Determination of root canal working length /certified fixed orthodontic courses by Indian dental academy

DETERMINATION OF
WORKING LENGTH

INDIAN DENTAL ACADEMY
Leader in Continuing Dental Education

www.indiandentalacademy.co

INTRODUCTION
BASIS FOR SUCCESSFUL ENDODONTICS
THE HISTORY:
As the awareness among dentists increased that
natural teeth function more efficiently than artificial ones, it
became prudent to save the pulpally involved teeth.
William hunter , an English physician in 1910 at Mc
gill university addressed on the role of sepsis and antisepsis in
which he criticized prosthetics and endodontics in particular by
asserting that gold fillings, caps , bridges,and dentures were islets
of frank infection and these were responsible for spread of
infection.


• Rhein adopted X rays in
dentistry for endodontic use
to determine canal length and
degree of filling.
• Coolidge, Prinz , Sharp,
Blayney, Appleton and others
launched a counter attack by
demonstrating successful
cases of endodontics on sound
biologic principles.
• By 1930s corner had been
turned and treatment of
pulpless teeth became integral
part of dentistry.

OBJECTIVES OF ENDODONTIC THERAPY

The objective of endodontic therapy is restoration of the treated
tooth to its proper form and function in the masticatory apparatus in
a healthy state.

Basic phases of therapy:
There are three basic phases of endodontic therapy
1. Diagnostic phase
2. Preparatory phase
3. Filling or obliteration of canal.
Endodontic therapy may be thought as a tripod with perfectly
treated teeth on a pedestal and every leg representing a basic phase.
If any leg is faulty entire system may fail.


Importance of debridement

Endodontic therapy is essentially a
debridement procedure that requires removal of
irritants from canal and periradicular tissues if
success is to be gained.
As the case demands debridement may be
carried out by instrumentation irrigation,
placement of intracanal medicament or
electrosurgery.


One of the most important steps in canal preparation
is determination of working length,
Significance of this procedure are;
1. Calculation determines how far into the canal
instruments are placed and worked, thus how
deeply into the tissues, debris, metabolites,end
products and other unwanted items are removed.
2. It will limit the depth to which canal instrument
may be placed.
3. It will affect degree of pain and discomfort that
patient will feel following appointment.
4. If calculated correctly it will play an important role
in determining success of treatment.


HISTORICAL PERSPECTIVE IN
DETERMINATION OF WORKING
LENGTH
In the early days of endodontic treatment
radiographs were not applied to dentistry yet and
working length was calculated to the site where
patient experienced feeling for an instrument
placed into the canal.
Obviously errors occurred, sometimes tissues
were left unextirpated resulting in short fillings
and sometimes fillings were too long.


DETERMINATION OF WORKING LENGTH
The determination of an accurate working length is
one of the most critical steps of endodontic therapy.
The endodontic Glossary as “the distance from a coronal
reference point to the point at which canal preparation
and obturation should terminate,”
The anatomic apex is the tip or the end of the root
determined morphologically, whereas the radiographic
apex is the tip or end of the root determined radiographically.
Root morphology and radiographic distortion may cause the location of the
radiographic apex to vary from the anatomic apex.
The apical foramen is the main apical opening of the
root canal. It is frequently eccentrically located away
from the anatomic or radiographic apex.
Kuttler’s investigation showed that this deviation occurred in 68
to 80% of teeth in his study.
An accessory foramen is an orifice on the surface of the
root communicating with a lateral or accessory canal. They may exist as a
single foramen or as multiple foramina.


Anatomic considerations
• The apical constriction (minor apical diameter) is the
apical portion of the root canal having the narrowest
diameter.
• This position may vary but is usually 0.5 to 1.0 mm
short of the center of the apical foramen.
• The minor diameter (a) widens apically to the foramen
major diameter (b) and assumes a funnel shape. The
apical third is the most studied region of the root canal.
• The cementodentinal junction is the region where the
dentin and cementum are united, the point at which the
cemental surface terminates at or near the apex of a
tooth.
• It must be pointed out, however, that the
cementodentinal junction is a histologic landmark that
cannot be located clinically or radiographically.
• Langeland reported that the cementodentinal junction
does not always coincide with the apical constriction.
The location of the cementinodentinal junction also
ranges from 0.5 to 3.0 mm short of the anatomic apex.
• Therefore, it is generally accepted that the apical
constriction is most frequently located 0.5 to 1.0 mm
short of the radiographic apex, but with variations.

Clinical Considerations
Before determining a definitive working length, the coronal access to the pulp
chamber must provide a straight line pathway into the canal orifice.
Modifications in access preparation may be required to permit the instrument
to penetrate, unimpeded, to the apical constriction.
A small stainless steel K file facilitates the process and the exploration of the canal.
Once the apical restriction is established, it is extremely
important to
monitor the working length periodically since the working length may change
as a curved canal is straightened (“a straight line is the shortest distance between two
points”).
The loss of working length may also be related to
1. The accumulation of dentinal and pulpal debris in the apical 2 to 3 mm of the canal
2. Failing to maintain foramen patency,
3. Skipping instrument sizes, or
4. Failing to irrigate the apical one third adequately.
5. Ledge formation or to
6. Instrument separation
7. Blockage of the canal.
There has been debate as to the optimal length of canal preparation and the
optimal level of canal obturation. Most dentists agree that the desired end point is the
apical constriction, which is not only the narrowest part of the canal but a morphologic
landmark that can help to improve the apical seal when the canal is obturated.

• The measurement should be made
from a secure reference point on the
crown, in close proximity to the straight-
line path of the instrument, a point that
can be identified and monitored
accurately.
• Stop Attachments. A variety of stop
attachments are available. Among the
least expensive and simplest to use are
silicone rubber stops. Several brands of
instruments are now supplied with the
stop attachments already in place on
the shaft. Special tear-shaped or marked
rubber stops can be positioned to align
with the direction of the curve placed in

Disadvantages of Using
Rubber
• Time consuming Stops.
• May move up or down the
shaft
• So the clinician should
develop a mental image of
the position of the rubber
stop on the instrument shaft
in relation to the base of the
handle. Any movement from
that position should be
immediately detected and
corrected.
• One should also develop a
habit of looking directly at
the rubber stop where it
meets the reference point on
the tooth.
• It is also essential to record

METHODS OF DETERMINING
WORKING LENGTH
• Ideal Method
• The requirements of an ideal
method for determining working
length include
• rapid location of the apical
constriction in all pulpal
conditions and all canal contents
• easy measurement
• rapid periodic monitoring and
confirmation
• patient and clinician comfort
• minimal radiation
• ease of use in special patients
such as those with severe gag
reflex, reduced mouth opening,
pregnancy etc; and cost
effectiveness.

Determination of Working Length by
Radiographic Method
The following items are essential to perform
this procedure:
• Good, undistorted, preoperative
radiographs showing the total length and
all roots of the involved tooth.
• Adequate coronal access to all canals.
• An endodontic millimeter ruler.
• Working knowledge of the average
length of all of the teeth.
• A definite, repeatable plane of reference
to an anatomic landmark on the tooth, a
fact that should be noted on the patient’s
record.
• It is imperative that teeth with fractured
cusps or cusps severely weakened by
caries or restoration be reduced to a
flattened surface, supported by dentin.
• Failure to do so may www.indiandentalacademy.co
result in cusps or
weak enamel walls being fractured

Ingle’s Method
• Measure the tooth on the preoperative
radiograph.
• Subtract at least 1.0 mm “safety allowance”
for possible image distortion or
magnification.
• Set the endodontic ruler at this tentative
working length and adjust the stop on the
instrument at that level.
• Place the instrument in the canal until the
stop is at the plane of reference unless pain
is felt (if anesthesia has not been used), in
which case, the instrument is left at that
level and the rubber stop readjusted to this
new point of reference.
• Expose, develop, and clear the radiograph.

• From this adjusted length of tooth, subtract
a 1.0mm “safety factor” to conform with the
apical termination of the root canal at the

Wein’s recommendations
• If, radiographically, there is no
resorption of the root end or bone,
shorten the length by the standard
1.0 mm.
• If periapical bone resorption is
apparent, shorten by 1.5 mm.
• root and bone resorption are
apparent, shorten by 2.0 mm.
The reasoning behind this is
• If there is root resorption, the
apical constriction is probably
destroyed—hence the shorter move
back up the canal.
• When bone resorption is apparent,
there probably is also root
resorption, even though it may not
be apparent radiographically.

• Set the endodontic ruler at this new
corrected length and readjust the
stop on the exploring instrument.
• Because of the possibility of
radiographic distortion, sharply
curving roots, and operator
measuring error, a confirmatory
radiograph of the adjusted length is
desirable.
• When the length of the tooth has
been accurately confirmed, reset
the endodontic ruler at this
measurement.
• Record this final working length
and the coronal point of reference
on the patient’s record.
• Once again, it is important to
emphasize that the final working
length may shorten by as much as
1 mm as a curved canal is
straightened out by instrumentation.
• It is therefore recommended that
the “length of the tooth” in a curved

Working Length Estimation by Direct
Digital Radiography or Xeroradiography

• ADVANTAGES
• Rapid imaging
• Reduction in
radiation


Digital Tactile Sense
• An experienced clinician may detect an increase in
resistance as the file approaches the apical 2 to 3
mm.
• This detection is by tactile sense.
• It is more accurate than other methods for an
experienced clinician.
However the drawbacks of this method include
• Difficulty in locating the apical constriction in teeth with
immature apex.
• Difficulty in locating the apical constriction in teeth
which have constricted canal throughout the length.

Determination of Working Length by Apical
Periodontal Sensitivity
• Any method of working length determination, based on
the patient’s response to pain, does not meet the ideal
method of determining working length.
• Working length determination should be painless.
• Endodontic therapy has gained a notorious reputation
for being painful, and it is incumbent on dentists to avoid
perpetuating the fear of endodontics by inserting an
endodontic instrument and using the patient’s pain
reaction to determine working length.
• If an instrument is advanced in the canal toward
inflamed tissue, the hydrostatic pressure developed
inside the canal may cause moderate to severe,
instantaneous pain. At the onset of the pain, the
instrument tip may still be several millimeters short of
the apical constriction.When pain is inflicted in this
manner, little useful information is gained by the
clinician.

Paper Point Measurement
• In a root canal with an immature
(wide open) apex working length is
determined by gently pass the
blunt end of a paper point into the
canal after profound anesthesia has
been achieved.
• The moisture or blood on the
portion of the paper point that
passes beyond the apex may be an
estimation of working length or the
junction between the root apex and
the bone.
• In cases in which the apical
constriction has been lost owing to
resorption or perforation, and in
which there is no free bleeding or
suppuration into the canal, the
moisture or blood on the paper
point is an estimate of the amount
the preparation is overextended.

APEX LOCATORS

Locating the Apical
Foramen with
Modern Technology


Electronic Apex Locators

HISTORY:

Suzuki (1942)- Consistent electrical resistance between
instrument in a root canal and an electrode on the
mucosa. They were also called first generation apex
locators. He calculated that resistance offered by
human mucosa and periodontal ligament was 6.5
kiloohms.
Example : Sonoexplorer
Disadvantages: Cannot be used if conducting fluid is
present. www.indiandentalacademy.co

History:
The Resistance Method (first generation)
Sunada (1962)
Root Canal Meter (1969)


History:
Impedance of the canal
(second generation)
Inoue (1971)
Examples
• Neosono
• Pio
• Apex finder
• Endo analyser


History:
Third generation
High Frequency
Examples:
• Endocator
• Endex
• Apex finder A F A
• Mark V plus
• Justy two
• Root ZX
• TRI AUTO ZX
able to make correct measurement in the presence
of conductive fluids with specially coated file

ENDEX


APEX FINDER A F A(All Fluids Allowed)


Tri AUTO ZX


The Root ZX


Clinical cases no. 1
A forty year old male patient
named Prakash Mali presented
to department of conservative
dentistry and endodontics of G
D C & H Mumbai with chief
complaint of discoloration of
tooth and history of trauma.
Patient was diagnosed with
chronic apical periodontitis and
root canal therapy was advised.
Following is a preoperative
radiograph showing a working
length of 22mm

Tentative working length


Final working length –21mm


Case no. 2
A thirty year old male patient
named Govind Amte presented
to department of conservative
dentistry and endodontics of G
D C & H Mumbai with chief
complaint of discoloration of
tooth and history of trauma.
Patient was diagnosed with
length of 20mm

Final working length-- 19mm


Case no.3(SLOB RULE)
A forty five year old female
patient named Usha Uttekar
presented to department of
conservative dentistry and
endodontics of G D C & H
Mumbai with chief complaint of
pain in lower right posterior
region. Patient was diagnosed
with acute exacerbation of
length of 17mm mesially and
18mm distally. www.indiandentalacademy.co

RADIOGRAPH WITHOUT ANY
HORIZONTAL ANGULATION


RADIOGRAPH WITH HORIZONTAL ANGULATION OF 20
DEGREES ON MESIAL SIDE NOTE 4 CANALS IN THE TOOTH
Final working length was calculated to
mesiobuccal 17mm mesiolingual 17mm
distobuccal 18mm distolingual 18mm


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