Done by;DR. ISRAA AWADHB.D.S.

Root Canal Preparation Techniques

Contents *Objectives of Root Canal Preparation.*The principles of shaping.*Standardized technique *Step back technique*Modified step back technique*Step down technique*Crown down technique*Hybrid technique*Double flared technique*Modified double flared technique*Balanced force technique

*Objectives of Root Canal Preparation

1.Eliminate microorganisms.

2.Remove remaining pulp tissues.

3.Remove debris.

4.Shape the root canal system so that it may be obturated.

*The principles of shaping

* Develop a continuously tapering funnel from the apex to coronal orifice.

* Maintain the original shape of the canal.

* Maintain the apical foramen in its original position.

* Keep the apical opening as small as possible.

Apical to coronal

Coronal to apical

Techniques can be divided to:

Techniques

Apical to coronal

1.Conventional2.Step back3.Modified step back

Coronal to apical

1.Step down2.Crown down3.Hybrid technique4.Double flared technique5.Modified double flared6.Balanced force technique

*Standardized technique

introduction*Also known as conventional technique. One of

the first technique to be used introduced by Ingle.

*In this technique standardized reamers of increasing sizes were used sequentially to enlarge the apical part of the canal.

*The coronal two third were prepared, again, mainly by reaming.

How to Do*Determine working length and select the initial apical file.

*Do circumferential filing by applying lateral pressure and then with drawn.

*Increase the apical constriction 2 to 3 files sizes more than initial apical file but with the same working length.

Drawback*Chances of loss of working length due to accumulation of dentin

debris.

*Does not take in to consideration the elliptical forms and large diameter of root canals.

*Obturation with this techniques dose not provide adequate sealing of root canal confines specially in curved canals .

*Passage of irrigants and medicaments is not adequately obtained through the root canals.

*Increased incidence of ledging, zipping and perforation in curved canals.

*Step back technique

*Introduction *Weine, Martin, Walton, and Mullaney were early advocated of the

step back in 1969. also called telescopic or serial root canal preparation.

*The essence of this technique is preparation of the a distinct apical stop and to over come the problem of the curved root canal.

* Its divided in to two phases;Phase I Is the apical preparation .

Phase II is the preparation of the remainder of the canal.

The completion of the preparation is the refining phases IIA and IIB to produce the continuing taper from apex to cervical portion of the canal.

Phase I* Is the apical preparation starting at the

apical constriction.*The apical region is first inserted with

initial apical file (IAF) which is a fine instruments tapered stainless steel file ( Nos 10,15, 20 or 25)

*Then it should be enlarged at least three sizes more than the IAF for four reason:

1. To remove bacteria and there substrates.2. To remove dead pulp tissue.3. To increase the capacity of root canal to

retain the larger amount of sterilizing agent.

4. To prepare the root receive the canal filling

Phase II Phase II is the step back preparation, which is achieved by increasing the size of files and by decreasing the length, that is, by using Nos 30, 35, and 40 files of 1, 2, and 3mm short of working length to produce a coronal taper.

In between placing each larger instruments, the master apical file is inserted to the working length to clear out any debris collecting in the apical part of the canal; this is referred to as Recapitulation.

Refining phases IIA and IIB of midcanal

*Ones the apical preparation is complete, use of Gate-Glidden drills for initial enlargement of the coronal part of root canal.

*Then use small Gates-Glidden drills to prepare the mid root level

*Finally use Hedstroem files to flare the apical part.

*RECAPITULATION ; Again the Nom 30 file should be used between each steps to maintain the apical preparation.

*This preparation allows an adequate amount of coronal space in the root for lateral compaction.

*Gates Glidden Drill 

*Gates-Glidden Drills are side cutting instruments with safety tips. They can be used with both crowns down as well as step back fashion to enlarge the coronal third of the canal during endodontic treatment.

*used with handpiece

*Different sizes , 6 sizes (#1 - #6) coded by rings or colored bands on shank.

*slightly flexible and will follow the canal shape but can perforate the canal if used too deeply.

*Should be used only in the straight sections of the canal.

Advantages of step back*Proper apical stop *Less chances of apical transportation*Greater flare coronally

Limitations*Debris extruded will block the canal*Loss of working length*Tendency to straiten the canal *Time consuming.

• Ones the apical preparation is completed,2-3 mm of the apical portion of the canal is prepared with the MAF. Step back procedure begins from the 3mm short of the apical constriction.

• Gives almost a parallel cylindrical retention form to primary gutta-percha point.

*Modified step back

*Step down technique

Extrusion of canal contents during instrumentation has shown to cause postoperative discomfort and delayed healing. This problem was found with most of instrumentation techniques.

To withstand this problem a different approach called the coronal to apical approach was introduced which advocated shaping the coronal aspect of a root canal first before apical instrumentation commented.

*introduction

*How to do * the pulp chamber filled with irrigant or lubricant now canal is

penetrated using Hedstroem files of sizes nos. 15, 20 and 25,the working length can be established at this time.

* The coronal thirds of the canal is then flared with Gates Glidden drills nos. 2 and 3 and no.4 are used sequentially shorter, thus, flaring the coronal segment of the root canal.

*This followed by apical instrumentation using a descending file sequence, progressing 1mm per consecutive instrument, apically. Its important to recapitulate with no.25 file to prevent blockage.

*Note; The apical portion of the canal prepared by enlarging the canal at the corrected working length 2-3sizes at least in order to get clear dentin.

*advantages*Permits straighter access to the apical

region.*Eliminate coronal interference which allows

better determination of apical canal sizes.*Removes bulk of tissue and microorganisms

before apical shaping.*Allows deeper penetration of irrigants.*The working length is less likely to change.*Less amount of necrotic debris could be

extruded throw the apical foramen.*Less chance of zipping near the apical

constriction due to increased in the access opening.

*Disadvantages

*More time consuming than the step back technique.*Excessively flared preparation in the

coronal and middle thirds may weaken the tooth and create problems.*If large, less flexible rotary instruments

are used too rapidly and deeply in the root canal, a ledge may form.*In canals that curve severely the rotary

instruments cannot be precurved.

*Crown down technique*Marshall and Pappin advocated a “Crown-Down

Pressureless Preparation” which involves early coronal flaring with Gates-Glidden burs, followed by incremental removal of dentin from a coronal to apical direction, hence the term “crown-down”.

*Straight k – type files are used in a large to small sequence with a reaming motion and no apical pressure, thereby “Pressureless”

*This technique resulted in a rounder canal shape when compared to usual step back technique.

*Hybrid technique *In this technique a combination of step-back and

crown-down preparation is used.*Both rotary and hand instruments are used to

prepare the canal.*Check the patency of canal using number 10 or 15

k flex files.*Prepare the coronal third of canal using hand or

Gates-Glidden drills till the point of curveture without applying excessive pressure.*Determine the working length.*Prepare the apical portion of canal using step back

technique.

*Recapitulate and irrigate the canal at every step so as to maintain patency of the canal.*Blend step back with step down procedure.

Advantages*Less chances of ledge formation.*This technique maintains the integrity of dentin by avoiding excessive removal of radicular dentin.

Double Flare Technique*It was introduced by Fava.

*In this, canal is explored using a small file. Then prepared in crown-down manner using k files in decreasing sizes.

*After this, step back technique is in 1mm increments with increasing file sizes.

*Frequent irrigation and recapitulation using master apical file is done during instrumentation.

Indications*Straight root canals.*Straight portion of curved canals of mature teeth.

Contraindications*Calcified canals.*Young permanent teeth.*Teeth with open apex as they have thin dentinal walls and great pulp volume.

Modified double flared*In this, preparation was commenced in the coronal

part of the root canal.*A #40 Flex R file was instrumented in the straight

part of the canal , using the balanced force technique.*Sequentially, larger sizes of files were used to

instrument the straight part of the canal using the balanced force technique and the coronal 4 to 5 mm of root canal was instrumented with Gates-Glidden drills.*A #20 Flex R file was taken to the working length

and the canal prepared using the balanced force technique by sequential use of files.

*Preparation at the working length was continued until clean dentin was removed, the master apical varying between #40 and #45.

*A step back technique using balanced forces was then used to prepare the remaining curved portion of the canal

Balanced force technique

*This technique was developed by Roane and Sabala in 1985.It’s involves using blunt-tipped files.*The balanced force technique recognizes the fact that

instruments are guided by the canal walls when rotated.*Since the files will cut in both a clockwise and

anticlockwise rotation, the balanced force concept of instrumentation consists of placing the file to length and then a clockwise rotation (less than 180 degrees) engages dentin. * This is followed by a anticlockwise rotation (at least

120 degrees) with apical pressure to cut and enlarge the canal.* The degree of apical pressure varies from light

pressure with small instruments to heavy pressure with large instruments

*. The clockwise rotation pulls the instrument into the canal in an apical direction. The anticlockwise cutting rotation forces the file in a coronal direction while cutting circumferentially.

* Following the cutting rotation the file is repositioned and the process is repeated until the corrected working length is reached. At this point a final clockwise rotation is employed to evacuate the debris.

Advantages *With the help of this technique, there are lesser

chances of canal transportation.

*One can manipulate the files at any point in the canal without creating a ledge or blockage.

*File cutting occurs only at apical extent of the file.

*Extrusion of material is less than with other techniques.

References

Textbook of Endodontics Anil KohliEndodontics, Volume 1 Ingle, Bakland