The relationship between the apical anatomy of first permanent molars and initial apical file

Objective To investigate the apical anatomy of maxillary and mandibular first permanent molars and its adaptability to the tip of initial apical file (IAF).Methods This investigation was carried out on 30 maxillary and mandibular first permanent molars, respectively. Post-preflaring IAF size was determined and the number, location, form of the foramen were observed with stereomicroscope. Canal diameters were measured at 0, 1, 2, and 3 mm from the apical foramen.Results A total of 78.1% of root canals had one apical foramen; 54.8% of main apical foramen existed at the apex, and 92.5% was oval. The diameters of apical foramen corresponded with those at 1mm from it. Canal diameters increased gradually at 1, 2, and 3mm from the apical foramen. The tip diameters of the IAF were slightly smaller than the canal minimal diameters at 1mm from apical foramen, and were three sizes smaller than the maximal diameters.Conclusion The IAF based on the canal minimal diameters can't adequately show working width, so root canals debridement is inadequate.