Objective:The present study was aimed to determine the value of cone beam CT (CBCT) in predicting the risk of lingual bone plate injury during extraction of impacted mandible third molar (IMTM).Methods:The original CBCT data of 150 teeth (50 in vertical, 50 in angular and 50 in horizontal ) in January 2018 to December 2019 in Panzhihua Central Hospital of Sichuan Province were collected and analyzed. The thickness of lingual bone plate in enamel cementum boundary (ECB), root middle (RM) and root tip (RT) of each IMTM was measured by the software of CBCT system, and datas were analyzed by one-way ANOVA.Results:The average thickness of lingual bone plate in ECB of IMTM was (1.36±0.43)mm, (1.21±0.44)mm and (1.28±0.40)mm in vertical, horizontal and angular groups, respectively, with no significant difference ( F=1.07, P=0.35). The average thickness of lingual bone plate in RM of IMTM was (1.48±0.33)mm, (1.06±0.57)mm and (1.11±0.45)mm, respectively, with statistically significant difference ( F=8.78, P<0.01). The average thickness of lingual bone plate in RT of IMTM was (1.44±0.49)mm, (0.84±0.58)mm and (0.86±0.64)mm, respectively, with statistically significant difference ( F=12.35, P<0.01). Compared with the mandibular second molar, there were statistically significant differences in the average thickness of the lingual bone plate in ECB ( F=5.03, P<0.01), the RM ( F=15.13, P<0.01) and the RT ( F=33.12, P<0.01) of the IMTM among the three groups. In addition, the horizontal and angular IMTM, the thinness of lingual bone plate in RT region was more likely to occur than in vertical, and the absence of lingual bone plate was most likely to occur in patients with partial buccal crown. Conclusions:The doctor-patient communication and risk prediction should be sufficient before IMTM extraction when CBCT shows that the lingual bone plate of RT region is thin or absent. At the same time, we should avoid violent operation and thoroughly protect the lingual bone plate in the process of tooth extraction, and guard against serious complications such as perforation or fracture of lingual bone plate of mandible, and root displacement.