Abstract: Objective: To evaluate the effect of CBCT on the selection of extraction method for mandibular third molar. Methods: 130 cases of mandibular third molar were selected, and two radiographic methods were used for preoperative examination.(1) Panoramic radiograph examination ; (2) CBCT examination. After radiological examination, the surgical procedure was determined: surgical removal or coronectomy. The first treatment plan was formulated according to the panoramic image, and the second was determined according to CBCT. After the CBCT was taken, the factors for the selection of coronectomy were recorded. Results: The operative plan was performed according to the second-step treatment plan. The first treatment plan of 113 (86.9%) samples was consistent with the second treatment plan, while the treatment plan of 17 (13.1%) samples after CBCT was changed. When the mandibular third molar was in direct contact with the inferior alveolar neural tube, the final choose was to use the coronectomy. However, direct contact was not an adequate influencing factor. In addition, the number of roots, the presence of cortical bone between the roots and the neural tube, the location of the neural tube in the hollow of the root, and the length of the contact between the root and the neural tube were also important factors influencing the selection of the coronal amputation. Conclusion: CBCT affected 13.1% of treatment plans. The direct contact between mandibular third molars and neural tube cavities, the position of the neural tube bending or depression near the apical complex, the presence of cortical bone between the root and neural tube, and the length of the root and neural tube contact observed in CBCT images were important factors influencing the decision of coronal amputation.

Key words: mandibular third molars, tooth extraction, CBCT, alveolar neural tube, coronectomy