Fig. 1

Preoperative and postoperative root canal therapy. a Orthopantomography. b Preoperative periapical radiograph of the tooth 3.7. A periapical radiolucent image around the distal root is observed. c Cone-beam computed tomography, axial view at the level of the middle third of the roots. Arrow: a third root is observed in the lingual area, radix entomolaris (RE) type, with a central location between the distal and mesial root components. d Cone-beam computed tomography, three-dimensional rendered image. The characteristics of the radix entomolaris (RE) are appreciated. Arrow: RE e Cone-beam computed tomography, axial view from the coronal third of the roots. Red lines: angle from the mesiolingual, distal and radix entomolaris canals. Yellow line: distance between the distal and radix entomolaris canals. f Pulp chamber floor of tooth 3.7 shown with the operating microscope (12×). The measures performed with the cone-beam computed tomography are transposed to a clinical setting. Red lines: angle from the mesiolingual, distal and radix entomolaris canals. Yellow line: distance between the distal and radix entomolaris canals. g Arrow: the orifice of the radix entomolaris (RE) is visualized. h Master cone radiograph. i Immediate postoperative radiograph. The four canals appear sealed Abbreviations, L: lingual; B: buccal; D: distal; M: mesial.