Fracture of endodontic instruments is a common complication in root canal treatment. With the popularization of endodontics and the use of nickel-titanium instruments, fracture of instruments during endodontic treatment occurs frequently. Once the instrument is broken in the root canal, it may cause the failure of the whole treatment and cause unnecessary pain and psychological burden to the patient due to infection or foreign body irritation. Therefore, how to successfully remove the broken instrument to complete the root canal treatment is getting more and more attention from clinicians. At present, the main methods used in clinical practice are ultrasonic extraction, H-files extraction, trocar extraction, forceps extraction, and pin-assisted extraction. Some studies have shown that the removal rate of fractured instruments ranges from 55% to 79%. Modern microscopic dentistry breaks the limitations of the hand alone with the help of a microscope, allowing direct vision of many previously unseen details and the fine structure of the root canal, increasing the success rate of difficult dental treatment. The use of a surgical microscope, combined with an ultrasonic device, can improve the extraction rate of fractured instruments in the root canal. It has been shown [6,7] that micro-ultrasonic techniques are currently the preferred method of fractured instrument removal. The light of the surgical microscope can enter the root canal, which allows the operator to determine the location of the fractured instrument above the curved section of the root canal in a narrow field of view, improving the operator’s control over the procedure and removing the fractured instrument under direct vision. [2] The ultrasonic energy generated by the vibration of the ultrasonic device can loosen the fractured instruments in the root canal, and the ultrasonic rinsing fluid can clean the debris in the root canal and act as a medium for ultrasonic energy to flush out the fractured instruments. In this group, 47 cases of fractured instruments could not be removed under naked eye conditions, and the microscopic ultrasound technique combining root canal microscope and ultrasound instruments was used for treatment. 34 cases were removed, and the removal rate was 72.3%, indicating that the microscopic ultrasound technique is a more effective method for removal. The success of microscopic ultrasonic extraction of fractured instruments is influenced by many factors. It is important to evaluate the difficulty of fractured instrument removal comprehensively from several aspects such as tooth position, root canal thickness, root canal curvature, root canal wall thickness, fractured instrument length, and fracture site before surgery. [5] In the data presented here, the extraction rate was higher when instruments were fractured in anterior or premolar teeth, while the extraction rate of fractured instruments in posterior root canals was lower. This is related to the clearer microscopic field of view in anterior or premolar teeth and the small curvature of the root canal. When the fractured instruments were located in the anterior part of the root canal curvature, the extraction rate was as high as 100%, while when the fractured instruments were located in the posterior part of the root canal curvature, the extraction rate was lower, 36.4%, which was close to the domestic reports. [6] The data in this paper also showed that the fracture rate of instruments in root canals with a curvature of less than 30 degrees was higher than that of those with a curvature of more than 30 degrees. The main reason for this is that most of the apical fractured instruments are located in small, curved root canals and in the middle and posterior part of the root canal curvature, which makes the microscopic visualization poor, the field of view not very clear, the positioning difficult, and the controllability of ultrasonic instruments poor. With the increasing improvement of micro-ultrasound technology, root canal microscopy combined with special ultrasound instruments will play an increasing role in solving the clinical problem of removing fractured instruments in the root canal, but we should deeply understand the complexity of the root canal system. Proper case selection, reasonable instrument selection, correct and careful root canal preparation procedures and timely instrument replacement are important measures to prevent instrument fracture.