Remaining root dentin thickness in mesiobuccal canals of maxillary first molars after attempted removal of broken instrument fragments.

The aim was to measure the minimal thickness of the remaining canal wall dentine in the mesiobuccal roots of maxillary first molars using a virtual model to simulate the attempt to remove fractured instruments. Thirty-seven molars were scanned by micro-computed tomography. The application framework for the simulation of the attempt to remove a broken instrument was constructed. The staging platform was created and followed by the use of ultrasonic tips to trephine dentine around the fragment to reveal the coronal 1.5 mm. The minimum canal wall thickness in the mesiobuccal roots was then measured. The concavity groove was found on all the distal aspects of the mesiobuccal root. The minimum thickness of the remaining canal wall distally to the canal was significantly thinner than mesially to the canals when sizes 25/0.06 and 25/0.02 instruments were broken at 3 and 5 mm away from the canal orifice. When the sizes 20/0.02 and 25/0.06 instruments were broken at 5 mm away from the canal orifice, the minimum thickness of the distal dentine wall was only 300-400 μm which was significantly less than when the instrument was broken at 3 mm.