Inferior Alveolar Nerve Injury in Trauma-Induced Mandible Fractures.

PURPOSE: This prospective observational cohort study sought to determine the prevalence of inferior alveolar nerve (IAN) injury after mandibular fractures before and after treatment and to elucidate factors associated with the incidence of post-treatment IAN injury and time to normalization of sensation. MATERIALS AND METHODS: Consenting patients with mandibular fractures (excluding dentoalveolar, pathologic, previous fractures, or mandibular surgery) were prospectively evaluated for subjective neurosensory disturbance (NSD) and underwent neurosensory testing before treatment and then 1 week, 1.5, 3, 6, and 12 months after treatment. RESULTS: Eighty patients (men, 83.8%; mean age, 30.0 yr; standard deviation, 12.6 yr) with 123 mandibular sides (43 bilateral) were studied. Injury etiology included assault (33.8%), falls (31.3%), motor vehicle accidents (25.0%), and sports injuries (6.3%). Half the fractures (49.6%) involved the IAN-bearing posterior mandible; all condylar fractures (13.0%) had no NSD. Treatment included open reduction and internal fixation (ORIF; 74.8%), closed reduction and fixation (22.0%), or no treatment (3.3%). Overall prevalence of IAN injury was 33.7% (95% confidence interval [CI], 24.8-42.6) before treatment and 53.8% (95% CI, 46.0-61.6) after treatment. In the IAN-bearing mandible, the prevalence was 56.2% (95% CI, 43.2-69.2) before treatment and 72.9% (95% CI, 63.0-82.7) after treatment. In contrast, this prevalence in the non-IAN-bearing mandible was 12.6% (95% CI, 4.1-21.1) before treatment and 31.6% (95% CI, 20.0-43.3) after treatment. Factors associated with the development of post-treatment IAN injury included fracture site and gap distance (a 1-mm increase was associated with a 27% increase in odds of post-treatment sensory alteration). Time to normalization after treatment was associated with type of treatment (ORIF inhibited normalization) and fracture site (IAN-bearing sites took longer to normalize). CONCLUSION: IAN injury was 4 times more likely in IAN-bearing posterior mandibular fractures (56.2%) than in non-IAN-bearing anterior mandibular fractures (12.6%). After treatment, IAN injury prevalence (in 12 months) was higher (72.9% in posterior mandible, 31.6% in anterior mandible).