Working Length Determination Dr. Sana Khan

1. WORKING LENGTH
DETERMINATION
PRESENTED BY:
DR. SANA KHAN
P.G. II YEAR
DEPARTMENT OF CONSERVATIVE DENTISTRY AND ENDODONTICS

2. • DEFINITIONS
• ANATOMY OF ROOT CANAL SYSTEM
• ANATOMY OF THE ROOT APEX
• SIGNIFICANCE OF WORKING LENGTH
• RADIOGRAPHIC AND NON RADHIOGRAPHIC METHODS OF
WORKING LENGTH DETERMINATION
• ERRORS IN DETERMINATION OF WORKING LENGTH

3. • “The healing processes after removal of a pulp, occur in the tissue
immediately adjacent to the point where the pulp was severed. It is,
therefore, of great importance to retain the vitality of these tissues in
order to make healing possible.”
R. Kronfeld , 1933
• “If the tooth is uncomfortable, however, or presents an area of
rarefaction, apical access must be obtained in order to negotiate the
canal throughout its entire length to reach the periapical tissues.”
L.I. Grossman, 1946
• “Factors that may influence a difference [in the method used for
working length determination] include the quality of radiographs,
superimposed anatomic structures, or anomalous positions of root
canal foramen.”
D.H. Pratt en, N.J. McDonald, 1996

4. DEFINITIONS
WORKING LENGTH
• The seventh edition of the Glossary of Endodontic Terms
defines the working length of a tooth as the distance from a
coronal reference point to the point at which canal
preparation and obturation should terminate.

5. REFERENCE POINT
• It is the site on the occlusal or incisal surface from which
measurements are made.
• This point is used throughout canal preparation & obturation.
Selection
• Should be easily visualized during preparation.
• Usually the incisal edges in anteriors & buccal cusp tip on
posteriors. The mesiobuccal cusp tip is preferred in molars.
Stability
A reference point that will not change during or between
appointments is selected.

6. • Don’t use weakened enamel walls or diagonal lines of fracture
as a reference site for length of tooth measurement
• Weakened cusps or incisal edges are reduced to a well
supported tooth structure
• Areas other than cusp tips, such as marginal ridges or the floor
of the chamber, are unreliable or difficult to visualize

7. Diagonal surfaces should be flattened to give an accurate site
of reference

8. ANATOMICCOMPONENTSOF THE ROOT
CANAL SYSTEM

9. • From the early work of Hess and Zurcher to more recent
studies demonstrating the anatomic complexities of the root
canal system, it has long been established that a root with a
tapering canal and a single foramen is the exception rather
than the rule.
• Investigators have shown multiple foramina, additional canals,
deltas, intercanal connections, C-shaped canals, and furcation
and lateral canals in most teeth.

10. CLASSIFICATION OF ROOT CANAL
SYSTEM
• Weine et al (1969) classified root canals systems into four
basic types, but Vertucci et al (1984) subsequently classified
them into eight configurations.
• The Vertucci classification may reflect the complex reality of
canal systems, in a way that the Weine system did not.

11. • Type I: A single canal extends from the pulp chamber to the
apex (1).
• Type II: Two separate canals leave the pulp chamber and join
short of the apex to form one canal (2-1).
• Type III: One canal leaves the pulp chamber and divides into
two in the root; the two then merge to exit as one canal (1-2-
1).
•

12. • Type IV: Two separate, distinct canals extend from the pulp chamber to the
apex (2).
• Type V: One canal leaves the pulp chamber and divides short of the apex
into two separate, distinct canals with separate apical foramina (1-2).
• Type VI: Two separate canals leave the pulp chamber, merge in the body of
the root, and redivide short of the apex to exit as two distinct canals (2-1-2).
• Type VII: One canal leaves the pulp chamber, divides and then rejoins in the
body of the root, and redivides into two distinct canals short of the apex (1-
2-1-2).

13. • Type VIII: Three separate, distinct canals extend from the pulp
chamber to the apex (3).

14. • Whenever a root contains two canals that join to form one,
the lingual/palatal canal generally is the one with direct access
to the apex. This anatomy is best treated by preparing and
obturating this canal to the apex and the buccal canal to the
point of juncture.

15. • When one canal separates into two, the
division is buccal and palatal/lingual, and
the lingual canal generally splits from the
main canal at a sharp angle, sometimes
nearly a right angle
• One investigator recommends visualizing
this configuration as a lower case letter h.
The buccal canal is the straight-line portion
of the h; the lingual canal exists about
midroot at a sharp angle from the buccal
canal. This requires modification of the
access to achieve unobstructed passage of
instruments into the lingual canal.

16. Average Working Length of teeth

17. 1.Tooth apex (radiographic apex)
2. Apical foramen (major diameter)
3. Apical constriction (minor diameter)
4. Cementodentinal Junction
Anatomy of the Root Apex
(Kutler’s studies)

18. TOOTH APEX:
It is the tip or the end of the root determined
radiographically.
It is also called as the radiographic apex

19. APICAL CONSTRICTION: (MINOR APICAL DIAMETER)
• It 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

20. • From the AC, or minor apical diameter,
the canal widens as it approaches the
AF, or major apical diameter.
• The space between the major and
minor diameters has been described as
funnel shaped or hyperbolic, or as
having the shape of a morning glory.
• The mean distance between the major
and minor apical diameters is 0.5 mm in
a young person and 0.67 mm in an older
individual

21. APICAL FORAMEN: (major
apical diameter)
“It is the circumference or
rounded edge, like a funnel
or crater, that differentiates
the termination of the
cemental canal from the
exterior surface of the root”
• It is the main apical
opening of the root canal.
It is frequently
eccentrically located away
from the anatomic or
radiographic apex

22. THE CEMENTODENTINAL JUNCTION
• It 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 is the point where pulp tissue ends and periodontal
• tissues begin.
• The location of the CDJ in the root canal varies considerably. It
generally is not in the same area as the AC, and estimates
place it approximately 1 mm from the AF.
• The location of the cementodentinal junction ranges from 0.5
to 3.0 mm short of the anatomic apex.

24. Distance between 1 and 2:
• The apical foramen deviates
from the apex in 50-98% of the
teeth.
• This deviation averages 0.3 to
0.6 mm but could be as much as
3 mm.

25. Distance between 2 and 3:
• 0.5 mm in 18-25 y old, and 0.7
in 55+ y old.
Distance between 1 and 3:
• 0.89 mm with a range of 0.1 to
2.7 mm.

26. • The morphology of the apical root varies tremendously; it
includes numerous accessory canals; areas of resorption and
repaired resorption; attached, embedded, and free pulp
stones; and varying amounts of irregular secondary dentin
• Considerable controversy exists over the exact termination
point for root canal therapy

27. SIGNIFICANCE OF WORKING
LENGTH
• Determines how far into the canal the instruments are placed
and worked and thus how deeply the tissues, debris,
metabolites are removed.
• Limits the depth to which the canal filling may be placed
• Affects the degree of pain & discomfort that the patient will
feel following the appointment
• If calculated within correct limits, it will play an important role
in determining the success of the treatment & conversely, if
calculated incorrectly, may doom the treatment to failure.

28. • An erroneously short working length leaves uncleaned and
unfilled canal space in the apical region.
• An erroneously long working length will lead to over-
instrumentation and overextended obturation, causing
significant post-operative discomfort.

29. WHERE TO TERMINATE?
• According to Ingle, The dentin–cementum junction has been
recommended as an ideal apical termination for root canal
preparation.
• The position of this histologic entity varies around the internal
circumference of the canal by up to 3 mm across opposing
walls.
• It is located approximately 1 mm away from the apical
foramen.
• It may or may not coincide with the apical constriction.

30. • Seltzer et al. were the first to report greater success in
terminating cleaning and obturating the root canal system just
short of the radiographic apex, rather than overfilling or
underfilling.
• Sjo ̈gren et al. investigated endodontic outcomes over an 8- to
10-year period in over 350 patients. They reported the best
outcome was when the root canal filling was between 0 to 2
mm short of the radiographic apex. Distances beyond the
radiographic apex, or more than 2 mm short of this point,
resulted in significantly lower success rates.

31. • The instrumentation and obturation of root canals should end
at the apical constriction (physiologic foramen) for the
following reasons:
 no apical injury
 no injury to the periodontal ligament
 maintenance of accessory lateral canals
 no extrusion of root canal filling material
 no apical transport of infected pulpal tissues
 adequate compaction of the root canal filling against the
canal walls
 no infected tissue remnants within the canal

32. METHODS TO DETERMINE WORKING
LENGTH

33. RADIOGRAPHIC METHODS

34. Grossmanmethod/ mathematic methodof
workinglength determination
• An instrument is inserted into the canal, stopper is fixed to
the reference point and radiograph taken.
• The formula to calculate actual length of the tooth is as
follows:

36. Ingle’s method
• Pre-op radiograph is used to calculate the working length.
• Measurement can be confirmed by placing an endodontic
instrument into the canal and taking a second radiograph
• Instrument inserted should be large enough not to be loose in the
canal because it can move while taking the radiograph and thus may
result in errors in determining the working length
• Fine instruments are often difficult to be seen in a radiograph
• The new working length is calculated by adding or subtracting the
distance between the instrument tip and desired apical termination
of the root.
• The correct working length is calculated by subtracting 1 mm as
safety factor from this new length.

38. Weine’s modification
A. If radiograph shows absence of any resorption i.e, bone or root
apex, shorten the length by 1mm
B. If periapical bone resorption is present, shorten it by 1.5mm
C. If both bone and root resorption is seen, shorten length by 2mm.

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 pre-op 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
instrument. If canal is wide, use 30 or 35 size instrument.
• Insert selected file in canal upto the estimated canal length and take
a radiograph.
• If file reaches major diameter, subtract 0.5mm from it for younger
patients and 0.67 for older patients.

40. NON RADIOGRAPHIC METHODS

41. Digital tactile sense
• Although it may appear to be very simple, it’s accuracy depends on
sufficient experience.
• The clinician should be able to literally feel the foramen by tactile
sense.
• Confirmation may be done either by the radiographic or electronic
method.
• If the coronal portion of the canal is not constricted, an experienced
clinician may detect an increase in resistance as the file approaches
the apical 2 to 3 mm.
• Tactile sensation, although useful in experienced hands, has many
limitations. The anatomical variations in apical constriction location,
size, tooth type and age make working length assessment unreliable.

42. Apical periodontal sensitivity
• File is inserted into the canal upto the point where patient
experiences pain or sensitivity, as the file reaches the
periapical region.

43. Paper Point Measurement
• In a root canal with an immature
(wide open) apex, the most
reliable means of determining
WL is to gently pass the blunt
end of a paper point into the
canal after profound anesthesia
• The moisture or blood on the
portion of the paper point that
passes beyond the apex - an
estimation of WL or the junction
between the root apex and the
bone.

44. This method, however, may give unreliable data:
• If the pulp not completely removed
• If the tooth is pulpless but a periapical lesion rich in blood
supply present
• If paper point is left in canal for a long time

45. • Recently millimeter
markings have been
added to paper points.
• These paper points
have markings at 18,
19, 20,22, and 24 mm
from the tip and can be
used to estimate the
point at which the
paper point passes out
of the apex.

46. Limitations of traditional
working length assesment
• When the apical foramen exits to the side of the root or in a buccal
or lingual direction it becomes difficult to view on the radiograph
• Dense bone and anatomical structures can make the visualization of
root canal files impossible by obscuring the apex
• The superimposition of the zygomatic arch has been shown to
interfere radiographically with 20% of maxillary first molar apices
and 42% of second molar apices (Tamse et al. 1980).
• The deposition of secondary dentine and cementum can move the
apical constriction further from accepted limits causing preparation
errors (Stein & Corcoran 1990, Chong & Pitt Ford 1994).

47. • Interpretation of the file’s position on the radiograph and the
surrounding anatomy is also prone to errors when using the
bisecting angle technique.
• Estimation of the canal length often varies greatly from actual
working length. The long-cone paralleling technique has been
shown to be more accurate

48. Limitations in radiographic methods of
working length determination
• A radiograph provides a two-dimensional image of a three-
dimensional structure and is technique sensitive in both its
exposure and interpretation.
• Cox et al. found that adjustments were required to working
length radiographicaly. 68% of examiners agreed adjustments
up to 0.5 mm were needed, but there was only 14%
agreement when adjustments greater than 1.0 mm were
required.
• Radiation exposure is always avoided in pregnant women.
• It’s difficult to take radiograph in patients have Gag reflex

49. • The preoperative radiograph is essential in endodontics to
determine the anatomy of the root canal system, the number
and curvature of roots, the presence or absence of disease,
and to act as an initial guide for working length.
• The electronic apex locator is an instrument, which used with
appropriate radio- graphs, allows for much greater accuracy of
working length control

50. ELECTRONIC APEX LOCATORS

51. • Although the term “apex locator” is commonly used and has
become accepted terminology, it is a misnomer.
• Some authors have used other terms to be more precise such
as Electronic Root Canal Length Measuring Instruments or
Electronic Canal Length Measuring Devices
• The apex of the root has a specific resistance to electric
current which is measured using a pair of electrodes i.e.
endodontic fie & lip clip. These devices, when connected to a
file, are able to detect the point at which the file leaves the
tooth and enters the periodontium.

52. Emergence
• The first reported use of electric current to measure root canal
working length was in 1918 by Custer.
• He noted a marked increase in the conductivity of a tooth at
the apical foramen when the canal was dry or filled with a
nonconductive medium. By placing a broach inside a tooth
and applying a voltage across it and the alveolus, Custer was
able to identify the apical foramen by observing a change in
the value on the milliammeter of the time

53. • In the year 1942, the idea was revisited by Suzuki(Japan). He
found that an electrode placed on the oral mucosa, and an
instrument placed in the root canal, gave consistent
measurements of electrical resistance.
• This is the basis for the resistance-based EALs. As the
advancing file, surrounded by insulating dentin and
cementum, approaches the conductive periodontal ligament,
the resistance decreases until the circuit is complete.

54. • Sunada, in 1962, used this principle to create a device, using
direct current, to estimate the root canal length in vivo.
• He found that when the file reached the canal terminus,
regardless of tooth shape, tooth type, or age of the patient,
the resistance measured was consistent at 6.5 kΩ
• Furthermore, the same resistance was recorded when the file
encountered an accidental perforation.

55. • Direct current apex locators have been associated with
patients experiencing electric shocks.
• Suchde and Talim proposed changing to alternating current,
which would result in less tissue damage and increased
stability of the electrolyte’s resistance in a wet canal. The
disadvantage, however, in determining canal length in this
manner, is the change in the capacitance of the circuit, along
with many other variables that affect accuracy

56. HOW DO EALs FUNCTION?
EALs functions by using the human body to complete an electrical
circuit.
• One side of the apex locator’s circuit subsequently connected
to the oral mucosa through a lip clip and the other side to a
file When the file is placed into the root canal and advanced
apically until its tip touches periodontal tissue at the apex, the
electrical circuit is completed

57. The classification of apex locators was given by Mc Donald
(1992) based on
1. Type of current flow (operating principle)
2. Opposition to the current flow and as well as on number of
current frequencies involved.

58. a. Dependingupontypeofcurrentinvolved

59. b. Resistancetypeapexlocators:
Theseapexlocatorshaveabuiltinresistancevalueof6.5kilo
Ohms.Theapexlocatorsareattachedtothepatient'sliponone
sideandtheothersideisattachedtothefile.Thefileisthen
advancedintothecanaluntilittouchestheperiodontaltissueat
theapexwhichthencompletesthecircuit.

60. c. Impedancetypeapexlocator:
Operateontheprinciplethatthereiselectricalimpedanceacross
thewallsoftherootcanalduetothepresenceofthetransparent
dentin.
Thetoothexhibitsincreasingelectricalimpedanceacrossthewalls
oftherootcanal,whichisgreaterapicallythancoronally.
AttheCDJ,thelevelofimpedancedropsdramatically.Theunit
detectsthesuddenchangeandindicatesitontheanaloguemeter.
Toovercometheproblemofawetenvironment,insulatedprobes
areutilized

61. d.Frequencydependentapexlocators:
Operateverysimilarlytotheimpedancetypebecauseitmeasures
theimpedanceoftoothattwodifferentfrequencies.
Inthecoronalportionofthecanal,theimpedancedifference
betweenthefrequenciesisconstant.Asthefileadvancedapically,
thedifferenceintheimpedancevaluebeginstodiffergreatlywith
maximumdifferencesattheapicalarea.

62. First Generation: Resistance Based
Apex Locators
• EALs of this generation apply a small direct current to the
tooth under investigation, of known voltage.
• The resistance at each level of the root canals can be
calculated using these two variables using Ohm’s Law.
• At the periodontal ligament space, the resistance of the circuit
will be equal to 6.5 kΩ and the apex locators are programmed
to detect this value.

63. • Although these devices were accurate under dry conditions,
their accuracy decreased when electrolytes, pulp tissue,
inflammatory exudate or excessive haemorrhage were
associated with the root canals.
• As soon as the file tip touched an electrolyte, the direct
current (DC) voltage would polarise the tissue, complete the
circuit and incorrectly register that the periodontal ligament
space had been reached.
• Furthermore, the use of a DC would often cause an electric
shock sensation to be felt by the patient which is clearly
disadvantageous.

64. • Easily operated, audible
indication, detects
perforation, can be used
with K file
• Unreliable, electrolytes,
exudate, hemorrhage, vital
pulp tissue, and excessive
moisture caused inaccurate
results.
• Patient sensitivity, requires
calibration, requires good
contact with lip clip

65. SecondGeneration:ImpedencebasedApex
Locator/Low frequencyApexLocator
• To overcome the aforementioned problems, the next set of
EALs were based on the impedance of the circuit set up within
the Root canals.
• However, the impedance of the root canals was dependent on
many variables and would vary between different root canals.
•
• Consequently, the biggest disadvantage for these apex
locators was the need for individual calibration between each
tooth.

66. • It works on the premise that although the many parameters
that determine impedance are varied in different canals under
altered conditions, the impedance between the oral mucosa
and depth of the gingival sulcus should be coincident with the
impedance value of a circuit across the oral mucosa and the
periodontal ligament.
• Thus, the device would indicate the canal terminus when the
two impedance values approached each other.
• The device had to be calibrated at the periodontal sulcus before
each use. This involved placing a file, shielded along its length
except for its tip, into the gingival sulcus, and listening for the
‘‘gingival crevice sound.’’ A file was then introduced into the
canal, and when the sound became identical to the ‘‘gingival
crevice sound,’’ the canal terminus had been reached.

67. • The literature pertaining to second generation EALS reports much
variation in terms of their accuracy.
• Fouad et al. looked at the Endo Analyser (Analytic/ Endo, Orange,
California, USA) and Apex Finder and noted that they were only
accurate 67% of the time at being +/− 0.5 mm from the apex.
• However, like most IBALs, it was found to be inaccurate in the
presence of conductive irrigants (with different diaelectric
constants), a shortcoming which the manufacturers were quick to
point out.

68. • Also they required calibration and complicated calculations,
required coated probes instead of normal endodontic
instrument, no digital readout was present and it was very
difficult to operate.
• The sheath caused problems because it would not enter
narrow canals, could be rubbed off and was affected by
autoclaving

69. Third Generation Apex Locator/
High frequency Apex Locator
• These use multiple frequencies to determine the distance
between an endodontic instrument and the end of a canal,
unlike second generation EALs which only use a single AC of
known frequency.
• Third generation EALs work by calculating the impedance ratio
of two electric currents with different wave frequencies. One
wave will be of a high frequency (HF) while the other will have
a low frequency (LF). 8 KHz- 0.4 KHz

70. Equation Ratio = HF / LF.
• The quotient of these two frequencies is nearly 1 when the
endodontic file is some distance from the apical terminus.
However, at the apical constriction, the ratio of Equation
approaches a value of 0.67.
• It is this change in ratio at the apical constriction which third
generation EALs detect.

71. • The Root ZX (J. Morita, Tokyo, Japan) is an example of a third
generation EAL.
• It is based on two electric currents which have a frequency of
either 8 kHz or 400Hz.
• It produces more stable electronic readings when the root
canals contains an electrolyte (such as NaOCl).
• In vitro when used on permanent teeth, the accuracy of the
Root ZX varies from 84% to 100%.
• In the presence of different irrigants, the accuracy was
similarly found to be very high, with reported accuracies
varying from 83% to 96%.
• In vivo studies that have extracted the teeth (after
investigation) have reported similar accuracies for the Root ZX

72. Fourth Generation Apex
Locator
• These are Ratio Type apex locators
which determine the impedance at
five frequencies and have built in
electronic pulp tester.
• Measures the resistance and
capacitance separately, rather than
the resultant impedance value.
• These devices not process the
impedance information as a
mathematical algorithm, but
instead take the resistance and
capacitance measurement and
compare them with a database to
determine the distance to the apex

73. • A significant disadvantage of the fourth generation devices is
that they need to perform in relatively dry or in partially dried
canals. In some cases, this necessitates additional drying. Also
in heavy exudates or blood it becomes inapplicable

74. Fifth Generation Apex Locator
• To cope with associated problems
associated with previous
generations of apex locators a new
measuring method has been
developed based on comparison of
the data taken from the electrical
characteristic of the canal and
additional mathematical
processing. And so the fifth
generation apex locators (Dual
Frequency Ratio Type) are now
being used.

75. • 5th generation apex locators was developed in 2003 as E-
magic Finder series.
• It measures the capacitance and resistance of the circuit
separately.
• It is supplied by diagnostic table that includes statistic of the
file.
• They claim to have best accuracy in any root canal condition
(dry, wet, bleeding, saline, EDTA, NaOCl).
• Devices employing this method experience considerable
difficulties while operating in dry canals. During clinical work it
is noticed that the accuracy of electronic root canal length
measurement varies with the pulp and periapical condition.

76. Sixth Generation Electronic Apex
Locators (Adaptive Apex Locators)
• The efficacy of 6th generation EALs in long term use yet to be
established.
• A major advantage of adaptive apex locator is eliminating
necessity of drying and moistening of the canal.
• Adaptive apex locators continuously define humidity of the
canal and immediately adapts to dry or wet canal. This way it
is possible to be used in dry or wet canals, canals with blood
or exudates

77. Other uses of apex locators
• To detect root perforations to clinically acceptable limits
• Determine the location of root and pulpal floor perforations
• To detect horizontal fractures
• To confirm suspected periodontal or pulpal perforations during
pinhole preparation
• Recognize any connection between the root canal & periodontal
membrane such as root fracture, cracks & internal or external
resorption.
• Some have ability to detect vitality of the tooth, also helpful in root
canal treatment of teeth with incomplete root formation, requiring
apexification & to determine working length of primary teeth.
• Combination of EALs & electronic handpiece (Ex. Root Zx II) are also
common and are able to achieve excellent result with same accuracy

78. Problems associated
• The majority of present generation apex locators are not
affected by irrigants within the root canal and the Root ZX has
been found to be more accurate in the presence of sodium
hypochlorite.
• Intact vital tissue, inflammatory exudates and blood can
conduct electric current and cause inaccurate readings so their
presence should be minimized before accepting apex reading.
• Canal shape, Lack of patency, the accumulation of dentine
debris and calcifications can affect accurate working length
determination with electronic apex locators.

79. • Electronic apex locators have the potential to interfere with
cardiac pacemakers. The manufacturer of electronic apex
locators specifically warns against their use with patients with
cardiac pacemaker. As there are many therapeutic uses and
types of pacemakers some may not be influenced by apex
locator use.

80. References
• Ingle JI. PDQ Endodontics. Hamilton, Ont.: BC Decker; 2005. p.
125.
• Olson AK, Goerig AC, Cavataio RE, Luciano J. The ability of the
radiograph to determine the location of the apical fora- men.
Int Endod J 1991;24:28–35.
• Forsberg J. A comparison of the paralleling and bisecting-angle
radiographic techniques in endodontics. Int Endod J 1987;
20:177–82.
• Amruta Khadse et al. Electronic Apex Locators- An overview,
Indian Journal of Conservative and Endodontics, April-
June,2017;2(2):35-40