Radiographic features of anatomic relationship between impacted third molar and inferior alveolar canal on coronal CBCT images: risk factors for nerve injury after tooth extraction

INTRODUCTION: The present study was aimed to identify the radiographic signs between impacted third molar root and inferior alveolar canal (IAC) on cone-beam CT (CBCT) images as risk factors and prognostic predictors associated with inferior alveolar nerve (IAN) damage following tooth removal. MATERIAL AND METHODS: A retrospective clinical study was performed involving 136 patients with 257 impacted lower third molars from January 2013 to December 2014. The neurosensory function of the lower lip and chin was subjectively evaluated and assessed by neurosensory tests before and after surgery. The preoperative CBCT data were retrieved and analyzed to identify the radiographic signs associated with postoperative IAN injury. RESULTS: The overall incidence of IAN injury in our patient cohort was 13.2%. Multiple radiographic features on coronal CBCT images including contact between IAC and root, IAC position relative to root, IAC shape and cortication status were found to be significantly associated with IAN damage (p < 0.05, χ(2) test). Furthermore, buccolingual position, teardrop/dumbbell shape and cortication status of IAC were identified as independent prognostic predictors for IAN damage. CONCLUSIONS: Our findings indicate that radiographic signs including direct contact between IAC and root, buccal/lingual IAC position relative to root, teardrop/dumbbell shape and cortication absence of the IAC on presurgical CBCT images are associated with high risk of IAN injury and postoperative neurosensory disturbance.