Working length determination in RCT

Prepared by: Dr. Didar S. Kwekha

Supervised by: Prof. Dr. Salam Al-Qaisy

introduction

Determination of an accurate working length(WL)is one of the most critical steps of endodontic therapy.the cleaning, shaping and obturation of root canal system cannot be acomplished accurately unless WL is determined precisely.

Definitions

According to endodontic glossary :W.L is defined as” the distance from a coronal reference point to a point at which canal preparation obturation should terminate.”

Reference point : is that site on occlusal or the incisal surface from which measurements are made .

A reference point is chosen which is stable and easily visualized during preparation.

Anatomic apex: is tip or end of root determined morphologically .

Radiographic apex: is tip or end of root determined radiographically.

Apical foramen: is main apical opening of root canal which may be located away from anatomic or radiographic apex.

Apical constriction: is apical portion of root canal having narrowest diameter .

It is usually 0.5-1mm short of apical foramen.

The Cementdentinal junction:is the region where cementum and dentine are united ,the point at which cemental surface terminate at or near the apex.

Different methods of WL estimation

Average root length from anatomic studies

Radiographic Mathematics method Tactile sensation Bleeding on paper point Apical periodontal sensitivity Electronic apex locator

Radiographic method1. Measure the estimated WL from preoperative

periapical radiograph2. Adjust stopper of instrument to this estimated WL

and place it in the canal up to the adjusted stopper

3. Take the radiograph4. On the radiograph measure the difference

between the tip of the instrument and the root apex add or subtract this length to the estimated WL to get the new WL.

5. correct WL is finally calculated by subtracting 1 mm from this new length .

Modification in the length subtraction

1. No resorption -subtract 1mm

2. Periapical bone lesion - subtract 1.5 mm

3. Periapical bone +root apex resorption -subtract 2 mm

Mathematic method

it is based on simple mathematical formulation to calculate the WL.

In this an instrument is inserted into the canal ,stopper is fixed to the reference point and radiograph is taken.

The formula to calculate actual length of the tooth ia as follow:

Actual length of tooth apperent length of tooth in x-ray-------------------------------- --- = ------------------------------------------------Actual length of instrument apperent length of instrument in radiographSo,

actual length of instrument X apperent length of tooth in radiographActual length of tooth= ------------------------------------------------------------ apperent length of instrument in radiograph

disadvantages

Wrong readings can occur because of :A. Variation in angles of radiographB. Curved rootC. S-shaped ,double curvature roots.

Other methods of WL determination including:

tactile sensation Apical periodontal sensitivity Paper point measurement These methods don’t always provide the accurate readings for example :In case of narrow canals instrument may feel increased resistance as file approaches apical 2-3mm and in case tooth with immature apex instrument can go beyond apex.So these methods should not used alone should be used as supplement to radiographs apex locators.

Electronic methodThe electronic method calculates the working length by comparing the electrical resistance of the periodontal membrane with that of the gingival surrounding the tooth, both of which should be similar. The processors of these both of these machines basically work on four mechanisms.§ Log readings § Subtract method § Taking averages § Taking ratios These mechanisms are more important as compared to the number of frequencies used to collect data, as these signify essentially how the device interprets the data. All apex locators function by using human body to complete a circuit. The apex locators are also classified based on the principle they work on.Suzuki conducted research in 1942 and this was used by Sunanda

The apex locators are base on three principles:

§ Resistance method § Impedance method § Frequency ratio method

Resistance Method(First Generation Apex Locators)

The apex locator has a built in resistant value of 6.5 kilo Ohms. The apex locator is attached to the patients lip on one side and the other side is attached to the file. The file is then advanced into the canal until it touches the periodontal tissue at the apex which then completes the circuit.

Impedance Method(Second Generation Apex Locators)

Operates on the principle that there is electrical impedance across the walls of the root canal due to the presence of the transparent dentin. The tooth exhibits an increasing electrical impedance across the walls of the root canal, which is greater apically than coronally. At the DCJ, the level of impedance drops dramatically. The unit detects the sudden change and indicates it on the analogue meter. To overcome the problem of a wet environment, insulated are utilized.

Frequency Ratio Method(Third Generation Apex Locators)

Operates very similarly to the Impedance-type because it measures the impedance of the tooth at two different frequencies. In the coronal portion of the canal, the impedance difference between the frequencies is constant. As the file is advanced apically, the difference in the impedance value begins to differ greatly with maximum difference at the apical area.

“fourth-generation” apex locators are marketed by Sybron Endo andincluded the AFA Apex Finder and the Elements Diagnostic Unit. Both are ratio type apex locators that determine the impedance at 5 frequencies and both have built-in electronic pulp testers.

Fifth generation of apex locater :this type of apex locater contain rotary endo system (built in)

Electronic apex locator

EAP are used for determining WL as an adjunct to radiography.

They are basically used to locate the apical constrictions or cementodentinal junction or apical foramen and not the radiographic apex.

Uses of apex locator

1. Provide high degree of accuracy2. Useful in conditions where apical portion is

obstructed.3. Useful in patient with gag reflex4. Pregnant patient 5. Root perforation ,resorption ,root fracture .6. Pulp vitality7. RCT of teeth with incomplete root

formation.

Advantages of EAL

Accurate Objective measurement Easy and fast Reduction of exposure to radiation Perforation can be detected Can measure pulp space exactly to

constriction Can detect resorption and root fracture

Basic conditions for accuracy of EAL

Canal should be free from debris Canal should be relatively dry No cervical leakage Proper contact of file with canal walls

and periapex No blockages or calcification in canal

Contraindication of EAL

In patient who have cardiac pace maker,electrical stimulation to such patient can interfere with pace maker function

In teeth with periapical radiolucency and necrotic pulp associated with root resorption the use of apex locator is not much beneficial.

Summery

The most important to understand when determining WL is morphology of apical one third of the canal.

The consideration should given to adopt the parameter 0.5-0.0mm(from apical constriction)as most ideal terminating point in canal.

We should use many of these techniques as possible during the course of treatment.

Thank you