When measuring working length without an apex locator, we aim to terminate at the apical constriction.
Understanding the Apical Anatomy
The average distances are:
- Apical constriction to radiographic apex: 0.89 mm
- Apical foramen to radiographic apex: 0.38 mm
Therefore, you are aiming for a working length that terminates approximately 0.38–0.89 mm short of the radiographic apex.
The last 0.5 mm of the rotary file does not cut. When obturating, you want to terminate approximately 0.88–1.39 mm from the radiographic apex.
Studies have shown better outcomes when the procedure ends within 2 mm of the radiographic apex.
Clinical Case
File system used: RC Blue, 25 mm
Working-Length PA — 4 June 2026
We were unable to achieve a “0” reading with the apex locator. A working-length periapical radiograph was therefore taken with the file at 25 mm.
Master-Cone Fit PA — 4 June 2026
The working length was determined to be 21.5 mm.
A total of 3.5 mm was trimmed from the master cone before the cone-fit PA was taken. The master cone was still deemed slightly long, so another 1 mm was trimmed.
Postoperative PA — 11 June 2026
A postoperative PA was taken at the one-week review.
Have we overfilled?
The six-month postoperative PA will be shared soon!
References
- Chapter 7—Tooth Morphology and Access Cavity Preparation. Cohen’s Pathways of the Pulp, Twelfth Edition.
- Dummer, P.M.H., McGinn, J.H. and Rees, D.G. “The Position and Topography of the Apical Canal Constriction and Apical Foramen.” International Endodontic Journal, 17: 192–198.
- Kerekes, K. and Tronstad, L. “Long-Term Results of Endodontic Treatment Performed with a Standardized Technique.” Journal of Endodontics, 5: 83–90.
