This document discusses methods for determining the working length in root canals. It defines key terms like working length, cementodentinal junction, and apical constriction. It describes the significance of accurately determining working length and consequences of being over or under extended. Both radiographic and non-radiographic methods are outlined, including their advantages and limitations. The document concludes that no single method is entirely satisfactory and that a combination of methods should be used to accurately determine working length.

1. WORKING
LENGTH
DETERMINATION
Dr. Sohail Yasin & Dr. Goutham Balakrishnan
1st Year PGs
Dept. of Conservative Dentistry and Endodontics
Vydehi Institute of Dental Sciences and Research

2. Definitions
 Working length:
According to Cohen’s 6th edition ,Every part of endodontic treatment is
controlled by a measurement of the instrument's penetration
depth into the canal. This length is typically determined in
millimeters. It is measured from a point on the tooth's
coronal surface that is within the clinician's field of view. It
varies from the complete canal length to some arbitrarily
determined point near the termination of the canal space.
According to endodontic glossary working length is defined as
“the distance from a coronal reference point to a point at
which canal preparation and obturation should terminate.”

3. History
 End of 18th century: WL was calculated when file was
placed in canal & patient experienced pain.
 1899 : Kells introduced X-rays in dentistry.
 1929 : Collidge studied the anatomy of root apex in
relation to treatment problems.
 1955 : Microscopically investigated the root apices.
 1962 : Sunada – Found electrical resistance between
periodontium and oral mucous membrane.
 1969 : Inove significantly contributed to evolution of
electronic apex locators.

4. SIGNIFICANCE OF
WORKING LENGTH
 Working length determines how far into canal,
instruments can be placed and worked.
 It affects degree of pain and discomfort which patient
will experience following appointment by virtue of
over and under instrumentation.
 If placed within correct limits, it plays an important
role in determining the success of treatment.

5.  Before determining a definite working length, there
should be straight line access for the canal orifice for
unobstructed penetration of instrument into apical
constriction.
 Once apical stop is calculated, monitor the working
length periodically because working length may change
as curved canal is straightened.

7. Consequences of over extended
working length:
 Perforation through apical constriction
 Overinstrumentation
 Overfilling of root canal
 Increased incidence of postoperative pain
 Prolonged healing period
 Lower success rate due to incomplete regeneration of
cementum, periodontal ligament and alveolar bone.

8. Consequences of working short
of actual working length:
 Incomplete cleaning and instrumentation of the canal
 Persistent discomfort due to presence of pulpal remnants
 Under filling of the root canal
 Incomplete apical seal
 Apical leakage which supports existence of viable bacteria, this
further leads to poor healing and periradicular lesion.

9. Causes of loss of working
length:
 Presence of debris in apical ⅔ of canal
 Failure to maintain apical patency
 Skipping instrument sizes
 Ledge formation
 Inadequate irrigation
 Instrument separation
 Canal blockage
 Taper lock.

10. Definitions:
 Anatomic apex:
It is the “tip or end of root determined morphologically .”

11.  Radiographic apex:
It is the “tip or end of root determined radio-graphically.”

12.  Apical foramen
It is main apical opening of the root canal which may
be located away from anatomic or radiographic apex.

13.  Apical constriction
It (minor apical diameter) is apical portion of root
canal having narrowest diameter. It is usually 0.5 to 1
mm short of apical foramen. The minor diameter
widens apically to foramen, i.e. major diameter.

15. TOPOGRAPHY OF APICAL
CONSTRICTION
According to “The position and topography of the apical canal
constriction and apical foramen” by PAUL M. H. DUMMER et al.
International Endodontic Journal - 1984

16. Definitions
 Reference point:
Reference point is that 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 incisal edge of
anterior teeth and buccal cusp of posterior teeth.
• It should not change between the appointments.
Therefore in case of teeth with undermined cusps
and fillings, they should be reduced considerably
before access preparation.

18. Conditions for Loss of
Reference Point:
 Fractured tooth surface
 Carious tooth structure
 Undermined cusps
 Undermined Fillings

19. Definitions
 Cementodentinal junction
It is the region where cementum and dentin are united, the point at
which cemental surface terminates at or near the apex of tooth.
• It is not always necessary that CDJ always coincide with apical
constriction.
• Location of CDJ ranges from 0.5 to 3 mm short of anatomic apex.
Cementum changes with age. It increases with age, due to deposition,
however CDJ doesn’t change.

20. Working Width:
Working width is defined as “initial and post
instrumentation horizontal dimensions of the root canal
system at working length and other levels”.
The minimum initial working width corresponds to initial
apical file size which binds at working length. The
maximum final working width corresponds to the master
apical file size.
Working width was described in “Endodontic
working width: current concepts and
techniques” by - Yi-Tai Jou et al in 2004 in
DCNA.

22. Reasons for widening root canal:
 To remove microorganism from the canal mechanically.
• To increase the area of root canal for better irrigation.
• To completely remove the pulp tissue.
• To attain a sound apical stop so as to achieve a three-
dimensional seal. The round shape conforms to the round
cross sectional tip of gutta percha.

23. Guidelines sufficient for
instrumentation:
1. Enlarge the root canal atleast three sizes beyond the
first instrument that binds the canal.
2. Enlarge the canal until it is clean. It is indicated by
white dentinal shavings on the instrument flutes.
BUT THESE GUIDELINES ARE NOT SOLE
CRITERIA IN ALL THE CASES.

24. Advantages of Narrow
Apex
 Decreases risk of canal transportation.
 Avoids extrusion of debris and obturating
material.

25. Disadvantages Of Narrow
Apex
 Incomplete removal of infected dentin.
 Not ideal for lateral compaction.
 Irrigants may not reach the apical-third of
canal.

26. Advantages of Wide
Apex
 Complete removal of infected dentin.
 Better disinfection of canal at apical third.

27. Disadvantages Of Wide
Apex
 Increased chances of extrusion of irrigants and
obturating material.
 Not recommended for thermoplastic
obturation.
 More chances of preparation errors.

28. Directional Stop
Attachments
 Most commonly used stoppers for endodontic
instruments are silicon rubber stops, though stop
attachments can be made up of metal, plastic or silicon
rubber.
 Stop attachments are available in tear drop or round
shapes.

29.  Irrespective of shape, the stop should be placed
perpendicular to the instrument not at any other
direction (oblique) so as to avoid variation in working
length.
 Advantage of using tear shaped stopper is that in curved
canal, it can be used to indicate the canal curvature by
placing its tear shape towards the direction of curve.

30. Different Methods Of Working
Length Determination
Radiographic Methods Nonradiographic
Methods
 Grossman formula
 Ingle’s method
 Weine’s method
 Kuttler’s method
 Radiographic grid
 Endometric probe
 Direct digital radiography
 Xeroradiography
 Subtraction radiography
 Digital tactile sense
 Apical periodontal
sensitivity
 Paper point method
 Electronic apex
locators

31. Radiographic Method of Length
Determination(Ingle’s Method)
 Before access opening, fractured cusps, cusps weakened by
caries or restorations are reduced to avoid fracture of
weakened enamel during the treatment. This will avoid the
loss of initial reference point and thus the working length.
 Measure the estimated working length from
preoperative periapical radiograph.

32.  Adjust stopper of instrument to this estimated
working length and place it in the canal up to the
adjusted stopper.
 Take the radiograph.
 On the radiograph, measure the difference between
the tip of the instrument and root apex. Add or
subtract this length to the estimated working length
to get the new working length.
 Correct working length is finally calculated by
subtracting 1 mm from this new length.

34. Weine’s Modification:
Modification in the length subtraction
 • No resorption - subtract 1 mm
 • Periapical bone resorption - subtract 1.5 mm
 • Periapical bone + root apex resorption - subtract 2
mm

35. Radiographic methods of working length
determination:
ADVANTAGES:
 One can see the anatomy of the tooth
 One can find out curvature of the root canal
 We can see the relationship between the adjacent
teeth and anatomic structures.

36. DISADVANTAGES
 Varies with different observers.
 Superimposition of anatomical structures.
 Two-dimensional view of three-dimensional
object.
 Cannot interpret if apical foramen has buccal or
lingual exit.
 Risk of radiation exposure.
 Time consuming.
 Limited accuracy.

37. GROSSMAN METHOD/MATHEMATICAL
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:

38. Disadvantages
Wrong readings can occur because of:
• Variations in angles of radiograph
• Curved roots
• S-shaped, double curvature roots

39. Kuttler’s Method
 According to Kuttler, canal preparation should terminate at
apical constriction, i.e. minor diameter.
 Technique:
• Locate minor and major diameter on preoperative
radiograph
• Estimate length of roots from preoperative radiograph
• Estimate canal width on radiograph. If canal is narrow,
use 10 or 15 size instrument. If it is of average width, use
20 or 25 size instruments. If canal is wide, use 30 or 35 size
instrument

40. Insert the selected file in the canal upto the estimated
canal length and take a radiograph
• If file is too long or short by more than 1 mm from minor
diameter, readjust the file and take second radiograph.
o If file reaches major diameter, subtract 0.5 mm from it
for younger patients and 0.67 for older patients.

41. Advantages
• Minimal errors
• Has shown many successful cases.
Disadvantages
• Time consuming and complicated
• Requires excellent quality radiographs.

42. Radiographic Grid
It was designed by Everett and Fixott in 1963. It is a
simple method in which a millimeter grid is
superimposed on the radiograph.
 This overcomes the need for calculation
 But it is not good method if radiograph is bent during
exposure.

43. 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.

44. Direct Digital Radiography
In this 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.

45. Non-radiographic Methods
Digital Tactile Sense
In this clinician may see an increase in resistance as
file reaches the apical 2 to 3 mm.
Advantages
• Time saving
• No radiation exposure.
Disadvantages
• Does not always provide the accurate readings
• In case of narrow canals, one may feel increased
resistance as file approaches apical 2 to 3 mm
• In case of teeth with immature apex, instrument
can go periapically.

46. Periodontal Sensitivity Test
Method is based on patient’s response to pain.
• does not always provide the accurate readings
• For example in case of narrow canals, instrument may
feel increased resistance as file approaches apical 2 to 3
mm and in case of teeth with immature apex instrument
can go beyond apex
• In cases of canal with necrotic pulp, instrument can pass
beyond apical constriction and in case of vital or inflamed
pulp, pain may occur several mm before periapex is
crossed by the instrument.

47. Paper Point Measurement
Method
In this method, paper point is gently passed in
the root canal to estimate the working length
• It is most reliable in cases of open apex where
apical constriction is lost because of perforation
or resorption
• Moisture of blood present on apical part of
paper point indicates that paper point has
passed beyond estimated working length
• It is used as supplementary method.

48. SUMMARY
 The cementodentinal junction or minor diameter
is a practical and anatomic termination point for
the preparation and obturation of the root canal –
and this cannot be determined radiographicaly.
 Modern apex locators can determine this position
with accuracies greater than 90% but with some
limitations.
 No individual method is truly satisfactory in
determining endodontic working length.
 Therefore, combination of methods should be used
to assess the accurate working length
determination

49. BIBLIOGRAPHY
 Endodontic practices and principles – 11th ed
Grossman
 Endodontics Book – 6th ed Ingle
 Pathways of Pulp – 10th ed Stephen Cohen
 Textbook of Endodontics - Nisha Garg
 Bramante CM, Berbert A. ‘Critical evaluation of
methods of determining working length.’ Oral Surg.
1974;37:463.
 Cluster LE, ‘Exact methods of locating the apical
foramen.’ J Nat Dent Assoc. 1918;5:815.
 Kuttler Y. ‘Microscopic investigation of root apexes.’
J Am Dent Assoc. 1955;50:544-52.
 Endodontic working width: current concepts and
techniques Yi-Tai Jou, DDS, DMD*, Bekir Karabucak, DMD,
MS, Jeffrey Levin, DMD, Donald Liu