Fig. 1

Representative axial CBCT sections showing the classification by Fan et al. [18]. 1a: class C1, a continuous C shaped canal. 1b: class C2, a mesiobuccal-distal (MB-D) ribbon-like canal and a mesiolingual (ML) canal. 1c: class C3a, a mesial (M) canal and a distal (D) canal. 1d: class C3b, a mesiobuccal (MB), a ML and a D canal. 1e: class C4, a single round or oval canal