Exploring the morphology and clinical relevance of accessory canals: A scoping review of classification, variations,...

Accessory canals are complex anatomical components of the root canal system that may provide communication between the pulp space and periodontal tissues. Their variable morphology, inconsistent terminology, and differences in detection methods have made comparison between studies difficult. Advances in three-dimensional imaging have improved their characterization, but the available evidence remains fragmented.

To map the existing evidence on accessory canal morphology, with particular emphasis on classification systems, anatomical distribution and variation, investigative and imaging methods, and clinical relevance in endodontic practice.

A scoping review was conducted using the methodological framework of the Joanna Briggs Institute and reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR). PubMed/MEDLINE, Scopus, Web of Science, and Google Scholar were searched from database inception to 30 June 2026. Studies investigating accessory canal morphology, anatomy, prevalence, classification, detection methods, or clinical relevance were eligible. Two reviewers independently screened records and charted data using a standardized, pilot-tested form. Findings were synthesized descriptively and thematically.

The search identified 767 records, from which 32 studies were included. The evidence demonstrated substantial variation in accessory canal prevalence and distribution according to tooth type, root region, population, and investigative method. Accessory canals were frequently reported in molars, particularly in furcation and apical regions, whereas anterior teeth generally showed lower prevalence. Traditional clearing and dye-penetration methods provided important anatomical information, while scanning electron microscopy enabled detailed visualization of accessory foramina. CBCT provided clinically applicable three-dimensional information, whereas micro-CT offered higher-resolution characterization of accessory canal morphology and connectivity. Classification systems have progressively evolved from simple location-based descriptions toward more structured approaches incorporating anatomical location, morphology, configuration, and canal pathways. However, no universally accepted classification system was identified.

This scoping review demonstrates considerable variation in the prevalence, distribution, and morphology of accessory canals across tooth types and anatomical regions. The evidence has progressed from conventional anatomical techniques to advanced three-dimensional imaging, particularly micro-CT, which has improved the characterization of complex canal anatomy. However, inconsistencies in terminology, classification systems, and methodological approaches continue to limit comparisons across studies. Standardized classification and reporting protocols, together with well-designed clinical research, are needed to clarify the clinical significance of accessory canals and facilitate the translation of anatomical knowledge into endodontic practice.