larger sizes used to instrument the straight part

• Coronal 4-5mm instrumented with GG (No. 2 & 3)

• #20 file extended to WL

• Canal prepared sequentially with balanced force technique.

• Preparation is continued until clean dentinal shavings are obtained.

• MAF varies between #40 - #45 file.

• Stepback with balanced force done to prepare remaining curved portion.

ADVANTAGES of Crown-Down Technique

• Shaping of canal is subjectively easier than stepback

• Removal of coronal obstructions allows removal of bulk of tissue, debris and micro-

organisms before apical shaping.

• Minimizes extrusion of debris

• Allows better access and control over the apical enlarging instrument, thus

decreasing incidence of zipping

• Allows better penetration of irrigants

• WL is less likely to change while employing this technique

Hybrid Technique

• Combination of Stepdown followed by Stepback.

• Both rotary and hand instruments are used

• Technique:

• Patency with #10 K file

• Coronal third preparation using hand or GG till point of curvature


• Apical portion prepared using stepback technique

• Recapitulation and irrigation

ADVANTAGES:

• Ability to shape canal predictably

• Less chances of ledge formation

• Maintains the integrity of dentin by avoiding excessive removal of

radicular dentin.

• Optimises the advantages of crown down & step back techniques

Canal Master Technique

• By Wildey & Senia

• Instrument used is Canal Master Instrument (SW)

• Here cutting portion is reduced to 1-2mm with 0.75mm non-cutting pilot tip

• Cutting portion resembles a reamer with blunted edges.

• Rest of the instrument is parallel sided shank of round cross section

• Maximum efficiency is with clockwise rotary motion

ADVANTAGES:

• Prevents transportation of the canal

• Small cutting head provides minimum cutting surface with maximum control

• Increased flexibility

• Instrument stays centered in the canal

• Gives finer tactile perception

• Does not require recapitulation

Non-Instrumentation Technique

• By Lussi et al

• Minimal Invasive Technique

• Uses controlled cavitation & hydrodynamic turbulence in the RC so as to clean them.

• Technique uses:

• Vaccum pump

• A Hose

• A special valve to pump irrigant which generates bubbles & cavitation that loosen the debris

• Debris is removed by suction.

• Enhances the ability of NaOCl to dissolve the organic pulp tissue.

• Technique:

• First reduced pressure at 0.7 bar generated, producing macroscopic &

microscopic voids (5-50μm)

• Followed by quick pressure rise to 0.1 bar leading to collapse of bubbles,

thus building up cavitation and turbulence.

• Allows irrigant to penetrate the whole of RC system

• Smooth exchange of irrigant is obtained using double tubing.

ADVANTAGES:

• Cleaning of canal, similar or better than hand instrumentation

• Better results in curved canals

• Less chances of extrusion of irrigant beyond the apex

• Treatment duration is independent of the number of RCs in the tooth

DISADVANTAGES:

• Does not shape the canal

• Tooth has to be insulated

Laser Assisted Canal Preparation

• By Weichmann & Johnson (1971)

• Nd.YAG, Argon, Excimer laser, Erbium Laser

• Nd YAG laser energy better absorbed by dark tissue and is transmitted by water.

• Excimer lasers and Erbium lasers are strongly absorbed by dental hard tissue.

• Dederich et al showed the melting and recrystallizing the dentin surface can create

clean and penetrable canal.

• Delivered through optical fibres which have a diameter of 200 – 400 μm equivalent to

#20-40 files

MECHANISM :

• Melting the dentin surface

• Vaporization of debris and pulpal tissue remnants.

INDICATIONS :

• Straight / Slightly curved canals

• Wide root canals

CONTRAINDICATIONS :

• Heat generated may injure the peripical tissues

• Curved canals cannot be assessed

• Expensive

Canal Preparation with Ultrasonic Instrumentation

• Introduced by Richman in 1957

• Barbed broach is connected to an ultrasonic delivery system for use in canalpreparation and apical resection.

• Howard Martin and Walter Cunningham in 1976

• Developed a device, tested and marketed it in 1976.

• Named the Cavitron endodontic system (Dentsply).

• Endosonics refers to the endodontic treatment by sonic, supersonic or subsonicsystem (Martin & Cunningham).

• Based on sound as an energy source (20-25khz) that activates endodontic files.

• Energy source – piezoelectric or magnetostrictive.

• Files oscillate at the frequency of 20,000- 25,000 vibrations /seconds.

• Magnetostrictive Unit

• Electromagnetic energy is converted into mechanical energy.

• It needs water coolant because it generates more heat.

• Expensive, more clumpsy and less powerful.

• Piezoelectric energy is induced by subjecting crystals of quartz or Rochelle salts tophysical force or pressure.

• Generates less heat

• Doesn’t require water as coolant

• Transfers more energy to the file, making it more powerful.

• Used for

• Location of calcified canals

• Retrieval of broken instrument

• Root end preparation.

• Handpiece holds a K-file, when activated produces movement of

shaft of file between 0.001” & 0.004” at freq. of 25-30KHz.

• Oscillating movement produces cutting action & creates ultrasonic

waves of the irrigant.

• Ultrasonic vibration - heat : increases the chemical effectiveness

of irrigant solution.

• 2 significant physical processes that occur :

• Cavitation

• Acoustic Streaming

• Growth and collapse of bubbles (Implosion) with resulting increase in

mechanical cleansing activity of the solution.

• Negative pressure : within the exposed cells of intracanal materials,

implosion breaks the cells.

• Irrigant/coolant : washes out broken cell parts.

• Increase in mechanical & thermal activity of irrigants

• Removal of debris & tissues from the isthmus

• Removal of smear layer are more efficient.

• Formation of small but intense eddy currents or fluid movement

around the oscillating instrument.

• Improves the cleaning ability of the irrigant : hydrodynamic

shear stress

• Eddying occurs closer to the tip than in the coronal end of the

file, with an apically directed flow at the tip.

Ultrasonics : Adv & DisAdv

ADVANTAGES

• Less time consuming.

• Produces cleaner canals because of synergetic effect.

• Heat produced increase the chemical effectiveness of sodium hypochlorite.

DISADVANTAGE

• Increased frequency of canal transportation.

Canal Preparation with Sonic Instrumentation

• Sonic endodontic handpiece attach to the regular handpiece at a

pressure of 0.4 Mpa

• Air pressure can be varied with an adjustable ring on the

handpiece to give an oscillatory range of 2 to 3 kHz.

• Tap water irrigant / coolant is delivered into the preparation from

handpiece.

• Sonically powered files oscillate in large elliptical motion at the tip.

• When loaded into the canal oscillation motion changes into a longitudinal

motion, up and down (Walmsley et al); efficient form of vibration for

preparing root canal. (Ingle)

• Types of files used in Sonic system

• Rispi Sonic, Shaper Sonic, Trio Sonic, Helio Sonic Files.

• Files have spiral blades protruding along their lengths and non cutting tips.

SONICS : Adv & DisAdv

ADVANTAGES

• Better shaping of canals than ultrasonic preparation.

• Due to constant irrigation, amount of debris extruding beyond apex is less.

• Produces clean canals free of debris and smear layer.

DISADVANTAGES

• Walls of prepared canals are rough.

• Chances of transportation more.

Special Anatomic Problems in Canal Cleaning and Shaping

• Management of Curved Canals

• Management of Calcified Canals

• Management of C-shaped Canals

• Management of S-shaped Canals

Management of Curved Canals

• First step : estimate the angle of curvature

• It estimates only the mesio-distal curve but not the bucco-lingual curve.

Degree of CurvatureInterior angle formed by intersection of 2 straight lines, one drawn from the orifice through the coronal portion of the

root and another from the apex through the apical portion of the curve

• Curved canals : occurrence of uneven cutting and cause errors.

• To avoid occurrence of such errors, there should be even contact of file to the dentin

• This can be done by:

1. Decreasing the force by means of which straight files apt to bend against the

curved dentin surface.

2. Decreasing the length of file which is aggressively cutting at the given span.

• Decreasing the force by means of which straight files apt to bend against the curved

dentin surface :

• Precurving the file

• Extravagant use of smaller number of files

• Use of intermediate sizes of files

• Use of flexible files

I. Precurving the File

2 types of precurving:

• Placing an extremely sharp curve near the tip of an instrument

• Degree of curvature is estimated by holding the file over the preoperative radiograph and increasing the curvature until the configurations of the file and canal match.

• Short sharp curve of 30 – 40 degrees is given.

• Uses :-• To bypass a ledge• To prepare a tooth with dilacerations• When retreating a failing case.

• Gradual precurve for the entire length of flutes

• RC instrumented with the precurved files : significantly lower debrisscore than those prepared with straight files.

• Matching the curvature of the file to the curvature of the canalfacilitates its insertion.

• Tear drop shape rubber stop can be used, with the point showing thecorrect direction of the curve.

• Smaller files follow canal curvature because of their flexibility.

• They should be used until larger files are able to negotiate the canal without force.

II. Extravagant Use Of Smaller Files

III. Flexible files

• Use of flexible files cause less alteration of canal shape than stiffer files.

• Maintain the shape of curve and avoid occurrence of errors.

IV. Intermediate files

• By cutting off a portion of the file tip, a new instrument size is

created which has the size intermediate to two consecutive

instruments.

• In severely curved canals clinician can cut .05 mm of the file to

increase the instrument diameter by .01mm.

• This allows smoother transition of instrument sizes to cause

smoother cutting in curved canals.

• Decreasing the length of file which is aggressively cutting at the given span

• Anticurvature filing

• Modifying the cutting edges of the instrument

• Changing the canal preparation techniques

• Cutting edges of curved instrument can be modified by dulling the flute of outer portion of

apical third and inner portion of middle third.

• Dulling of the flutes can be done with diamond file.

II. Modifiying Cutting Edges

• Crown-down technique

Removes the coronal interferences and allow the files to reach up to the apex

more effectively.

III. Changing Canal Preparation Techniques

Management of Calcified Canals

• Common occurrence

• Pulpal Calcifications: signs of pathosis, but not the cause.

• Occur nearest to irritant to which pulp is reacting

• Most are seen in coronal portion of pulp and least in apical part into the canal

• Etiological Factors: caries, trauma, drugs and aging.

• Access preparation

• Location of canal orifice

• DG – 16 explorer

• Canal pathfinder

• Penetration and negotiation of calcified canals

• No .8 K file

• Before inserting, precurve the file in its apical 1mm.

• Forceful probing – false canals – perforation.

• Confirm the position of instrument with radiograph.

Guidelines For Negotiating Calcified Canals

• Copious irrigation with 2.5% -5.25% NaOCl.

• Always advance the instrument slowly in calcified canals.

• Always clean the instrument on withdrawal & inspect before reinserting.

• When a fine instrument reaches canal length, obtain a radiograph immediately.

• Use chelating agents to assist canal penetration.

• Flaring of canal orifice and enlargement of coronal third of canal space improves tactile

perception.

• Avoid removing large amount of dentin in the hope of finding a canal orifice.

• Small round burs should be used to create a glide path to the orifice.

Management of C-shaped canals

• Difficult to remove pulp tissue & necrotic debris, excessive haemorrhage,

persistent discomfort during instrumentation.

• Continuous circumferential filing + 5.25% NaOCl for tissue removal and

control of bleeding.

• If bleeding is continuous, ultrasonic removal of tissue or placement of

Ca(OH)2 between appointments.

• Over preparation should be avoided : only little dentin between external

root surface and canal system.

Management of S-shaped / Bayonet shaped canal

• Involves at least two curves with the apical curve having maximum deviations in anatomy.

• Usually identified radiographically : mesiodistally

• Buccolingually

• Multi-angled radiographs

• When IAF is removed : simulates multiple curves

• Common :

• Maxillary lateral incisors, canines, premolars

• Mandibular molars

• 3D nature of the canals must be visualised

• Failure may lead to stripping along inner surface

• Unrestricted access to initial curve : Flared access preparation.

• Once entire canal is negotiated, passive shaping of coronal curve is done first.

• Constant recapitulation and copious irrigation.

• Gradual use of small files with short amplitude strokes is essential to manage these canals.

• To prevent stripping, anticurvature filing is recommended, with pressure being placed away

from curve of coronal curvature.

Evaluation Criteria of Canal Preparation

• Canal should exhibit “glassy smooth” walls

• There should be no evidence of unclean dentin filings, debris, or irrigant in the canal.

• Spreader should be able to reach within 1mm of the working length.

Iatrogenic Errors

Those unfortunate occurrences that happen during treatment, some owing to

inattention to detail, others totally unpredictable. - INGLE

• Ledge formation

• Perforation

• Zipping / Elliptication

• Canal Blockage

• Separated Instruments

Ledge

• An artificially created irregularity on the surface of the root canal wall that preventsthe placement of instruments to the apex of an otherwise patent canal.

Causes:

• Forcing and driving the instrument into the canal

• Attempting to prepare calcified root canals

• Excessive enlargement of curved canal with files

• Packing debris in the apical portion of the canal

• Anatomic complexities - roots curved towards buccal or lingual side.

Perforation

• Creating a ledge in the canal wall during initial preparation and perforating

through the side of the root at the point of obstructions / root curvature.

• Using too large or too long an instrument and either perforating directly

through the apical foramen or wearing a hole in the lateral surface of the root

by over instrumentation.

Zip / Elliptication

• Transportation of the apical portion of the canal

ie. an elliptical shape formed in the apical foramen during preparation of curved canals.

• Creation of an ‘elbow’ is associated with zipping – at the narrow region of the root canal

at the point of maximum curvature

Ie. the irregular widening that occurs coronally along the inner aspect and apically

along the outer aspect of the curve.

Canal Blockage

• Due to lack of recapitulation

• Insufficient irrigation

Instrument Separation

• Overuse of instruments

• Instrumentation in a dry canal

• Excessive pressure applied

• Manufacturing defects

Conclusion

• Shaping and cleaning are important interdependent steps in the root canal

treatment.

• The combination of anatomic, biologic & pathophysiologic knowledge of the tooth

and the skill of the operator play a major role in optimizing the quality of the

root canal treatment.

Keep in Mind

• Do no harm to the tooth structure

• Totally clean the canal system

• Create a continuous taper

• Do not alter the minor diameter

• Assume curvature in all canals

• Avoid aggressive apical instrumentation

• Avoid overzealous shaping

• Accurately pre-bend files

• Avoid apical blockage

• Develop a tri-dimensional image through

visual & tactile awareness.

References

• Textbook of Endodontics – Ingle

• Principles & Practice – Walton & Torabinejad

• Pathways of the Pulp – Cohen

• Textbook of Endodontics – Nisha Garg

• Endodontic practice – Grossman

• Endodontics – Stock, Walker, Gulabivala

• Endodontic Science – Carlos Estrela

“Cleaning and Shaping is a game and, as such, can be played at

various skill levels. Visualizing and executing great play can

move the clinician towards mastery and winning the inner game

of endodontics.”

- Clifford J. Ruddle

cleaning & shaping

Education