WHAT ARE OBJECTIVES OF BIOMECHANICAL PREPARATION OF ROOT CANALS?
Biologic objectives of biomechanical preparation are to
remove the pulp tissue, bacteria and their by-products from the root canal space.
Mechanical Objectives of Root Canal Preparation (given by Schilder) (Fig. 13.1)
1. The root canal preparation should develop a continuously tapering cone.
2. Making the preparation in multiple plane which introduces the concept of “Flow”.
3. Making the canal narrower apically and widest coronally.
4. Avoid transportation of foramen.
5. Keep the apical opening as small as possible.
WHAT ARE BASIC PRINCIPLES OF CANAL INSTRUMENTATION?
1. There should be a straight line access to the canal orifices.
2. Files are always worked with in a canal filled with irrigant.
3. Preparation of canal should be completed while retaining its original form and the shape.
4. Canal enlargement should be done by using instru- ments in the sequential order without skipping sizes. 5. All the working instruments should be kept in
confines of the root canal to avoid any procedural accidents.
6. After each insertion and removal of the file, its flutes should be cleaned and inspected.
7. Recapitulation is regularly done to loosen debris by returning to working length.
8. Over preparation and too aggressive over enlarge- ment of the curved canals should be avoided. 9. Never force the instrument in the canal.
10. Establish the apical patency before starting the biomechanical preparation of tooth. Apical patency of the canal established and checked, by passing a smaller number file (No. 10) across the apex.
WHAT IS STEP BACK TECHNIQUE FOR ROOT CANAL PREPARATION?
1. Step back technique is also known as Telescopic canal preparation or serial root canal preparation. 2. Step back technique emphasizes keeping the apical
preparation small, in its original position and producing a gradual taper coronally.
Figs 13.1A and B: Diagrammatic representation of objectives
of canal preparation: (A) Unprepared canal, (B) Prepared root canal
Cleaning and Shaping of Root Canals 59
3. Basically, this technique involves the canal prepara- tion into two phases; phase I involves the preparation of apical constriction and phase II involves the preparation of the remaining canal.
Phase I
1. Initially prepare the access cavity and locate the canal orifices (Fig. 13.2).
2. Establish the working length.
3. Now insert the first instrument into the canal with watch winding motion (Fig. 13.3).
4. Remove the instrument and irrigate the canal. 5. Place the next larger size file to the working length in
similar manner and again irrigate the canal.
6. Don’t forget to recapitulate the canal with previous smaller number instrument.
7. Repeat the process until a size 25 K-file reaches the working length.
Phase II
1. Repeat the above procedure with successively larger files at 1 mm increments from the previously used file.
2. Finally, refining of the root canal is done by master apical file with push-pull strokes to achieve a smooth taper from of the root canal.
Advantages
• Less likely to cause periapical trauma.
• One can achieve apical matrix or step which prevents overfilling.
• Greater condensation pressure can be exerted to fill lateral canals.
WHAT IS BALANCED FORCE TECHNIQUE? Technique
1. In balanced force technique, first file to bind short of working length is inserted into the canal and rotated clockwise a quarter of a turn. This causes flutes to engage a small amount of dentin (Fig. 13.4A). 2. Now file is rotated counterclockwise with apical
pressure at least one-third of a revolution. It is the counterclockwise rotation with apical pressure which actually provides the cutting action by shearing off small amount of dentin engaged during clockwise rotation (Fig. 13.4B).
3. Then a final clockwise rotation is given to the instrument which loads the flutes of file with loosened debris and the file is withdrawn (Fig. 13.5).
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.
Fig. 13.2: Prepare the access cavity and
locate the canal orifices
CROWN-DOWN TECHNIQUE
In the crown-down technique, one prepares the canal from crown of the tooth, shaping the canal while moving towards the apical portion of the canal (Fig. 13.6).
Technique
1. Locate the canal orifices with sharp explorer and start preflaring of the canal orifices. Preflaring of the coronal third of the canal can be done by using hand instruments, Gates-Glidden drills or the nickle- titanium rotary instruments.
2. Frequent irrigation with sodium hypochlorite and recapitulation with a smaller file to prevent canal blockage.
3. After establishing coronal and mid root enlargement explore the canal and establish the working length with small instruments.
4. Introduce larger files to coronal part of the canal and prepare it. Subsequently introduce progressively smaller number files deeper into the canal in sequential order and prepare the apical part of the canal.
5. Final apical preparation is prepared and finished along with frequent irrigation of the canal system.
Clinical Advantages
• Enhanced tactile sensation with instruments because of removal of coronal interferences.
• In curved canals, after doing coronal flaring, files can go up to apex more effectively due to decrease deviation of instruments in the canal curvature. • Provides more space of irrigants.
• Desired shape of canal can be obtained that is narrow at apex, wider at coronal.
• Decreased frequency of canal blockages.
WHAT IS CLINICAL TECHNIQUE FOR USE OF DIFFERENT ROTARY INSTRUMENTS?
Clinical Technique using Profile System
1. Estimate the working length of the canal from preoperative radiograph.
Figs 13.4A and B: (A) Engaging dentin with quarter clockwise
turn (B) Cutting action by anticlockwise motion with apical pressure
Fig. 13.5: Now file is turned quarter clockwise.
It picks the debris and withdraws the instrument
Cleaning and Shaping of Root Canals 61
2. Use orifices shapers sizes 4, 3, 2, and 1 in the coronal third of the canal.
3. Perform crown-down technique using the profile instruments of taper/size 0.06/30, 0.06/25, 0.04/30 and 0.04/25 to the resistance. For larger canals use 0.06/35, 0.06/30, 0.04/35 and 0.04/30.
4. Now determine the exact working length by inserting conventional number 15 K-file.
5. After this complete the crown-down procedure up until this length. Use profile 0.04/25, 0.04/30 for apical preparation.
Clinical Technique using ProTaper Files
1. After gaining straight line access to the canal orifices prepare the coronal third of the canal by inserting S1 into the canal using passive pressure.
2. Irrigate and recapitulate the canal using number 10 file.
3. In shorter teeth, use of Sx is recommended.
4. After this S2 is worked up to the estimated canal length.
5. Now confirm the working length using small stainless steel K-files.
6. Use F1, F2 and F3 finishing files up to established working length and complete the apical preparation.
Clinical Technique using Quantec File System
1. Obtain the straight line access to the canal orifices. 2. Establish the patency of canal using number 10 or 15
stainless steel files.
3. Insert the Quantec number 25, taper 0.06 file passively into the canal.
4. After negotiation of the canal using Quantec file, prepare the canal from 0.12 to 0.03 taper.
5. Finally, complete the apical preparation of canal using 40 or 45 No., 0.02 taper hand or rotary files.
WHAT IS EVALUATION CRITERIA OF CANAL PREPARATION?
1. Spreader should be able to reach within 1 mm of the working length if spreader does not reach the estimated length, it indicates canal is not well prepared.
2. After canal preparation, when master apical file is pressed firmly against each walls should feel smooth.
WHAT PRECAUTIONS SHOULD BE TAKEN WHILE PREPARING CURVED CANALS?
In curved canals, frequently seen problem is occurrence of uneven cutting. File can cut dentine evenly only if it engages dentine around its entire circumference. Once it becomes loose in a curved canal, it will tend to straighten up and will contact only at certain points along its length. These areas are usually outer portion of curve apical to the curve, on inner part of curve at the height of curve and outer or inner curve coronal to the curve. All this can lead to occurrence of procedural errors like formation of ledge, transportation of foramen, perforation or formation of elbow and zip in a curved canal. To avoid these problems following measures should be taken:
i. Precurving the file: A precurved file has shown to
traverse the curve better than a straight file.
ii. Extravagant use of smaller number files: Since
smaller sized instruments can follow the canal curvature because of their flexibility, they should be used until the larger files are able to negotiate the canal without force.
iii. Use of intermediate sizes of files: In severely
curved canals the clinician can cut 0.05 mm of the file to increase the instrument diameter by 0.01 mm. This allows the smoother transition of the instrument sizes to cause smoother cutting in curved canals.
iv. Use of flexible files: Flexible files help in main-
taining the shape of the curve and avoid occurrence of procedural errors like formation of ledge, elbow or zipping of the canal.
v. Modifying cutting edges of the instrument: The cutting edges of the curved instrument can be modified by dulling the flute on outer portion of the apical third and inner portion of the middle third. Dulling of the flutes can be done with the help of diamond file (Fig. 13.7).
WHAT ARE GUIDELINES FOR
NEGOTIATING CALCIFIED CANALS?
• To locate the calcified orifice, first mentally visualize and plan the normal spatial relationship of the pulp space onto a radiograph of calcified tooth.
• After this access preparation is initiated, with the rotary instrument directed toward the assumed location of pulpal space.
Fig. 13.7: Dulling of flutes is done with the help of
diamond file
• In a tooth with a calcified pulp chamber, the distance from the occlusal surface to the pulp chamber is measured from the preoperative radiograph.
Guidelines
• Always advance instruments slowly in calcified canals.
• When a fine instrument has reached the approximate canal length, do not remove it; rather obtain a radiograph to ascertain the position of the file. • Use chelating agents to assist in canal penetration. • Well angulated periapical and bite using radiographs
should be taken.
• 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. This will further ease the instru- ments into the proper lane to allow effortless intro- duction of files into the canals.