1. Working Length Determination
Dr. Ahmed Jawad

2. Working length- definition
The distance from a coronal reference point to the point at which canal preparation and obturation should terminate.
The first step in cleaning and shaping is working length determination.

3. Significance: 1) Determine the instrument length in the canal.
2) Limits the depth to which the canal filling maybe placed.
3) Limits the postoperative pain & discomfort as instrumentation shorter than the apical constriction leaves uncleaned space, while beyond the apical constriction irritate the periapical tissues, violate the apical zone and affect the compaction of the filling material against the apex.
4) Determination of the success of treatment.

4. Anatomy of the Apex Tooth apex (radiographic apex)1 2 3
Tooth apex (radiographic apex)
Apical foramen (major foramen)
Apical constriction (minor foramen)

5. 1 2 3
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.
Tooth apex (radiographic apex)
Apical foramen (major foramen)
Apical constriction (minor foramen)

6. Distance between 2 and 3: 0.5 mm in 18-25 y old, and 0.7 in 55+ y old.
0.89 mm with a range of 0.1 to 2.7 mm. 1 2 3
Tooth apex (radiographic apex)
Apical foramen (major foramen)
Apical constriction (minor foramen)

7. Anatomical Apex & Radiographic Apex
is the tip or the end of the root determined morphologically, which is the natural apical constriction formed by the cemento-dentinal junction (narrowest part in the canal).
Radiographic apex:
is the tip or the end of the root determined radio-graphically.

8. Reference points
It is the site on the occlusal or incisal surface from which measurements are made.
This point is used throughout canal preparation & obturation.
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.
A definite, repeatable plane of reference to an anatomic land mark on the tooth – necessary.
(usually the incisor edge in anterior teeth , the cusp tip in posterior teeth).

9. Reference points
Don’t use weakened enamel walls, temporary filling or diagonal lines of fracture as a reference site for Length of tooth measurement.
Diagonal surfaces should be flattened to give an accurate site of reference.
Weakened cusps or incisal edges are reduced to a well – supported tooth structure.

10. Requirements of W.L. Determination
Knowledge of pulp anatomy and average length of each individual root.
Good, undistorted preoperative radiographs showing the total length and all roots of the involved tooth.
Strait-line access.
Small stainless steel K-files facilitate the process and the exploration of the canal.
A definite, repeatable plane of reference, it should be noted on the patient record.

11. Techniques of W.L Determination
Radiographic methods
Digital tactile methods
Paper point evaluation
By apical periodontal sensitivity
Electronic apex locators

12. 1.Radiographic Methods Preoperative radiograph
Radiograph of the tooth with endodontic instrument placed to its tentative working length.
Parallel technique is preferable over bisecting technique

13. A. Grossmann Formula
𝑎𝑐𝑡𝑢𝑎𝑙 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡𝑜𝑜𝑡ℎ 𝑟𝑎𝑑𝑖𝑜𝑔𝑟𝑎𝑝ℎ𝑖𝑐 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡𝑜𝑜𝑡ℎ = 𝑎𝑐𝑡𝑢𝑎𝑙 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑖𝑛𝑠𝑡𝑟𝑢𝑚𝑒𝑛𝑡 𝑟𝑎𝑑𝑖𝑜𝑔𝑟𝑎𝑝ℎ𝑖𝑐 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑖𝑛𝑠𝑡𝑟𝑢𝑚𝑒𝑛𝑡
Actual length of tooth = 𝑎𝑐𝑡𝑢𝑎𝑙 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑖𝑛𝑠𝑡𝑟𝑢𝑚𝑒𝑛𝑡×𝑟𝑎𝑑𝑖𝑜𝑔𝑟𝑎𝑝ℎ𝑖𝑐 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡𝑜𝑜𝑡ℎ 𝑟𝑎𝑑𝑖𝑜𝑔𝑟𝑎𝑝ℎ𝑖𝑐 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑖𝑛𝑠𝑡𝑟𝑢𝑚𝑒𝑛𝑡

14. B. Ingles Method 1. Measure the tooth on the preoperative radiograph.
2. Subtract at least 1.0mm " safety allowance "
for possible image distortion.
3. Set the endodontic ruler at this tentative working length and adjust the stop on instrument at that level
4. Place the instrument in the canal until the stop is at the plane of reference
5. On the radiograph, measure the difference 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.

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

16. 2. Digital tactile method
Although it may appear to be very simple, its 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.
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.
In some cases the canal is sclerosed or the
constriction has been destroyed by inflammatory
resorption

17. 3. Paper point evaluation
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 is an estimation of WL or the junction between the root apex and the bone.
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 – left in canal for a long time

18. Some 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.

19. 4. By apical periodontal sensitivity
By insertion of a small instrument beyond the apical constriction to stimulate pain.
It is not an accurate method and has the following disadvantages:
In inflamed tissue hydrostatic pressure developed may cause moderate to severe instant pain.
When pain is afflicted in this manner, little useful information is gained by clinician, and considerable damage is done to patient’s trust.
Sometimes remnants of pulp tissue could induce pain leading to underestimation of working length.

20. 5. Electronic apex locators
In today’s practice - one of the most important and essential instrument in endodontic practice
These devices all attempt to locate the apical constriction, the cemento-dentinal junction, or the apical foramen.

21. First-Generation Apex Locators
First-generation apex locator devices, also known as resistance apex locators
Measure opposition to the flow of direct current or resistance.
When the tip of the reamer reaches the apex in the canal, the resistance value is 6.5 kilo-ohms (current 40 mA)
Disadvantage: often yield inaccurate results in presence of electrolytes, excessive moisture, vital pulp tissue, exudates and blood.

22. Second-Generation Apex Locators.
Second-generation apex locators, also known as impedance apex locators
measure opposition to the flow of alternating current or impedance
Uses the electronic mechanism that the highest impedance is at the apical constriction where impedance changes drastically
Same disadvantage of the first generation.

23. Third-Generation Apex Locators.
Use multiple frequencies to determine the position of the file in the canal
Use alternating current
Can be used in wet/dry fields
Most accurate among three

24. Fourth-Generation Apex Locators
Measures resistance and capacitance separately
There can be different combination of values of capacitance and resistance that provides the same foraminal reading
This is broken down into primary components and measures separately for better accuracy and thus less chances of occurrence of errors

25. Fifth-Generation Apex Locators
Propex® II Apex Locator features a new generation. It has the latest multi frequency technology incorporated into this 5th generation apex locator and an extended apical zoom function, which activates when the file reaches the apical area, assisting the dentist to locate the apex in most types of root canal conditions.

26. Advantages of Apex Locators.
Devices are mobile, light weight and easy to use.
Much less time required.
Additional radiation to the patient can be reduced (particularly useful in cases of pregnancy).
% accuracy observed

27. Disadvantages of apex locators
An experienced practitioner is required
Accuracy limited to mature root apices
Extensive periapical lesion can give faulty readings
Weak batteries can affect accuracy
Can interfere with functioning of artificial cardiac pacemakers – cuatious use in such patients