## 1 Introduction  
Interior alveolar nerve injury is one of the major complications following the removal of the mandibular third molar, and still represents an issue in surgical planning [1, 2, 3]. Inferior alveolar nerve injury is reported to occur in 0.4-8% of cases [4]. Depth of impaction and third molar angulation have been claimed to be risk factors related to nerve injury.  
Preoperative radiographic assessment is necessary to determine the relative anatomic relationship of the inferior alveolar nerve canal with third molar roots. Although panoramic radiography can be supportive in identifying high risk patients, a three-dimensional (3D) visualization of the anatomical structures of interest is often needed [5].  
The introduction of cone-beam computed tomography (CBCT) for the study of high-risk patients has led to an improvement in surgical performance by providing additional information on the nerve position [6, 7]. CBCT is becoming increasingly used due to the lower radiation dose to the patient compared to multi-slice CT, the possibility to perform focused examinations with a reduced field of view, and the lower costs [8]. However, CBCT presents limited contrast resolution, which hinders the evaluation of lesions involving both hard and soft tissues [9]. Moreover, it should be borne in mind that CBCT finds indication when first level diagnostic imaging techniques, and in particular panoramic radiography, highlight the presence of a close relationship between the inferior third molar and the inferior alveolar nerve canal [10]. The current recommendation is therefore to prescribe CBCT of the mandibular third molar when the surgeon has a very specific clinical question in an individual patient case that cannot be answered by conventional imaging [11].  
The topographic relationship between the inferior alveolar nerve canal and the third molar is a well-recognized factor associated with postoperative sensory dysfunction [6]. The direct contact between the nerve and third molar roots, a buccal or lingual position of the nerve, a narrowing of the canal, and the loss of canal cortical bone appear to be associated with higher risk of nerve injury following third molar surgery [6]. Moreover, severe compression of the inferior alveolar canal can result in a significantly increased risk of postoperative inferior alveolar nerve injury [12]. Importantly, when a close relationship between the mandibular third molar and inferior alveolar canal is detected, CBCT imaging appears to significantly reduce the incidence of temporary nerve impairment after third molar removal [4].  
In several medical fields, image post-processing of 3D datasets obtained from CBCT studies, and in particular segmentation, has been extensively applied to retrieve further information from diagnostic imaging [13; 14; 15]. Segmentation techniques have been predominantly reported for the selective localization and analysis of structures of interest by extracting and labeling groups of voxels of selected density, obtaining relevant information on different anatomical structures and providing a voxel-specific 3D reconstruction [16; 17].  
The aim of the present work was to assess the potential role of segmentation in the pre-surgical evaluation of the relationship between impacted third molars and inferior alveolar nerve canal.