The results showed that overall, all instruments may leave filling material inside the root canal. During retreatment there is a risk of instrument breakage, especially rotary instruments.

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A total of 160 resin-simulated canal blocks with 20-degree or 30-degree curvature were prepared by ProFile rotary instruments, GT rotary files, and the balanced force technique with Flex-R files. Using an image analysis computer application, the pre- and postoperative images were stored and superimposed, and then the amount of material removed from the preoperative inner and outer curved walls was measured at five levels in the apical 5 mm of the canal. The time required for canal preparation, including irrigation, and the time taken to change instruments was recorded. At 1 mm from the apical end, the directions of canal transportation were most frequently toward the outer aspect of the curvature, with the only exception being the canals shaped by the balanced force technique in which more was removed from the inner aspect. The balanced force technique required more preparation time than the rotary instrumentation.

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