ObjectiveTo measure the relevant data of impacted mandibular third molar(IMTM) by panoramic radiography, and analyze the influencing factors of inferior alveolar tube injure during extraction of IMTM.

MethodsThe preoperative curved radiograph examination in 108 patients with IMTM were implemented, and the relevant indexes around IMTM, which included the clarity of inferior alveolar nerve canal; distance between impacted tooth from upper wall to inferior alveolar nerve and Pell & Gregory classification of impacted teeth, were measured.The IMTM were removed according to the standard surgical procedure.After the extraction of teeth, a blunt head probe was used to detect a nerve tube damage, and the influencing factors of inferior alveolar tube injure during extraction of IMTM were analyzed.

ResultsA total of 193 IMTM in 108 patients were extracted, 38 cases with inferior alveolar nerve injury and 4 cases with numbness in lower lip(the numbness rate for 2.07%) were found.One hundred and fifty-five cases without inferior alveolar nerve injury and numbness in the lower lip were identified.The differences of the curved root of IMTM, clear upper and lower wall of neural tube, Pell & Gregory classification, distance from IMTM to upper wall of neural tube and angle between IMTM and MSM on the long axis were statistically significant between patients with and without injury(P < 0.01).The results of logistic regression analysis showed that the curved root of IMTM, clear upper and lower wall of neural tube, Pell&Gregory classification, distance from IMTM to upper wall of neural tube and angle between IMTM and MSM on the long axis were the independent risk factor of lower alveolar nerve wall injury during IMTM extraction(P < 0.05 to P < 0.01).

ConclusionsThe oral surface tomography can better evaluate the risk factors of inferior alveolar neural tube injury during the extraction of IMTM.The indicators have certain guiding significance for the clinical guidance of the extraction of IMTM.