Correlation of the radiological predictive factors of inferior alveolar nerve injury with cone beam computed tomography findings: Predictive signs of IAN injury correlated to CBCT

Aim:  This study assessed the radiological signs considered predictive of inferior alveolar nerve (IAN) injury and correlated them with findings from cone beam computed tomography (CBCT). Material and methods:  This was a prospective study of patients who underwent CBCT scanning of mandibular third molars when panoramic radiographs indicated an ‘increased risk’ of IAN injury during extraction. Results:  Seventy-eight per cent of the teeth identified showed darkening across the root. Thinning or perforation of the cortical plate was found on CBCT. The group that exhibited loss of radiopaque lines across the root (68%), all of the scans showed contact between the nerve and root, with loss of cortication of the canal. Thirty per cent of the cases exhibited diversion of the canal. There was contact with the tooth in all cases, with the nerve either coursing through the roots (33%) or being ‘sandwiched’ between the root and the cortex to such an extent that the distortion resulted in part of the nerve being displaced beyond the apex of the tooth, creating an apparent change in direction. Conclusion:  Loss of radiopaque line and diversion of the canal were both associated with loss of cortication of the canal on CBCT, indicating that there was contact between the root and the contents of the canal. These two signs are crucial predictive signs of increased risk of IAN injury during third molar extraction. Darkening of the root displayed root and nerve contact in 76.9% of the cases studied and therefore very likely to indicate risk.