Isthmus
Pronunciation: IS-mus
A narrow ribbon-shaped communication or corridor between two root canals within the same root, forming part of the complex root canal anatomy.
Full Definition
An isthmus is a thin anastomosis connecting two or more root canals in the same root; it may be complete (fully patent corridor) or incomplete (partial connection). Isthmuses are clinically significant because they harbour residual pulp tissue, microorganisms, and debris that standard round instruments cannot fully debride. They are most commonly found in the mesial root of mandibular molars and the mesiobuccal root of maxillary molars. Recognition of isthmus anatomy is critical in both orthograde preparation and endodontic microsurgery (root-end resection and retrograde filling). Editors should be careful not to confuse 'isthmus' with 'anastomosis' or 'fin'; while related, these terms describe morphologically distinct structures.
Usage
Usage note: Plural is 'isthmuses' (not 'isthmi') in contemporary endodontic literature. Do not use 'anastomosis' as a direct synonym without clarification.
In Context
- "Complete debridement of the isthmus between the mesial canals was achieved using passive ultrasonic irrigation." — Case report — endodontic microsurgery
- "The isthmus was identified on CBCT and factored into the root-end resection design." — Surgical planning report