Fig. 6

Five Krasner and Rankow laws can be applied in trifurcated left mandibular first premolars, A Law of symmetry 1: the mesiobuccal (MB) and distobuccal (DB) root canal orifices are equidistant to the lingual (L) orifice on a line draw in a mesial-distal direction across the center of the floor of the pulp chamber (M-D line), Law of symmetry 2: the orifices of the canals lie on a line perpendicular to M-D line. B Law of Color Change: the color of the pulp-chamber floor is always darker than the walls, Law of Orifice Location 1 and 2: the orifices of the root canals are located at the angles in the floor-wall junction, and Law of Orifice Location 3: the orifices of the root canals are located at the terminus of the root developmental fusion lines, C a radiograph with files inside the root canals from left to right are mesiobuccal (MB), distobuccal (DB), and lingual (L) root canal respectively. Dashed line indicates M-D line and the solid line indicates the line perpendicular to M-D line