The role of CBCT in improving the detection and management of the second mesiobuccal canal in first maxillary molars compared with the operative microscope alone

Background : During root canal therapy, one of the most often overlooked anatomical structures in maxillary first molars is the second mesiobuccal canal. Even with the use of ultrasonic devices and magnification, its detection remains difficult. Aim : To evaluate whether cone beam computed tomography provides additional clinical benefit for identifying and negotiating the second mesiobuccal canal after exploration under a dental operating microscope combined with ultrasonic troughing. Methods : A total of 129 maxillary first molars undergoing primary endodontic treatment were examined using a two-stage clinical protocol. In the first stage, canal identification was performed under a dental operating microscope and ultrasonic endodontic tips. Teeth in which the second mesiobuccal canal could not be located or fully negotiated proceeded to the second stage, which included a cone beam computed tomography scan. When an additional canal was visualized, a second clinical attempt at detection and negotiation of the MB2 canal was performed. Detection rates, canal morphology, and negotiation outcomes were recorded and analyzed statistically. Results : The second mesiobuccal canal was detected in 79.1% of teeth during microscopic exploration, with full negotiation achieved in most cases. Cone beam computed tomography identified an additional canal in 40.7% of teeth that remained undetected after the first stage. The combined approach resulted in an overall detection rate of 87.6%. Canal morphology, particularly patency and canal confluence, strongly influenced detectability. Conclusion : Cone beam computed tomography provides added value for identifying the second mesiobuccal canal only when microscopic and ultrasonic methods fail. Its benefit depends on anatomical conditions, while favorable morphology remains the key determinant of successful canal detection and negotiation.