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TitleBiomechanical Preparation of Root Canal
TagsTypes Reviews
File Size171.6 KB
Total Pages20
Table of Contents
                            A) Follow-withdraw
B) Cart
C) Carve
D) Smooth
E) Patency
B) Reaming
C) Turn-and-pull(Combination)
D) Watch-winding
E) Watch-winding and pull
                        
Document Text Contents
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BIOMECHANICAL PREPARATION OF THE ROOT
CANAL

Cleaning refers to the removal of all contents of the root canal system before
and during shaping: organic substrates, microflora, bacterial by products, food ,caries,
denticles, pulp stones, dense collagen, previous root canal filling material and dentinal
filings resulting from root canal preparation.
Objective: The objective of cleaning is to eliminate or at least to minimize existing or
potential debris from the canal space. This debris can be tissue remnants, bacteria’s,
altered dentin, food debris, caries and saliva.

Since it is not always possible to remove all irritants completely, the attempt is
made to reduce remaining debris to sub critical level or to seal these irritants within
the canal space and prevent their escape into the periapical area.
Techniques: It is a combined mechanical and chemical process. It begins with
establishment of straight line access, which allows better visualization, control in
instrumentation and loosening of debris and irritants. These irritant are further
removed physically by flushing action or chemically by dissolution by irrigating
solutions. Microorganisms are also destroyed by chemicals and then physically
removed by flushing action. Although sound in theory, complete debridement is very
difficult and in some cases impossible.
Evaluation: Historically, presence of clean dentinal shavings were considered end
point for cleaning. It is however, difficult see shavings on file at all. Research has also
shown little relationship between clean shavings and quality of debridement. Another
in accurate measurement is presence of clean irrigating solution. ‘Glassy smooth’
walls are preferred criteria indicating that dentin has been planed in as many areas as
possible. Although not totally accurate, this is best in available lot.
Shaping

Shaping refers to preparing a specific cavity form with five design objectives.
Objective: the purpose of shaping is to enlarge and taper the canal to receive
obturating material. The selected obturation technique will thus dictate the approach
and outcome of shaping.
Techniques: It is a pure mechanical process. It is achieved by reaming and filing the
canal by one of the various techniques using hand and /or rotary instruments.
Evaluation: Historically, it was evaluated by measuring size of instrument which is
first to show binding when inserted upto working length. Then enlargement is done
which is two or three sizes beyond the binding instrument with minimum of upto file
size no 25. The most accurate method is by using condensing instrument. The
attainment of adequate canal enlargement and flaring is determined by the ability of
the spreader or plugger to penetrate close to working length.
The shaping always facilitates ‘cleaning’ by eliminating pulp, bacteria and their
toxins; by removing restrictive dentin, which allows an effective volume of irrigant to
work deeper and more quickly to potentially circulate into all aspects of the root canal
system.
Apical preparation

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CANAL

successively larger instruments, each to the working length, starting with small sizes
and enlarging, using combinations of reaming and circumferential filing. In straight
canals enlargement was done till three sizes more than initial file which binds.
However, in curved and narrow canals it was kept at maximum of file no 25. If canal
cannot be prepared by reaming throughout its length, the remain canal is filed
circumferentially and apical part (3 to 4 mm) is left as it was prepared into round and
slightly tapering shape to receive initial canal material. The copious irrigation and
recapitulation is performed to prevent clogging of apical part. The shape of final
preparation resembles the “Washington Monument”, the silhouette of obelisk, tapering
to end in a pyramidal shape with apex showing 750 point of the instrument.

This technique was designed for single-cone filling techniques.
Disadvantages:

• This technique has shown accumulation of dentinal debris at apical area,
• Formation of less defined taper in the preparation,
• Occurrence of apical transportation and procedural errors.
• Studies have shown that a standardized shape cannot be formed in curved

canals.

2. Step back technique
It was first described by Clem (1969) and Martin (1974). It was also known as

telescoping technique as final preparation resembles open telescope, its size
increasing, section by section from apex to chamber. The other name for it was
serializing technique.

This method results in more defined taper and smaller apical preparation. It is
divided in three phases by Mullaney (1979)

Phase I Establishing apical stop and preparing the apical section
Phase II Stepping back and cleansing the preparation

A. Refinement with Gates glidden drills
B. Apical stepping refinement

After establishing straight line access and patency of canal, small K file (no
10/15) is used to determine working length. Under copious amount of irrigation, most
apical portion of the canal is prepared with reaming action. This is done at only or two
or three sizes larger than the first file which binds minimum of file size 25. When
preparing curved canal at the apex, no 25 file is the maximum size used. With straight
or slightly curved canals this size could be increased. If canal is larger than file size
25 at the apex, do not enlarge apical region more than the first file that shows the
binding. The instrument last used to prepare the apical region is known as the master
apical file (MAF).

Once apical preparation is complete, the step back procedure begins. The taper
is created by shortening the working length of each successively larger instrument by
1 mm using peripheral filing as opposed to reaming .The Walton et al (1976)
suggested step back to be performed by shortening by 0.5mm as it allows for

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BIOMECHANICAL PREPARATION OF THE ROOT
CANAL

preparation that allows maximum insertion of spreader. With the circumferential
filing, the tip of the file is pressed against all walls of the canal on the outstroke. The
successive increase in instrument size and the decreasing length of the file will create
the step back taper. Generally, stepping back is continued to at least size of a no 60 or
no 70 file. This generally gives adequate debridement as well as sufficient taper.
Large canals will require flaring to larger sizes.

Recapitulation is critical and necessary to maximize debridement and
minimize procedural errors. After each step back file, return to full canal length with
the instrument smaller than the master apical file. Spin and wriggle file to carefully
loosen the debris and dentin chips that invariably become packed into the apical
region of the canal.

Frequent use of irrigating solution in copious amounts is also critical for
debridement. Following each file size and after recapitulation, used at least 2 ml of
irrigant to flush the loosened debris from the canal. To prevent forcing debris and
irrigating solution beyond the apex, it is mandatory to inject with minimal pressure
and to prevent binding of needle to canal walls.

Completion of preparation is next step which consists of enlarging and
cleaning the canal in the mid root and coronal areas and smoothening of canal walls.
It has two components

1. Coronal and mid root preparation
2. Apical stepping refinement

Then there is final irrigation and canal is dried with paper points. Dry filing is
last step which is done using last size file used to the working length. The file is spun
carefully to the length to remove dentin chips that have become packed during drying.

Dry filing are not indicated if there is no apical stop, as this step will remove dentin
chips which have formed a partial plug or seal or may actually open the apex further.

The one of the modification of step back preparation advocate step back to be
started 2 to 3 mm above working length after apical preparation is completed. This
gives a short almost parallel retention form to receive filling material which shows
better tug back.
According to Lim (1985) step back is considered best in preparing curved root
canal and is considered as better method to prevent complications such as formation
of ledges, perforations.

Some dentists believe that apex should be enlarged to minimum of a no 40 file
regardless of canal curvature. The techniques given to achieve this were Ohio state
technique and Southern California technique.

3. Ohio state technique
After establishing straight line access and patency of canal, small K file (no

10/15) is used to determine working length. Under copious amount of irrigation, most
apical portion of the canal is prepared with reaming action. The enlargement of the

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BIOMECHANICAL PREPARATION OF THE ROOT
CANAL

CONCLUSION
As it is seen not a single method is such that it can be universally used in all canal
shapes, curvatures. All methods have their indications, advantages and disadvantages.
So, proper examination of root canal for its shape size and curvature with
understanding of mechanics of biomechanical techniques will only help operator to
choose suitable technique for achieving high success.

REFERENCES
1. Abou-Rass M, Frank AL, Glick DH. The anti curvature filing
method to prepare the curved root canal. J Am Dent Assoc 1980: 101: 792–
794.
2. Backman CA, Oswald RJ, Pitts DL. A radiographic comparison of
two root canal instrumentation techniques. J Endod 1992: 18: 19–24.
3. Fava L. The double-flared technique: an alternative for
biomechanical preparation. J Endod 1983: 9: 76–80.
4. Goerig AC, Michelich RJ, Schultz HH. Instrumentation of root
canals in molar using the step-down technique. J Endod 1982: 8: 550–554.
5. Gutman J L, Dumsa T. Cleaning and shaping of root canal system.
In Pathways of the pulp by Cohen S and Burns R C, 4th ed. C V Mosby
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Endodontics by Ingle J I, Taintor J F, 3rd ed. Lea and Febiger, Philadelphia.
10. Lim S, Stock CJ. The risk of perforation in the curved canal: anti
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11. Morgan L, Montgomery S. An evaluation of the crown-down-
pressure less-technique. J Endod 1984:10: 491–498.
12. Mullaney T P. Instrumentation of finely curved canals. Dent Clin
North Am, 1979; 23(4): 575-592.
13. Roane JB, Sabala CL, Duncanson MG Jr. The ‘balanced force’
concept for instrumentation of curved canals. J Endod 1985: 11: 203–211.

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