• OUTLINE
• INTRODUCTION
• DEFINITIONS
• METHODS
OF DETERMING WORKING LENGTH
• CONCLUSION
INTRODUCTION
Working length is defined as the distance from a coronal reference point
to the point at which canal preparation and obturation should terminate.
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.
SELECTION OF REFERENCE POINT
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.
Incisal edge is preferred in
incisors.
Do not 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.
Diagonal surfaces should be flattened to give
an accurate site of reference
TERMINOLOGIES IN DETERMING WORKING LENGTH
• Anatomic apex: It is defined as the tip or end of the root
determined morphologically.
• Radiographic apex: It is defined as
the tip or end of the root determined radiographically.
• Apical foramen(Major Apical Diameter): it is the main apical opening
of the root canal.it is frequently eccentrically located away from the anatomic
or radiographic apex.
• Apical Constriction (Minor Apical
Diameter): Apical portion of the root canal having the narrowest diameter of
blood supply. This is the apical termination of the working length.
• APICAL REGION OF THE TOOTH
he CDJ does
not always coincide with apical constriction and is located 0.5 -3mmshort of
anatomic apex
METHODS OF DETERMINING WORKING LENGTH
RADIOGRAPHICAL METHOD
1.Grossman’s
formula[Mathematical method]
2. Ingles
method
3. Weine’s
method
4. Xeroradiography
NON RADIOGRAPHICAL METHOD OF DETERMING WORKING LENGTH
1.Electronic
apex locator
2.Digital
tactile sense
3.Apical
periodontal sensitivity
4.Paper
point method
DETERMINATION OF WORKING LENGTH BY RADIOGRAPHIC METHODS
1. Good, undistorted, preoperative radiographs showing the
total length and all roots of the involved tooth.
2. Adequate coronal
access to all canals.
3. An endodontic
millimeter ruler.
4. Working knowledge
of the average length of all of the teeth.
5. A definite, repeatable plane of reference to
an anatomic landmark on the tooth, a fact that should be noted on the patient’s
record.
GROSSMAN METHOD OF DETERMING WORKING LENGTH
GROSSMAN METHOD
INGLE’S METHOD OF DETERMING WORKING LENGTH
• Tooth length is measured in the preoperative
radiograph
• 1 mm “safety allowance” is
subtracted for possible image distortion
WEINE’S MODIFICATION OF DETERMING WORKING LENGTH
A .If, radiographically, there is no resorption of the root
end or bone, shorten the length by the standard 1.0 mm.
B. If periapical bone resorption is apparent, shorten by 1.5
mm, and
C. If both root and bone resorption are apparent, shorten by
2.0 mm
WEINE’S MODIFICATION
• WEINE’S METHOD CONT.
• The endodontic file is set at this
tentative working length, and the instrument is inserted in the canal.
• On the radiograph the difference
between the end of file and root end is measured and this value is either
subtracted or added to the initial working length measurement depending on
weather the file is short of apex or extended beyond apex.
• From this adjusted working length
1mm “ safety allowance” is subtracted again to confirm with the apical
termination of instrument.
ELECTRONIC METHOD OF DETERMINING
WORKING LENGTH:
• With an apex locator, the working
length is determined by comparing the electrical resistance of the periodontal
membrane with that of gingiva surrounding the tooth, both of which should be
similar.
• A probe , such as a file, is
attached to an electronic instrument with an electric cord and is inserted
through the root canal until it contacts the surrounding PDL.
• When the probe touches the soft
tissues of the PDL, the electrical resistance gauges for both gingiva and PDL
would have similar readings.
• By measuring the depth of insertion
of the probe, one may determine the exact working length of root canal
Electronic Apex Locator
• First-generation
apex locators – based on Resistance
• Second-generation
apex locators – based on Impedance
• Third-generation
apex locators – based on Frequency or comparative
impedance
• Fourth generation apex locator- measures resistance and capacitance
separately rather than the
resulting
impedance
ADVANTAGES OF APEX LOCATOR
• 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)
• 80
- 97 % accuracy observed
DISADVANTAGES OF APEX LOCATOR
• 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 – cautious use in
such patients.
DIGITAL TACTILE SENSE
Its accuracy depends on sufficient experience although it
appears simple.
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
of apical constriction, tooth size,
tooth type, age make working length assessment unreliable.
In some cases the
canal is sclerosed or the constriction has been destroyed by inflammatory
resorption
• APICAL PERIODONTAL SENSITIVITY
•
Based on patient’s pain perception
•
Any method of working length determination,
based on the patient’s response to pain, does not meet the ideal method of
determining working length.
• PAPER POINT METHOD
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.
This method, however, may give unreliable data
•
If the pulp not completely removed
•
If the tooth – pulpless but a periapical
lesion rich in
blood supply present
•
If paper point – left in canal for a long time
C0NCLUSION
An error in access cavity
preparation would compromise all subsequent work.
The success of endodontic
treatment depends on precise, proper execution of access cavity preparation.
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
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