Evaluation of the effects on dentinal microcracks formation of trephan and ultrasonic methods used in removal of broken instruments: A micro-CT study

Separation of instruments during root canal treatment is a common complication and may affect the outcome. Different techniques are described in the literature to remove separated instruments from the canal. The purpose of this study was to evaluate the microcracks in mesial roots of mandibular molars after attempted removal of the separated instruments with 2 different techniques: ultrasonics and trephan bur technique by using micro-CT imaging. In this study 70 freshly extracted human mandibular molar teeth were used. First, the teeth were decoronated and mesial roots were separated. After the standardization of length and curvature angle, samples were embedded in acrylic blocks with putty material to simulate the clinical condition. The root canals were instrumented with the step-back technique to a size 20 H-file. After the micro-CT scanning, samples has microcracks in root dentin were discarded. Then, size 25 stainless steel H-file was separated in the middle third of the root. Samples were randomly divided into two experimental groups of 10 and a control group of 5. Separated files were removed by using trephan technique or ultrasonic technique under operation microscope. Then samples were scanned by micro-CT again and evaluated for crack existency. As a result, the amount of crack formation in the trephan group was found significantly higher from the control and ultrasonic group (p<0.05).