Risk Factors Associated With Inferior Alveolar Nerve Injury After Extraction of Impacted Lower Mandibular Third Molars: A Prospective Cohort Study

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BackgroundInferior alveolar nerve (IAN) injury is one of the complications of impacted lower mandibular third molar (LM3) extraction. Given the unknown prognosis of IAN injuries and limited treatment options, it is critical to understand the risk factors of IAN injury before LM3 extraction. PurposeThe study purpose was to identify risk factors associated with IAN injury after LM3 extraction. Study design, setting, sampleThis was a prospective cohort study including patients who underwent LM3 extraction from May to December in 2021 at authors’ institution. Patients with systemic diseases, previous maxillofacial surgeries or sensory abnormalities were excluded. Predictor variable(s)The predictor variable is composed of several risk factors. The variables were grouped into four categories: demographic, radiographic, procedure-related, and surgeon experience. Main outcome variable(s)The outcome variable was postoperative neurosensory disturbance coded as present or absent and was measured as one-month (transient) and one-year (permanent). CovariatesNot applicable. AnalysesThe measurement data were represented by mean and standard deviation (SD). The association of each variable with the presence of IAN injury was tested by the chi-square test. Statistical significance was accepted at p < 0.05. ResultsThe study sample was consisted of 705 patients (37.0% male) with an average age of 28.51 ± 6.51 years. A total of 17/705 (2.4%) and 4/705 (0.57%) patients developed transient and permanent IAN injury. The results demonstrated that the following factors were associated with higher rates of transient injury: use of chisels during surgeries (6.4%; 95% CI: 2.7-12.3; p=0.02; RR=11.4), LM3s located below the IAN canal (8.7%; 95% CI: 4.3-15.7; p<0.01; RR=7.3), compressed contact between LM3s and the IAN canal (36.4%; 95% CI: 12.3-78.2; p<0.001; RR=25.4), and not using corticosteroids after surgeries (3.8%; 95% CI: 1.9-6.5; p=0.03; RR=3.1). The only factor associated with permanent injury was compressed contact between LM3s and the IAN canal (18.2%; 95% CI: 2.2-62.3; p<0.001; RR=48.2). Conclusions and RelevanceClose proximity between LM3s and IAN canal, and the use of chisels, increase the risk of transient IAN injury. Corticosteroid treatment may promote nerve recovery. Compressed contact between LM3s and IAN canal is the only risk factor for permanent injury.