Abstract: Objective: To evaluate the effect of oral microscope on the identification of the second mesiobuccal canal in maxillary molars. Methods: The study sample consisted of 80 extracted maxillary molars, which were subjected to CBCT detection. The teeth were opened under naked eye to identify MB2 canal, and then visualized under oral microscope again. The accuracy with naked eyes and microscope was compared, and the false positive and false negative root canal types were analyzed. Results: CBCT showed 51.25% of MB2 canal in maxillary molars. When compared to naked eye (26.25%), the oral microscope (42.50%) improved the detection rate of MB2 canal. The discovery rate and sensitivity of the microscope were significantly higher than those of the naked eye, while the false positive rate and false negative rate under the microscope were significantly lower than those of the naked eye. There was no significant difference between different teeth. The MB2 of some long oval canals is still difficult to judge under the microscope. Conclusion: The application of microscope can improve the accuracy of root canal positioning. The combined use of microscope and CBCT has a high clinical value on the long oval canals.

Key words: Maxillary molar , Oral microscope, Location , Second mesiobuccal canal Long oval canal