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Updated: May 23, 2025
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Published on: February 23, 2024
Is cone beam computed tomography accurate in predicting inferior alveolar nerve exposure during mandibular third
Kenan Chen1, Youbai Chen2, Peng Chen3
1Department of Oral and Maxillofacial Surgery, Peking University School and Hospital of Stomatology & National Center of Stomatology & National Clinical Research Center for Oral Diseases & National Engineering Research Center of Oral Biomaterials and Digital Medical Devices & Beijing Key Laboratory of Digital Stomatology & Research Center of Engineering and Technology for Computerized Dentistry, Ministry of Health & NMPA Key Laboratory for Dental Materials, Beijing, P.R. China.
Objectives:
This study aims to evaluate the accuracy of cone beam computed tomography (CBCT) in predicting the exposure of inferior alveolar nerve (IAN) during complicated mandibular third molars (M3M) extraction.
Methods:
115 M3Ms with canal cortical defect signs on preoperative CBCT were extracted. Candidate variables included sex, age, types of CBCT machine, the Winter classification of M3Ms, the size of root entering the canal on CBCT, the size of cortical defect on CBCT. The primary outcome was the exposure of IAN and the exposed neurovascular bundle size which was recorded measured under endoscope. The independent sample t-test, Bland-Altman analysis was performed to assess the agreement between the CBCT and endoscopic measurements. The regression analysis was performed to determine if there was a correlation between the measurements of CBCT and endoscope. The Chi-square test was used to evaluate whether the proportion of IAN exposure in different impacted M3M types were consistent. ANOVA was used to test the correlation between the actual size of exposed IAN and (1) Winter classification types; (2) types of CBCT machine.
Results:
85/115 (73.9%) M3Ms with canal cortical defect signs on preoperative CBCT had intraoperative exposure of IAN. The average length and width of the exposed IAN were 5.89 ± 1.72 mm and 2.48 ± 0.79 mm, which were significantly smaller than the size of root entering the canal on CBCT (9.69 ± 3.05 mm and 3.26 ± 0.87 mm, P < 0.001) but larger than the cortical defect size (5.06 ± 2.05 mm and 2.10 ± 0.54 mm, P < 0.05). The regression analysis showed that IAN exposure was significantly associated with the cortical defect length (0.1 mm) on CBCT (OR = 1.38, P = 0.001). The probability of intraoperative IAN exposure was statistically different among different Winter classifications of M3M and the probability of IAN exposure was higher in non-horizontal impacted type according to Chi-square test results. ANOVA showed statistical difference between exposed IAN length and Winter classification types (p = 0.001).
Conclusions:
Not all M3Ms with tooth-IAN contact signs on preoperative CBCT indicated intraoperative IAN exposure. The size of root entering the canal on CBCT were mostly larger than the intraoperative endoscopic measurements. IAN exposure can be accurately predicted by the length of cortical defect on CBCT. Non-horizontal impaction predisposed the M3M to a higher risk of intraoperative IAN exposure.
Clinical Relevance:
Endoscope provides the possibility to observe and record the IAN exposure directly. IAN exposure can be accurately predicted by the length of cortical defect instead of the size of root entering the canal on CBCT. Non-horizontal impaction predisposed the M3M to a higher risk of intraoperative IAN exposure.
Clinical Trial Number:
Not applicable.
