What is the most important anatomical landmark for determining the working length in root canal therapy?

The working length in endodontics is the measured distance from a coronal reference point to the termination of the root canal preparation. The ideal apical endpoint is the apical constriction (also called the minor apical foramen or cementodentinal junction), which is the narrowest part of the root canal and the point where the canal transitions from pulp tissue to periapical tissue. Instrumenting and obturating to the apical constriction optimizes healing outcomes. Radiographic apex and actual apical foramen often differ by 0.5–3 mm. Electronic apex locators (EAL) are the preferred method for locating the apical constriction, supplemented by radiographic confirmation.