Working LengthDetermination

By: Dr. Jaffar Raza

DEFINITIONS

• “the distance from a coronal reference point to a point at which canal preparation and obturation should terminate”

• 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 the root canal whichmay be located away from anatomic or radiographic apex.

• Apical constriction (minor apical diameter) is apical portionof root canal having narrowest diameter. It is usually 0.5 -1 mmshort of apical foramen. The minor diameter widensapically to foramen, i.e. major diameter.

Cementodentinal junction

• is the region where cementum and dentin are united, the point at which cemental surfaceterminates at or near the apex of tooth.

• It is not always necessary that CDJ always coincide with apical constriction.

• Location of CDJ ranges from 0.5 - 3 mm short of anatomic apex

DIFFERENT METHODS OFWORKING LENGTH DETERMINATION

• Various methods for determining working length include

• Using average root lengths from anatomic studies,

• Preoperative radiographs,

• tactile sensation, etc.

• Other common methods include

• use of paper point,

• working length radiograph,

• Electronic apex locators

• or any combination of the above

ELECTRONIC APEX LOCATORS

• Electronic apex locators (EAL) are used fordetermining working length as an adjunct to radiography.

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

Components of Electronic Apex Locators

• • Lip clip• File clip• Electronic device• Cord which connects above three parts.

• Advantages of Apex Locators

• Provide objective information with high degree of accuracy.• Accurate in reading (90-98% accuracy)• Some apex locators are also available in combination with pulp tester, so can be used to test pulp vitality.

• Disadvantages

• a. Can provide inaccurate readings in following cases:-i. Presence of pulp tissue in canalii. Too wet or too dry canaliii. Use of narrow fileiv. Blockage of canalv. Incomplete circuitvi. Low battery

• b. Chances of over estimation

• c. May pose problem in teeth with immature apex.

Uses of Apex Locators

• 1. Provide objective information with high degree of accuracy.

• 2. Useful in conditions where apical portion of canal system is obstructed by:

a. Impacted teeth

b. Zygomatic arch

c. Tori

d. Excessive bone density

e. Overlapping roots

f. Shallow palatal vault.

• In such cases, they can provide information whichradiographs cannot.

• 3. Useful in patient who cannot tolerate X-ray film placement because of gag reflex.

• 4. In case of pregnant patients, to reduce the radiationexposure, they can be valuable tool.

• 5. Useful in children who may not tolerate taking radiographs,disabled patients and patients who are heavily sedated.

• 6. Valuable tool for:

a. Detecting site of root perforations

b. Diagnosis of external and internal resorption which have penetrated root

surface

c. Detection of horizontal and vertical root fracture

d. Determination of perforations caused during post preparation

e. Testing pulp vitality

• 7. Helpful in root canal treatment of teeth with incomplete root formation, requiring apexification and to determine working length in primary teeth.

Contraindications to the Use of Apex Locator

• Older apex locators were contraindicated in the patients whohave cardiac pacemaker functions. Electrical stimulation to suchpatients could interfere with pacemaker function. But thisproblem has been overcome in newer generation of apexlocators.

• periapical radiolucencies,

• necrotic pulps associated with root resorption, etc.

• In such cases there is alteration of apical constriction and lack of viable periodontal ligament tissue to respond to EAL which may cause abnormally long readings.

Basic Conditions for Accuracy of EALs

• • 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 calcifications in canal