Apical delta refers to the branching pattern of small accessory canals and minor foramina seen at the tip or apex of some tooth roots. The pattern is said to be reminiscent of a river delta when sectioned and viewed using a microscope. Because the anatomy of this area is very small and complex with several portals of entry to the root canal i.e. more than one apical foramen this may make successful endodontic treatment less likely.
The root tip is removed during apicoectomy to eliminate the apical delta and maximise the chance of successful healing.
Color Atlas and Textbook of Oral Anatomy, Histology, and Embryology by B. K. Berkovitz, G. R. Holland, B. J. Moxham Hardcover, Mosby, ISBN 0-8151-0697-1 (0-8151-0697-1)