Objectives of cleaning and shaping
1. To remove and/or eliminate from the root canal, all of its
contents that may lead to the growth of micro-organisms or
breakdown of toxic products into the peri-radicular space.
2. To remove the irregularities of
canal walls as well as
obstructions such as calcifications, filling materials etc.
3. To prepare the root canal not only for its disinfection but also
to develop a shape a shape that permits the simplest and
most effective 3D filling.
Principle of cleaning :
Removal of the necrotic tissue and irritants from the root
Instruments must contact and plane the canal walls to
debride the canals
How to assess cleaning??
Presence of clean dentinal shavings
The colour of the irrigant
Canal enlargement three sizes larger than the size of the
first instrument that binds with the canal
Obtaining Glassy smooth walls : properly prepared
canals should feel smooth in all dimensions when the
tip of a small file is pushed against the canal walls
Principle of Shaping:
Provide a shape that facilitates cleaning and a 3 Dimensional
Main objective is to provide a continuously tapering
Prepration must flow and progressively
narrow in an apical direction
Starting at orifice and moving apically,
every cross sectional diameter of
preparation should decrease
Original anatomy maintained
Position of the foramen maintained
Foramen as small as practical
• Files shape and irrigants clean the
Working Length Determination
Working Length :
Defined as the distance from a predetermined
reference point to the point the cleaning and shaping, and
obturation should terminate
a) Radiographic apex
The termination of the root, as shown on the radiograph.
Not a true indicator especially buccal/lingually curved
b) Minor constriction/minor foramina:
Narrowest portion of the root at the apex
Corresponds to the junction of dentin cementum (CDJ)
c) Major constriction:
It is the anatomic apex of the root
Bordered by cementum
Corresponds with the radiographic apex
Till many years the endodontic treatment was restricted to
0.5-2 mm short of the radiographic apex.
It should be 1mm from the radiographic apex
Working short → apical blockage ← dentin chips
Apical blockage → combination of pulp, bacteria and their
endotoxins → dentin mud.
Methods of Working Length Determination
Predetermined normal tooth length
Electronic Apex Locators
Radiographic apex location
Though not very accurate, provide with a baseline measurements
After access preparation small file is used to explore
the canal and check the patency.
The largest file to bind at the apex is then inserted.
-Small file may get dislodged
-The tip of the file is not very clear on a radiograph
Instrument is placed in the canal, inserted to a point until pain is felt [not
Rubber stopper is then adjusted to a plane of reference on the tooth.
Radiograph is then taken and the radiographic length is measured.
At least 1 mm is subtracted as ‘Safety allowance’ for possible image distortion
A. Do not use weakened enamel walls or
diagonal lines of fracture as a reference
site for length-of-tooth measurement.
B. Weakened cusps or incisal edges are
structure. Diagonal surfaces should be
flattened to give an accurate site of
When 2 canals are superimposed a mesially directed
radiograph is taken
SLOB RULE :
Same side lingual opposite side buccal
MLM when an X-ray is directed mesially the lingual
canal appears more mesial.
MBD when as X-ray is directed mesially the buccal
canal is projected towards the distal on the film.
When 2 canals are present, it is always advisable to use
2 instruments & use MLM rule/MBD
Electronic Apex locators:
Electronic devices used for the determination of the working
It consists of a lip clip, a file clip, a connection cord and the
The lip clip is placed into the metal ring / loop attached to the
carrier tray of the Modu PRO kit.
Attach the endodontic file to the file clip and introduce into the
The display on the Apex locator will indicate the distance of
the file tip to the apex.
Apical canal Preparation
Termination of the preparation
Apical enlargement or Apical size
Minimum of three sizes larger than the first file
that binds at the apex
Larger the size more efficient will be the
Elimination of etiology
Files alone cannot eliminate the etiology
Irrigants, intracanal medicaments
Various motions of the hand instruments:
Watch winding / Twiddling:
•Reciprocating clockwise /counterclockwise rotation of
the instrument in an arc of 30 o – 90 o.
•Used to negotiate canals and to work the files to the
Defined as the clockwise
cutting rotation of the file.
Instrument is placed into the
canal until binding is
encountered and then rotated
180-360 degrees to plane walls
and enlarge the canal
•Defined as placing the file into the canal and
pressing it laterally while whitdrawing it along the
path of insertion to scrape the wall
•Indicates push-pull motion
•There is very little rotation
•Scraping or Rasping action
•May lead to canal ledging, perforations and other
Turn- pull Technique:
•Modification of the filing technique
•Placing the file to the point of binding, rotating the
instrument 90 degrees and pulling the instrument along
the canal wall
Circumferential Filing :
Used for canals that are larger and are not round.
The file is placed in the canal and withdrawn in a
directional manner sequentially against the mesial,
distal, buccal and lingual walls
Canal preparation techniques can be broadly divided into those
that adopt an ‘apical to coronal’ preparation procedure and
those that adopt a ‘coronal to apical’ approach
Step back technique
Step down technique
Passive Step Back Technique
Balanced Force Technique
Nickel Titanium Rotary preparation
STEP BACK PREPARATION
Also called Telescopic or Serial root canal preparation.
Phase I – Apical Preparation
Canal is generally explored with a fine instrument
Working length is then determined
1st instrument to be inserted should be a fine (No. 8,10 or
15) K-file, pre-curved and coated with a lubricant
Motion is generally ‘watch winding’- 2 or 3 quarter turns
clockwise- anti clockwise and then retraction.
Upon removal, the instrument is wiped clean, recurved,
Procedure is repeated until the instrument is loose in
Then the next size K-file is used
By the time a size 25- K file has been used to full length,
Phase I is complete.
In curved canals the apical preparation with instruments
of sizes > 25 would pose a danger of zipping.
The instruments, as they become larger also become
The instruments also tend to straighten with in the
During the whole procedure recapitulation with a smaller
file & copious irrigation is essential so as to ensure
patency of the canal
Hazards of overenlarging the apical curve.
A. Small flexible instruments (No. 10 to No. 25) readily negotiate the curve.
B. Larger instruments (No. 30 and above) markedly increase in stiffness and cutting
efficiency, causing ledge formation.
C. Persistent enlargement with larger instruments results in perforation.
D. A “zip” is formed when the working length is fully maintained and larger
instruments are used.
In a fine canal, step back process begins with a N0: 30 K-file
with a working length set 1mm shorter.
The instrument is pre-curved, lubricated, carried down the
canal to the new WL, watch wound and retracted.
Process is repeated
till #30 file is loose within the canal.
Recapitulation to the full length with a # 25 K file follows to
assure patency to the constriction.
Thus, preparation steps back up the canal one millimeter and
one large instrument at a time.
When the mid-canal is reached, where the instruments no
longer fit, perimeter/ circumferential filing may begin.
H- Files can be used at this stage as they are more
A Gates-Glidden drill can be used at this stage. Starting
with a smaller drill (no. 1& 2) and then gradually
increasing the size to 4,5 &6.
The drill should be used with great care.
A proper continuing taper is developed to finish Phase II A
Refining Phase II B is a return to size No. 25 instrument,
smoothening all around the walls to perfect the taper from
the apical constriction to the canal orifice.
STEP BACK PREPARATION
PHASE II [Coronal Preparation]
PHASE II A
REFINING PHASE II B
transportation, ledging and apical perforation
Results in significant apical extrusion of debris, Apical
blockage, canal deviation, alteration of working length