Most accurate method of determination of working length in a tooth with open apex:

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 of apex locators Can provide inaccurate readings in following cases: Presence of pulp tissue in canal Too wet or too dry canal Use of narrow file Blockage of canal Incomplete circuit Low battery Chances of overestimation. May pose problem in teeth with immature apex. Incorrect readings in teeth with periapical radiolucencies, and necrotic pulp associated with root resorption, etc., because of lack of viable periodontal ligament.