Vertical distribution of accessory canals in different tooth types: A systematic review and meta-analysis

To systematically analyze the vertical distribution of accessory canals and propose potential root-end resection levels in different tooth types.

Proportional distribution of accessory canals (PD-AC) in 1 mm intervals, cumulative proportions within 2 mm and 3 mm (CP-AC_0-2 and CP-AC_0-3), mean distance from accessory foramen to root apex or main foramen (MD-AF), and prevalence of accessory canals in 2D cross-sections (PR-AC-2D).

A systematic search of electronic databases was conducted through December 25, 2025. The review was registered in PROSPERO (CRD420251107855).

Two reviewers independently performed study selection, data extraction, and risk of bias assessment using the AQUA tool. Nineteen studies were included for qualitative synthesis, of which eleven provided sufficient data for meta-analysis. A random-effects model was used, and subgroup analyses were stratified by tooth type, accessory canal type, and country. Within 0-1 mm, 1-2 mm, 2-3 mm, and 3-4 mm from the apex, 41.5%, 34.3%, 9.9%, and 4.4% of accessory canals were located, respectively. Molars had significantly higher proportions than anterior teeth both within 2 mm (90.0% vs. 72.4%) and 3 mm (96.9% vs. 87.5%). Of apical ramifications, 86.4% were within 2 mm. The pooled MD-AF was 1.472 mm. PR-AC-2D decreased from 29.3% at 1 mm to 1.3% at 5 mm. All studies presented moderate to high risk of bias.

A 2 mm root-end resection level may be sufficient for molars, whereas anterior teeth may require a higher level. Further randomized controlled trials are needed.

A 2 mm resection may adequately expose or remove most accessory canals in molars, potentially preserving more root length while maintaining treatment efficacy. In anterior teeth, a traditional 3 mm resection remains advisable until further evidence becomes available.