Evaluation of Two Trephine Techniques for Removal of Fractured Rotary Nickel-titanium Instruments from Root Canals

The aim of this in vitro study was to evaluate the effects on root dentin of 2 trephining techniques using an ultrasonic tip or a trepan bur in the mesial canals of mandibular molars during attempts to remove fractured file fragments using micro-computed tomographic imaging.

Twenty-one teeth with a similar anatomic configuration in mesial (buccal and lingual) canals were selected. A 4-mm apical segment of K3 file size 25/.06 was fractured in each mesiobuccal and mesiolingual canal 5 mm apically from the canal orifice. A staging platform was prepared at the coronal aspect of the broken instrument followed by either ultrasonics or a new trepan bur technique to expose a 1- to 1.5-mm length of the fragment. If the broken instrument could not be removed by exposing it either by ultrasound or the trepan bur, a microtube device was used to attach to and withdraw the fragment. Micro-CT scanning was performed before and after removing the broken instrument. Canal volume, diameter, and furcal root dentin thickness were measured by using image analysis software. The time required for the removal of the instrument fragments was recorded. The result was statistically analyzed using the paired t test.

The trepan bur technique had significantly less impact on canal volume, diameter, and furcal root dentin thickness change than the ultrasonic technique (P < .001). The time consumed for successful removal of the fragments was significantly less in the trepan bur group (8.9 ± 3.5 minutes) than in the ultrasonic group (25 ± 11.9 minutes) (P < .001).

A new small-sized trepan bur technique was superior to the use of ultrasound with regard to the amount of dentin removed and the speed in the removal of fractured instruments from root canals.