The aim of this study was to evaluate the frequency of the identification of middle mesial (MM) canals in extracted permanent first and second mandibular molars before and after executing a troughing technique with high magnification. Sample consisted of 105 mandibular molars. After gaining access to the pulp chamber and cleaning the chamber floor, root canals were detected in three different stages. The initial location was performed under direct viewing without magnification. In the second stage, a dental operating microscope was employed at 12 magnification. If the MM canal was not observed, a standardized troughing technique was executed with the use of an ultrasonic tip between the mesiobuccal and mesiolingual canals under magnification. Statistical differences in the frequency of MM canals before and after troughing were determined using McNemar’s test, with the significance level set at 5%. No significant increase in the identification of the MM canal was found when comparing observations before (9.52%) and after (12.38%) the troughing technique under high magnification. However, viewing under magnification and the execution of troughing significantly increased the location of the MM canal (12.38%) when compared to viewing without magnification (3.81%) (p<0.01). The troughing technique with the aid of a dental operating microscope significantly improved the identification of MM canals compared to viewing without magnification. Troughing is a safe, minimally invasive procedure that benefits the treatment of mandibular molars.