Working length is the distance from a coronal reference point to the point where canal preparation and obturation should terminate. It is important to determine working length precisely using radiographs or electronic apex locators. The radiographic method involves measuring the total length of the tooth on preoperative radiographs, subtracting 1mm as a safety factor, and confirming length under radiograph after instrumentation. Electronic apex locators use electric current to detect the apical foramen. Tactile methods are unreliable due to risk of over-instrumentation or under-instrumentation.

1. Prepared by
Dr . Hamed Mohammed AL- Haddad
1

2. Working Length Determination
The cleaning, shaping, and obturation of the .
root canal system cannot be accomplished
accurately unless the working length is
. determined precisely
2

3. :Definition
Working length is defined as the distance from a coronal
reference point to the point at which canal preparation
. and obturation should terminate
3

4. REFERENCE POINT
The reference point is the site on the
occlusal or incisal surface from which
measurements are made. This point is
used throughout canal preparation
.and obturation
4

5. Selection of Reference pointٍ
A reference point is chosen that is stable and
easily visualized during preparation. Usually
this is the highest point on the incisal edge on
anterior teeth and a buccal cusp tip on
posterior teeth. The same reference point is best
used for all canals in multirooted teeth. The
mesiobuccal cusp tip is
.preferred in molars
5

6. Stability of Reference Point
Reference Point should not change between the.
.appointments
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
6

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

8. Anatomic apex: Is the tip or the end of
the root determined morphologically,
whereas the
8

9. radiographic apex is the tip or end of the
.root determined radiographically
9

10. (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 O,5 to 1.0
mm short of the center of the apical
.foramen
10

11. Apical foramen: Is the main apical opening of
the root canal. It is frequently eccentrically
located away from the anatomic or
.radiographic apex
11

12. . The minor diameter widens apically to the
foramen (major diameter).
12
12

13. Clinical Considerations
Before determining a definitive working.
length, the coronal access to the pulp
chamber must provide a straight
.pathway into the canal orifice
Loss of working length during cleaning.
and shaping can be a frustrating
.procedural error
13

14. It is extremely important to monitor the .
working length periodically since the
working length may change as a curved
.canal is straightened
The loss may also be related to the .
accumulation of dentinal and pulpal
. debris in the apical area
14

15. Loss of working length may also be due to.
ledge formation or instrument
.separation and blockage of the canal
Most dentists agree that the desired end.
point is the apical construction, which is
not only the narrowest part, but a
morphological Land – Mark that can help
.to improve the apical seal
15

16. If the length being too long, this may lead to .
perforation through the apical construction,
with subsequent overfilling or overextension,
which mean postoperative pain, prolonged
.healing period
Incomplete cleaning and filling may cause .
persistent discomfort, also apical leakage may
occur into the uncleaned and unfilled space
. short of the apical constriction
16

17. TECHNIQUE & Methods FOR W- L
DETERMINATION
There is Different techniques have been
used, studied , and advocated for
determining working length
Radiographic method- 1
Electronic method-2
tactile methods-3
17

18. Determination of Working Length by
Radiographic Methods
This method is known as the Ingle method, .
. which proved to be superior to others
It showed a high percentage of success with a .
smaller variability. This method first
proposed more than 40 years ago, and
.become the most commonly used method
18

19. Radiographic Apex Location: The following
items of materials and conditions are
:essential to perform this procedure
Good, preoperative radiographs showing .1
the total length and all roots of the
. involved tooth
. Adequate coronal access to all canals . 2
19

20. .An Endodontic millimeter ruler. 3
Working knowledge of the average.4
. length of all the teeth
A definite, repeatable plane of. 5
reference to an anatomic landmark on
.the tooth
20

21. To establish the length of the tooth, a.
stainless steel reamer or file with an
.instrument stop on the shaft is needed
21

22. The instrument site must be small enough to .
negotiate the total length of the canal but large
.enough not to be lose in the canal
No. 8 or 10 files should not be used to take
working length radiographs; small file tips
fade out and are usually not visible. On molar
.radiographs, No. 15 file tips are often obscure
22

23. Measure the tooth on the preoperative .1
. radiograph
23

24. Subtract at least 1.0mm " safety allowance " for. 2
.possible image distortion
Set the endodontic ruler at this tentative working length. 3
. and adjust the stop on the instrument at that level
24

25. Place the instrument in the canal until the . 4
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
25

26. On the radiograph, measure the difference . 5
between the end of the instrument and the
end of the root and add this amount to the
original measured length the instrument
. extended into the tooth
26

27. From this adjusted length of tooth, subtract . 6
a 1.0mm "Safely factor" to conform with
apical termination of the root canal at the
. apical constriction
Set the endodontic ruler at this new .7
corrected length and readjust the stop on
. the exploring instrument
27

28. 28

29. When the length of the tooth accurately .8
confirmed, reset the endodontic ruler at
.this measurement
Record this length and the coronal point of . 9
. reference on the patients record
29

30. It is important to emphasize that the. 10
final working length may shorten by as
much as 1mm as a curved canal is
straightened out by instrumentation. It
is therefore recommended that the
"length of the tooth" in a curved canal
be reconfirmed after instrumentation
. is completed
30

31. Modification of length
substraction in case of Resorption
Working length distance from the apex is
determined when the following are seen
:radiograpbically
No bone or root resorption: 1 mm from. 1
.apex
Bone but no root resorption: 1.5 mm from. 2
.apex
.Bone and root resorption: 2 mm from apex . 3
31

32. 32

33. Electronic Method by Using
Electronic Apex Locators
33

34. Principle of measuring by Using
Electronic Apex Locators
A root canal instrument is connectedto the
measuring device with aclip. An electric current is
passed through the file into the root canal. A lip
or hand electrode serves as the opposite electrode.
The device indicates the apical foramen by an
absolute resistance value that is presented by the
manufacturer. Currents alternating at different
frequencies minimize the influence of
electrochemical polarizing processes
34

35. Principle of measuring by Using
Electronic Apex Locators
35

36. Tactile Methods
tactile methods are too unreliable.
Radiographs are usually made to
determine the working length
36

37. Tactile Methods
There are problems with this approach
.also. First, the procedure is painful for the patient
Second, a necrotic pulp frequently contains
vital inflamed tissue that extends several
millimeters into the canal . This tissue may be very
sensitive and respond to instrument contact short
. of the apex
Third, a patient feels pain after canal
preparation is complete from hydraulic pressure
even though instruments do not reach the apical
.region
37

38. Tactile Methods
The opposite of pain with instruments short of
length is lack of pain response when instruments
are beyond the apex. This has been observed in
,some situations when, in an unanesthetized patient
an instrument has passed several millimeters
out of the apex without being detected
38

39. Determination of Working Length by
Paper Point Measurement
In a root canal with an immature (wide open) apex, the.
most reliable means of determining working length is
to gently pass the blunt end of a paper point into the
.canal
The moisture or blood on the portion of the paper point.
that passes beyond the apex may be an estimation of
. working length
39

40. Determination of Working Length by
Paper Point Measurement
40

41. This paper point measurement method is a .
. supplementary one
A new dimension has recently been added to .
paper points by the addition of millimeter
markings. These paper points have
markings at 18,19,20,22 and 24mm from the
. tip
41

42. The accuracy of these markings should be .
. checked an a millimeter ruler
42