The effect of rotary instrumentation on dentin thickness in the danger zone of the MB2 canal of maxillary first molars

The aim of this study was to measure the initial and remaining dentin thickness in the danger zone of the second mesiobuccal (MB2) canal of maxillary first molars after rotary instrumentation using cone beam computed tomography (CBCT) imaging. After determining initial dentin thickness, each sample was subjected to a standardized protocol of rotary instrumentation files: ProTaper Gold Sx Orifice Opener (maximum depth of 7 mm); Vortex Blue 15.04, 20.04, 25.04, ProTaper Gold S1, S2, F1, F2, and finally Vortex Blue 30.06. Subsequent CBCT measurements were made to compare changes in remaining dentin thickness in comparison to initial presentation. Preoperative dentin thickness in the danger zone had a mean of 0.82 ± 0.17mm. Significant levels of dentin removal in the danger zone were noted after all instrumentation groups when compared to the pre-instrumentation mean (Sx P < 0.001, 25.04 P < 0.0006, F2 P < 0.0001, 30.06 P < 0.0001). It was concluded that a thin area of dentin exists along the distal wall of the MB2 (danger zone) from the furcation to 4 mm apically.