Panoramic radiographic risk factors for inferior alveolar nerve injury after third molar extraction

The purpose of this study was to estimate the association between specific panoramic radiographic signs and inferior alveolar nerve (IAN) injury during mandibular third molar removal.

A case-control study design was used; the sample consisted of patients who underwent removal of impacted mandibular third molars. Cases were defined as patients with confirmed IAN injury after third molar extraction, whereas controls were defined as patients without nerve injury. Five surgeons, who were blinded to injury status, independently assessed the preoperative panoramic radiographs for the presence of high-risk radiographic signs. Bivariate analyses were completed to assess the relationship between radiographic findings and IAN injury. The sensitivity, specificity, and positive and negative predictive values were computed for each radiographic sign.

The sample was composed of 8 cases and 17 controls. Positive radiographic signs were statistically associated with an IAN injury (P <.0001). The presence of radiographic sign(s) had positive predictive values that ranged from 1.4% to 2.7%, representing a 40% or greater increase over the baseline likelihood of injury (1%) for the individual patient. Absence of these radiographic findings had a strong negative (>99%) predictive value.

This study confirms previous analyses showing that panoramic findings of diversion of the inferior alveolar canal, darkening of the third molar root, and interruption of the cortical white line are statistically associated with IAN injury. Based on the estimated predictive values, the absence of positive radiographic findings was associated with a minimal risk of nerve injury, whereas, the presence of one or more of these findings was associated with an increased risk for nerve injury.