To explore techniques for retrieving separated instruments from root canals without direct access and with complex resistance, analyze the key points, advantages, and risks of the bypass-based retrieval method, and evaluate treatment outcomes.

Cases were collected from the Department of Endodontics at Xiangya Stomatological Hospital, Central South University, between 02/2017 and 01/2025. Preoperative imaging confirmed instrument separation within the root canals, where non-sleeve or ultrasonic methods were not indicated. Instead, endodontic files were used to bypass and prepare the canals around the separated instruments for retrieval. Follow-up data were collected for at least six months postoperatively. Patient demographics, instrument location, length, material, type, root canal morphology, postoperative imaging, clinical outcomes, and follow-up data were summarized. The frequency of each variable was recorded, and relevant influencing factors and treatment outcomes were analyzed.

A total of 175 patients (175 teeth, 176 fractured instruments) were included, comprising 52 males (29.7%) and 123 females (70.3%). The oldest patient was 73 years old, while the youngest was nine years old, and the average age was 28 years. Separated instruments were made of stainless steel in 44 cases, nickel-titanium in 108 cases, and carbon steel in 24 cases with an average length of 4.1 mm and an average fragment diameter of 0.32 mm. The fragments were located in the apical third of 67.6% of cases, with 46 cases (26.1%) occurring in the blind zone. The average distance from the canal orifice was 5.6 mm. The file tip extended beyond the apical foramen in 17 cases. Moderate to severe root canal curvature (≥10°) was observed in 93.7% of cases, with an average curvature angle of 29.3°. Preoperative periapical radiolucency was observed in 151 cases (86 of which had symptoms), while 24 cases showed no periapical radiolucency (seven of which had clinical symptoms). Complete retrieval was achieved in 160 cases. Secondary separation occurred in four cases, and retrieval failed in six cases. Postoperative imaging revealed significant canal deviation in 34 cases (including three cases with deviation and perforation), while no significant morphological deviation was observed in 141 cases (80.6%). Follow-up results showed that among patients with preoperative periapical radiolucency and symptoms, 83 cases experienced symptom relief or healing after retrieval, while one case still had symptoms and periapical radiolucency after six months. Among asymptomatic patients with preoperative periapical radiolucency, two cases developed symptoms after retrieval, and two cases still had symptoms after six months, though one of these showed healing of periapical radiolucency. Among symptomatic patients without preoperative periapical radiolucency, two cases experienced symptom relief after retrieval, while three cases still had symptoms after six months, with one of these developing radiolucency. Asymptomatic patients without preoperative periapical radiolucency (17 cases) remained symptom-free after retrieval, though four cases developed symptoms after six months, with two of these showing periapical radiolucency.

The bypass technique can serve as a safe and reliable method for retrieving separated instruments from root canals with complex resistance but direct access.