Working length
Establish a reproducible endpoint using an apex locator together with clinical judgement and appropriate imaging.
Understand
Working length is an estimate of the intended apical extent of preparation and obturation. The radiographic apex and physiological constriction are not identical.
Assess
Combine an electronic apex locator with appropriate imaging and tactile information. Repeat measurement when canal conditions, reference point or file path change.
Apply
Record a stable coronal reference point. Avoid over-instrumentation and extrusion, but also recognise that a short or blocked canal may leave infected tissue.
Key distinctions
An apex locator responds to electrical conditions in the canal, so moisture, perforation, open apices or contact with metal may alter readings. Radiographic confirmation supplies another perspective but also has projection limits. A reproducible reference point is essential when comparing length through treatment; record the final chosen working length and why.
Think through a case
An apex locator reading suddenly changes after a reference cusp fractures. Establish a new stable reference and recheck length before filling.
The distinction to remember
Do not equate the radiographic root tip with a precise biological endpoint or rely on one measurement without context.
Test your recall
What is the purpose of a working-length estimate?
Show answer
To guide cleaning and filling within the intended canal extent.