DETERMINATION OF WORKING LENGTH

INTRODUCTION�

• The determination of accurate working length is one of the most critical steps in endodontic therapy.

​

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

• Significance

​

• Determines how far into the canal the instruments are placed and worked

​

• Limit the depth to which the canal filling are placed

​

• Affect the degree of pain and discomfort that the patient will feel following the appointment.

DEFNITION

​

​

• The distance from a coronal reference point to the point at which canal preparation and obturation should terminate (Ingle)

​

• The distance between the apical limit of instrumentation and the point from which measurement is to be made coronally (Nicholls)

• A. RADIOGRAPHIC METHOD
• 1.Grossman’s Method
• 2.Ingle’s Method
• 3.According to Kuttlers studies
• 4.Best’s Method
• 5.Bregman’s Method
• 6.Bramante’s Method
• 7.X-ray Grid System
• 8.Xero Radiography
• 9.Direct Digital Radiography

• B. NON-RADIOGRAPHIC METHOD
• Tactile Method
• Paper Point Evaluation Method
• Electronic Apex Locators

ANATOMIC CONSIDERATIONS & TERMINOLOGY

• Anatomic apex
• Radiographic apex
• Apical foramen
• Apical constriction
• CD Junction

• Failure to maintain working length :
• Apical perforation
• Overfilling with increased incidence of post-operative pain
• Prolonged healing period and increased failure due to incomplete regeneration of cementum, periodontal ligament, and alveolar bone

• Incomplete instrumentation may lead to:

​

• persistent pain and discomfort from inflamed and retained pulp tissues
• Under filling
• Continued periradicular lesion and increased incidence of failure.

REFERENCE POINT

• The W/L measurement should be made from a secure reference point on the crown, in close proximity to the straight line path of the instrument.
• Selection:
• A point that can be identified & monitored accurately
• Usually highest point on incisal edges-anterior teeth
• Buccal cusp tip –posterior teeth
• Same reference point-all the canals-multicanaled, multicuspid tooth
• Mesiobuccal cusp is preferred –molars (Walton & Torabenojed)

• It is imperative that teeth with fractured cusps or cusps severely weakened by caries/restoration be reduced to a flattened surface, supported by dentin.
• Failure to do so- result in cusps being fractured between appointments.

VARIOUS METHODS FOR CALCULATING WORKING � LENGTH�

​

• 1)RADIOGRAHIC METHODS

​

• 2)NONRADIOGRAPHIC METHODS

INGLES METHOD

• MATERIALS & CONDITIONS
• Good, undistorted preoperative radiograph showing total length & all roots of the involved tooth .

1. Measure the tooth on a pre operative radiograph
2. Subtract 1mm safety allowance for possible image distortion or magnification
3. Set the endodontic ruler at this tentative working length and adjust stop on the instrument at that level

• Place the instrument in the canal until the stop is at the plane of reference or until the patient feels pain in which case the instrument is left at that level and rubber stop readjusted to the new point

5. On the radiograph, measure the difference between the end of the instrument & end of the root. Add this to the original measured length.�If the exploring instrument has gone beyond the apex, subtract this difference.

• From this adjusted length, subtract 1mm safety factor to confirm with the apical termination of the root canal at apical constriction
• Set the endodontic ruler at this new corrected length and readjust the stop.
• In case of sharply curving roots, confirmatory radiograph is necessary
• Record the final working length and coronal point of reference.

WEINE’S MODIFICATION

KUTTLER’S METHOD

Best’s Method

BREGMAN’S METHOD�

BRAMANTE’S METHOD�

X-RAY GRID SYSTEM�

XERORADIOGRPHY (1937)�

Radio-Visiography or Direct Digital Radiography�

• A new radiographic system called DDR digitizes ionizing radiation.

​

DIGITAL TACTILE SENSATION

• 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 3mm.

​

• DISADVANTAGES
• often inexact
• ineffective in narrow constricted canals
• ineffective in immature apex
• ineffective in curved canals

APICAL PERIODONTAL SENSITIVITY

• This is based on patient’s response to pain.

​

• DISADVANTAGES

​

• If an instrument is advanced in the canal towards inflamed tissue, the hydrostatic pressure developed inside the canal may produce moderate to severe instantaneous pain

​

• If remnants of pulp tissue are present in the canal, patient may feel pain much before apex is reached

​

• In case of large periapical lesion, patient may not feel pain even if the instrument has gone beyond the apex.

PAPER POINT MEASUREMENT

​

• In a root canal with an immature apex, the most reliable means of determining working length is to gently pass the blunt end of the paper point into the canal after local anaesthesia.

​

• The blood or moisture on the portion of the paper point that passes beyond the apex may be an estimation of working length or the junction between root apex and bone.

DETERMINATION OF WORKING LENGTH BY ELECTRONICS

• EVOLUTION OF APEX LOCATORS
• 1918 Cluster - first to report the use of electric current to determine the working length.
• 1942 - Suzuki reported a device that measured the electrical resistance between P.dl & oral mucosa
• 1960- Gordon was the 2nd to report the use of a clinical device for the electrical measurement of root canals

Function :

• using the human body to complete an electrical circuit.

​

• One side of the circuitry is connected to an endo instrument & the other end to the patients body-- patients lip or by an electrode held in the patients hand.

CLASSIFICATION

FIRST GENERATION APEX LOCATORS

( Resistance apex locators.)

​

• It measures the 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 kΩ
• Eg sono-explorer

SECOND GENERATION APEX LOCATORS�

(Impedance apex locators )

• It measures opposition to the flow of alternating current or impedance.
• It uses the electronic mechanism that the highest impedance is at the apical constricture,- narrowest portion of the canal – impedence changes drastically,when a canal is thought of being a narrow tube
• Eg: Endocator

THIRD GENERATION APEX LOCATORS

(Frequency – dependent apex locators)

​

In biologic settings, the reactive component facilitates the flow of alternating current ,more for higher than low frequencies.

Thus, a tissue through which two alternating currents of differing frequencies are flowing will impede the low frequency current more than the high frequency current.

​

When this occurs, the impedence offered by the circuit to current of differing frequencies will change relative to each other.

Advantage

-works in the presence of pus and electroconductive environment in the canal

Disadv :

-calibration to be done each time

Root ZX

​

​

• dual frequency

​

• comparative impedance principle-described by Kobayashi (1991)

• measures the impedences of 0.4kHZ and 8kHZ at the same time

​

• A micro processor - calculate the ratio of the two impedences

.

• The quotient is displayed on the LCD panel and represents the position of the instrument tip inside the canal.�

Advantages

•   Does not require calibration

​

• Can be used when the canal is filled with strong electrolyte or when the canal is empty and moist

​

•   Allows shaping and cleaning of the canal with simultaneous monitoring of the working length.

ADVANTAGES OF ELECTRONIC APEX LOCATORS

• Only method that can measure to the apical foramen, not to the radiographic apex.
• Accurate
• Easy and fast
• Reduction of x-ray exposure
• Artificial perforation can be recognized
• Can be used in pregnant women – because of no risk of radiation

• Can used in patient with gagging reflex
• Can be used when dense zygomatic arch is over lapping the apices of upper molars
• Can be used unerupted impacted tooth over shadows the apex
• Patients who have a phobia of radiographic exposure.

DISADVANTAGES

• Requires a special device
• Accuracy is influenced by the electrical conditions in the root canal
• Difficult in tooth with open apex
• Inconsistent results

THANK U