Prediction of inferior alveolar nerve injury in complicated mandibular wisdom teeth extractions: a new classification system

Purpose: To introduce and validate a new classification system for the inferior alveolar nerve (IAN) injury based on the proximity and positional relation between the tooth root and the inferior alveolar canal (IAC). Methods: In this retrospective study, consecutive patients, who underwent piezosurgery extractions of complicated impacted mandibular third molars from March to November 2014, were reviewed. Only teeth in close proximity to the IAC in orthopantomogram (OPG) were included. Then, teeth were classified according to the proximity of the root to the IAC (grade I: contacting; grade II: compressing; and grade III: penetrating) in both OPG and Cone-beam CT (CBCT), as well as, the relation to the IAC (class I: on the lingual side; class II: above the IAC; class III: on the buccal side; and class IV: roots surrounding the IAC) in CBCT. The incidence of the IAN injury in all patients was recorded. χ2 test and Fisher test was used to analyze the data. Results: 92 teeth (84 patients) in close proximity to the IAC were extracted and recorded. Of these, 33.70%, 28.26% and 38.04% were in grades I, II, and III, respectively, based on OPG; while, 36.95%, 33.70% and 29.35% were in grades I, II, and III, respectively, based on CBCT. Furthermore, the percentages of teeth in classes I, II, III and IV were 31.52%, 55.43%, 11.96%, and 1.09%. 7.61% of all the extractions led to the IAN injury. There was a positive correlation between the degree of root proximity to the IAC and IAN injury (P<0.05) with the highest incidence being in class III (P<0.05). Conclusion: The novel classification system seems well reproducible, facilitating the recognition of patients with higher risk of IAN injury during extraction of complicated lower wisdom teeth.