The Apical File Size according to the Root Canal System of Premolars with Single Root

Purpose: To investigate the discrepancies between the apical root canal diameter and initial apical file according to the shape of apical foramen. Materials and Methods: Sixty extracted premolars were assigned to three groups according to the root canal system (type 1, 2, 3) of 20 teeth each. After chamber opening, the initial apical file (IAF) was inserted into root canal until the file tip was just visible through apical foramen under the microscope and fixed with methaacrylate in the root canal. The root tip was cut horizontally 1 mm from the anatomical apex and the apical cross-section was visualized using microscope at ×50 magnification. Results: 1. Mean diameter of IAF was 0.36 mm in type 1, 0.34 mm in type 2, and 0.29 mm in type 3. There were no significant differences among groups. 2. The ratio between the area of apical root canal and IAF was 40.05% in type 1, 27.05% in type 2, and 34.63% in type 3. There was a significant difference between group 1 and 2 (p<0.05). Conclusion: The IAF of premolar was more than size 30 regardless the root canal system, and it was much smaller than real apical canal size in view of the ratio between the area of apical root canal and IAF.