Fig. 1

Images of the right mandibular first molar. (a). Preoperative radiograph showed a mesio-occlusal radiolucency approaching the pulp space. (b). Clinical view of the C-shaped orifice on the pulp floor (B: buccal, L:lingual). (c). Clinical view of the access cavity preparation showing four distinct root canal orifices (red arrow; DM: mesiobuccal, ML: mesiolingual, DB: distobuccal, DL: distolingual). (d). Axial CBCT section from the pulp chamber: C-shaped orifice. (e). Axial CBCT section from the coronal third: two canals separately, either canal cross-sectional angles less than 60° (C3c). (f). Axial CBCT section from the middle third: four canals separately (C3?). (g). Axial CBCT section from the apical third: one fused mesial canal and one fused distal canal (C3c). (h). Periapical radiography for working length determination with gutta-percha (size 25, 06 taper) in four separate canals. (i). Postoperative radiograph for root obturation. (j). Intraoral photograph showing four separate canals after root obtruation. (k). Postoperative radiograph with resin composite restoration. (l). Six-month follow-up radiograph indicates the health periapical tissue