WORKING LENGTH DETERMINATION.pptx fir dental students

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WORKING
LENGTH
DETERMINATION

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CONTENTS
SHAPING OF ROOT CANAL SYSTEM
CORONAL PRE-ENLARGEMENT
TERMINOLOGIES
WORKING LENGTH DETERMINATION & ITS SIGNIFICANCE
RADIOGRAPHIC METHODS
NON- RADIOGRAPHIC METHODS
ROLE OF CBCT IN WL DETERMINATION
CLINICAL CONSIDERATIONS
CONCLUSION
REFERENCES

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Phase I: Glide path determination (canal patency)
Phase II: Coronal pre-enlargement (orifice
enlargement)
Phase III: Working length measurement
Phase IV: Root canal shaping techniques
Phase V: Root canal working width
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Gopikrishna V. Grossman‘s Endodontic Practice. 14th edition. New Delhi, India: Wolters Kluwer Pvt. Ltd; 2021.

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CORONAL PRE-ENLARGEMENT
(ORIFICE ENLARGEMENT)
It is a concept of enlarging the
coronal third of the root canal prior
to the estimation of the working
length.
The working length of the tooth
should be determined only after
coronal pre-enlargement of the
canal is completed.

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THIS CONCEPT OF CORONAL PRE-ENLARGEMENT IS
RECOMMENDED FOR THE FOLLOWING REASONS:
 Root canals have multiplanar
curvatures that increase the
torsional stresses on shaping
instruments as they proceed
apically.
 Enlarging the orifice and 2–3 mm of
the coronal third reduces the
stresses on subsequent shaping
instruments.
The coronal third of the root canal
contains the maximum pulp tissue
and enlarging this space reduces the
amount of periapical debris
extrusion during subsequent shaping
procedures as well as during
estimation of the working length.

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Coronal pre-enlargement is achieved
with the help of orifice enlargers (in
NiTi systems, or with Gates-Glidden
drills (currently not recommended)
Orifice enlargers are instruments
that are meant for enlarging the
canal only at the level of the orifice
and hence the instrument and
enlargement should be restricted to
a depth of 2–3 mm into the canal
orifice.

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TERMINOLOGIES
Anatomical apex: It is defined as the tip or the end
of the root determined morphologically.
Radiographic apex: It is defined as the tip or the
end of the root determined radiographically.
Apical foramen (major diameter): It is the main
apical opening of the root canal. It is frequently
eccentrically located away from the anatomical or
radiographic apex.
Apical constriction (minor diameter): It is the
apical portion of the root canal having the
narrowest diameter.

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Cementodentinal junction: It is the region
where the dentin and cementum are united.
It is a histologic landmark.
 It is not always necessary that CDJ
always coincide with apical
constriction.
 Location of CDJ ranges from 0.5 mm to
3 mm short of anatomic apex.

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DEFINITION
Working length is defined as the distance from a
coronal reference point to the point at which
canal preparation and obturation should
terminate.
This is usually the apical terminus of the root
canal, also termed the minor constriction or the
minor diameter of the apical foramen.

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ANATOMICAL CONSIDERATIONS
 Theoretically, the canal preparation should extend apically
to the cementodentinal junction. This junction is located at
or near the greatest constriction (minor diameter) of the
apical foramen.
 The cementodentinal junction does not always coincide
with apical constriction and is located 0.5–0.75 mm short of
the anatomical apex.
 Thus, it is clinically recommended to terminate
instrumentation and obturation within 0.5–1.0 mm short of
the radiographic apex.

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KUTTLER’S STUDY
 The apical foramen does not normally exit at the
anatomical apex.
 It deviates by 0.5–3 mm.
 This variation is more marked due to continuous
deposition of cementum in older patients.
 Young teeth- 0.5mm
 Mature teeth- 0.75mm

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REFERENCE POINT
Reference point is the site on occlusal or the
incisal surface from which measurements are
made.
 It should be stable and easily visualized during
preparation.
 Usually, it is the highest point on the incisal edge
of anterior teeth and buccal cusp of posterior
teeth.
 It should not change between the appointments.
 Therefore to have stable reference point,
undermined cusps and restorations should be
reduced before access preparation.
Garg N, Garg A. Textbook of endodontics. Boydell & Brewer Ltd; 2010.

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SIGNIFICANCE OF WORKING LENGTH
 Working length determines how far into canal instruments
can be placed and worked.
 If placed within correct limits, it plays an important role in
determining the success of the treatment.
 It affects the degree of pain and discomfort the patient
will experience during or after the treatment.
 If proper care is not taken, over or underinstrumentation
can occur.

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CONSEQUENCES OF OVER EXTENDED WORKING LENGTH
 Pain as a result of acute inflammatory response
from mechanical damage to the periapical
tissue.
 In infected teeth, leads to the extrusion of
microbes and infected debris.
 Overfilling that causes mechanical and chemical
irritation of the periapical tissue along with
foreign body reaction.
 Prolonged healing time and lower success rate.

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CONSEQUENCES OF SHORT WORKING LENGTH
 Accumulation of infected debris apically
which impairs or prevents healing.
 Incomplete apical seal which supports
existence of viable bacteria resulting in
poor prognosis of the treatment.

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METHODS OF WORKING LENGTH DETERMINATION
 Best’s method
 Bregman’s method
 Bramante’s method
 Grossman formula
 Ingle’s method
 Weine’s method
 Kuttler’s method
 Radiographic grid
 Endometric probe
 Direct digital radiography
 Xeroradiography
 Digital tactile sense
 Apical periodontal sensitivity
 Paper point method
 Electronic apex locators
RADIOGRAPHIC METHODS NONRADIOGRAPHIC METHODS

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TWO SCHOOLS OF THOUGHTS
Cementodentinal junction is
impossible to locate clinically and the
radiographic apex is the only
reproducible site available for length
determination.
Position of radiographic apex is not
reproducible.
Its position depends on number of
factors like angulation of tooth,
position of film, film holder, length of
X-ray cone, and presence of adjacent
anatomic structures, etc.
Radiographic apex has been used as the termination point in working length
determination since many years and it has showed promising results.

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Among the two commonly used techniques,
paralleling technique has been shown to be
superior compared to bisecting angle technique
in determination and reproduction of apical
anatomy.

When two superimposed canals are present
(e.g., buccal and palatal canals of maxillary
premolar, mesial canals of mandibular molar),
one should take the following steps:-
Take two individual radiographs with
instrument placed in each canal
Take radiograph at different
angulations, usually 20–40° at
horizontal angulation
Insert two different instruments, e.g., K
file in one canal, H file/reamer in other
canal, and take radiograph at different
angulations
Apply SLOB rule; expose tooth from
mesial or distal horizontal angle; canal
which moves to same direction is
lingual, whereas canal that moves to
opposite direction is buccal
In curved canals, canal length is reconfirmed
because final working length may shorten up to 1
mm as canal is straightened out by
instrumentation
CLINICAL
TIPS
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BEST’S METHOD
 It was introduced in 1960 by Best.
 In this, a steel 10 mm pin is fixed to the labial
surfaces of root with utility wax, keeping it
parallel to the long axis of the tooth
 Radiograph is taken and measurements were
made using a gauge

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GROSSMAN METHOD OF WORKING LENGTH DETERMINATION
 It is based on simple mathematical formulations to calculate the
working length.
 In this, an instrument is inserted into the canal, stopper is fixed
to the reference point and radiograph is taken.
The formula to calculate actual length of the
tooth is as follows:

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Diagnostic radiograph used to estimate the working
length of the tooth by measuring the tooth from a
stable occlusal reference point till the radiographic
apex
Subtract atleast 1 mm from this length as-:
Minor constriction is always present short of the
anatomic apex
Compensation for radiographic image distortion
This measurement is transferred to a diagnostic
instrument with a silicon stop, which is placed in
the root canal and working length radiograph taken
INGLES METHOD

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On the radiograph, measure the difference between the end
of the instrument and the radiographic apex of the root
Tip of the instrument ends 0.5 mm–1.0
mm from the radiographic root apex
(Working length established)
Short of the radiographic
apex by more than 1.0 mm
Beyond the radiographic
apex
 Add this value to the
earlier estimated length
and adjust stopper on
the diagnostic instrument
accordingly
 Retake the working
length radiograph
 Reduce this value from
the earlier estimated
length and adjust stopper
on the diagnostic
instrument accordingly
 Retake the working
length radiograph

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WEINE’S MODIFICATION
Weine modified calculation of working length according
to presence or abscence of resorption.
No resorption
Periapical bone
resorption
Periapical bone+root
apex

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KUTTLER’S METHOD
Locate minor and major diameter on preoperative
radiograph
Estimate length of roots from preoperative
radiograph
Estimate canal width on radiograph.
If the canal is narrow, use 10 or 15 size instrument. If
it is of average width, use 20 or 25 size instruments. If
the canal is wide, use 30 or 35 size instrument
According to Kuttler,
canal preparation
should terminate at
apical constriction
(minor diameter)

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Insert the selected file in the canal up to the estimated
canal length and take a radiograph
If the file is too long or short by >1 mm from minor
diameter, readjust the file and take second radiograph
If the file reaches major diameter, subtract 0.5 mm from it
for younger patients and 0.67 for older patients

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 Everett & Fixott in 1963 designed a diagnostic X-ray
grid system for determining the length of the tooth.
 The diagnostic X-ray grid designed consists of lines 1
mm apart running lengthwise and cross-wise.
 A heavier line to make the reading easier on the
radiograph accentuates every fifth millimeter.
 The grid is taped to a film to lie in-between the tooth
& film during exposure so patterns become in
cooperated in the finished film.
RADIOGRAPHIC GRID

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Preoperative metrics with radiographic grid along with apex
locator is a better WL measuring tool compared to the
conventional radiographic WL in single-rooted teeth, thus
preventing a confirmation radiograph at final WL and can be
useful in patients who need not to be exposed to repeated
radiation because of mental, medical, or oral conditions.
Rambabu T, Srikanth V, Sajjan GS, Ganguru S, Gayatri C, Roja K. Comparison of Tentative Radiographic Working
Length with and without grid Versus Electronic Apex Locator. Contemp Clin Dent. 2018;9(1):88-91.

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ENDOMETRIC PROBE
 In this method, one uses the graduations
on diagnostic file which are visible on
radiograph.
 But its main disadvantage is that the
smallest file size to be used is number 25.

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DIRECT DIGITAL RADIOGRAPHY
Digital image is formed which is represented by
spatially distributed set of discrete sensors and
pixels.
Two types of digital radiography:
1. Radiovisiography
2. Phosphor imaging system

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XERORADIOGRAPHY
 It is a new method for recording images without
film in which image is recorded on an aluminum
plate coated with selenium particles
 Radiations are projected on film which cause
selective discharge of the particles
 This forms the latent image and is converted to
a positive image by a process called
“development” in the processor unit

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 This technique offers “edge
enhancement” and good detail
 Ability to have both positive and
negative prints together
 Improves visualization of files and
canals
 It is two times more sensitive than
conventional D-speed films
 Since saliva may act as a medium for
flow of current, the electric charge
over the film may cause discomfort
to the patient
 Exposure time varies according to
thickness of the plate
 The process of development cannot
be delayed beyond 15 min

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Accuracy of digital radiography is comparable with
conventional radiography in measuring working length,
so considering the advantages of the digital radiography,
it can be used for working length determination
arida A, Maryam E, Ali M, Ehsan M, Sajad Y, Soraya K. A comparison between conventional and digital radiography in root canal
working length determination. Indian J Dent Res 2013;24(2):229-33.

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ADVANTAGES AND DISADVANTAGES OF
RADIOGRAPHIC METHOD
Varies with different observers
Superimposition of anatomic
structures
Radiation exposure
Cannot interpret if apical foramen
has buccal or lingual exit
Time consuming
One Can appreciate
 anatomy of tooth
 curvature in root canals
 relationship with adjacent teeth &
anatomic structures

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NONRADIOGRAPHIC METHODS
OF WORKING LENGTH
DETERMINATION

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DIGITAL TACTILE SENSE
The root canal orifices were widened and coronal preflaring was done
A 20 K-file was introduced into the canal until an increase in tactile
resistance was detected.
Rubber stopper was adjusted on the file in such a way that it touched
the reference point.
The 20 K-file was carefully withdrawn and the distance from the tip of
the file to the rubber stop was measured using an Endoguage
And the values are noted down and registered as TWL.
Abu Naeem FM, Abdelaziz SM, Ahmed GM. Accuracy of apex locators versus radiographic method in working length
determination: a systematic review and meta-analysis. Int J Adv Res. 2017;5(11):506-18.

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 Time saving
 No radiation exposure
 Does not always provide the accurate
readings
 In the case of narrow canals, one may
feel increased resistance as file
approaches apical 2–3 mm
 In the case of teeth with immature
apex, instrument can go periapically

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APICAL PERIODONTAL SENSITIVITY TEST
 This method is based on patient’s response to pain.
 But this method does not always provide the accurate readings.
 In the cases of canal with necrotic pulp, instrument can pass
beyond apical constriction and in the case of vital or inflamed
pulp, pain may occur several mm before periapex is crossed by
the instrument.

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PAPER POINT MEASUREMENT METHOD
Simon S, Machtou P, Adams N, Tomson P, Lumley P. Apical limit and working length in endodontics. Dental update.
2009;36(3):146-53.
 Repeated points are used to determine the wet/dry point
and the working length can therefore be determined
before final refinement of the apical preparation or filling
of the canal.
 A minute amount of blood or tissue fluid at the end of
the point is an indication that it has been inserted
beyond the foramen.
 This method consists of placing a feathered tip paper
point in the prepared canal, knowing that the canal has
been cleared of all its contents.

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BASIC PHYSICS AND CURRENT ELECTRICITY
 Voltage (V): Also known as potential difference and
measured in volts. It provides the driving force/energy to
allow charged particles to move through an electrical
circuit.
 Current (I): Refers to the movement of charged particles
(electrons or ions) throughout a circuit and is measured in
amperes.
 Direct current (DC) refers to a fixed amount of current per unit
time.
 Alternating current (AC) refers to a phenomenon where the
amount of current under investigation alternates over time.
Ali R, Okechukwu NC, Brunton P, Nattress B. An overview of electronic apex locators: part 1. Br. Dent. J 2013;214(4):155-8.

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 Resistance (R): Refers to a material’s ability to resist the
movement of charged particles within it.
 It varies with the type of material under investigation and
is measured in Ohms.
 An insulator is a material that has a high resistivity and
thus offers high resistance to the movement of
electrons or ions.
 The term ‘resistance’ strictly applies to DC while the
term ‘impedance’ is reserved for AC.

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Capacitor: this refers to any structure consisting of two
conductive materials sandwiching an insulator (or a dielectric).
It is able to store charge. The amount of charge it stores is
called its capacitance (C)
These features can be compared to an endodontic
instrument in the RCS of a tooth, surrounded by the
periodontium. Therefore a tooth also has the ability to
act as a capacitor, a feature exploited by modern EALs

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 A tooth can be compared to a capacitor.
 Dentine and cementum are insulators of current.
 The periodontal ligament (PDL), and a file in the
RCS are all conductors of electricity.
 Therefore an advancing file in the RCS and the
PDL surrounding the radicular dentine will act as
the conductors in a capacitor.
 The dentine, cementum and any associated fluid
or tissue within the RCS will act as the insulator
of the system and will have its own dielectric
constant.

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ELECTRONIC APEX LOCATORS
EALs are devices used in root canal therapy to determine
the position of the apical foramen and thus determine
the length of the root canal space

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DEVELOPMENT
 Cluster (1918): Proposed the concept of measuring
the canal length electronically
 Suzuki (1942): Principle and design of an EAL
 Sunada (1962): Introduction of the first commercial
EAL

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The working length is determined by comparing the electrical
impedance of the periodontal membrane with that of the oral
mucosa both of which should be similar at 6.5 kΩ.
CONCEPT
This is done with the help of an EAL cord that has two ends.
One end is termed a “lip hook” that is kept in contact with the
oral mucosa of the patient while the other end is termed “file
holder” that is a probe which is attached to an endodontic
instrument (K-file or rotary file).

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The attached file is slowly inserted into the root canal up to the
estimated working length.
When the endodontic file touches the soft tissues of the periodontal
membrane, the electrical-resistance gauges for both oral mucosa and
periodontal ligament would have similar readings.
By measuring the depth of insertion of the endodontic file, one may
determine the exact working length of the root canal.

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 No individual technique is truly satisfactory in determining
endodontic working length.
 The CDJ is a practical and anatomic termination point for the
preparation and obturation of the root canal and this cannot be
determined radiographically.
 Modern electronic apex locators can determine this position with
accuracies of greater than 90% but still have some limitations.
Gordon MP, Chandler NP. Electronic apex locators. International endodontic journal. 2004 Jul;37(7):425-37.

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FIRST GENERATION
The first generation of EALs, also known as resistance EALs, measure
opposition to the flow of direct current or resistance.
Pain was commonly felt while using this device due to the high current.
The device was later improved and released as the Endodontic Meter
and the Endodontic Meter SII that used lower currents of less than 5
µA.
Sono Explorer (Salatec)
Neosono-D, MC, and
Ultima EZ (Amadent)
Apex Finder
The first device, Root Canal Meter (Onuki Medical Co., Tokyo, Japan),
was developed in 1969.
Rotstein I, Ingle JI. Ingle's endodontics. 7 th edition. North Carolina: PMPH USA Ltd; 2019.

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These first generation devices caused
sensitivity during use, required a dry
environment and files that had a snug fit in
the canals.
They were also contraindicated in patients
with pacemakers.

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SECOND GENERATION
Second generation EALs, also known as impedance EALs,
measure opposition to the flow of alternating current or
impedance.
These devices operate on the principle that there is
electrical impedance across the canal walls.
The tooth exhibits variable electrical impedance across
the walls of the root that is greater apically than
coronally.

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This method was introduced in 1971 as the Sono-
Explorer.
The second-generation EALs used single high
frequency impedance measurements instead of
resistance to measure locations within the canal.

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 These second generation devices produced
measurements that were inaccurate and required
calibration at the periodontal pocket of each
tooth.
 Some models, such as the Apex Finder and the
Endo Analyzer were self-calibrating but also
delivered varying degrees of accuracy.

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THIRD GENERATION
Third generation EALs were similar to second
generation but used multiple frequency rather
than single frequency impedance, and the first one
commercially available was the Apit, also known
as Endex.
This device worked by comparing the difference in
impedances using the relative value of two
alternating currents at frequencies of 1 kHz and 5
kHz.

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 As the file advanced apically, the difference increased
until it reached its maximum value at the apical
constriction.
 With their powerful microprocessors they were able to
handle mathematical quotient algorithm calculations to
provide accurate readings.
 In 1991, Kobayashi introduced the ratio method
that allows two electric currents with different sine
wave frequencies to have measurable impedance
that can be compared as a ratio.

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 In 1994, the first Root ZX EAL ( J Morita, Tokyo, Japan)
was launched. The ratio method allowed the Root ZX to
self-calibrate by measuring the impedances of 0.4 kHz
and 8 kHz at the same time, calculate the quotient of the
impedances, and express this quotient in terms of the
position of the file inside the canal.
 This allowed more accurate reading regardless of the
type of electrolyte.
Endo Analyzer Model
8005 that used five
different frequencies

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FOURTH GENERATION
This generation EALs also used multiple frequencies,
but only one frequency at a time yielding increased
accuracy.
In 2003, the Elements Diagnostic Unit and EAL
(SybronEndo, Anaheim, CA, U.S.A.) was introduced to
the market and claimed by the manufacturer to provide
more accurate measurements by comparing the
resistance and capacitance measurements to a stored
database to determine the distance to the apex of the
root canal.

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It used a composite waveform of two signals, 0.5 kHz and
4 kHz, instead of 8 kHz and 0.4 kHz used with the Root
ZX.
A significant disadvantage of the fourth
generation was the requirement of dry or
semi-dry canals that rendered it
impractical in a variety of clinical
conditions.

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FIFTH GENERATION
This generation EALs were developed in 2003.
They also measure the capacitance and resistance
of the circuit separately as did the fourth
generation EALs, but they were able to overcome
disadvantages inherent in the fourth generation
devices

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Nevertheless, these devices had considerable
difficulties operating in dry canals, and they
also had measurement reliability factors that
varied with pulpal and periapical conditions.

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SIXTH GENERATION
The Adaptive Apex Locator is claimed to be a sixth generation
EAL with the ability to overcome the problems associated with
the fourth and fifth generation devices.
This device functions in dry or wet canals
by continuously defining the canal
humidity via mathematical analysis
and algorithm to adapt according to the
moisture characteristics of the canal to
accurately determine canal length.

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Measuring the location of the minor foramen using the two apex
locators was more accurate than radiographs and would reduce the
risk of instrumenting and filling beyond the apical foramen.
Vieyra JP, Acosta J, Mondaca JM. Comparison of working length determination with radiographs and two
electronic apex locators. International Endodontic Journal. 2010;43(1):16-20.

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E
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F
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T
S
EALs can accurately measure
canal length and may perform
better than radiography alone.
When combined with canal
length radiographs and master
cone radiographs, the patient
benefits from reduced errors and
reduced radiation exposure
when determining the working
length.

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In the clinical scenario, EAL when used in combination with radiographs will
give much greater accuracy of working length and can reduce the number of
radiographs required and CBCT showing similar correlation with EAL and
actual length can be a reliable alternative of working length determination
in the near future.
Kamaraj PS, Parandhaman H, Raguganesh V. Comparison of Five different methods of Working length
determination: An ex vivo study. Endodontology. 2020 Oct 1;32(4):187.

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L
I
M
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T
A
T
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N
S
THE ACCURACY OF EAL MAY BE
ALTERED IN TEETH WITH THE
FOLLOWING
 Immature apices (open apex).
 Calcified or blocked canals.
 Excessive hemorrhage/excessive
inflammatory exudate in the canal.
 Measurements get altered when the
file contacts any metallic
restoration or when measurement
is taken through a tooth having a
metallic crown prosthesis.

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Within the limitation of this review, it is suggested that electronic apex
locators are comparable in the accuracy of working length determination
to the radiographic method.
However, electronic apex locators and digital radiographic methods
were found to be beneficial from the perspective of radiation dose
reduction.
Abu Naeem FM, Abdelaziz SM, Ahmed GM. Accuracy of apex locators versus radiographic method in
working length determination: a systematic review and meta-analysis. Int J Adv Res. 2017;5(11):506-18.

72
TRI AUTO ZX
ENDY 7000 SAFY ZX
COMBINATION OF APEX LOCATOR AND ENDODONTIC HANDPIECE

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CLINICAL CONSIDERATIONS
RADIOGRAPHS
A pre-operative radiograph is
essential to obtain information
about the RCS’s shape/ anatomy,
before accessing the pulp chamber
and using an EAL to determine the
estimated WL.
THE ACCESS CAVITY
Any metallic restorations should be
removed from the access cavity to
prevent electrical shunting. There
should be no fluid in the pulp
chamber.

THE IRRIGATING MEDIA
 The presence of different irrigating
media in the RCS does not impact
significantly on the performance of
third/fourth generation apex locators.
 One simply must ensure that the
irrigant has not flooded the pulp
chamber.
THE ENDODONTIC FILE
 An endodontic file that will contact the
walls of the RCS should be attached to
the EAL.
 The metal which the file is made of
does not affect the accuracy of the EAL.
THE ‘APEX (OR 0)’ READING
 Advance the file until the visual
analogue displays ‘Apex’ or ‘0’. EALs are
most accurate when the file contacts
the PDL and the display shows an ‘Apex’
or ‘0’ reading.
74

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RE-CHECKING THE WL
 The working length should be re-
checked with an EAL, after the
coronal two thirds of the RCS has
been shaped.
PERFORATIONS
 If a periodontal perforation is suspected, an
EAL can be used to check whether the integrity
of the RCS has been breached.
 A small file should be attached to the device (to
minimise any further trauma to the PDL space)
and applied to the suspected perforation site.
 Any contact with exposed PDL will complete
the circuit and register as an ‘Apex (or zero)’
reading.

UNSTABLE READINGS
 The ‘Apex reading’ should only be accepted as
being accurate if the scale bar of the EAL visual
analogue is (a) stable and (b) moves in symphony
with the movements of the file in the RCS.
 If the visual scale bar of the EAL (a) flashes
intermittently, (b) moves erratically from one
position to another or (c) displays no bars at all,
the ‘Apex reading’ should not be accepted as
being accurate.
Ali R, Okechukwu NC, Brunton P, Nattress B. An overview of electronic apex locators: part 2. Br. Dent. J.
2013;214(5):227-31.
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THE BATTERY
 Low voltages cause electronic
errors.
 Therefore ensure that the EAL’s
batteries are well charged before
using them, to prevent erroneous
readings from being generated.

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USE OF CONE BEAM COMPUTED TOMOGRAPHY
(CBCT) IN WL DETERMINATION
 CBCT is a relatively new radiographic
imaging system that can provide images in
3 dimensions.
Paterson A, Franco V, Patel S, Foschi F. Use of preoperative cone-beam computed tomography to aid in establishment of
endodontic working length: A systematic review and meta-analysis. Imaging science in dentistry. 2020;50(3):183-95.
 Recently, it has been established that the
AF can be identified on preoperative
CBCT, and proprietary measuring software
can be used to measure its distance from a
coronal reference point(CRP).

78
 Unfortunately, even under optimized conditions,
CBCT provides a dose that is 4 to 10 times higher,
and therefore carries a higher risk of a somatic
stochastic effect, than the alternative technique
(periapical radiography).
Because of this higher risk, it is not currently
recommended that preoperative or intraoperative
CBCT be taken for the purpose of estimating working
length.
Paterson A, Franco V, Patel S, Foschi F. Use of preoperative cone-beam computed tomography to aid in establishment of
endodontic working length: A systematic review and meta-analysis. Imaging science in dentistry. 2020;50(3):183-95.

79
Using a simplified method, CBCT images of 0.2 mm voxel size
can be used to accurately determine endodontic WL.
Connert T, Hülber J M, Godt A, Löst C, ElAyouti A. Accuracy of endodontic working length determination
‐
using cone beam computed tomography. Int. Endod. J.. 2014;47(7):698-703.

80
The determination of the working length of root canal using CBCT images
was precise when compared to radiographic method and electronic apex
locator.
de Morais AL, de Alencar AH, de Araújo Estrela CR, Decurcio DA, Estrela C. Working length determination using
cone-beam computed tomography, periapical radiography and electronic apex locator in teeth with apical
periodontitis: a clinical study. Iran Endod J.2016;11(3):164-9.

81
 Determination of accurate working length and its
maintenance during cleaning and shaping
procedures are key factors for successful
endodontic treatment.
 The cleaning, shaping, and obturation cannot be
accomplished accurately unless the working length
is determined correctly.
Thus, predictable endodontic success demands an
accurate working length determination of the root
canal. The procedure for establishment of working
length should be performed with skill, using
techniques which have shown to give valuable and
accurate results and are practical and successful.

82
 Rotstein I, Ingle JI. Ingle's endodontics. 7 th edition. North Carolina: PMPH USA Ltd; 2019.
 Gopikrishna V. Grossman‘s Endodontic Practice. 14th edition. New Delhi, India: Wolters
Kluwer Pvt. Ltd; 2021.
 de Morais AL, de Alencar AH, de Araújo Estrela CR, Decurcio DA, Estrela C. Working length
determination using cone-beam computed tomography, periapical radiography and
electronic apex locator in teeth with apical periodontitis: a clinical study. Iran Endod
J.2016;11(3):164-9.
 Connert T, Hülber J M, Godt A, Löst C, ElAyouti A. Accuracy of endodontic working length
‐
determination using cone beam computed tomography. Int. Endod. J.. 2014;47(7):698-703.
 Paterson A, Franco V, Patel S, Foschi F. Use of preoperative cone-beam computed
tomography to aid in establishment of endodontic working length: A systematic review
and meta-analysis. Imaging science in dentistry. 2020;50(3):183-95.
 Abu Naeem FM, Abdelaziz SM, Ahmed GM. Accuracy of apex locators versus radiographic
method in working length determination: a systematic review and meta-analysis. Int J Adv
Res. 2017;5(11):506-18.
 Ali R, Okechukwu NC, Brunton P, Nattress B. An overview of electronic apex locators: part
2. Br. Dent. J. 2013;214(5):227-31.
 Ali R, Okechukwu NC, Brunton P, Nattress B. An overview of electronic apex locators: part
1. Br. Dent. J. 2013;214(5):227-31.
R
E
F
E
R
E
N
C
E
s

85
DUMMER CLASSIFICATION OF APICAL
CONSTRICTION
Dummer P M, McGinn J H, Rees D G. The position and topography of the apical canal constriction and
apical foramen. Int Endod J 1984; 17(1): 192–8.

86
Orthopantograph (OPG) radiographs are not advocated
for calculating tentative working length because gross
magnification of 13–28% employed in OPG may lead to
errors in calculation of accurate readings.

BREGMAN’S METHOD
 In this, 25–mm length flat probes are prepared which
have a steel blade fixed with acrylic resin as a stop,
leaving a free end of 10 mm for placing in root canal.
 After this, radiograph is taken and working length is
measured using the following formula:-
 RLT = RLI × ALT/ALI RLT
 Real length of tooth RLI : Real length of
instrument ALT : Apparent length of tooth
ALI : Apparent length of instrument
87

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