Durability of Self-Adjusting File Used in Different Canal Curvatures

Objective: This study intended to assess durability of a Self-Adjusting File (SAF) in preparing root canals with different curvatures. Method: 47 SAFs were allocated into 5 study groups and used in mesial canals of extracted lower molars with a different angle (α) and radius (r) of curvatures: Group A (α=20-40⁰, r<6mm), Group B (α=20-40⁰, r>6mm), Group C (α>40⁰,r<6mm), Group D (α>40⁰,r>6mm) and Group E (control) (α<20⁰). The file was used inside one canal for maximum of 4 minutes. Every 1 minute the file was taken out from the canal and visualized under Dental Operating Microscope to identify any fracture or deformation. If there was no fracture or deformation, the operation continued with the same file in the same canal. After 4 minutes, if the file was still undamaged, it was operated in the new root canal and the procedures repeated. If a fracture or deformation was noticed at any time, the experiment was discontinued. The new SAF was used in a new root canal and the experiment repeated. The time when the first mechanical changes detected was registered and this file was re-examined using both a Stereo Microscope (SM) and a Scanning Electron Microscope (SEM) respectively. Result: SAF operated in Group E (straight canal) showed the highest durability of 19 minutes followed by Group D (7.2 minutes), Group C (7.0 minutes), Group B (5.7 minutes) and Group A (4.9 minutes). There was a significant difference between Group E and other experimental groups at P=0.0001. However, there were no significant differences among the experimental groups (P>0.05). The file failure occurred most commonly on the middle part. A fractographic analysis exhibited fatigue striations and dimpling patterns. Conclusion: SAF was more durable to be used in straight canal than in canal with moderate and severe curvature.