Correlation of the radiological predictive factors of inferior alveolar nerve injury with cone beam computed tomography findings

Abstract

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.

Elimination of permanent injuries to the inferior alveolar nerve following surgical intervention of the “high risk” third molar

“…1 The reported incidence varies widely. 2 To discover the relation between the nerve and the tooth, standard preoperative evaluation relies on panoramic imaging, and two-dimensional images may be examined for signs indicative of increased risk of damage to the nerve. 3 It is generally accepted that unless the root of a mandibular third molar appears on the radiograph to lie in close proximity to, or to overlap the inferior alveolar canal, there is little (if any) physical risk to the nerve; but surgical risk, which depends on the operator and the technique, 4 should also be considered.…”

Pre-operative assessment of impacted mandibular third molar and inferior alveolar canal using orthopantomograhpy and cone beam computed tomography

“…12, 13 In another study, it was found that loss of radiopaque border and deviation of canal was an indicator of contact with the canal and increased risk of inferior alveolar nerve injury. 5 The findings of CBCT was encouraging in detecting anatomical position of inferior alveolar canal and impacted mandibular third molar tooth and is definitely superior to orthopantomogram. Therefore, CBCT is a promising test in preoperative assessment of impacted mandibular third molar position and inferior alveolar canal.…”

“…4 Radiographic signs include-root darkening, roots deflection, root narrowing, dark and bifid root, interruption of the white line, diversion and narrowing of the of inferior alveolar canal. 5 However, opinion regarding the frequencies of the above mentioned signs for predicting the inferior alveolar nerve position or clinical complications such as paraesthesia after removal of mandibular third molar. If the panaromic radiographs indicates there is a close relationship between the third molar and the mandibular canal, supplement investigation using CT may be recommended to verify.…”

Notes on coronectomy

“…15 Umar et al reviewed 50 cases that had been identified as high risk on plain films and then correlated the CBCT findings with their appearance. Loss of lamina dura of the canal was linked to contact with the canal in all cases, darkening was related to canal cortical loss in 78% of cases, contact with the nerve in 60% and grooving of the root in one case.…”