Root Canal Preparation Basics

This lecture explain the basic of root canal preparation in endodontic treatment. It is not meant to be a comprehensive lecture, rather an preliminary one

1. Straight Canals V.s. Curved Canals
Continuous Tapering Funnel
Development Of Preparation Techniques
Standardized Technique
Step-Back Technique
Step-Down Technique
Instrument Manipulation
Canal Irrigation
Working Length Determination
Precurving Manual Instruments
Negotiating Canals
Recapitulation
Canal Preparation Techniques Explained
STRAIGHT CANALS V .S. CURVED CANALS
Posterior teeth characterize by more than one root.
These roots often exhibit a network system of fins,
ramifications, and lateral canals, and most importantly
curved canals.
Research also has shown that anterior teeth often have
curved canals, that directed bucally or lingually, so we
see them as straight canals in the radiograph.
In the past, all root canals treated as they were straight,
and instrumentation was done using standardized tech-
nique. This led to occurrences of procedural errors and
often failure of treatment.
Recent development in the past 60 has led to the inven-
tion of new techniques that minimize time and proce-
dural accidents, and guarantee a successful delivery of
treatment
CONTINUOUS TAPERING FUNNEL
The goal of canal preparation is to clean root canal sys-
tem and shape it as tapering funnel to receive obutation
material.
This tapering funnel, is wide coronally and start to nar-
row as it move apically, and ends in the apical stop,
which represent the narrowest part of the canal system
and where the obturation material should ends.
DEVELOPMENT OF PREPARATION
TECHNIQUES
In order to fully understand the preparation techniques
that are written in textbooks, it is necessary to view
them in their historical order, and view their draw-
backs that led to development of new, less aggressive
techniques.
ROOT CANAL PREPARATION
Osama Asadi, B.D.S, Published for Iraqi Dental Academy Blog
Success in endodontic treatment depend largely on shaping and cleaning of root canal system. In recent
years, there has been a significant move away from the hand taper 2% standardized instrumentation into
rotary Ni-Ti variable taper crown-down instrumentation.
In addition to that the concept of cleaning and shaping has been turned into shaping and cleaning. As the
shaping process proceed cleaning process and it determine the quality of root canal cleaning.
LECTURE OUTLINE
CHAPTER
Figure 1: Continuous tapering funnel
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2. Preparation techniques are (in historical order):
• Standardized technique
• Step-back technique
• Step down technique (or crown-down)
• Hybrid technique (or double-flare technique)
STANDARDIZED TECHNIQUE
This technique was used for many years and now it is
outdated. It involve inserting each size of file to the full
working length. The canal enlarged until white shaving
dentin is seen at apical few millimeters of the file. The
canal is then instrumented for further 2-3 files
The problem with this technique was:
• It works fine for straight canals, but not for curved
canals
• It led to procedural errors such as ledging, zipping,
perforation
• Loss of working length sometimes due to packing
of debris
This led to development of step-back technique
STEP-BACK TECHNIQUE
This technique was created to overcome the problems
in curved canals The root canal is prepared for the full
working length to master apical file size 25 or 30.
Then successively, each larger instrument is inserted 1
mm less than the previous instrument. Between each
instrument, master apical file is inserted to the full
working length to clear any debris. This is called reca-
pitulation.
Some modification of this technique is passive step-
back technique, in which each successive file is inserted
not 1 mm shorter, but to the distance where resistance is
felt and rotated, then withdrawn.
Step-back technique overcomed the procedural errors
occurred with standardized technique in moderately
curved canals. But procedural accidents still occur in
severe curved canals. Also this technique is time con-
suming. This led to development of step-down tech-
nique
STEP-DOWN TECHNIQUE
This technique was first invented by Schilder in 1974,
and described in detail by Goerig et al.
The principle of this technique is that the coronal aspect
of root canal is widened and cleaned first before the
apical part. This has some advantages:
• It allow straight access to the apical area of the root
canal.
• It eliminate dentinal interference found in the cor-
onal two-thirds of the canal, which allow fast and
efficient apical instrumentation.
• It remove the coronal pulp and debris first, which
reduce the incidence of post-operative pain
• It allow irrigant solution to clean the canal more
efficiently.
This technique is the most widely used preparation
technique, and it is represent the gold-standard of root
canal preparation.
INSTRUMENT MANIPULATION
During years of dentistry, many techniques for han-
dling manual instruments has been introduced:
• Watch-winding: it involve reciprocating clock-
wise, counterclockwise rotation of the instrument.
• Reaming: it involve clockwise rotation of the in-
strument.
• Filing: it involve up and down movement of the
instrument, while pressing the instrument against
canal wall.
• Circumferential filing: it is the same as filing
motion, but each mesial, distal, bucall, and lingual
side of the wall is worked against the instrument
successively.
• Anti-curvature filing: it involve filing of the in-
strument away from the furcation area or what
called danger zone, to avoid perforation.
• Balanced force: It is the best technique. It involve
clockwise rotation of instrument for 90 degree,
then counterclockwise rotation of instrument with
apical pressure (you may hear clicking sound,
which is natural)for 120 degree, then final clock-
wise rotation and the instrument is withdrawn.
.
The recommended technique in modern endodontics
is the balanced force technique, and it should be fol-
lowed.
Figure 2: Red area represent danger zone, which should be
avoided during preparation
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3. CANAL IRRIGATION
Practioner should have some basic knowledge of root
canal irrigation. It has been described in previous lec-
tures. Here are some facts about irrigation:
• During preparation, root canals should be kept wet,
with copious irrigation used for each instrument,
and recapitulation between each instrument is a
must.
• It is established that sodium hypochlorite is the
irrigation of choice
• Heating of irrigant can increase its efficiency
• Diluting sodium hypochlorite will not reduce its an-
tibacterial action, but reduce the dissolving capacity
• Care should be taken not to extrude irrigant beyond
the apex as it lead to unhappy events
• EDTA should be used to remove smear layer and
opens dentinal tubules
• Passive ultrasonic activation of irrigant is one of
modern advances in root canal cleaning.
WORKING LENGTH DETERMINATION
The working length can be determined radiographically
or electronically using apex locater, or both for accurate
results. First, measure the the length of the tooth from
reference point to the apex by holding the ruler parallel
to the preoperative radiograph. This is the initial work-
ing length.
Then subtract 0.5 - 1 mm from the initial working
length and insert small file inside the canal and take a
radiograph.
Check the radiograph, if the file is short of the apex add
this distance to the working length. The final working
length should be 0.5-1 mm short of the apex.
PRECURVING MANUAL INSTRUMENTS
Each hand instrument should be precurved according to
root canal curvature, regardless of the technique used in
canal preparation. This is has an advantage. In non-pre-
curved instruments when a file face an obstruction or
curvature it will stuck in the way. But if we precurve
the file and and insert it into the canal when it faces an
obstruction we can rotate it to set it free, which will not
occur if we use straight files.
Figure 4: Two types of precurving. On the right,
precurving for canal preparation. On the left,
precurving for separated instrument bypass
Figure 3: Balanced force technique
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4. NEGOTIATING CANALS
After access opening and pulp extirpation, the canal is
negotiated using fine files, not reamers, in filing motion
only (up and down). This prevent instrument breakage.
After few files, the balanced motion should be used af-
ter the canal has been clean and wide enough.
It worth mentioning that British Dental Journal do not
recommend using reamers, as it lead to more procedur-
al errors
RECAPITULATION
While the canal is full of irrigant, take a small file (#10,
#15) and advance it to the full working length.
It should be done between each successive files regard-
less of the technique used. The purpose of recapitula-
tion is to maintain the patency of the canal and avoid
blockage of canal by debris.
CANAL PREPARATION TECHNIQUES
IN DETAIL
Here I will describe root canal preparation techniques
that are available in the textbooks in summary.
Standardized technique
Steps:
• Determine working length as described earlier
• Precurve the file and insert it to the full working
length
• Using balanced force or watch-winding technique
rotate the file inside the canal until it loose
• Irrigate with sodium hypochlorite
• Use next larger file to the full working length
• Irrigate with sodium hypochlorite and recapitulate
with the first file
• Repeat the steps with successively larger files to
the full working length until white shaving dentin
is noticed at the apical few millimeter of the file,
then use 2 or 3 more larger instrument while irrigat-
ing and recapitulating. The canal now should have
a continuous tapering funnel shape.
Worth-mentioning that this technique is no longer rec-
ommended as it lead to procedural errors in curved ca-
nals. A step-back or step-down technique is preferred
.
Step-back technique
Steps:
• Determine working length as described previously
• Precurve the the first file (e.g., #10) and insert it to
the full working length.
• Using watch-winding or balanced force technique
rotate the file inside the canal until it is loose
• Irrigate and insert next file to the full working length
• Insert successive files until one of the files can not
reach the full working length. The final file that
reach to the full working length (usually #25 or #30)
is called master apical file (MAF), and it is used to
recapitulate the canal between each successive file.
• Irrigate the canal and insert next larger instrument
than MAF, with 1 mm shorter of the working length
• And keep inserting files 1 mm shorter of the previ-
ous file, with frequent irrigation and recapitulation
This technique has overcome the problem with stan-
dardized technique and works fine in moderately
curved canals. However, in severely curved canals it
can lead to procedural errors. Also it is a time consum-
ing procedure.
Step-down technique
This technique is divided into two phases:
1. Coronal flaring
2. Apical Preparation
Coronal flaring is done using Gates Glidden drill or ro-
tary Orifice Shapers, but it also can be done using hand
Figure 5: Standarized Technique
4
Figure 6: Step-back Technique

5. files if GG is not available. Apical preparation is done
with hand files or rotary instruments
Coronal flaring
The purpose of this step is to enlarge the coronal two
third of the canal so it can receive rotary instruments or
hand files, also to permit efficient delivery of irrigant to
the canal.
This can be accomplished using Gates Glidden drills
from #4 to #2 (some canals can accept #6 size drill, but
most canals accept size #4). It is important to use hand
files first before GG to avoid fracture of such instru-
ments. GG should be used only in straight portion of
the canals, and not passed beyond the canal curvature.
Alternatively, rotary orifice shapers can be used instead
of GG. If both are not present at current time, large
hand files can be used instead.
Apical preparation
After the process of coronal flaring is completed,
further canal preparation is started. Hand file (or rotary)
matching the size of last GG drill is used to prepare the
canal. Then a smaller sizes are used to further works
in the canal. Each files will go deeper into the canal.
When reaching at 3 mm short of the estimated working
length, the file is inserted into the canal and radiograph
is taken. After confirmation of working length, smaller
files are worked into the canal to the size #15. Frequent
irrigation and recapitulating is a must.
This is the best technique available and represent the
modern practice of dentistry. It is also called crown-
down technique.
Hybrid technique
It involve combination of coronal flaring, step-down
technique, then working four files to the full working
length, then step-back technique. It is also highly rec-
ommended.
Also many other combination of rotary instruments are
available for the hybrid technique.
Temporary filling
In multi-visit endodontic treatment it is important to
seal the cavity with temporary filling material between
visits. There are several temporary filling materials
available in the market. Most common one is Cav-
it. Although it has low wear resistance, it can be used
in combination with GIC temporary filling to provide
strong temporary filling that can lasts for several weeks
and can withstand wearing action of oral environment.
In this concept, Cavit is placed for the lower layers and
GIC for the outer layers that faces oral environment.
The proper way to place temporary filling is by layering
technique shown in this picture:
REFERENCES
• PDQ Endodontics
• Endodontics, Volume II, Arnaldo Castellucci
• Cohen’s Pathways of Pulp
• Pocket Atlas of Endodontics, Rudolf Beer
• Endodontics Principles and Practice, Mahmoud
Torbinejad
• A Clinical Guide to Endodontics, British Dental
Journal, P. Carrote
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Figure 7: Step-down technique