Summary. A method to remove broken instruments in root canals was developed employing a new ultrasonic device for root canal treatment. The results, using extracted teeth, showed that broken instruments locked tightly in round root canals were more difficult to remove compared with those in irregularly shaped root canals. This method was applied in 39 clinical cases, and in 26 of these the fragment was removed successfully while in six cases it was possible to bypass a file alongside the fragment. Therefore, in 32 out of the 39 clinical cases with broken instruments, it was possible to instrument to the apex.
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Nagai et al. (1986) studied this question.