Root and canal-specific features of maxillary first molars with fused roots

Background / Aim. Maxillary first molars are one of the most challenging teeth for endodontic therapy. There are certain disparities in number of roots and canals, and canal inter-relationship within the same root, particularly in those with fused roots. The aim was to evaluate ex vivo features of roots, root canals and canal walls in maxillary first molars with fused roots. Methods. Sixty-four extracted maxillary first molars with fused roots were included for cone-beam computed tomographic and microscopic studies. Tooth dimensions at the level of pulp chamber floor, number, location and distance between orifices, number and canal morphology, canal wall thickness, and features of apical foramina were examined and measured. Results. Incidence of maxillary first molars with root fusion was 17.5%, of which 60.0% was palatal fused to disto-buccal root. At the level of pulp chamber floor bucco-palatal dimension was significantly larger with 10.4 mm than mesio-distal with 7.0 mm. Four canal orifices were detected in 65.6%, with the shortest distance of 1.95 mm between mb1 and mb2. In fused roots most frequently were two or three canals strongly correlating to the number of major apical foramina. No fusion of canals was found in fused roots. The thinnest canal wall in mesio-buccal and disto-buccal fused root was mesial with 1.25 mm, and distal with 1.31 mm, while for the palatal root the thinnest was palatal wall with 1.97 mm. Conclusion. The most frequent type of fusion was between palatal and disto-buccal root. Bucco-palatal dimension at the level of pulp chamber floor was significantly larger than mesio-distal, with the shortest inter-orifice distance between mb1 and mb2 orifice. Number of canals was either two or three, strongly coinciding with the number of major apical foramina. There was no fusion of the canals in fused roots. The thinnest canal wall was either mesial or distal.